WorldWideScience

Sample records for evapotranspiration

  1. Evapotranspiration Calculator Desktop Tool

    Science.gov (United States)

    The Evapotranspiration Calculator estimates evapotranspiration time series data for hydrological and water quality models for the Hydrologic Simulation Program - Fortran (HSPF) and the Stormwater Management Model (SWMM).

  2. shoot water content and reference evapotranspiration for ...

    African Journals Online (AJOL)

    ACSS

    Penmann-Monteith equation and finally calculation of crop evapotranspiration. The objective of this study was to establish crop coefficients and evapotranspiration of different soybean varieties using shoot water content and reference evapotranspiration (ET0). MATERIALS AND METHODS. Reference evapotranspiration.

  3. On variability of evapotranspiration

    DEFF Research Database (Denmark)

    Ringgaard, Rasmus

    This dissertation is part of the long-term catchment-scale hydrological observatory, HOBE, situated in the Skjern River catchment covering 2500 km2 on the western coast of Denmark. To gain a more detailed knowledge of how evapotranspiration is controlled by the local surface and weather patterns...

  4. Evapotranspiration studies for protective barriers: Experimental plans

    Energy Technology Data Exchange (ETDEWEB)

    Link, S.O.; Waugh, W.J.

    1989-11-01

    This document describes a general theory and experimental plans for predicting evapotranspiration in support of the Protective Barrier Program. Evapotranspiration is the combined loss of water from plants and soil surfaces to the atmosphere. 45 refs., 1 fig., 4 tabs.

  5. A Citizen's Guide to Evapotranspiration Covers

    Science.gov (United States)

    This guide explains Evapotranspiration Covers which are Evapotranspiration (ET) covers are a type of cap placed over contaminated material, such as soil, landfill waste, or mining tailings, to prevent water from reaching it.

  6. Developing simplified Regional Potential Evapotranspiration (PET ...

    African Journals Online (AJOL)

    Regional Potential Evapotranspiration (PET) estimation method was developed to estimate the potential evapotranspiration (reference evapotranspiration) over Abbay Basin as a function of basin maximum and minimum temperature, and modulated by site specific elevation data. The method is intended to estimate PET in ...

  7. Partitioning evapotranspiration fluxes using atmometer

    Science.gov (United States)

    Orsag, Matej; Fischer, Milan; Trnka, Miroslav; Kucera, Jiri; Zalud, Zdenek

    2013-04-01

    This effort is aimed to derive a simple tool for separating soil evaporation and transpiration from evapotranspiration, measured by Bowen ration energy balance method (BREB) in short rotation coppice (SRC). The main idea is to utilize daily data of actual evapotranspiration (ETa) measured above bare soil (spring 2010 - first year following harvest), reference evapotranspiration (ETo) measured by atmometer ETgage and precipitation data, in order to create an algorithm for estimation evaporation from bare soil. This approach is based on the following assumption: evaporation of wetted bare soil same as the ETo from atmometer is assumed to be identical in days with rain. In first and further days with no rain (and e.g. high evaporative demand) the easily evaporable soil water depletes and ETa so as crop coefficient of bare soil (Kcb) decreases in a way similar to decreasing power function. The algorithm represents a parameterized function of daily cumulated ETo (ETc) measured by atmometer in days elapsed from last rain event (Kcb = a*ETc^b). After each rain event the accumulation of ETo starts again till next rain event (e. g. only days with no rain are cumulated). The function provides decreasing Kcb for each day without rain. The bare soil evaporation can be estimated when the atmometer-recorded value is multiplied by Kcb for particular day without rain. In days with rain Kcb is assumed to be back at 1. This method was successfully tested for estimating evaporation from bare soil under closed canopy of poplar-based SRC. When subtracting the estimated soil evaporation from total ETa flux, measured above the canopy using BREB method, it is possible to obtain transpiration flux of the canopy. There is also possibility to test this approach on the contrary - subtracting transpiration derived from sap-flow measurement from total ETa flux is possible to get soil evaporation as well. Acknowledgements: The present experiment is made within the frame of project Inter

  8. Comparison of soybean evapotranspirations measured by weighing ...

    African Journals Online (AJOL)

    STORAGESEVER

    2010-07-26

    Jul 26, 2010 ... atmosphere relations and considered as basic method to calibrate evapotranspiration ..... are the turbulent exchange coefficients for heat transport and water vapor transfer (m2s-1), ∆q is the ..... Forest Meteorol. 111: 109-120.

  9. Wetlands Evapotranspiration Using Remotely Sensed Solar Radiation

    Science.gov (United States)

    Jacobs, J. M.; Myers, D. A.; Anderson, M. C.

    2001-12-01

    The application of remote sensing methods to estimate evapotranspiration has the advantage of good spatial resolution and excellent spatial coverage, but may have the disadvantage of infrequent sampling and considerable expense. The GOES satellites provide enhanced temporal resolution with hourly estimates of solar radiation and have a spatial resolution that is significantly better than that available from most ground-based pyranometer networks. As solar radiation is the primary forcing variable in wetland evapotranspiration, the opportunity to apply GOES satellite data to wetland hydrologic analyses is great. An accuracy assessment of the remote sensing product is important and the subsequent validation of the evapotranspiration estimates are a critical step for the use of this product. A wetland field experiment was conducted in the Paynes Prairie Preserve, North Central Florida during a growing season characterized by significant convective activity. Evapotranspiration and other surface energy balance components of a wet prairie community dominated by Panicum hemitomon (maiden cane), Ptilimnium capillaceum (mock bishop's weed), and Eupatorium capillifolium (dog fennel) were investigated. Incoming solar radiation derived from GOES-8 satellite observations, in combination with local meteorological measurements, were used to model evapotranspiration from a wetland. The satellite solar radiation, derived net radiation and estimated evapotranspiration estimates were compared to measured data at 30-min intervals and daily times scales.

  10. Agro-ecological Differentials in Soybean Crop Evapotranspiration ...

    African Journals Online (AJOL)

    This study estimated soybean crop evapotranspiration from weather data using the cropwat model. The effects of reference evapotranspiration, crop coefficients, and yield response factor were quantified for three different agroecological zones in Cameroon. The evapotranspiration of soybean was observed to be 281.03 ...

  11. shoot water content and reference evapotranspiration for ...

    African Journals Online (AJOL)

    ACSS

    is the slope of saturation vapour pressure curve at air temperature T (kPa °C-1), T is air temperature (°C). Crop coefficient. Shoot water content was assumed to be crop coefficient, as crop evapotranspiration is always determined under unlimited water supply (Pereira et al., 2015), and hence the shoot water content reflects ...

  12. Review: Estimating evapotranspiration using remote sensing and ...

    African Journals Online (AJOL)

    Review: Estimating evapotranspiration using remote sensing and the Surface Energy Balance System – A South African perspective. ... It is therefore recommended that any further research using the SEBS model in South Africa should be limited to agricultural areas where accurate vegetation parameters can be obtained, ...

  13. Measuring forest evapotranspiration--theory and problems

    Science.gov (United States)

    Anthony C. Federer; Anthony C. Federer

    1970-01-01

    A satisfactory general method of measuring forest evapotranspiration has yet to be developed. Many procedures have been tried, but only the soil-water budget method and the micrometeorological methods offer any degree of success. This paper is a discussion of these procedures and the problems that arise in applying them. It is designed as a reference for scientists and...

  14. Evapotranspiration Derived from Satellite Observed Surface Temperatures

    NARCIS (Netherlands)

    Klaassen, Wim; Berg, Wim van den

    1985-01-01

    Evapotranspiration is calculated from surface temperatures using an energy balance method. This method is sensitive to the temperature difference between the surface and the air above, and somewhat to the windspeed. In this study we consider the influence of the spatial variability of air

  15. shoot water content and reference evapotranspiration for ...

    African Journals Online (AJOL)

    ACSS

    Determination of water requirement for crops in resource limited areas is challenging, yet worsened by the common assumption that all crop varieties within a species have similar water requirements. The objective of the study was to indirectly determine crop evapotranspiration of soybean varieties, using reference ...

  16. Groundwater Recharge, Evapotranspiration and Surface Runoff ...

    African Journals Online (AJOL)

    Groundwater Recharge, Evapotranspiration and Surface Runoff Estimation Using WetSpass Modeling Method in Illala Catchment, Northern Ethiopia. ... Abstract. Hydrometeorological information is important in planning and management of natural resources. The northern Ethiopia in general and Illala sub-basin in particular ...

  17. Dynamics of MODIS evapotranspiration in South Africa

    CSIR Research Space (South Africa)

    Jovanovic, Nebojsa

    2015-01-01

    Full Text Available dependent on rainfall and potential evapotranspiration (PET) in 4 climatically different regions of South Africa. Average ET in South Africa (2000–2012) was estimated to be 303 mm·a-1 or 481.4 x 109 m3·a1 (14% of PET and 67% of rainfall), mainly in the form...

  18. Obtaining evapotranspiration and surface energy fluxes with ...

    African Journals Online (AJOL)

    In this study, SEBAL (Surface Energy Balance Algorithm for Land), a remote sensing based evapotranspiration model, has been applied with Landsat ETM+ sensor for the estimation of actual ... The land uses in this study area consists of irrigated agriculture, rain-fed agriculture and livestock grazing. The obtained results ...

  19. Groundwater Recharge, Evapotranspiration and Surface Runoff ...

    African Journals Online (AJOL)

    Bheema

    this unit at different parts of the catchment. Hence, in the ... decrease currently due to different soil and water conservation practices conducted especially in .... water body. Actual evapotranspiration is one components of water balance to determine groundwater recharge of Illala catchment using the WetSpass model.

  20. Areal potential Haude-evapotranspiration for Northern Germany

    Energy Technology Data Exchange (ETDEWEB)

    Beinhauer, R.

    1988-02-01

    Daily observations of 66 stations in Northern Germany were used to calculate Haude's potential evapotranspiration. A variogram analysis tested spatial reproduction. A long range annual mean of 1951-80 of potential evapotranspiration is presented in a chart together with charts of mean evapotranspiration for oats, apples, winterwheat, beetroot, winterbarley, maize and pasture within their phenological phases emergence to maturity or end of season.

  1. National Weather Service Forecast Reference Evapotranspiration

    Science.gov (United States)

    Osborne, H. D.; Palmer, C. K.; Krone-Davis, P.; Melton, F. S.; Hobbins, M.

    2013-12-01

    The National Weather Service (NWS), Weather Forecasting Offices (WFOs) are producing daily reference evapotranspiration (ETrc) forecasts or FRET across the Western Region and in other selected locations since 2009, using the Penman - Monteith Reference Evapotranspiration equation for a short canopy (12 cm grasses), adopted by the Environmental Water Resources Institute of the American Society of Civil Engineers (ASCE-EWRI, 2004). The sensitivity of these daily calculations to fluctuations in temperatures, humidity, winds, and sky cover allows forecasters with knowledge of local terrain and weather patterns to better forecast in the ETrc inputs. The daily FRET product then evolved into a suite of products, including a weekly ETrc forecast for better water planning and a tabular point forecast for easy ingest into local water management-models. The ETrc forecast product suite allows water managers, the agricultural community, and the public to make more informed water-use decisions. These products permit operational planning, especially with the impending drought across much of the West. For example, the California Department of Water Resources not only ingests the FRET into their soil moisture models, but uses the FRET calculations when determining the reservoir releases in the Sacramento and American Rivers. We will also focus on the expansion of FRET verification, which compares the daily FRET to the observations of ETo from the California Irrigation Management Information System (CIMIS) across California's Central Valley for the 2012 water year.

  2. Estimating seasonal evapotranspiration from temporal satellite images

    Science.gov (United States)

    Singh, Ramesh K.; Liu, Shu-Guang; Tieszen, Larry L.; Suyker, Andrew E.; Verma, Shashi B.

    2012-01-01

    Estimating seasonal evapotranspiration (ET) has many applications in water resources planning and management, including hydrological and ecological modeling. Availability of satellite remote sensing images is limited due to repeat cycle of satellite or cloud cover. This study was conducted to determine the suitability of different methods namely cubic spline, fixed, and linear for estimating seasonal ET from temporal remotely sensed images. Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) model in conjunction with the wet METRIC (wMETRIC), a modified version of the METRIC model, was used to estimate ET on the days of satellite overpass using eight Landsat images during the 2001 crop growing season in Midwest USA. The model-estimated daily ET was in good agreement (R2 = 0.91) with the eddy covariance tower-measured daily ET. The standard error of daily ET was 0.6 mm (20%) at three validation sites in Nebraska, USA. There was no statistically significant difference (P > 0.05) among the cubic spline, fixed, and linear methods for computing seasonal (July–December) ET from temporal ET estimates. Overall, the cubic spline resulted in the lowest standard error of 6 mm (1.67%) for seasonal ET. However, further testing of this method for multiple years is necessary to determine its suitability.

  3. Evapotranspiration and Crop Coefficients of Grain Legumes in Semi ...

    African Journals Online (AJOL)

    Crop evapotranspiration (ETc) is a very important parameter in irrigation management. It can be either directly measured using water balance approach or estimated. A field experiment was carried out at Hudeiba Research Station farm in Sudan to determine crop evapotranspiration (ETc) and coefficients (kc) for faba bean ...

  4. Evapotranspiration studies on Themeda triandra Forsk. under field ...

    African Journals Online (AJOL)

    Hydraulic non-floating lysimeters were used to determine the evapotranspiration (Et) of a Themeda triandra grass cover under field conditions. The highest evapotranspiration losses were recorded during December and January when the plants were in the reproductive phase, provided the soil moisture was not limiting.

  5. Blaney-Morin-Nigeria (BMN) Evapotranspiration Model (A Technical ...

    African Journals Online (AJOL)

    Duru [1] presented a modified form of the Blaney-Morin potential evapotranspiration equation christened Blaney-Morin- Nigeria (BMN) Evapotranspiration (ET) model for use in Nigeria. In this work, Duru recognize the very wide variability of relative humidity in Nigeria and consequently the very important role this parameter ...

  6. Potential Evapotranspiration Estimates (mm) for for Alaska, CRU TS3.0. The Wilderness Society, 2011.

    Data.gov (United States)

    Arctic Landscape Conservation Cooperative — Potential Evapotranspiration (PET): These data represent decadal mean totals of potential evapotranspiration estimates (mm). The file name specifies the decade the...

  7. Potential Evapotranspiration Estimates (mm) for for Alaska, CCCMA - A1B scenario. The Wilderness Society, 2011.

    Data.gov (United States)

    Arctic Landscape Conservation Cooperative — Potential Evapotranspiration (PET): These data represent decadal mean totals of potential evapotranspiration estimates (mm). The file name specifies the decade the...

  8. Seasonal contributions of vegetation types to suburban evapotranspiration

    Science.gov (United States)

    Peters, Emily B.; Hiller, Rebecca V.; McFadden, Joseph P.

    2011-03-01

    Evapotranspiration is an important term of energy and water budgets in urban areas and is responsible for multiple ecosystem services provided by urban vegetation. The spatial heterogeneity of urban surface types with different seasonal water use patterns (e.g., trees and turfgrass lawns) complicates efforts to predict and manage urban evapotranspiration rates, necessitating a surface type, or component-based, approach. In a suburban neighborhood of Minneapolis-Saint Paul, Minnesota, United States, we simultaneously measured ecosystem evapotranspiration and its main component fluxes using eddy covariance and heat dissipation sap flux techniques to assess the relative contribution of plant functional types (evergreen needleleaf tree, deciduous broadleaf tree, cool season turfgrass) to seasonal and spatial variations in evapotranspiration. Component-based evapotranspiration estimates agreed well with measured water vapor fluxes, although the imbalance between methods varied seasonally from a 20% overestimate in spring to an 11% underestimate in summer. Turfgrasses represented the largest contribution to annual evapotranspiration in recreational and residential land use types (87% and 64%, respectively), followed by trees (10% and 31%, respectively), with the relative contribution of plant functional types dependent on their fractional cover and daily water use. Recreational areas had higher annual evapotranspiration than residential areas (467 versus 324 mm yr-1, respectively) and altered seasonal patterns of evapotranspiration due to greater turfgrass cover (74% versus 34%, respectively). Our results suggest that plant functional types capture much of the variability required to predict the seasonal patterns of evapotranspiration among cities, as well as differences in evapotranspiration that could result from changes in climate, land use, or vegetation composition.

  9. Evaluation of six potential evapotranspiration models for estimating crop potential and actual evapotranspiration in arid regions

    Science.gov (United States)

    Li, Sien; Kang, Shaozhong; Zhang, Lu; Zhang, Jianhua; Du, Taisheng; Tong, Ling; Ding, Risheng

    2016-12-01

    Using potential evapotranspiration (PET) to estimate crop actual evapotranspiration (AET) is a critical approach in hydrological models. However, which PET model performs best and can be used to predict crop AET over the entire growth season in arid regions still remains unclear. The six frequently-used PET models, i.e. Blaney-Criddle (BC), Hargreaves (HA), Priestley-Taylor (PT), Dalton (DA), Penman (PE) and Shuttleworth (SW) models were considered and evaluated in the study. Five-year eddy covariance data over the maize field and vineyard in arid northwest China were used to examine the accuracy of PET models in estimating daily crop AET. Results indicate that the PE, SW and PT models underestimated daily ET by less than 6% with RMSE lower than 35 W m-2 during the four years, while the BC, HA and DA models under-predicted daily ET approximately by 10% with RMSE higher than 40 W m-2. Compared to BC, HA and DA models, PE, SW and PT models were more reliable and accurate for estimating crop PET and AET in arid regions. Thus the PE, SW and PT models were recommended for predicting crop evapotranspiration in hydrological models in arid regions.

  10. Educational Software for Illustration of Drainage, Evapotranspiration, and Crop Yield.

    Science.gov (United States)

    Khan, A. H.; And Others

    1996-01-01

    Describes a study that developed a software package for illustrating drainage, evapotranspiration, and crop yield as influenced by water conditions. The software is a tool for depicting water's influence on crop production in western Kansas. (DDR)

  11. Evapotranspiration Input Data for the Central Valley Hydrologic Model (CVHM)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This digital dataset contains monthly reference evapotranspiration (ETo) data for the Central Valley Hydrologic Model (CVHM). The Central Valley encompasses an...

  12. Evapotranspiration-based irrigation scheduling of lettuce and broccoli

    Science.gov (United States)

    Estimation of crop evapotranspiration supports efficient irrigation water management, which in turn supports water conservation, mitigation of groundwater depletion/degradation, energy savings, and crop quality maintenance. Past research in California has revealed strong relationships between fract...

  13. Comparison of Crop Evapotranspiration Estimates from Reference Evapotranspiration Equations and a Variational Data Assimilation Approach

    Science.gov (United States)

    Bateni, S. M.; Michalik, T.; Multsch, S.; Breuer, L.

    2015-12-01

    Crop evapotranspiration (ETc) is a key component of water resources management in irrigation of farmlands as it determines the crop water consumption. Numerous methods have been used to estimate ETc for scheduling irrigation and evaluating the soil water balance. However, there is a significant difference in ETc estimates from various models, which leads to a large uncertainty in the soil water balance, crop water consumption, and irrigation scheduling. In this study, several commonly-used ETc equations (Turc, Priestley-Taylor, Hargreaves-Samani, Penman-Monteith) are compared with the variational data assimilation approach (VDA) of Bateni et al. (2013). The ETc equations initially estimate the reference evapotranspiration (ETo), which is the evapotranspiration from a healthy and actively-transpiring grass field with ample water in the soil. Thereafter, ETc is calculated by multiplying ETo by the crop coefficient (Kc), which accounts for the crop type and soil water stress. To properly apply the Kc to non-standard conditions, a daily water balance estimation for the root zone is required, which is done by two soil water budget models (Cropwat, Hydrus-1D) that compute incoming and outgoing water flows in the soil profile. In contrast to these methods that estimate ETc in two steps, the VDA approach directly predicts ETc by assimilating sequences of land surface temperature into the heat diffusion equation and thus it is expected to provide more accurate ETc estimates. All approaches are applied over three cropland sites namely, Bondville, Fermi, and Mead in the summer of 2006 and 2007. These sites are part of the AmeriFlux network and provide a wide variety of hydrological conditions. The results show that the variational data assimilation approach performs better compared to other equations.

  14. NASA GLDAS Evapotranspiration Data and Climatology

    Science.gov (United States)

    Rui, Hualan; Beaudoing, Hiroko Kato; Teng, William L.; Vollmer, Bruce; Rodell, Matthew

    2012-01-01

    Evapotranspiration (ET) is the water lost to the atmosphere by evaporation and transpiration. ET is a shared component in the energy and water budget, therefore, a critical variable for global energy and water cycle and climate change studies. However, direct ET measurements and data acquisition are difficult and expensive, especially at the global level. Therefore, modeling is one common alternative for estimating ET. With the goal to generate optimal fields of land surface states and fluxes, the Global Land Data Assimilation System (GLDAS) has been generating quality-controlled, spatially and temporally consistent, terrestrial hydrologic data, including ET and other variables that affect evaporation and transpiration, such as temperature, precipitation, humidity, wind, soil moisture, heat flux, and solar radiation. This poster presents the long-term ET climatology (mean and monthly), derived from the 61-year GLDAS-2 monthly 1.0 deg x 1.0 deg. NOAH model Experiment-1 data, and describes the basic characteristics of spatial and seasonal variations of the climatology. The time series of GLDAS-2 precipitation and radiation, and ET are also discussed to show the improvement of GLDAS-2 forcing data and model output over those from GLDAS-1.

  15. Evapotranspiration of rose cultivated in protected environment

    Directory of Open Access Journals (Sweden)

    Eduardo C. Oliveira

    2014-03-01

    Full Text Available The objective of this study was to determine the evapotranspiration and crop coefficient for the cut rose (cv. Carola cultivated in protected environment and the coefficient of small tank installed inside the greenhouse during the period of one year. Five rows of plants were planted with spacing of 1.20 m between rows and 0.20 m between plants. Each line consisted of five plots with five plants per plot. Plants of the second and fourth rows and of the second and fourth plots were installed in four drainage lysimeters with dimensions of 1.20 x 1.20 x 0.80 m. The plants of the remaining plots were considered as border plants. A drip irrigation system was used. An automatic weather station was installed in the greenhouse and the data were collected and stored daily at an interval of one hour in a data-logger. The crop coefficient (Kc showed mean values of 0.75 in the vegetative phase and 1.18 during the productive phase. The small pan (tank coefficient (Ktr was 0.72.

  16. Evapotranspiration seasonality across the Amazon Basin

    Science.gov (United States)

    Eiji Maeda, Eduardo; Ma, Xuanlong; Wagner, Fabien Hubert; Kim, Hyungjun; Oki, Taikan; Eamus, Derek; Huete, Alfredo

    2017-06-01

    Evapotranspiration (ET) of Amazon forests is a main driver of regional climate patterns and an important indicator of ecosystem functioning. Despite its importance, the seasonal variability of ET over Amazon forests, and its relationship with environmental drivers, is still poorly understood. In this study, we carry out a water balance approach to analyse seasonal patterns in ET and their relationships with water and energy drivers over five sub-basins across the Amazon Basin. We used in situ measurements of river discharge, and remotely sensed estimates of terrestrial water storage, rainfall, and solar radiation. We show that the characteristics of ET seasonality in all sub-basins differ in timing and magnitude. The highest mean annual ET was found in the northern Rio Negro basin (˜ 1497 mm year-1) and the lowest values in the Solimões River basin (˜ 986 mm year-1). For the first time in a basin-scale study, using observational data, we show that factors limiting ET vary across climatic gradients in the Amazon, confirming local-scale eddy covariance studies. Both annual mean and seasonality in ET are driven by a combination of energy and water availability, as neither rainfall nor radiation alone could explain patterns in ET. In southern basins, despite seasonal rainfall deficits, deep root water uptake allows increasing rates of ET during the dry season, when radiation is usually higher than in the wet season. We demonstrate contrasting ET seasonality with satellite greenness across Amazon forests, with strong asynchronous relationships in ever-wet watersheds, and positive correlations observed in seasonally dry watersheds. Finally, we compared our results with estimates obtained by two ET models, and we conclude that neither of the two tested models could provide a consistent representation of ET seasonal patterns across the Amazon.

  17. Monitoring cropland evapotranspiration using MODIS products in Southern Brazil

    Science.gov (United States)

    Ruhoff, Anderson; Aparecida Moreira, Adriana; de Arruda Souza, Vanessa; Roberti, Debora Regina

    2017-04-01

    Evapotranspiration (ET), including water loss from plant transpiration and land evaporation, is of vital importance for understanding hydrological processes and climate dynamics. In this context, remote sensing is considered as the most important tool for estimate ET over large areas. The Moderate Resolution Imaging Spectroradiometer (MODIS) offers an interesting opportunity to evaluate ET with spatial resolution of 1 km. The MODIS global evapotranspiration algorithm (MOD16) considers both surface energy fluxes and climatic constraints on ET (water or temperature stress) to estimate plant transpiration and soil evaporation based on Penman-Monteith equation. The algorithm is driven by remotely sensed and reanalysis meteorological data. In this study, MOD16 algorithm was applied to the State of Rio Grande do Sul (in Southern Brazil) to analyse cropland and natural vegetation evapotranspiration and its impacts during drought events. We validated MOD16 estimations using eddy correlation measurements and water balance closure at monthly and annual time scales. We used observed discharge data from three large rivers in Southern Brazil (Jacuí, Taquari and Ibicuí), precipitation data from TRMM Multi-satellite Precipitation Analysis (3B43 version 7) and terrestrial water storage estimations from the Gravity Recovery and climate Experiment (GRACE). MOD16 algorithm detected evapotranspiration in different land use and land cover conditions. In cropland areas, the average evapotranspiration was 705 mm/y, while in pasture/grassland was 750 mm/y and in forest areas was 1099 mm/y. Compared to the annual water balance, evapotranspiration was underestimated, with mean relative errors between 8 and 30% and coefficients of correlation between 0.42 to 0.53. The water storage change (dS/dt) computed from the water balance closure at monthly time scales showed a significant correlation with the terrestrial water storage obtained from GRACE data, with a coefficient of correlation of 0

  18. TDR Technique for Estimating the Intensity of Evapotranspiration of Turfgrasses.

    Science.gov (United States)

    Janik, Grzegorz; Wolski, Karol; Daniel, Anna; Albert, Małgorzata; Skierucha, Wojciech; Wilczek, Andrzej; Szyszkowski, Paweł; Walczak, Amadeusz

    2015-01-01

    The paper presents a method for precise estimation of evapotranspiration of selected turfgrass species. The evapotranspiration functions, whose domains are only two relatively easy to measure parameters, were developed separately for each of the grass species. Those parameters are the temperature and the volumetric moisture of soil at the depth of 2.5 cm. Evapotranspiration has the character of a modified logistic function with empirical parameters. It assumes the form ETR(θ (2.5 cm), T (2.5 cm)) = A/(1 + B · e (-C · (θ (2.5 cm) · T (2.5 cm)), where: ETR(θ (2.5 cm), T (2.5 cm)) is evapotranspiration [mm · h(-1)], θ (2.5 cm) is volumetric moisture of soil at the depth of 2.5 cm [m(3) · m(-3)], T (2.5 cm) is soil temperature at the depth of 2.5 cm [°C], and A, B, and C are empirical coefficients calculated individually for each of the grass species [mm · h(1)], and [-], [(m(3) · m(-3) · °C)(-1)]. The values of evapotranspiration calculated on the basis of the presented function can be used as input data for the design of systems for the automatic control of irrigation systems ensuring optimum moisture conditions in the active layer of lawn swards.

  19. Global daily reference evapotranspiration modeling and evaluation

    Science.gov (United States)

    Senay, G.B.; Verdin, J.P.; Lietzow, R.; Melesse, Assefa M.

    2008-01-01

    Accurate and reliable evapotranspiration (ET) datasets are crucial in regional water and energy balance studies. Due to the complex instrumentation requirements, actual ET values are generally estimated from reference ET values by adjustment factors using coefficients for water stress and vegetation conditions, commonly referred to as crop coefficients. Until recently, the modeling of reference ET has been solely based on important weather variables collected from weather stations that are generally located in selected agro-climatic locations. Since 2001, the National Oceanic and Atmospheric Administration’s Global Data Assimilation System (GDAS) has been producing six-hourly climate parameter datasets that are used to calculate daily reference ET for the whole globe at 1-degree spatial resolution. The U.S. Geological Survey Center for Earth Resources Observation and Science has been producing daily reference ET (ETo) since 2001, and it has been used on a variety of operational hydrological models for drought and streamflow monitoring all over the world. With the increasing availability of local station-based reference ET estimates, we evaluated the GDAS-based reference ET estimates using data from the California Irrigation Management Information System (CIMIS). Daily CIMIS reference ET estimates from 85 stations were compared with GDAS-based reference ET at different spatial and temporal scales using five-year daily data from 2002 through 2006. Despite the large difference in spatial scale (point vs. ∼100 km grid cell) between the two datasets, the correlations between station-based ET and GDAS-ET were very high, exceeding 0.97 on a daily basis to more than 0.99 on time scales of more than 10 days. Both the temporal and spatial correspondences in trend/pattern and magnitudes between the two datasets were satisfactory, suggesting the reliability of using GDAS parameter-based reference ET for regional water and energy balance studies in many parts of the world

  20. Tomato and cowpea crop evapotranspiration in an unheated greenhouse

    Directory of Open Access Journals (Sweden)

    Xu Junzeng

    2008-06-01

    Full Text Available With the development of protected cultivation of vegetables in China, it is necessary to study the water requirements of crops in greenhouses. Lysimeter experiments were carried out to investigate tomato (2001 and cowpea (2004 crop evapotranspiration (ETc in an unheated greenhouse in Eastern China. Results showed remarkably reduced crop evapotranspiration inside the greenhouse as compared with that outside. ETc increased with the growth of the crops, and varied in accordance with the temperature inside the greenhouse and 20-cm pan evaporation outside, reaching its maximum value at the stage when plants’ growth was most active. Differences between the variation of crop evapotranspiration and pan evaporation inside the greenhouse were caused by shading of the pan in the later period when the crops were taller than the location where the pan was installed, 70 cm above ground. The ratio of crop evapotranspiration to pan evaporation was not constant as reported in previous studies, and the variation of the inside ratio αin lagged behind that of the outside ratio αout. Simulation of crop evapotranspiration based on 20-cm pan evaporation inside the greenhouse is more reasonable than that based on 20-cm pan evaporation outside, although pan evaporation outside is more consistent with ETc than that inside. The value of αin, calculated based on air temperature, relative humidity, and ground temperature inside, plays a dominant role in the calculation of ETc. As the crop height increases, altering the location of the inside pan and placing it above the canopy, out of the shade, would help to achieve more reasonable values of crop evapotranspiration.

  1. Tomato and cowpea crop evapotranspiration in an unheated greenhouse

    Directory of Open Access Journals (Sweden)

    Xu Junzeng

    2008-06-01

    Full Text Available With the development of protected cultivation of vegetables in China, it is necessary to study the water requirements of crops in greenhouses. Lysimeter experiments were carried out to investigate tomato (2001 and cowpea (2004 crop evapotranspiration (ETc in an unheated greenhouse in Eastern China. Results showed remarkably reduced crop evapotranspiration inside the greenhouse as compared with that outside. ETc increased with the growth of the crops, and varied in accordance with the temperature inside the greenhouse and 20-cm pan evaporation outside, reaching its maximum value at the stage when plants' growth was most active. Differences between the variation of crop evapotranspiration and pan evaporation inside the greenhouse were caused by shading of the pan in the later period when the crops were taller than the location where the pan was installed, 70 cm above ground. The ratio of crop evapotranspiration to pan evaporation was not constant as reported in previous studies, and the variation of the inside ratio αin lagged behind that of the outside ratio αout. Simulation of crop evapotranspiration based on 20-cm pan evaporation inside the greenhouse is more reasonable than that based on 20-cm pan evaporation outside, although pan evaporation outside is more consistent with ETc than that inside. The value of αin, calculated based on air temperature, relative humidity, and ground temperature inside, plays a dominant role in the calculation of ETc. As the crop height increases, altering the location of the inside pan and placing it above the canopy, out of the shade, would help to achieve more reasonable values of crop evapotranspiration.

  2. Assessing reference evapotranspiration in a subhumid climate in NE Austria

    Science.gov (United States)

    Nolz, Reinhard; Eitzinger, Josef; Cepuder, Peter

    2015-04-01

    Computing reference evapotranspiration and multiplying it with a specific crop coefficient as recommended by the Food and Agriculture Organization of the United Nations (FAO) is the most widely accepted approach to estimate plant water requirements. The standardized form of the well-known FAO Penman-Monteith equation, published by the Environmental and Water Resources Institute of the American Society of Civil Engineers (ASCE-EWRI), is recommended as a standard procedure for calculating reference evapotranspiration. Applied and validated under different climatic conditions it generally achieved good results compared to other methods. However, several studies documented deviations between measured and calculated reference evapotranspiration depending on local environmental conditions. Consequently, it seems advisable to evaluate the model under local environmental conditions. Evapotranspiration was determined at a subhumid site in Austria (48°12'N, 16°34'E; 157 m asl) using a large weighing lysimeter operated at (limited) reference conditions and compared with calculations according to ASCE-EWRI. The lysimeter had an inner diameter of 1.9 m and a hemispherical bottom with a maximum depth of 2.5 m. Seepage water was measured at a free draining outlet using a tipping bucket. Lysimeter mass changes were sensed by a weighing facility with an accuracy of ±0.1 mm. Both rainfall and evapotranspiration were determined directly from lysimeter data using a simple water balance equation. Meteorological data for the ASCE-EWRI model were obtained from a weather station of the Central Institute for Meteorology and Geodynamics, Austria (ZAMG). The study period was from 2005 to 2010, analyses were based upon daily time steps. Daily calculated reference evapotranspiration was generally overestimated at small values, whereas it was rather underestimated when evapotranspiration was large, which is supported also by other studies. In the given case, advection of sensible heat proved

  3. Drought impacts and resilience on crops via evapotranspiration estimations

    Science.gov (United States)

    Timmermans, Joris; Asadollahi Dolatabad, Saeid

    2015-04-01

    Currently, the global needs for food and water is at a critical level. It has been estimated that 12.5 % of the global population suffers from malnutrition and 768 million people still do not have access to clean drinking water. This need is increasing because of population growth but also by climate change. Changes in precipitation patterns will result either in flooding or droughts. Consequently availability, usability and affordability of water is becoming challenge and efficient use of water and water management is becoming more important, particularly during severe drought events. Drought monitoring for agricultural purposes is very hard. While meteorological drought can accurately be monitored using precipitation only, estimating agricultural drought is more difficult. This is because agricultural drought is dependent on the meteorological drought, the impacts on the vegetation, and the resilience of the crops. As such not only precipitation estimates are required but also evapotranspiration at plant/plot scale. Evapotranspiration (ET) describes the amount of water evaporated from soil and vegetation. As 65% of precipitation is lost by ET, drought severity is highly linked with this variable. In drought research, the precise quantification of ET and its spatio-temporal variability is therefore essential. In this view, remote sensing based models to estimate ET, such as SEBAL and SEBS, are of high value. However the resolution of current evapotranspiration products are not good enough for monitoring the impact of the droughts on the specific crops. This limitation originates because plot scales are in general smaller than the resolution of the available satellite ET products. As such remote sensing estimates of evapotranspiration are always a combination of different land surface types and cannot be used for plant health and drought resilience studies. The goal of this research is therefore to enable adequate resolutions of daily evapotranspiration estimates

  4. Potential Evapotranspiration Estimates (mm) for for Alaska, ECHAM5 - A1B scenario. The Wilderness Society, 2011.

    Data.gov (United States)

    Arctic Landscape Conservation Cooperative — Potential Evapotranspiration (PET): These data represent decadal mean totals of potential evapotranspiration estimates (mm). The file name specifies the decade the...

  5. In-Situ Determination Of Actual Evapotranspiration Using Zero Flux ...

    African Journals Online (AJOL)

    Physical expression and analytical approach of the plane of zero flux method was demonstrated in determining the values of actual evapotranspiration of the maize crop grown in the field. The method was simple to use and did not require the values of hydraulic conductivity, which are often very laborious to determine in the ...

  6. Modelling annual evapotranspiration in a semi-arid, African savanna ...

    African Journals Online (AJOL)

    Modelling annual evapotranspiration in a semi-arid, African savanna: functional convergence theory, MODIS LAI and the Penman–Monteith equation. ... and, when used independently of the eddy covariance data, ETMODIS predicted an annual ET of 378 mm in 2007 for the semi-arid savanna around the Skukuza flux site.

  7. Hydrological model uncertainty due to spatial evapotranspiration estimation methods

    Czech Academy of Sciences Publication Activity Database

    Yu, X.; Lamačová, Anna; Duffy, Ch.; Krám, P.; Hruška, Jakub

    2016-01-01

    Roč. 90, part B (2016), s. 90-101 ISSN 0098-3004 R&D Projects: GA MŠk(CZ) LO1415 Institutional support: RVO:67179843 Keywords : Uncertainty * Evapotranspiration * Forest management * PIHM * Biome -BGC Subject RIV: EH - Ecology, Behaviour Impact factor: 2.533, year: 2016

  8. Estimating evapotranspiration using remote sensing and the Surface ...

    African Journals Online (AJOL)

    2013-07-08

    Jul 8, 2013 ... Remote sensing-based evapotranspiration (ET) algorithms developed in recent years are well suited for estimating evapo- transpiration and its spatial trends over time. In this paper the application of energy balance methods in South Africa is reviewed, showing that the Surface Energy Balance Algorithm ...

  9. Validation of remotely-sensed evapotranspiration and NDWI using ...

    African Journals Online (AJOL)

    Remote sensing techniques and products have recently been developed for the estimation of water balance variables. The objective of this study was to test the reliability of LandSAF (Land Surface Analyses Satellite Applications Facility) evapotranspiration (ET) and SPOT-Vegetation Normalised Difference Water Index ...

  10. Trend analysis of evapotranspiration over India- observed from long ...

    Indian Academy of Sciences (India)

    3

    in this study to validate satellite derived monthly ET data over India from 1983 to 2006. 3.3 Climate data: Several climatic parameters affect the land evapotranspiration. The influence of some of the important parameters such as precipitation, air temperature, soil moisture and incident solar radiation on ET over India was ...

  11. Trend Analysis of Evapotranspiration over India- Observed from ...

    Indian Academy of Sciences (India)

    3

    Abstract. Owing to the lack of consistent spatial time series data on actual evapotranspiration (ET), very few studies have been conducted on the long-term trend and variability in ET at a national scale over the Indian subcontinent. The present study uses biome specific ET data derived from NOAA satellite's Advanced Very ...

  12. Evapotranspiration in three plant communities of a Rhigozum ...

    African Journals Online (AJOL)

    Evapotranspiration losses in three Rhigozum trichotomum plant communities namely, pure grass, pure R. trichotomum and a mixed stand of grass and R. trichotomum were determined during the 1985-86 growing season. Three hydrologically isolated plots in each community type were irrigated and changes in soil water ...

  13. Evapotranspiration and water use efficiency of different grass ...

    African Journals Online (AJOL)

    Evapotranspiration (Et) and water use efficiency (WUE) were determined for each of seven grass species during the 1986/87 seasons. The highest and lowest mean daily Et of 2, 39 and 1, 66 mm were recorded respectively for Themeda triandra and Sporobolus fimbriatus. Between species, the average Et for the two ...

  14. Modeling Using Dryness Index to Predict Evapotranspiration in a ...

    African Journals Online (AJOL)

    Based on crop-climate studies from the viewpoint of modeling and predictability, this paper presents a new dryness index (DI), the ratio of rainfall over reference evapotranspiration (ET), for Ilorin (8.48o N) in the transition zone between humid and semi-arid climatic belts in Nigeria. The ET values were computed using the ...

  15. Estimation of monthly reference evapotranspiration (ETO) for areas ...

    African Journals Online (AJOL)

    In this paper monthly reference evapotranspiration (ETo)- altitude regression equations are developed for the country using 125 stations meteorological data. ETo are calculated based on radiation (sunshine hours), temperature, relative humidity, and wind speed data. FA O-Penman Monteith formula is applied to calculate ...

  16. Effect of evapotranspiration models on optimised values of apron ...

    African Journals Online (AJOL)

    The purpose of tank irrigation system is to provide a mechanism for making better and sustainable use of the scarce and infrequent rainfall resource occurring in arid and semi-arid regions for agricultural production. Three models which attempt to explain the mode of evapotranspiration under drip irrigated agriculture in ...

  17. Thermal remote sensing data for estimating evapotranspiration on a ...

    African Journals Online (AJOL)

    The amount of evapotranspiration (ET) is an essential input for modelling the water balance equation, and also has substantial value in the overall estimation of available water for long-term planning of the water resources of regional or very large river basins, such as the Nile, Congo, Niger and Volta. As an alternative to ...

  18. the sensitivity of evapotranspiration models to errors in model ...

    African Journals Online (AJOL)

    Dr Obe

    used in Nigeria, their sensitivity analysis is important. Again, Jensen [4], writing on the use of empirical formulae for the determination of evapotranspiration rates, said that such formulae. (models) can be used when the "absolute accuracy" of the measured climatic variables have been found adequate. Through sensitivity.

  19. Measurement and modelling of evapotranspiration in three fynbos ...

    African Journals Online (AJOL)

    Evapotranspiration (ET) was quantified at each site during specific periods using a boundary layer scintillometer and energy balance system. A simple dual source model in which the stand ET was calculated as the algebraic sum of outputs from soil evaporation and transpiration sub-models was used to scale up the ET ...

  20. Forest evapotranspiration: measurements and modeling at multiple scales

    Science.gov (United States)

    Ge Sun; J-C. Domec; Devendra Amatya

    2016-01-01

    Compared with traditional engineering hydrology, forest hydrology has a relatively long history of studying the effects of vegetation in regulating streamflow through evapotranspiration (Hewlett, 1982; Swank and Crossley, 1988; Andreassian, 2004; Brown et al., 2005; Amatya et al., 2011, 2015, 2016; Sun et al., 2011b; Vose et al., 2011). It is estimated that more than...

  1. The Sensitivity of Evapotranspiration Models to Errors in Model ...

    African Journals Online (AJOL)

    Five evapotranspiration (Et) model-the penman, Blaney - Criddel, Thornthwaite, the Blaney –Morin-Nigeria, and the Jensen and Haise models – were analyzed for parameter sensitivity under Nigerian Climatic conditions. The sensitivity of each model to errors in any of its measured parameters (variables) was based on the ...

  2. Estimation of evapotranspiration over the terrestrial ecosystems in China

    Science.gov (United States)

    Xianglan Li; Shunlin Liang; Wenping Yuan; Guirui Yu; Xiao Cheng; Yang Chen; Tianbao Zhao; Jinming Feng; Zhuguo Ma; Mingguo Ma; Shaomin Liu; Jiquan Chen; Changliang Shao; Shenggong Li; Xudong Zhang; Zhiqiang Zhang; Ge Sun; Shiping Chen; Takeshi Ohta; Andrej Varlagin; Akira Miyata; Kentaro Takagi; Nobuko Saiqusa; Tomomichi Kato

    2014-01-01

    Quantifying regional evapotranspiration (ET) and environmental constraints are particularly important for understanding water and carbon cycles of terrestrial ecosystems. However, a large uncertainty in the regional estimation of ET still remains for the terrestrial ecosystems in China. This study used ET measurements of 34 eddy covariance sites within China and...

  3. A note on India's water budget and evapotranspiration

    Indian Academy of Sciences (India)

    Some recent analyses of India 's water budget are based on information attributed to the Ministry of Water Resources.An examination of the budget components indicates that they imply an evapotranspiration estimate that is significantly lower than what one may expect based on information from other sources.If such is the ...

  4. Annual evapotranspiration of a forested wetland watershed, SC

    Science.gov (United States)

    Devendra M. Amatya; Carl Trettin

    2007-01-01

    In this study, hydro-meteorological data collected from 1 964 to 1 9 76 on an approximately 5, 000 ha predominantly forested coastal watershed (Turkey Creek) at the Francis Marion National Forest near Charleston, SC were analyzed to estimate annual evapotranspiration (E T) using four different empirical methods. The first one, reported by Zhang et a/. (2001), that...

  5. Estimation of evapotranspiration rate in irrigated lands using stable isotopes

    Science.gov (United States)

    Umirzakov, Gulomjon; Windhorst, David; Forkutsa, Irina; Brauer, Lutz; Frede, Hans-Georg

    2013-04-01

    Agriculture in the Aral Sea basin is the main consumer of water resources and due to the current agricultural management practices inefficient water usage causes huge losses of freshwater resources. There is huge potential to save water resources in order to reach a more efficient water use in irrigated areas. Therefore, research is required to reveal the mechanisms of hydrological fluxes in irrigated areas. This paper focuses on estimation of evapotranspiration which is one of the crucial components in the water balance of irrigated lands. Our main objective is to estimate the rate of evapotranspiration on irrigated lands and partitioning of evaporation into transpiration using stable isotopes measurements. Experiments has done in 2 different soil types (sandy and sandy loam) irrigated areas in Ferghana Valley (Uzbekistan). Soil samples were collected during the vegetation period. The soil water from these samples was extracted via a cryogenic extraction method and analyzed for the isotopic ratio of the water isotopes (2H and 18O) based on a laser spectroscopy method (DLT 100, Los Gatos USA). Evapotranspiration rates were estimated with Isotope Mass Balance method. The results of evapotranspiration obtained using isotope mass balance method is compared with the results of Catchment Modeling Framework -1D model results which has done in the same area and the same time.

  6. Stable isotope measurements of evapotranspiration partitioning in a maize field

    Science.gov (United States)

    Hogan, Patrick; Parajka, Juraj; Oismüller, Markus; Strauss, Peter; Heng, Lee; Blöschl, Günter

    2017-04-01

    Evapotranspiration (ET) is one of the most important processes in describing land surface - atmosphere interactions as it connects the energy and water balances. Furthermore knowledge of the individual components of evapotranspiration is important for ecohydrological modelling and agriculture, particularly for irrigation efficiency and crop productivity. In this study, we tested the application of the stable isotope method for evapotranspiration partitioning to a maize crop during the vegetative stage, using sap flow sensors as a comparison technique. Field scale ET was measured using an eddy covariance device and then partitioned using high frequency in-situ measurements of the isotopic signal of the canopy water vapor. The fraction of transpiration (Ft) calculated with the stable isotope method showed good agreement with the sap flow method. High correlation coefficient values were found between the two techniques, indicating the stable isotope method can successfully be applied in maize. The results show the changes in transpiration as a fraction of evapotranspiration after rain events and during the subsequent drying conditions as well as the relationship between transpiration and solar radiation and vapor pressure deficit.

  7. Emulation of recharge and evapotranspiration processes in shallow groundwater systems

    Science.gov (United States)

    Doble, Rebecca C.; Pickett, Trevor; Crosbie, Russell S.; Morgan, Leanne K.; Turnadge, Chris; Davies, Phil J.

    2017-12-01

    In shallow groundwater systems, recharge and evapotranspiration are highly sensitive to changes in the depth to water table. To effectively model these fluxes, complex functions that include soil and vegetation properties are often required. Model emulation (surrogate modelling or meta-modelling) can provide a means of incorporating detailed conceptualisation of recharge and evapotranspiration processes, while maintaining the numerical tractability and computational performance required for regional scale groundwater models and uncertainty analysis. A method for emulating recharge and evapotranspiration processes in groundwater flow models was developed, and applied to the South East region of South Australia and western Victoria, which is characterised by shallow groundwater, wetlands and coastal lakes. The soil-vegetation-atmosphere transfer (SVAT) model WAVES was used to generate relationships between net recharge (diffuse recharge minus evapotranspiration from groundwater) and depth to water table for different combinations of climate, soil and land cover types. These relationships, which mimicked previously described soil, vegetation and groundwater behaviour, were combined into a net recharge lookup table. The segmented evapotranspiration package in MODFLOW was adapted to select values of net recharge from the lookup table depending on groundwater depth, and the climate, soil and land use characteristics of each cell. The model was found to be numerically robust in steady state testing, had no major increase in run time, and would be more efficient than tightly-coupled modelling approaches. It made reasonable predictions of net recharge and groundwater head compared with remotely sensed estimates of net recharge and a standard MODFLOW comparison model. In particular, the method was better able to predict net recharge and groundwater head in areas with steep hydraulic gradients.

  8. Vertical structure of evapotranspiration at a spruce forest site

    Science.gov (United States)

    Staudt, K.; Falge, E.; Serafimovich, A.; Pyles, D.; Foken, T.

    2009-12-01

    The Advanced Canopy-Atmosphere-Soil Algorithm (ACASA) was used to model the turbulent fluxes of heat, water vapor and momentum as well as the carbon dioxide exchange within and above a spruce canopy at the FLUXNET-station Waldstein-Weidenbrunnen (DE-Bay) in the Fichtelgebirge mountains in northern Bavaria, Germany. ACASA is a multilayer canopy-surface-layer model that incorporates a third-order closure method to calculate turbulent transfer within and above the canopy and was developed at the University of California, Davis. Within the EGER (ExchanGE processes in mountainous Regions) project, comprehensive micrometeorological and plant physiological measurements were performed during two intensive observation periods in fall 2007 and summer 2008. This data base allowed us to extensively test the ability of the ACASA model to simulate the exchange of energy and matter at our site. Here, the vertical structure of evapotranspiration within and above the canopy for a few days is investigated in detail. The ACASA model provides profiles of all components of evapotranspiration, such as transpiration and evaporation from the soil, and estimates the interception of precipitation and the corresponding evaporation from wet plant surfaces. Fluxes of momentum, heat, carbon dioxide and water vapor were measured with six eddy-covariance systems below, within and above the canopy on a 36 m high tower. Furthermore, xylem sapflow measurements at six heights within the canopy were performed for the determination of canopy transpiration. This combination of multilevel measurements allowed us to estimate all components of evapotranspiration of and within the spruce forest. Model results and measurements of evapotranspiration are analyzed with regard to the partitioning between its components as well as between the canopy layers. Furthermore, the ability of the ACASA model to reproduce evapotranspiration profiles for different exchange regimes of the subcanopy and the canopy is

  9. TDR Technique for Estimating the Intensity of Evapotranspiration of Turfgrasses

    Directory of Open Access Journals (Sweden)

    Grzegorz Janik

    2015-01-01

    Full Text Available The paper presents a method for precise estimation of evapotranspiration of selected turfgrass species. The evapotranspiration functions, whose domains are only two relatively easy to measure parameters, were developed separately for each of the grass species. Those parameters are the temperature and the volumetric moisture of soil at the depth of 2.5 cm. Evapotranspiration has the character of a modified logistic function with empirical parameters. It assumes the form ETRθ2.5 cm,T2.5 cm=A/1+B·e-C·θ2.5 cm·T2.5 cm, where: ETRθ2.5 cm,T2.5 cm is evapotranspiration [mm·h−1], θ2.5 cm is volumetric moisture of soil at the depth of 2.5 cm [m3·m−3], T2.5 cm is soil temperature at the depth of 2.5 cm [°C], and A, B, and C are empirical coefficients calculated individually for each of the grass species [mm·h1], and [—], [(m3·m−3·°C−1]. The values of evapotranspiration calculated on the basis of the presented function can be used as input data for the design of systems for the automatic control of irrigation systems ensuring optimum moisture conditions in the active layer of lawn swards.

  10. RIP-ET: A riparian evapotranspiration package for MODFLOW-2005

    Science.gov (United States)

    Maddock, Thomas; Baird, Kathryn J.; Hanson, R.T.; Schmid, Wolfgang; Ajami, Hoori

    2012-01-01

    A new evapotranspiration package for the U.S. Geological Survey's groundwater-flow model, MODFLOW, is documented. The Riparian Evapotranspiration Package (RIP-ET) provides flexibility in simulating riparian and wetland transpiration not provided by the Evapotranspiration (EVT) or Segmented Function Evapotranspiration (ETS1) Packages for MODFLOW 2005. This report describes how the RIP-ET package was conceptualized and provides input instructions, listings and explanations of the source code, and an example. Traditional approaches to modeling evapotranspiration (ET) processes assume a piecewise linear relationship between ET flux and hydraulic head. The RIP-ET replaces this traditional relationship with a segmented, nonlinear dimensionless curve that reflects the eco-physiology of riparian and wetland ecosystems. Evapotranspiration losses from these ecosystems are dependent not only on hydraulic head, but on the plant types present. User-defined plant functional groups (PFGs) are used to elucidate the interaction between plant transpiration and groundwater conditions. Five generalized plant functional groups based on transpiration rates, plant rooting depth, and water tolerance ranges are presented: obligate wetland, shallow-rooted riparian, deep-rooted riparian, transitional riparian and bare ground/open water. Plant functional groups can be further divided into subgroups (PFSGs) based on plant size, density or other characteristics. The RIP-ET allows for partial habitat coverage and mixtures of plant functional subgroups to be present in a single model cell. RIP-ET also distinguishes between plant transpiration and bare-ground evaporation. Habitat areas are designated by polygons; each polygon can contain a mixture of PFSGs and bare ground, and is assigned a surface elevation. This process requires a determination of fractional coverage for each of the plant functional subgroups present in a polygon to account for the mixture of coverage types and resulting

  11. Estimating riparian and agricultural evapotranspiration by reference crop evapotranspiration and MODIS Enhanced Vegetation Index

    Science.gov (United States)

    Nagler, Pamela L.; Glenn, Edward P.; Nguyen, Uyen; Scott, Russell; Doody, Tania

    2013-01-01

    Dryland river basins frequently support both irrigated agriculture and riparian vegetation and remote sensing methods are needed to monitor water use by both crops and natural vegetation in irrigation districts. We developed an algorithm for estimating actual evapotranspiration (ETa) based on the Enhanced Vegetation Index (EVI) from the Moderate Resolution Imaging Spectrometer (MODIS) sensor on the EOS-1 Terra satellite and locally-derived measurements of reference crop ET (ETo). The algorithm was calibrated with five years of ETa data from three eddy covariance flux towers set in riparian plant associations on the upper San Pedro River, Arizona, supplemented with ETa data for alfalfa and cotton from the literature. The algorithm was based on an equation of the form ETa = ETo [a(1 − e−bEVI) − c], where the term (1 − e−bEVI) is derived from the Beer-Lambert Law to express light absorption by a canopy, with EVI replacing leaf area index as an estimate of the density of light-absorbing units. The resulting algorithm capably predicted ETa across riparian plants and crops (r2 = 0.73). It was then tested against water balance data for five irrigation districts and flux tower data for two riparian zones for which season-long or multi-year ETa data were available. Predictions were within 10% of measured results in each case, with a non-significant (P = 0.89) difference between mean measured and modeled ETa of 5.4% over all validation sites. Validation and calibration data sets were combined to present a final predictive equation for application across crops and riparian plant associations for monitoring individual irrigation districts or for conducting global water use assessments of mixed agricultural and riparian biomes.

  12. Estimating Riparian and Agricultural Actual Evapotranspiration by Reference Evapotranspiration and MODIS Enhanced Vegetation Index

    Directory of Open Access Journals (Sweden)

    Russell L. Scott

    2013-08-01

    Full Text Available Dryland river basins frequently support both irrigated agriculture and riparian vegetation and remote sensing methods are needed to monitor water use by both crops and natural vegetation in irrigation districts. We developed an algorithm for estimating actual evapotranspiration (ETa based on the Enhanced Vegetation Index (EVI from the Moderate Resolution Imaging Spectrometer (MODIS sensor on the EOS-1 Terra satellite and locally-derived measurements of reference crop ET (ETo. The algorithm was calibrated with five years of ETa data from three eddy covariance flux towers set in riparian plant associations on the upper San Pedro River, Arizona, supplemented with ETa data for alfalfa and cotton from the literature. The algorithm was based on an equation of the form ETa = ETo [a(1 − e−bEVI − c], where the term (1 − e−bEVI is derived from the Beer-Lambert Law to express light absorption by a canopy, with EVI replacing leaf area index as an estimate of the density of light-absorbing units. The resulting algorithm capably predicted ETa across riparian plants and crops (r2 = 0.73. It was then tested against water balance data for five irrigation districts and flux tower data for two riparian zones for which season-long or multi-year ETa data were available. Predictions were within 10% of measured results in each case, with a non-significant (P = 0.89 difference between mean measured and modeled ETa of 5.4% over all validation sites. Validation and calibration data sets were combined to present a final predictive equation for application across crops and riparian plant associations for monitoring individual irrigation districts or for conducting global water use assessments of mixed agricultural and riparian biomes.

  13. Predicting water suppy and actual evapotranspiration of street trees

    Science.gov (United States)

    Wessolek, Gerd; Heiner, Moreen; Trinks, Steffen

    2017-04-01

    It's well known that street trees cool air temperature in summer-time by transpiration and shading and also reduce runoff. However, it's difficult to analyse if trees have water shortage or not. This contribution focus on predicting water supply, actual evapotranspiration, and runoff by using easily available climate data (precipiation, potential evapotranspiration) and site characteristics (water retention, space, sealing degree, groundwater depth). These parameter were used as input data for Hydro-Pedotransfer-Functions (HPTFs) allowing the estimation of the annual water budget. Results give statements on water supply of trees, drought stress, and additional water demand by irrigation. Procedure also analyse, to which extent the surrounding partly sealed surfaces deliver water to the trees. Four representative street canyons of Berlin City were analysed and evaluated within in training program for M.A. students of „Urban Eco-system Science" at the Technische Universität Berlin.

  14. Geohydrology and evapotranspiration at Franklin Lake playa, Inyo County, California

    Energy Technology Data Exchange (ETDEWEB)

    Czarnecki, J.B.

    1997-12-31

    Franklin Lake playa is one of the principal discharge areas of the Furnace Creek Ranch-Alkali Flat ground-water-flow system in southern Nevada and adjacent California. Yucca Mountain, Nevada, located within this flow system, is being evaluated by the US Department of Energy to determine its suitability as a potential site for a high-level nuclear-waste repository. To assist the U.S. Department of Energy with its evaluation of the Yucca Mountain site, the US Geological Survey developed a parameter-estimation model of the Furnace Creek Ranch-Alkali Flat ground-water-flow system. Results from sensitivity analyses made using the parameter-estimation model indicated that simulated rates of evapotranspiration at Franklin Lake playa had the largest effect on the calculation of transmissivity values at Yucca Mountain of all the model-boundary conditions and, therefore, that evapotranspiration required careful definition.

  15. Estimating watershed evapotranspiration across the United States using multiple methods

    Science.gov (United States)

    Ge Sun; Shanlei Sun; Jingfeng Xiao; Peter Caldwell; Devendra Amatya; Suat Irmak; Prasanna H. Gowda; Sudhanshu Panda; Steve McNulty; Yang Zhang

    2016-01-01

    Evapotranspiration (ET) is the largest watershed water balance component only next to precipitation in the United States. ET is closely coupled with ecosystem carbon and energy fluxes, affects flooding or drought magnitude, and is also a good predictor for biodiversity at a regional scale.Thus, accurately estimating ET is of paramount importance to quantify the effects...

  16. Contradictions in the Dynamics of Remote Sensing based Evapotranspiration Calculation

    Science.gov (United States)

    Dhungel, R.

    2016-12-01

    The significance of accurate evapotranspiration (ET) need not be overstated because of the current prolonged drought, water scarcity, increasing population, and climate change in many parts of the world. The remote sensing based ET calculation methods had been taken as one of the reliable tools for estimating ET at larger temporal and spatial resolution. The linearity between temperature difference (DT) and surface temperature (Ts) from the thermal band of the satellite is utilized in many operational evapotranspiration (ET) models (SEBAL/METRIC) invoking the anchor pixel concept. In these models, the surface-air temperature difference in anchor pixels (dThot/cold) are calculated based on known the sensible heat flux (H) from the surface energy balance method. We explored the inherent differences while inverting the aerodynamic equation of H with the actual surface-air temperature (dTact) to dThot/cold. The results showed that this formulation possibly underestimates H with smaller dT slope, which overall overestimates the ET. The major finding and innovative aspect of this study are to present the two inconsistent behaviors of the identical process of energy transformation, which had been utilized by remote sensing based evapotranspiration models. This study will help to understand the uncertainty in H calculations in these models, explore the limitations of this methodology (dThot, cold), and warrant further discussion of this application in remote sensing and micrometeorology community.

  17. Estimating Potential Evapotranspiration by Missing Temperature Data Reconstruction

    Directory of Open Access Journals (Sweden)

    Eladio Delgadillo-Ruiz

    2015-01-01

    Full Text Available This work studies the statistical characteristics of potential evapotranspiration calculations and their relevance within the water balance used to determine water availability in hydrological basins. The purpose of this study was as follows: first, to apply a missing data reconstruction scheme in weather stations of the Rio Queretaro basin; second, to reduce the generated uncertainty of temperature data: mean, minimum, and maximum values in the evapotranspiration calculation which has a paramount importance in the manner of obtaining the water balance at any hydrological basin. The reconstruction of missing data was carried out in three steps: (1 application of a 4-parameter sinusoidal type regression to temperature data, (2 linear regression to residuals to obtain a regional behavior, and (3 estimation of missing temperature values for a certain year and during a certain season within the basin under study; estimated and observed temperature values were compared. Finally, using the obtained temperature values, the methods of Hamon, Papadakis, Blaney and Criddle, Thornthwaite, and Hargreaves were employed to calculate potential evapotranspiration that was compared to the real observed values in weather stations. With the results obtained from the application of this procedure, the surface water balance was corrected for the case study.

  18. Groundwater Modelling For Recharge Estimation Using Satellite Based Evapotranspiration

    Science.gov (United States)

    Soheili, Mahmoud; (Tom) Rientjes, T. H. M.; (Christiaan) van der Tol, C.

    2017-04-01

    Groundwater movement is influenced by several factors and processes in the hydrological cycle, from which, recharge is of high relevance. Since the amount of aquifer extractable water directly relates to the recharge amount, estimation of recharge is a perquisite of groundwater resources management. Recharge is highly affected by water loss mechanisms the major of which is actual evapotranspiration (ETa). It is, therefore, essential to have detailed assessment of ETa impact on groundwater recharge. The objective of this study was to evaluate how recharge was affected when satellite-based evapotranspiration was used instead of in-situ based ETa in the Salland area, the Netherlands. The Methodology for Interactive Planning for Water Management (MIPWA) model setup which includes a groundwater model for the northern part of the Netherlands was used for recharge estimation. The Surface Energy Balance Algorithm for Land (SEBAL) based actual evapotranspiration maps from Waterschap Groot Salland were also used. Comparison of SEBAL based ETa estimates with in-situ abased estimates in the Netherlands showed that these SEBAL estimates were not reliable. As such results could not serve for calibrating root zone parameters in the CAPSIM model. The annual cumulative ETa map produced by the model showed that the maximum amount of evapotranspiration occurs in mixed forest areas in the northeast and a portion of central parts. Estimates ranged from 579 mm to a minimum of 0 mm in the highest elevated areas with woody vegetation in the southeast of the region. Variations in mean seasonal hydraulic head and groundwater level for each layer showed that the hydraulic gradient follows elevation in the Salland area from southeast (maximum) to northwest (minimum) of the region which depicts the groundwater flow direction. The mean seasonal water balance in CAPSIM part was evaluated to represent recharge estimation in the first layer. The highest recharge estimated flux was for autumn

  19. Forecasting the Reference Evapotranspiration Using Time Series Model

    Directory of Open Access Journals (Sweden)

    H. Zare Abyaneh

    2016-10-01

    Full Text Available Introduction: Reference evapotranspiration is one of the most important factors in irrigation timing and field management. Moreover, reference evapotranspiration forecasting can play a vital role in future developments. Therefore in this study, the seasonal autoregressive integrated moving average (ARIMA model was used to forecast the reference evapotranspiration time series in the Esfahan, Semnan, Shiraz, Kerman, and Yazd synoptic stations. Materials and Methods: In the present study in all stations (characteristics of the synoptic stations are given in Table 1, the meteorological data, including mean, maximum and minimum air temperature, relative humidity, dry-and wet-bulb temperature, dew-point temperature, wind speed, precipitation, air vapor pressure and sunshine hours were collected from the Islamic Republic of Iran Meteorological Organization (IRIMO for the 41 years from 1965 to 2005. The FAO Penman-Monteith equation was used to calculate the monthly reference evapotranspiration in the five synoptic stations and the evapotranspiration time series were formed. The unit root test was used to identify whether the time series was stationary, then using the Box-Jenkins method, seasonal ARIMA models were applied to the sample data. Table 1. The geographical location and climate conditions of the synoptic stations Station\tGeographical location\tAltitude (m\tMean air temperature (°C\tMean precipitation (mm\tClimate, according to the De Martonne index classification Longitude (E\tLatitude (N Annual\tMin. and Max. Esfahan\t51° 40'\t32° 37'\t1550.4\t16.36\t9.4-23.3\t122\tArid Semnan\t53° 33'\t35° 35'\t1130.8\t18.0\t12.4-23.8\t140\tArid Shiraz\t52° 36'\t29° 32'\t1484\t18.0\t10.2-25.9\t324\tSemi-arid Kerman\t56° 58'\t30° 15'\t1753.8\t15.6\t6.7-24.6\t142\tArid Yazd\t54° 17'\t31° 54'\t1237.2\t19.2\t11.8-26.0\t61\tArid Results and Discussion: The monthly meteorological data were used as input for the Ref-ET software and monthly reference

  20. Applicability of three complementary relationship models for estimating actual evapotranspiration in urban area

    Directory of Open Access Journals (Sweden)

    Nakamichi Takeshi

    2015-06-01

    Full Text Available The characteristics of evapotranspiration estimated by the complementary relationship actual evapotranspiration (CRAE, the advection-aridity (AA, and the modified advection-aridity (MAA models were investigated in six pairs of rural and urban areas of Japan in order to evaluate the applicability of the three models the urban area. The main results are as follows: 1 The MAA model could apply to estimating the actual evapotranspiration in the urban area. 2 The actual evapotranspirations estimated by the three models were much less in the urban area than in the rural. 3 The difference among the estimated values of evapotranspiration in the urban areas was significant, depending on each model, while the difference among the values in the rural areas was relatively small. 4 All three models underestimated the actual evapotranspiration in the urban areas from humid surfaces where water and green spaces exist. 5 Each model could take the effect of urbanization into account.

  1. Encounter risk analysis of rainfall and reference crop evapotranspiration in the irrigation district

    Science.gov (United States)

    Zhang, Jinping; Lin, Xiaomin; Zhao, Yong; Hong, Yang

    2017-09-01

    Rainfall and reference crop evapotranspiration are random but mutually affected variables in the irrigation district, and their encounter situation can determine water shortage risks under the contexts of natural water supply and demand. However, in reality, the rainfall and reference crop evapotranspiration may have different marginal distributions and their relations are nonlinear. In this study, based on the annual rainfall and reference crop evapotranspiration data series from 1970 to 2013 in the Luhun irrigation district of China, the joint probability distribution of rainfall and reference crop evapotranspiration are developed with the Frank copula function. Using the joint probability distribution, the synchronous-asynchronous encounter risk, conditional joint probability, and conditional return period of different combinations of rainfall and reference crop evapotranspiration are analyzed. The results show that the copula-based joint probability distributions of rainfall and reference crop evapotranspiration are reasonable. The asynchronous encounter probability of rainfall and reference crop evapotranspiration is greater than their synchronous encounter probability, and the water shortage risk associated with meteorological drought (i.e. rainfall variability) is more prone to appear. Compared with other states, there are higher conditional joint probability and lower conditional return period in either low rainfall or high reference crop evapotranspiration. For a specifically high reference crop evapotranspiration with a certain frequency, the encounter risk of low rainfall and high reference crop evapotranspiration is increased with the decrease in frequency. For a specifically low rainfall with a certain frequency, the encounter risk of low rainfall and high reference crop evapotranspiration is decreased with the decrease in frequency. When either the high reference crop evapotranspiration exceeds a certain frequency or low rainfall does not exceed a

  2. Prediction of Evapotranspiration in a Mediterranean Region Using Basic Meteorological Variables

    OpenAIRE

    Jato Espino, Daniel; Charlesworth, Susanne M.; Perales-Momparler, Sara; Andrés-Doménech, Ignacio

    2017-01-01

    A critical need for farmers, particularly those in arid and semiarid areas is to have a reliable, accurate and reasonably accessible means of estimating the evapotranspiration rates of their crops to optimize their irrigation requirements. Evapotranspiration is a crucial process because of its influence on the precipitation that is returned to the atmosphere. The calculation of this variable often starts from the estimation of reference evapotranspiration, for which a variety of methods have ...

  3. CMS: Evapotranspiration and Meteorology, Water-Limited Shrublands, Mexico, 2008-2010

    Data.gov (United States)

    National Aeronautics and Space Administration — This data set provides daily average observations for evapotranspiration (measured and gap-filled), precipitation, net radiation, soil water content, air...

  4. Analysis of Numerical Weather Predictions of Reference Evapotranspiration and Precipitation

    Science.gov (United States)

    Bughici, Theodor; Lazarovitch, Naftali; Fredj, Erick; Tas, Eran

    2017-04-01

    This study attempts to improve the forecast skill of the evapotranspiration (ET0) and Precipitation for the purpose of crop irrigation management over Israel using the Weather Research and Forecasting (WRF) Model. Optimized crop irrigation, in term of timing and quantities, decreases water and agrochemicals demand. Crop water demands depend on evapotranspiration and precipitation. The common method for computing reference evapotranspiration, for agricultural needs, ET0, is according to the FAO Penman-Monteith equation. The weather variables required for ET0 calculation (air temperature, relative humidity, wind speed and solar irradiance) are estimated by the WRF model. The WRF Model with two-way interacting domains at horizontal resolutions of 27, 9 and 3 km is used in the study. The model prediction was performed in an hourly time resolution and a 3 km spatial resolution, with forecast lead-time of up to four days. The WRF prediction of these variables have been compared against measurements from 29 meteorological stations across Israel for the year 2013. The studied area is small but with strong climatic gradient, diverse topography and variety of synoptic conditions. The forecast skill that was used for forecast validation takes into account the prediction bias, mean absolute error and root mean squared error. The forecast skill of the variables was almost robust to lead time, except for precipitation. The forecast skill was tested across stations with respect to topography and geographic location and for all stations with respect to seasonality and synoptic weather system determined by employing a semi-objective synoptic systems classification to the forecasted days. It was noticeable that forecast skill of some of the variables was deteriorated by seasonality and topography. However, larger impacts in the ET0 skill scores on the forecasted day are achieved by a synoptic based forecast. These results set the basis for increasing the robustness of ET0 to

  5. Spatiotemporal Variability in Potential Evapotranspiration across an Urban Monitoring Network

    Science.gov (United States)

    Miller, G. R.; Long, M. R.; Fipps, G.; Swanson, C.; Traore, S.

    2015-12-01

    Evapotranspiration in urban and peri-urban environments is difficult to measure and predict. Barriers to accurate assessment include: the wide range of microclimates caused by urban canyons, heat islands, and park cooling; limited instrument fetch; and the patchwork of native soils, engineered soils, and hardscape. These issues combine to make an accurate assessment of the urban water balance difficult, as evapotranspiration calculations require accurate meteorological data. This study examines nearly three years of data collected by a network of 18 weather stations in Dallas, Texas, designed to measure potential evapotranspiration (ETo) in support of the WaterMyYard conservation program (http://WaterMyYard.org). Variability amongst stations peaked during the summer irrigation months, with a maximum standard deviation of 0.3 mm/hr and 4 mm/d. However, we found a significant degree of information overlap in the network. Most stations had a high correlation (>0.75) with at least one other station in the network, and many had a high correlation with at least 10 others. Correlation strength between station ETo measurements did not necessarily decrease with Euclidean distance, as expected, but was more closely related to differences in station elevation and longitude. Stations that had low correlations with others in the network typically had siting and fetch issues. ETo showed a strong temporal persistence; average station autocorrelation was 0.79 at a 1-hour lag and 0.70 at a 24-hour lag. To supplement the larger-scale network data, we deployed a mobile, vehicle-mounted weather station to quantify deviations present in the atmospheric drivers of evapotranspiration: temperature, humidity, wind, and solar radiation. Data were collected at mid-day during the irrigation season. We found differences in mobile and station ETo predictions up to 0.2 mm/hr, primarily driven by wind speed variations. These results suggest that ETo variation at the neighborhood to municipality

  6. Evaluation of satellite-based evapotranspiration estimates in China

    Science.gov (United States)

    Huang, Lei; Li, Zhe; Tang, Qiuhong; Zhang, Xuejun; Liu, Xingcai; Cui, Huijuan

    2017-04-01

    Accurate and continuous estimation of evapotranspiration (ET) is crucial for effective water resource management. We used the moderate resolution imaging spectroradiometer (MODIS) standard ET algorithm forced by the MODIS land products and the three-hourly solar radiation datasets to estimate daily actual evapotranspiration of China (ET_MOD) for the years 2001 to 2015. From the point scale validations using seven eddy covariance tower sites, the results showed that the agreement of ET_MOD estimates and observations was higher for monthly and daily values than that of instantaneous values. Under the major river basin and subbasin levels' comparisons with the variable infiltration capacity hydrological model estimates, the ET_MOD exhibited a slight overestimation in northern China and underestimation in southern China. The mean annual ET_MOD estimates agreed favorably with the hydrological model with coefficients of determination (R2) of 0.93 and 0.83 at major river basin and subbasin scale, respectively. At national scale, the spatiotemporal variations of ET_MOD estimates matched well with those ET estimates from various sources. However, ET_MOD estimates were generally lower than the other estimates in the Tibetan Plateau. This underestimation may be attributed to the plateau climate along with low air temperature and sparsely vegetated surface on the Tibetan Plateau.

  7. Evapotranspiration Cycles in a High Latitude Agroecosystem: Potential Warming Role

    Science.gov (United States)

    Ruairuen, Watcharee

    2015-01-01

    As the acreages of agricultural lands increase, changes in surface energetics and evapotranspiration (ET) rates may arise consequently affecting regional climate regimes. The objective of this study was to evaluate summertime ET dynamics and surface energy processes in a subarctic agricultural farm in Interior Alaska. The study includes micrometeorological and hydrological data. Results covering the period from June to September 2012 and 2013 indicated consistent energy fractions: LE/Rnet (67%), G/Rnet (6%), H/Rnet (27%) where LE is latent heat flux, Rnet is the surface net radiation, G is ground heat flux and H is the sensible heat flux. Additionally actual surface evapotranspiration from potential evaporation was found to be in the range of 59 to 66%. After comparing these rates with those of most prominent high latitude ecosystems it is argued here that if agroecosystem in high latitudes become an emerging feature in the land-use, the regional surface energy balance will significantly shift in comparison to existing Arctic natural ecosystems. PMID:26368123

  8. Mapping reference evapotranspiration from meteorological satellite data and applications

    Directory of Open Access Journals (Sweden)

    Ming-Hwi Yao

    2017-01-01

    Full Text Available Reference evapotranspiration (ETo is an agrometeorological variable widely used in hydrology and agriculture. The FAO-56 Penman-Monteith combination method (PM method is a standard for computing ETo for water management. However, this scheme is limited to areas where climatic data with good quality are available. Maps of 10-day averaged ETo at 5 km × 5 km grid spacing for the Taiwan region were produced by multiplying pan evaporation (Epan, derived from ground solar radiation (GSR retrieved from satellite images using the Heliosat-3 method, by a fixed pan coefficient (Kp. Validation results indicated that the overall mean absolute percentage error (MAPE and normalized root-mean-square deviation (NRMSD were 6.2 and 7.7%, respectively, when compared with ETo computed by the PM method using spatially interpolated 10-day averaged daily maximum and minimum temperature datasets and GSR derived from satellite inputs. Land coefficient (KL values based on the derived ETo estimates and long term latent heat flux measurements, were determined for the following landscapes: Paddy rice (Oryza sativa, subtropical cypress forest (Chamaecyparis obtusa var. formosana and Chamaecyparis formosensis, warm-to-temperate mixed rainforest (Cryptocarya chinensis, Engelhardtia roxburghiana, Tutcheria shinkoensis, and Helicia formosana, and grass marsh (Brachiaria mutica and Phragmites australis. The determined land coefficients are indispensable to scale ETo in estimating regional evapotranspiration.

  9. Evapotranspiration of applied water, Central Valley, California, 1957-78

    Science.gov (United States)

    Williamson, Alex K.

    1982-01-01

    In the Central Valley, Calif., where 57% of the 20,000 square miles of land is irrigated, ground-water recharge from agricultural lands is an important input to digital simulation models of ground-water flow. Several methods of calculating recharge were explored for the Central Valley Aquifer Project and a simplified water budget was designed where net recharge (recharge minus pumpage) equals net surface water diverted minus evapotranspiration of applied water (ETAW). This equation eliminates the need to determine pumpage from the water-table aquifer, assuming that the time lag for infiltration is not longer than the time intervals of interest for modeling. This study evaluates only the evapotranspiration of applied water. Future reports will describe the other components of the water budget. ETAW was calculated by summing the products of ETAW coefficients and respective crop areas for each 7 1/2-minute quadrangle area in the valley, for each of three land-use surveys between 1957 and 1978. In 1975 total ETAW was 15.2 million acre-feet, a 43% increase since 1959. The largest increases were in the south, especially Kern County, which had a sixfold increase, which was caused by the import of surface water in the California Aqueduct. (USGS)

  10. Experimental study and simulations of infiltration in evapotranspiration landfill covers

    Directory of Open Access Journals (Sweden)

    Wen-xian Zhang

    2009-09-01

    Full Text Available Various cover systems have been designed for landfill sites in order to minimize infiltration (percolation into the underlying waste. This study evaluated the soil water balance performance of evapotranspiration covers (ET covers and simulated percolation in the systems using the active region model (ARM. Experiments were conducted to measure water flow processes and water balance components in a bare soil cover and different ET covers. Results showed that vegetation played a critical role in controlling the water balance of the ET covers. In soil profiles of 60-cm depth with and without vegetation cover, the maximum soil water storage capacities were 97.2 mm and 62.8 mm, respectively. The percolation amount in the bare soil was 2.1 times that in the vegetation-covered soil. The ARM simulated percolation more accurately than the continuum model because it considered preferential flow. Numerical simulation results also indicated that using the ET cover system was an effective way of removing water through evapotranspiration, thus reducing percolation.

  11. Processes driving nocturnal transpiration and implications for estimating land evapotranspiration

    Science.gov (United States)

    de Dios, Víctor Resco; Roy, Jacques; Ferrio, Juan Pedro; Alday, Josu G.; Landais, Damien; Milcu, Alexandru; Gessler, Arthur

    2015-06-01

    Evapotranspiration is a major component of the water cycle, yet only daytime transpiration is currently considered in Earth system and agricultural sciences. This contrasts with physiological studies where 25% or more of water losses have been reported to occur occurring overnight at leaf and plant scales. This gap probably arose from limitations in techniques to measure nocturnal water fluxes at ecosystem scales, a gap we bridge here by using lysimeters under controlled environmental conditions. The magnitude of the nocturnal water losses (12-23% of daytime water losses) in row-crop monocultures of bean (annual herb) and cotton (woody shrub) would be globally an order of magnitude higher than documented responses of global evapotranspiration to climate change (51-98 vs. 7-8 mm yr-1). Contrary to daytime responses and to conventional wisdom, nocturnal transpiration was not affected by previous radiation loads or carbon uptake, and showed a temporal pattern independent of vapour pressure deficit or temperature, because of endogenous controls on stomatal conductance via circadian regulation. Our results have important implications from large-scale ecosystem modelling to crop production: homeostatic water losses justify simple empirical predictive functions, and circadian controls show a fine-tune control that minimizes water loss while potentially increasing posterior carbon uptake.

  12. Determination of crop and soil evaporation coefficients for estimating evapotranspiration in a paddy field

    NARCIS (Netherlands)

    Yan, H.; Zhang, C.; Oue, Hiroki; Peng, Guang Jie; Darko, Ransford Opoku

    2017-01-01

    Accurate estimation of evapotranspiration is important in efficient water management for improving water use efficiency. In order to obtain evapotranspiration and evaporation beneath the canopy using the Food and Agriculture Organization (FAO) method, pan evaporation was used instead of reference

  13. Evapotranspiration from understory vegetation in an eastern Siberian boreal larch forest, Agricultural and Forest Meteorology

    NARCIS (Netherlands)

    Iida, S.; Ohta, T.; Matsumoto, K.; Nakai, T.; Kuwada, T.; Konovov, A.V.; Maximov, T.C.; van der Molen, M.K.; Dolman, A.J.; Tanaka, H.; Yabuki, H.

    2009-01-01

    We measured evapotranspiration in an eastern Siberian boreal forest, in which the understory was cowberry and the overstory was larch, during the entire growing seasons of 2005 and 2006. We compared evapotranspiration from the understory vegetation above the forest floor E

  14. Potential crop evapotranspiration and surface evaporation estimates via a gridded weather forcing dataset

    Science.gov (United States)

    Lewis, Clayton S.; Allen, L. Niel

    2017-03-01

    Absent local weather stations, a gridded weather dataset can provide information useful for water management in irrigated areas including potential crop evapotranspiration calculations. In estimating crop irrigation requirements and surface evaporation in Utah, United States of America, methodology and software were developed using the ASCE Standardized Penman-Monteith Reference Evapotranspiration equation with input climate drivers from the North American Land Data Assimilation System (NLDAS) gridded weather forcing dataset and a digital elevation model. A simple procedure was devised to correct bias in NLDAS relative humidity and air temperature data based on comparison to weather data from ground stations. Potential evapotranspiration was calculated for 18 crops (including turfgrass), wetlands (large and narrow), and open water evaporation (deep and shallow) by multiplying crop coefficient curves to reference evapotranspiration with annual curve dates set by summation of Hargreaves evapotranspiration, cumulative growing degree days, or number of days. Net potential evapotranspiration was calculated by subtracting effective precipitation estimates from the Daymet gridded precipitation dataset. Analysis of the results showed that daily estimated potential crop evapotranspiration from the model compared well with estimates from electronic weather stations (1980-2014) and with independently calculated potential crop evapotranspiration in adjacent states. Designed for this study but open sourced for other applications, software entitled GridET encapsulated the GIS-based model that provided data download and management, calculation of reference and potential crop evapotranspiration, and viewing and analysis tools. Flexible features in GridET allows a user to specify grid resolution, evapotranspiration equations, cropping information, and additional datasets with the output being transferable to other GIS software.

  15. Measuring Evapotranspiration in Urban Irrigated Lawns in Two Kansas Cities

    Science.gov (United States)

    Shonkwiler, K. B.; Bremer, D.; Ham, J. M.

    2011-12-01

    Conservation of water is becoming increasingly critical in many metropolitan areas. The use of automated irrigation systems for the maintenance of lawns and landscapes is rising and these systems are typically maladjusted to apply more water than necessary, resulting in water wastage. Provision of accurate estimates of actual lawn water use may assist urbanites in conserving water through better adjustment of automatic irrigation systems. Micrometeorological methods may help determine actual lawn water use by measuring evapotranspiration (ET) from urban lawns. From April - August of 2011, four small tripod-mounted weather stations (tripods, five total) were deployed in twelve residential landscapes in the Kansas cities of Manhattan (MHK) and Wichita (ICT) in the USA (six properties in each city). Each tripod was instrumented to estimate reference crop evapotranspiration (ETo) via the FAO-56 method. During tripod deployment in residential lawns, actual evapotranspiration (ETactual) was measured nearby using a stationary, trailer-mounted eddy covariance (EC) station. The EC station sampled well-watered turf at the K-State Rocky Ford Turfgrass Center within 5 km of the study properties in MHK, and was also deployed at a commercial sod farm 15 - 40 km from the study residences in the greater ICT metro area. The fifth tripod was deployed in the source area of the EC station to estimate ETo in conjunction with tripods in the lawns (i.e., to serve as a reference). Data from EC allowed for computation of a so-called lawn coefficient (Kc) by determining the ratio of ETo from the tripods in residential lawns to ETo from the EC station (ETo,EC); hence, Kc = ETo,tripod / ETo,EC. Using this method, ETactual can be estimated for individual tripods within a lawn. Data suggests that it may be more accurate to quantify ET within individual lawns by microclimate (i.e., determine coefficients for "shaded" and "open/unshaded" portions of a lawn). By finding microclimate coefficients

  16. Seasonal comparison of two spatially distributed evapotranspiration mapping methods

    Science.gov (United States)

    Kisfaludi, Balázs; Csáki, Péter; Péterfalvi, József; Primusz, Péter

    2017-04-01

    More rainfall is disposed of through evapotranspiration (ET) on a global scale than through runoff and storage combined. In Hungary, about 90% of the precipitation evapotranspirates from the land and only 10% goes to surface runoff and groundwater recharge. Therefore, evapotranspiration is a very important element of the water balance, so it is a suitable parameter for the calibration of hydrological models. Monthly ET values of two MODIS-data based ET products were compared for the area of Hungary and for the vegetation period of the year 2008. The differences were assessed by land cover types and by elevation zones. One ET map was the MOD16, aiming at global coverage and provided by the MODIS Global Evaporation Project. The other method is called CREMAP, it was developed at the Budapest University of Technology and Economics for regional scale ET mapping. CREMAP was validated for the area of Hungary with good results, but ET maps were produced only for the period of 2000-2008. The aim of this research was to evaluate the performance of the MOD16 product compared to the CREMAP method. The average difference between the two products was the highest during summer, CREMAP estimating higher ET values by about 25 mm/month. In the spring and autumn, MOD16 ET values were higher by an average of 6 mm/month. The differences by land cover types showed a similar seasonal pattern to the average differences, and they correlated strongly with each other. Practically the same difference values could be calculated for arable lands and forests that together cover nearly 75% of the area of the country. Therefore, it can be said that the seasonal changes had the same effect on the two method's ET estimations in each land cover type areas. The analysis by elevation zones showed that on elevations lower than 200 m AMSL the trends of the difference values were similar to the average differences. The correlation between the values of these elevation zones was also strong. However weaker

  17. Convolutional neural networks for estimating spatially distributed evapotranspiration

    Science.gov (United States)

    García-Pedrero, Angel M.; Gonzalo-Martín, Consuelo; Lillo-Saavedra, Mario F.; Rodriguéz-Esparragón, Dionisio; Menasalvas, Ernestina

    2017-10-01

    Efficient water management in agriculture requires an accurate estimation of evapotranspiration (ET). There are available several balance energy surface models that provide a daily ET estimation (ETd) spatially and temporarily distributed for different crops over wide areas. These models need infrared thermal spectral band (gathered from remotely sensors) to estimate sensible heat flux from the surface temperature. However, this spectral band is not available for most current operational remote sensors. Even though the good results provided by machine learning (ML) methods in many different areas, few works have applied these approaches for forecasting distributed ETd on space and time when aforementioned information is missing. However, these methods do not exploit the land surface characteristics and the relationships among land covers producing estimation errors. In this work, we have developed and evaluated a methodology that provides spatial distributed estimates of ETd without thermal information by means of Convolutional Neural Networks.

  18. Modelling of evapotranspiration at field and landscape scales. Abstract

    DEFF Research Database (Denmark)

    Overgaard, Jesper; Butts, M.B.; Rosbjerg, Dan

    2002-01-01

    The overall aim of this project is to couple a non-hydrostatic atmospheric model (ARPS) to an integrated hydrological model (MIKE SHE) to investigate atmospheric and hydrological feedbacks at different scales. To ensure a consistent coupling a new land-surface component based on a modified...... Shuttleworth-Wallace scheme was implemented in MIKE SHE. To validate the new land-surface component at different scales, the hydrological model was applied to an intensively monitored 10 km2 agricultural area in Denmark with a resolution of 40 meter. The model is forced with half-hourly metorological...... observations from a nearby weather station. Detailed land-use and soil maps were used to set up the model. Leaf area index was derived from NDVI (Normalized Difference Vegetation Index) images. To validate the model at field scale the simulated evapotranspiration rates were compared to eddy...

  19. Exploring standardized precipitation evapotranspiration index for drought assessment in Bangladesh.

    Science.gov (United States)

    Miah, Md Giashuddin; Abdullah, Hasan Muhammad; Jeong, Changyoon

    2017-10-09

    Drought is a critical issue, and it has a pressing, negative impact on agriculture, ecosystems, livelihoods, food security, and sustainability. The problem has been studied globally, but its regional or even local dimension is sometimes overlooked. Local-level drought assessment is necessary for developing adaptation and mitigation strategies for that particular region. Keeping this in understanding, an attempt was made to create a detailed assessment of drought characteristics at the local scale in Bangladesh. Standardized precipitation evapotranspiration (SPEI) is a new drought index that mainly considers the rainfall and evapotranspiration data set. Globally, SPEI has become a useful drought index, but its local scale application is not common. SPEI base (0.5° grid data) for 110 years (1901-2011) was utilized to overcome the lack of long-term climate data in Bangladesh. Available weather data (1955-2011) from Bangladesh Meteorology Department (BMD) were analyzed to calculate SPEI weather station using the SPEI calculator. The drivers for climate change-induced droughts were characterized by residual temperature and residual rainfall data from different BMD stations. Grid data (SPEI base ) of 26 stations of BMD were used for drought mapping. The findings revealed that the frequency and intensity of drought are higher in the northwestern part of the country which makes it vulnerable to both extreme and severe droughts. Based on the results, the SPEI-based drought intensity and frequency analyses were carried out, emphasizing Rangpur (northwest region) as a hot spot, to get an insight of drought assessment in Bangladesh. The findings of this study revealed that SPEI could be a valuable tool to understand the evolution and evaluation of the drought induced by climate change in the country. The study also justified the immediate need for drought risk reduction strategies that should lead to relevant policy formulations and agricultural innovations for developing

  20. ANALYZING TRENDS IN REFERENCE EVAPOTRANSPIRATION IN NORTHWEST PART OF IRAN

    Directory of Open Access Journals (Sweden)

    Mohammadreza Azizzadeh

    2015-02-01

    Full Text Available Evapotranspiration is one of the most important components of the hydrological cycle. It is essential in all of hydro climatological studies, irrigation and drainage calculations, water balance, and crop water requirements. The aim of this study is to investigate temporal trends of reference evapotranspiration (ETo in the Northwest part of Iran. For this purpose, the meteorological data from 20 synoptic stations over a 22-year time period (1986–2007 were used. After the calculation of ETo using the Penman-Monteith FAO-56 method, the non-parametric Mann-Kendall test was used to investigate the temporal trends on monthly, seasonal and annual scales. The Sen’s estimator method was used and to calculate the slope of the trend line. The results indicated that the ETo trend was increasing (positive in various months, except for the Sarab station in December. On a monthly scale, the Maragheh station showed the highest positive slope in August, and the Bijar station showed the highest negative slope in May. 43.34% of the stations showed a significant trend, and 56.66% did not show a significant trend. In seasonal and annual time periods there was not a significant decreasing trend in any of the stations. The analysis of the results shows that in the spring 20%, in the summer 55%, in the fall 70%, in the winter 75%, and on an annual scale 60% of the stations under study showed an increasing trend. For modeling these changes, the spatial distribution of ETo trends (on monthly, seasonal, and annual scales were mapped in ArcGIS. Final models determine that most stations in this study show an increasing trend on monthly, seasonal and annual scales.

  1. Drone based estimation of actual evapotranspiration over different forest types

    Science.gov (United States)

    Marzahn, Philip; Gampe, David; Castro, Saulo; Vega-Araya, Mauricio; Sanchez-Azofeifa, Arturo; Ludwig, Ralf

    2017-04-01

    Actual evapotranspiration (Eta) plays an important role in surface-atmosphere interactions. Traditionally, Eta is measured by means of lysimeters, eddy-covariance systems or fiber optics, providing estimates which are spatially restricted to a footprint from a few square meters up to several hectares . In the past, several methods have been developed to derive Eta by means of multi-spectral remote sensing data using thermal and VIS/NIR satellite imagery of the land surface. As such approaches do have their justification on coarser scales, they do not provide Eta information on the fine resolution plant level over large areas which is mandatory for the detection of water stress or tree mortality. In this study, we present a comparison of a drone based assessment of Eta with eddy-covariance measurements over two different forest types - a deciduous forest in Alberta, Canada and a tropical dry forest in Costa Rica. Drone based estimates of Eta were calculated applying the Triangle-Method proposed by Jiang and Islam (1999). The Triangle-Method estimates actual evapotranspiration (Eta) by means of the Normalized Difference Vegetation Index (NDVI) and land surface temperature (LST) provided by two camera systems (MicaSense RedEdge, FLIR TAU2 640) flown simultaneously on an octocopter. . Results indicate a high transferability of the original approach from Jiang and Islam (1999) developed for coarse to medium resolution satellite imagery tothe high resolution drone data, leading to a deviation in Eta estimates of 10% compared to the eddy-covariance measurements. In addition, the spatial footprint of the eddy-covariance measurement can be detected with this approach, by showing the spatial heterogeneities of Eta due to the spatial distribution of different trees and understory vegetation.

  2. A Percolation‐Based Approach to Scaling Infiltration and Evapotranspiration

    Directory of Open Access Journals (Sweden)

    Allen G. Hunt

    2017-02-01

    Full Text Available Optimal flow paths obtained from percolation theory provide a powerful tool that can be used to characterize properties associated with flow such as soil hydraulic conductivity, as well as other properties influenced by flow connectivity and topology. A recently proposed scaling theory for vegetation growth appeals to the tortuosity of optimal paths from percolation theory to define the spatio‐temporal scaling of the root radial extent (or, equivalently, plant height. Root radial extent measures the maximum horizontal distance between a plant shoot and the root tips. We apply here the same scaling relationship to unsteady (horizontal flow associated with plant transpiration. The pore‐scale travel time is generated from the maximum flow rate under saturated conditions and a typical pore size. At the field‐scale, the characteristic time is interpreted as the growing season duration, and the characteristic length is derived from the measured evapotranspiration in that period. We show that the two scaling results are equivalent, and they are each in accord with observed vegetation growth limits, as well as with actual limiting transpiration values. While the conceptual approach addresses transpiration, most accessed data are for evapotranspiration. The equivalence of the two scaling approaches suggests that, if horizontal flow is the dominant pathway in plant transpiration, horizontal unsteady flow follows the same scaling relationship as root growth. Then, we propose a corresponding scaling relationship to vertical infiltration, a hypothesis which is amenable to testing using infiltration results of Sharma and co‐authors. This alternate treatment of unsteady vertical flow may be an effective alternative to the commonly applied method based on the diffusion of water over a continuum as governed by Richards’ equation.

  3. Response of mean annual evapotranspiration to vegetation changes at catchment scale

    Science.gov (United States)

    Zhang, L.; Dawes, W. R.; Walker, G. R.

    2001-03-01

    It is now well established that forested catchments have higher evapotranspiration than grassed catchments. Thus land use management and rehabilitation strategies will have an impact on catchment water balance and hence water yield and groundwater recharge. The key controls on evapotranspiration are rainfall interception, net radiation, advection, turbulent transport, leaf area, and plant-available water capacity. The relative importance of these factors depends on climate, soil, and vegetation conditions. Results from over 250 catchments worldwide show that for a given forest cover, there is a good relationship between long-term average evapotranspiration and rainfall. From these observations and on the basis of previous theoretical work a simple two-parameter model was developed that relates mean annual evapotranspiration to rainfall, potential evapotranspiration, and plant-available water capacity. The mean absolute error between modeled and measured evapotranspiration was 42 mm or 6.0%; the least squares line through the origin had as lope of 1.00 and a correlation coefficient of 0.96. The model showed potential for a variety of applications including water yield modeling and recharge estimation. The model is a practical tool that can be readily used for assessing the long-term average effect of vegetation changes on catchment evapotranspiration and is scientifically justifiable.

  4. Land surface evapotranspiration modelling at the regional scale

    Science.gov (United States)

    Raffelli, Giulia; Ferraris, Stefano; Canone, Davide; Previati, Maurizio; Gisolo, Davide; Provenzale, Antonello

    2017-04-01

    Climate change has relevant implications for the environment, water resources and human life in general. The observed increment of mean air temperature, in addition to a more frequent occurrence of extreme events such as droughts, may have a severe effect on the hydrological cycle. Besides climate change, land use changes are assumed to be another relevant component of global change in terms of impacts on terrestrial ecosystems: socio-economic changes have led to conversions between meadows and pastures and in most cases to a complete abandonment of grasslands. Water is subject to different physical processes among which evapotranspiration (ET) is one of the most significant. In fact, ET plays a key role in estimating crop growth, water demand and irrigation water management, so estimating values of ET can be crucial for water resource planning, irrigation requirement and agricultural production. Potential evapotranspiration (PET) is the amount of evaporation that occurs when a sufficient water source is available. It can be estimated just knowing temperatures (mean, maximum and minimum) and solar radiation. Actual evapotranspiration (AET) is instead the real quantity of water which is consumed by soil and vegetation; it is obtained as a fraction of PET. The aim of this work was to apply a simplified hydrological model to calculate AET for the province of Turin (Italy) in order to assess the water content and estimate the groundwater recharge at a regional scale. The soil is seen as a bucket (FAO56 model, Allen et al., 1998) made of different layers, which interact with water and vegetation. The water balance is given by precipitations (both rain and snow) and dew as positive inputs, while AET, runoff and drainage represent the rate of water escaping from soil. The difference between inputs and outputs is the water stock. Model data inputs are: soil characteristics (percentage of clay, silt, sand, rocks and organic matter); soil depth; the wilting point (i.e. the

  5. Evapotranspiration and cloud variability at regional sub-grid scales

    Science.gov (United States)

    Vila-Guerau de Arellano, Jordi; Sikma, Martin; Pedruzo-Bagazgoitia, Xabier; van Heerwaarden, Chiel; Hartogensis, Oscar; Ouwersloot, Huug

    2017-04-01

    In regional and global models uncertainties arise due to our incomplete understanding of the coupling between biochemical and physical processes. Representing their impact depends on our ability to calculate these processes using physically sound parameterizations, since they are unresolved at scales smaller than the grid size. More specifically over land, the coupling between evapotranspiration, turbulent transport of heat and moisture, and clouds lacks a combined representation to take these sub-grid scales interactions into account. Our approach is based on understanding how radiation, surface exchange, turbulent transport and moist convection are interacting from the leaf- to the cloud scale. We therefore place special emphasis on plant stomatal aperture as the main regulator of CO2-assimilation and water transpiration, a key source of moisture source to the atmosphere. Plant functionality is critically modulated by interactions with atmospheric conditions occurring at very short spatiotemporal scales such as cloud radiation perturbations or water vapour turbulent fluctuations. By explicitly resolving these processes, the LES (large-eddy simulation) technique is enabling us to characterize and better understand the interactions between canopies and the local atmosphere. This includes the adaption time of vegetation to rapid changes in atmospheric conditions driven by turbulence or the presence of cumulus clouds. Our LES experiments are based on explicitly coupling the diurnal atmospheric dynamics to a plant physiology model. Our general hypothesis is that different partitioning of direct and diffuse radiation leads to different responses of the vegetation. As a result there are changes in the water use efficiencies and shifts in the partitioning of sensible and latent heat fluxes under the presence of clouds. Our presentation is as follows. First, we discuss the ability of LES to reproduce the surface energy balance including photosynthesis and CO2 soil

  6. MODIS/Terra Net Evapotranspiration Yearly L4 Global 500m SIN Grid V006

    Data.gov (United States)

    National Aeronautics and Space Administration — The MOD16A3 Version 6 Evapotranspiration/Latent Heat Flux product is a yearly composite product produced at 500 meter pixel resolution. The algorithm is based on the...

  7. MODIS/Aqua Net Evapotranspiration 8-Day L4 Global 500m SIN Grid V006

    Data.gov (United States)

    National Aeronautics and Space Administration — The MYD16A2 Version 6 Evapotranspiration/Latent Heat Flux product is an 8-day composite product produced at 500 meter pixel resolution. The improved algorithm is...

  8. MODIS/Terra Net Evapotranspiration 8-Day L4 Global 500m SIN Grid V006

    Data.gov (United States)

    National Aeronautics and Space Administration — The MOD16A2 Version 6 Evapotranspiration/Latent Heat Flux product is an 8-day composite product produced at 500 meter pixel resolution. The algorithm used for the...

  9. MODIS/Aqua Net Evapotranspiration Yearly L4 Global 500m SIN Grid V006

    Data.gov (United States)

    National Aeronautics and Space Administration — The MYD16A3 Version 6 Evapotranspiration/Latent Heat Flux product is a yearly composite product produced at 500 meter pixel resolution. The improved algorithm is...

  10. Measurement and partitioning of evapotranspiration (ET) for application to vadose zone studies

    Science.gov (United States)

    Partitioning evapotranspiration (ET) into its constituent components, soil evaporation (E) and plant transpiration (T), is important for vadose zone studies because E and T are often parameterized separately. However, partitioning ET is challenging, and many longstanding approaches have significant ...

  11. Upflow Evapotranspiration System for the Treatment of On-Site Wastewater Effluent

    National Research Council Canada - National Science Library

    Sean Curneen; Laurence Gill

    2015-01-01

      Full-scale willow evapotranspiration systems fed from the base with septic tank or secondary treated domestic effluent from single houses have been constructed and instrumented in Ireland in order...

  12. Evaluation of clear-sky incoming radiation estimating equations typically used in remote sensing evapotranspiration algorithms

    CSIR Research Space (South Africa)

    Sun, Z

    2013-09-01

    Full Text Available Net radiation is a key component of the energy balance, whose estimation accuracy has an impact on energy flux estimates from satellite data. In typical remote sensing evapotranspiration (ET) algorithms, the outgoing shortwave and longwave...

  13. Classification of evapotranspiration units in major discharge areas of Death Valley regional

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — The raster-based classification of evapotranspiration (ET) units is for nine major discharge areas in the Death Valley regional flow system. The ET units delineate...

  14. Mean annual runoff, precipitation, and evapotranspiration in the glaciated northeastern United States, 1951-80

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Two maps, compiled at 1:1,000,000 scale, depict mean annual runoff, precipitation, and evapotranspiration in the part of the United States east of Cleveland, Ohio...

  15. Estimation of daily evapotranspiration over Africa using MODIS/Terra and SEVIRI/MSG data

    CSIR Research Space (South Africa)

    Sun, Z

    2012-08-01

    Full Text Available Most existing remote sensing-based evapotranspiration (ET) algorithms rely exclusively on polar-orbiting satellites with thermal infrared sensors, and therefore the resulting ET values represent only “instantaneous or snapshot” values. However...

  16. Critical review of methods for the estimation of actual evapotranspiration in hydrological models

    CSIR Research Space (South Africa)

    Jovanovic, Nebojsa

    2012-01-01

    Full Text Available The chapter is structured in three parts, namely: i) A theoretical overview of evapotranspiration processes, including the principle of atmospheric demand-soil water supply, ii) A review of methods and techniques to measure and estimate actual...

  17. Low Evapotranspiration Enhances the Resilience of Peatland Carbon Stocks to Fire

    Science.gov (United States)

    Kettridge, N.; Lukenbach, M. C.; Hokanson, K. J.; Hopkinson, C.; Devito, K. J.; Petrone, R. M.; Mendoza, C. A.; Waddington, J. M.

    2017-09-01

    Boreal peatlands may be vulnerable to projected changes in the wildfire regime under future climates. Extreme drying during the sensitive postfire period may exceed peatland ecohydrological resilience, triggering long-term degradation of these globally significant carbon stocks. Despite these concerns, we show low peatland evapotranspiration at both the plot- and landscape-scale postfire, in water-limited peatlands dominated by feather moss that are ubiquitous across continental western Canada. Low postfire evapotranspiration enhances the resilience of carbon stocks in such peatlands to wildfire disturbance and reinforces their function as a regional source of water. Near-surface water repellency may provide an important, previously unexplored, regulator of peatland evapotranspiration that can induce low evapotranspiration in the initial postfire years by restricting the supply of water to the peat surface.

  18. Upflow evapotranspiration system for the treatment of on-site wastewater effluent

    OpenAIRE

    Sean Curneen; Laurence Gill

    2015-01-01

    Full-scale willow evapotranspiration systems fed from the base with septic tank or secondary treated domestic effluent from single houses have been constructed and instrumented in Ireland in order to investigate whether the technology could provide a solution to the problem of on-site effluent disposal in areas with low permeability subsoils. Continuous monitoring of rainfall, reference evapotranspiration, effluent flows and water level in the sealed systems revealed varying evapotranspiratio...

  19. FAO-56 dual approach combined with multi-sensor remote sensing for regional evapotranspiration estimations

    OpenAIRE

    Amri, R.; Zribi, M.; Lili-Chabaane, Z.; Szczypta, C; Calvet, J.C.; Boulet, G.

    2013-01-01

    The aim of this paper is to use a dual, modified version of the FAO-56 methodology for the estimation of regional evapotranspiration. The proposed approach combines the FAO-56 technique with remote sensing. Two vegetation classes are considered in the evapotranspiration estimations. In the case of cereals, crop coefficients and cover fractions are estimated using relationships established with the Normalized Difference Vegetation Index (NDVI), retrieved from SPOT-VG...

  20. Evaluation of evaporation-measuring equipments for estimating evapotranspiration within a greenhouse

    OpenAIRE

    Blanco,Flávio F.; Folegatti,Marcos V.

    2004-01-01

    With the objective of evaluating the performance of simple evaporation measuring equipments in estimating the evapotranspiration in greenhouse, an experiment was conducted in Piracicaba, SP, during a tomato-growing season. Daily water evaporation rate from Piche atmometer, modified atmometer and a reduced evaporation pan installed inside the greenhouse and a Class A pan installed outside were compared to the evapotranspiration rates calculated with Penman-Monteith equation. Results showed tha...

  1. Propagation of soil moisture memory to streamflow and evapotranspiration in Europe

    Directory of Open Access Journals (Sweden)

    R. Orth

    2013-10-01

    Full Text Available As a key variable of the land-climate system soil moisture is a main driver of streamflow and evapotranspiration under certain conditions. Soil moisture furthermore exhibits outstanding memory (persistence characteristics. Many studies also report distinct low frequency variations for streamflow, which are likely related to soil moisture memory. Using data from over 100 near-natural catchments located across Europe, we investigate in this study the connection between soil moisture memory and the respective memory of streamflow and evapotranspiration on different time scales. For this purpose we use a simple water balance model in which dependencies of runoff (normalised by precipitation and evapotranspiration (normalised by radiation on soil moisture are fitted using streamflow observations. The model therefore allows us to compute the memory characteristics of soil moisture, streamflow and evapotranspiration on the catchment scale. We find considerable memory in soil moisture and streamflow in many parts of the continent, and evapotranspiration also displays some memory at monthly time scale in some catchments. We show that the memory of streamflow and evapotranspiration jointly depend on soil moisture memory and on the strength of the coupling of streamflow and evapotranspiration to soil moisture. Furthermore, we find that the coupling strengths of streamflow and evapotranspiration to soil moisture depend on the shape of the fitted dependencies and on the variance of the meteorological forcing. To better interpret the magnitude of the respective memories across Europe, we finally provide a new perspective on hydrological memory by relating it to the mean duration required to recover from anomalies exceeding a certain threshold.

  2. Comparison of Four Different Energy Balance Models for Estimating Evapotranspiration in the Midwestern United States

    OpenAIRE

    Singh, Ramesh K.; Senay, Gabriel B.

    2015-01-01

    The development of different energy balance models has allowed users to choose a model based on its suitability in a region. We compared four commonly used models—Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC) model, Surface Energy Balance Algorithm for Land (SEBAL) model, Surface Energy Balance System (SEBS) model, and the Operational Simplified Surface Energy Balance (SSEBop) model—using Landsat images to estimate evapotranspiration (ET) in the Midweste...

  3. Geohydrology and evapotranspiration at Franklin Lake playa, Inyo County, California; with a section on estimating evapotranspiration using the energy-budget eddy-correlation technique

    Science.gov (United States)

    Czarnecki, John B.; Stannard, David I.

    1997-01-01

    Franklin Lake playa is one of the principal discharge areas of the ground-water-flow system associated with Yucca Mountain, Nevada, the potential site of a high-level nuclear-waste repository. By using the energy-budget eddy-correlation technique, measurements made between June 1983 and April 1984 to estimate evapotranspiration were found to range from 0.1 centimeter per day during winter months to about 0.3 centimeter per day during summer months; the annual average was 0.16 centimeter per day. These estimates were compared with evapotranspiration estimates calculated from six other methods.

  4. Mapping Evapotranspiration over Agricultural Land in the California Central Valley

    Science.gov (United States)

    Melton, F. S.; Huntington, J. L.; Guzman, A.; Johnson, L.; Morton, C.; Nemani, R. R.; Post, K. M.; Rosevelt, C.; Shupe, J. W.; Spellenberg, R.; Vitale, A.

    2015-12-01

    Recent advances in satellite mapping of evapotranspiration (ET) have made it possible to largely automate the process of mapping ET over large areas at the field-scale. This development coincides with recent drought events across the western U.S. which have intensified interest in mapping of ET and consumptive use to address a range of water management challenges, including resolving disputes over water rights, improving irrigation management, and developing sustainable management plans for groundwater resources. We present a case study for California that leverages two automated ET mapping capabilities to estimate ET at the field scale over agricultural areas in the California Central Valley. We utilized the NASA Earth Exchange and applied a python-based implementation of the METRIC surface energy balance model and the Satellite Irrigation Management Support (SIMS) system, which uses a surface reflectance-based approach, to map ET over agricultural areas in the Central Valley. We present estimates from 2014 from both approaches and results from a comparison of the estimates. Though theoretically and computationally quite different from each other, initial results from both approaches show good agreement overall on seasonal ET totals for 2014. We also present results from comparisons against ET measurements collected on commercial farms in the Central Valley and discuss implications for accuracy of the two different approaches. The objective of this analysis is to provide data that can inform planning for the development of sustainable groundwater management plans, and assist water managers and growers in evaluating irrigation demand during drought events.

  5. COMS-Based Retrieval of Daily Actual Evapotranspiration over Korea

    Directory of Open Access Journals (Sweden)

    Na-Yeon Park

    2017-01-01

    Full Text Available Evapotranspiration (ET from the land surface is an important hydrometeorological factor in the exchange of energy between the atmosphere and land surface. The accurate quantification for management of water resources and understanding of climate change are crucial, requiring continuous temporal and spatial monitoring. The objective of this study is to apply and estimate daily actual ET using semiempirical method, B-method, which is based on surface energy balance over heterogeneous area, Korea. To estimate daily ET, we used geostationary meteorological satellite data (Communication, Ocean and Meteorological Satellite, COMS and polar-orbiting satellite data (Système Pour ľObservation de la Terre, SPOT. Estimated daily ET using only satellite data was relatively accurate and reflects land surface characteristics. It had high periodicity and spatial resolution over a wide area on clear-sky days. The daily ET was overestimated by about 1 mm/day at the two flux tower measurements sites, but the simulated seasonal variation and pattern were in good agreement with flux tower measurements. In the mixed forest, the root-mean-square error (RMSE was 0.94 mm/day and the bias was 1.05 mm/day, while, in the rice paddy, RMSE was 1.12 mm/day and bias was 1.21 mm/day.

  6. [Quantitative estimation of evapotranspiration from Tahe forest ecosystem, Northeast China].

    Science.gov (United States)

    Qu, Di; Fan, Wen-Yi; Yang, Jin-Ming; Wang, Xu-Peng

    2014-06-01

    Evapotranspiration (ET) is an important parameter of agriculture, meteorology and hydrology research, and also an important part of the global hydrological cycle. This paper applied the improved DHSVM distributed hydrological model to estimate daily ET of Tahe area in 2007 using leaf area index and other surface data extracted TM remote sensing data, and slope, aspect and other topographic indices obtained by using the digital elevation model. The relationship between daily ET and daily watershed outlet flow was built by the BP neural network, and a water balance equation was established for the studied watershed, together to test the accuracy of the estimation. The results showed that the model could be applied in the study area. The annual total ET of Tahe watershed was 234.01 mm. ET had a significant seasonal variation. The ET had the highest value in summer and the average daily ET value was 1.56 mm. The average daily ET in autumn and spring were 0.30, 0.29 mm, respectively, and winter had the lowest ET value. Land cover type had a great effect on ET value, and the broadleaf forest had a higher ET ability than the mixed forest, followed by the needle leaf forest.

  7. Evapotranspiration from irrigated turfgrass in the Los Angeles Metropolitan area

    Science.gov (United States)

    Litvak, E.; Bijoor, N. S.; Pataki, D.

    2011-12-01

    In the United States, turfgrasses cover an area larger than any cultivated crop. In arid and semiarid cities, where up to 75% of household water is used for irrigation, turfgrass may contribute to a substantial portion of evapotranspiration (ET) from urban landscapes. However, urban ET and the role of turfgrass have seldom been directly quantified. Using portable chambers, we directly measured ET from irrigated turfgrass in 8 locations in the Los Angeles metropolitan area. We addressed the following questions: (1) How does ET from irrigated turfgrass compare with transpiration of urban trees in the study region? (2) What are the major environmental controls on turfgrass ET? (3) How variable is turfgrass ET spatially and temporally? We found summertime ET from irrigated turfgrass to vary from 2.2 ± 0.2 mm/d to 8.8 ± 0.8 mm/d, which exceeded the maximum, plot-level transpiration of irrigated trees in the study region. The main driver of spatial variability of turfgrass ET was incoming solar radiation. This allowed us to evaluate ET from turfgrass partially shaded by trees as a function of tree canopy cover. Our results contribute to an improved representation of irrigated lawns in urban water budgets and can inform decisions about water-wise landscape planning, which is vital in semi-arid cities facing water shortages.

  8. Evapotranspiration from Urban Green Spaces in the Northeast United States

    Science.gov (United States)

    DiGiovanni, K. A.; Montalto, F. A.; Gaffin, S.

    2012-12-01

    The measurement and estimation of urban evapotranspiration (ET) has historically received limited consideration from researchers in the hydrologic and climatologic communities yet are arguably vital to both. In the studies presented, ET rates from four different urban green spaces have been measured using weighing lysimeter setups for periods ranging from one to three years. The experimental sites predominantly include in-situ engineered urban green spaces or green infrastructure installations throughout the boroughs of New York City, specifically a green roof, irrigated bioretention area, un-irrigated bioretention area, and a wooded area in one of the last remaining sections of old growth urban forest in NYC. Comparison of ET rates between these urban green spaces at a daily time-step show statistically significant differences between the rates at each site at the 0.05 significance level. Examination of the factors impacting ET rates across sites (including net radiation, wind speed, relative humidity, air temperature and media volumetric water content) was also performed for a total of eight (8) sites including the four at which ET was directly measured using weighing lysimeters. Findings suggest that statistically significant differences in micro-climate conditions do exist across the city and that these are partially responsible for differences in rates of ET. Soil moisture (irrigated vs. un-irrigated bioretention areas) conditions and vegetation types (green roof vs. bioretention area) also play a role.

  9. Evapotranspiration data to determine agro-climatic zones in Egypt

    Directory of Open Access Journals (Sweden)

    Ouda Samiha A. H.

    2017-03-01

    Full Text Available The objective of this paper was to compare between agro-climatic zones developed from 10-year interval of weather data from 2005-2014, 20-year interval of weather data from 1995-2014 and the zoning developed by [NORELDIN et al. 2016] using 30-year interval from 1985-2014 in the old cultivated land of Egypt in the Nile Delta and Valley. Monthly means of weather data were calculated for each year, and then monthly values for 10-year and 20-years were calculated for each governorate. Basic Irrigation scheduling model (BISm was used to calculate reference evapotranspiration (ETo. Analysis of variance was used and the means was separated and ranked using least significant difference test (LSD0.05. Our results showed that agro-climatic zoning using 20-year values of ETo was similar to the zones developed with 30-year values of ETo, with different values of average ETo in each zone. Furthermore, using 10-year values of ETo resulted in higher values of ETo in each zone, compared to 20-year and 30-year ETo values. However, the average value of ETo over the three classifications was close to each other. Thus, depending on the availability of weather data, either zoning can be sufficient to develop agro-climatic zones.

  10. Combining surface reanalysis and remote sensing data for monitoring evapotranspiration

    Science.gov (United States)

    Marshall, M.; Tu, K.; Funk, C.; Michaelsen, J.; Williams, Pat; Williams, C.; Ardö, J.; Marie, B.; Cappelaere, B.; Grandcourt, A.; Nickless, A.; Noubellon, Y.; Scholes, R.; Kutsch, W.

    2012-01-01

    Climate change is expected to have the greatest impact on the world's poor. In the Sahel, a climatically sensitive region where rain-fed agriculture is the primary livelihood, expected decreases in water supply will increase food insecurity. Studies on climate change and the intensification of the water cycle in sub-Saharan Africa are few. This is due in part to poor calibration of modeled actual evapotranspiration (AET), a key input in continental-scale hydrologic models. In this study, a model driven by dynamic canopy AET was combined with the Global Land Data Assimilation System realization of the NOAH Land Surface Model (GNOAH) wet canopy and soil AET for monitoring purposes in sub-Saharan Africa. The performance of the hybrid model was compared against AET from the GNOAH model and dynamic model using eight eddy flux towers representing major biomes of sub-Saharan Africa. The greatest improvements in model performance are at humid sites with dense vegetation, while performance at semi-arid sites is poor, but better than individual models. The reduction in errors using the hybrid model can be attributed to the integration of a dynamic vegetation component with land surface model estimates, improved model parameterization, and reduction of multiplicative effects of uncertain data.

  11. Isotope-based evapotranspiration partition in semi-arid environments

    Science.gov (United States)

    Wang, Lixin; Parkes, Stephen; McCabe, Matthew; Azcurra, Cecilia; Wang, Jin; Graham, Peter

    2013-04-01

    Evapotranspiration (ET) partitioning is important for quantifying the water budget and understanding vegetation control on water cycles in various ecosystems. With the development of spectroscopy-based techniques for in-situ isotope measurements, the use of stable isotope based ET partition is rising rapidly. The sub-daily scale ET partition, however, is still rarely seen in the literature. In this study, we conducted an intensive field campaign measuring ET partition using laser-based isotope and chamber techniques in a pasture system between May and June 2012 in eastern Australia. Six soil collars were used, three of which had natural vegetation and the other three were bare soil collars where vegetation was artificially removed. The vegetated and bare soil collars were used to determine the isotopic composition of ET and evaporation, respectively. The isotopic composition of the transpiration flux was determined using a Licor leaf chamber for grasses inside the vegetated collars. The diurnal patterns in dET, dE and dT are observed. In the morning, they are depleted and became more enriched and level off during mid-day. Overall the total ET flux is dominated by evaporation, though transpiration contributions are relatively higher between 10am and 12pm. D-excess is a conservative tracer of ET components and may not be useful in ET partition. This study demonstrated the use of chamber-based measurements for direct partitioning of ET at sub-daily scale and showed a rarely observed diurnal pattern of ET partition.

  12. Measurement and Modeling of Cucumber Evapotranspiration Under Greenhouse Condition

    Directory of Open Access Journals (Sweden)

    R. Moazenzadeh

    2017-01-01

    Full Text Available Introduction: In two last decades, greenhouse cultivation of different plants has developed among Iranian farmers, approximately 45 percent of national greenhouse cultures consisting of cucumber, tomato and pepper. As huge amounts of agricultural water in Iran are extracted from groundwater resources and a large number of Iranian plains are in critical conditions, and because irrigation is the major consumer of water (95 percent, it must be performed in a scientific manner. One approach to this is to obtain the knowledge of the consumptive use of major crops which is named evapotranspiration (ETc. Materials and Methods: This research was carried out in a north-south greenhouse belonging to Plant Protection Research Institute, located on northern Tehran, Iran, for estimating greenhouse cucumber evapotranspiration. Trickle irrigation method was used, and meteorological data such as temperature, humidity and solar radiation were measured daily. Physical and chemical measurements were conducted and electric conductivity (EC and pH values of 3.42 dsm-1 and 7.19, respectively, were recorded. Soil texture and bulk density were measured as to be sandy loam and 1.4 gr cm-3, respectively. In order to measure the actual evapotranspiration, cucumber seeds were also cultured in six similar microlysimeters and irrigation of each microlysimeter was based on FC moisture. If any drained water was available, it was measured. Finally, with measured meteorological characteristics in greenhouse which are suggested to have an effect on ET and were measurable, the best multiple linear regression and artificial neural network were established. The average data from three microlysimeters were used for calibration and that from three other microlysimeters were used for validation set. Results and Discussion: In the former case, when we used one multiple linear regression with measurable meteorological variables inside the greenhouse to predict cucumber ET for the entire

  13. Estimation of regional evapotranspiration in the extended Salado Basin (Argentina) from satellite gravity measurements

    Science.gov (United States)

    Cesanelli, Andrés; Guarracino, Luis

    2011-05-01

    In this study, regional evapotranspiration is estimated in a wide flatland area that includes Salado River Basin and four tributary basins by using gravity measurements of the space mission Gravity Recovery and Climate Experiment (GRACE). Monthly estimates of large-scale variations in the land-water storage are obtained from the satellite data. Evapotranspiration is computed with the water-balance equation using the GRACE land-water solutions, rainfall data from the Global Precipitation Climatology Center and runoff values obtained as 5% of the precipitation. GRACE-derived evapotranspiration values are consistent with the different climatic scenarios observed, and they satisfactorily agree with estimates provided by a global hydrological model. The overall results show that the method used is a valid tool for characterizing the evapotranspiration in the Argentine Pampas and that it can be used to detect and examine changes in the evapotranspiration pattern associated with the occurrence of extreme climatic events. This study illustrates the ability of GRACE to analyze and predict evapotranspiration and other processes on a regional scale in a flatland area.

  14. Monitoring Daily Evapotranspiration in California Vineyards Using Landsat 8

    Science.gov (United States)

    Anderson, M. C.; Semmens, K. A.; Kustas, W. P.; Gao, F.; Alfieri, J. G.; McKee, L.; Prueger, J. H.; Hain, C.; Cammalleri, C.

    2014-12-01

    In California's Central Valley, due to competing demands for limited water resources, it is critical to monitor evaporative water loss and crop conditions at both individual field scales and over larger areas in support of water management decisions. This is particularly important for viticulture because grape vines must be maintained under highly controlled conditions in order to maximize production of quality fruit. Thus, regular high resolution temporal monitoring of hundreds of acres is required, a task only efficiently achieved with satellite remote sensing, combining multiple earth observations. In this research, we evaluate the utility of a multi-scale system for monitoring evapotranspiration (ET) and crop water stress applied over two vineyard sites near Lodi, California during the 2013 growing season. The system employs a data fusion methodology (STARFM: Spatial and Temporal Adaptive Reflective Fusion Model) combined with multi-scale ET modeling (ALEXI: Atmosphere Land Exchange Inverse Model) to compute daily 30 m resolution ET. ALEXI ET fluxes (4 km resolution, daily) are integrated with ET fluxes from Landsat 8 thermal data (30 m resolution, ~16 day) and Moderate Resolution Imaging Spectroradiometer (MODIS) data (1 km resolution, daily). The high spatial resolution Landsat retrievals are then fused with high temporal frequency MODIS data using STARFM to produce daily estimates of crop water use that resolve within field variation in ET for individual vineyards. Estimates of daily ET generated in two fields of Pinot Noir vines of different maturity agreed well with ground-based flux measurements collected within each field with relative errors of about 15%. Spatial patterns of cumulative ET correspond to yield estimates and indicate areas of variable crop moisture, condition, and yield within the vineyards that could require additional management strategies due to variation in soil type/texture, nutrient conditions and other environmental factors.

  15. Estimating Evapotranspiration Using an Observation Based Terrestrial Water Budget

    Science.gov (United States)

    Rodell, Matthew; McWilliams, Eric B.; Famiglietti, James S.; Beaudoing, Hiroko K.; Nigro, Joseph

    2011-01-01

    Evapotranspiration (ET) is difficult to measure at the scales of climate models and climate variability. While satellite retrieval algorithms do exist, their accuracy is limited by the sparseness of in situ observations available for calibration and validation, which themselves may be unrepresentative of 500m and larger scale satellite footprints and grid pixels. Here, we use a combination of satellite and ground-based observations to close the water budgets of seven continental scale river basins (Mackenzie, Fraser, Nelson, Mississippi, Tocantins, Danube, and Ubangi), estimating mean ET as a residual. For any river basin, ET must equal total precipitation minus net runoff minus the change in total terrestrial water storage (TWS), in order for mass to be conserved. We make use of precipitation from two global observation-based products, archived runoff data, and TWS changes from the Gravity Recovery and Climate Experiment satellite mission. We demonstrate that while uncertainty in the water budget-based estimates of monthly ET is often too large for those estimates to be useful, the uncertainty in the mean annual cycle is small enough that it is practical for evaluating other ET products. Here, we evaluate five land surface model simulations, two operational atmospheric analyses, and a recent global reanalysis product based on our results. An important outcome is that the water budget-based ET time series in two tropical river basins, one in Brazil and the other in central Africa, exhibit a weak annual cycle, which may help to resolve debate about the strength of the annual cycle of ET in such regions and how ET is constrained throughout the year. The methods described will be useful for water and energy budget studies, weather and climate model assessments, and satellite-based ET retrieval optimization.

  16. Simulation of Evapotranspiration using an Optimality-based Ecohydrological Model

    Science.gov (United States)

    Chen, Lajiao

    2014-05-01

    Accurate estimation of evapotranspiration (ET) is essential in understanding the effect of climate change and human activities on ecosystem and water resource. As an important tool for ET estimation, most of the traditional hydrological or ecohydrological models treat ET as a physical process, controlled by energy, vapor, pressure and turbulence. It is at times questionable as transpiration, major component of ET, is biological activity closely linked to photosynthesis by stomatal conductivity. Optimality-based ecohydrological models consider the mutual interaction of ET and photosynthesis based on optimality principle. However, as a rising generation of ecohydrological models, so far there are only a few applications of the optimality-based model in different ecosystems. The ability and reliability of this kind of models for ecohydrological modeling need to be validated in more ecosystems. The objective of this study is to validate the optimality hypothesis for water-limited ecosystem. To achieve this, the study applied an optimality-based model Vegetation Optimality Model (VOM) to simulate ET and its components based on optimality principle. The model is applied in a semiarid watershed. The simulated ET and soil waster were compared with long term measurement data in Kendall and Lcukyhill sites in the watershed. The result showed that the temporal variations of simulated ET and soil water are in good agreement with observed data. Temporal dynamic of soil evaporation and transpiration and their response to precipitation events can be well captured with the model. This could come to a conclusion the optimality-based ecohydrological model could be a potential approach to simulate ET.

  17. A hybrid approach for estimating spatial evapotranspiration from satellite imagery

    Science.gov (United States)

    Neale, C. M. U.; Gonzalez-Dugo, M. P.; Mateos, L.; Kustas, W. P.; Kaheil, Y.

    2007-10-01

    Two common approaches for estimating crop evapotranspiration (ET) using satellite imagery are the reflectance-based crop coefficient method and the energy balance method. The reflectance-based crop coefficient method relates a reflectance-based vegetation index such as the soil adjusted vegetation index (SAVI) to ET basal crop coefficients such as those described by Wright (1982) [1] and the FAO 56 manual [2]. A time-series of remotely sensed inputs is then used to build the crop coefficient curve in each field being monitored. In order to obtain actual ET, a water balance must be maintained in the root zone of the crop in order to make the appropriate adjustments due to soil moisture deficits and wet soil surface from irrigation and/or rain. Ground meteorological data must be provided by a weather station located in the modeled area for the estimation of reference ET. In the energy balance approach, surface temperatures are used in the estimation of sensible heat fluxes and depending on the complexity of the model, different methods are used to either handle the aerodynamic temperature term or deal with sparse canopies (empirical approaches, two-source model, SEBAL model). Remotely sensed inputs are also used for the estimation of net radiation and soil heat flux, with latent heat flux (ET) obtained as a residual from the energy balance equation. The energy balance approach results in the actual ET being estimated directly. Instantaneous values of ET must be extrapolated to the entire day and over time in between satellite overpass inputs. This paper describes a hybrid approach that uses both methods in combination to monitor actual ET over a growing season for irrigated and non-irrigated crops. The model has been coded in an ArcGIS environment, using visual basic for the calculations. This paper describes the modeling environment and coded ET models within and presents some application results.

  18. Parametric Modelling of Potential Evapotranspiration: A Global Survey

    Directory of Open Access Journals (Sweden)

    Aristoteles Tegos

    2017-10-01

    Full Text Available We present and validate a global parametric model of potential evapotranspiration (PET with two parameters that are estimated through calibration, using as explanatory variables temperature and extraterrestrial radiation. The model is tested over the globe, taking advantage of the Food and Agriculture Organization (FAO CLIMWAT database that provides monthly averaged values of meteorological inputs at 4300 locations worldwide. A preliminary analysis of these data allows for explaining the major drivers of PET over the globe and across seasons. The model calibration against the given Penman-Monteith values was carried out through an automatic optimization procedure. For the evaluation of the model, we present global maps of optimized model parameters and associated performance metrics, and also contrast its performance against the well-known Hargreaves-Samani method. Also, we use interpolated values of the optimized parameters to validate the predictive capacity of our model against monthly meteorological time series, at several stations worldwide. The results are very encouraging, since even with the use of abstract climatic information for model calibration and the use of interpolated parameters as local predictors, the model generally ensures reliable PET estimations. Exceptions are mainly attributed to irregular interactions between temperature and extraterrestrial radiation, as well as because the associated processes are influenced by additional drivers, e.g., relative humidity and wind speed. However, the analysis of the residuals shows that the model is consistent in terms of parameters estimation and model validation. The parameter maps allow for the direct use of the model wherever in the world, providing PET estimates in case of missing data, that can be further improved even with a short term acquisition of meteorological data.

  19. Urban Evapotranspiration and Carbon Dioxide Flux in Miami - Dade, Florida

    Science.gov (United States)

    Bernier, T.; Hopper, W.

    2010-12-01

    Atmospheric Carbon Dioxide (CO2) concentrations are leading indicators of secular climate change. With increasing awareness of the consequences of climate change, methods for monitoring this change are becoming more important daily. Of particular interest is the carbon dioxide exchange between natural and urban landscapes and the correlation of atmospheric CO2 concentrations. Monitoring Evapotranspiration (ET) is important for assessments of water availability for growing populations. ET is surprisingly understudied in the hydrologic cycle considering ET removes as much as 80 to over 100% of precipitation back into the atmosphere as water vapor. Lack of understanding in spatial and temporal ET estimates can limit the credibility of hydrologic water budgets designed to promote sustainable water use and resolve water-use conflicts. Eddy covariance (EC) methods are commonly used to estimate ET and CO2 fluxes. The EC platform consist of a (CSAT) 3-D Sonic Anemometer and a Li-Cor Open Path CO2/ H2O Analyzer. Measurements collected at 10 Hz create a very large data sets. A EC flux tower located in the Snapper Creek Well Field as part of a study to estimate ET for the Miami Dade County Water and Sewer project. Data has been collected from December 17, 2009 to August 30, 2010. QA/QC is performed with the EdiRe data processing software according to Ameri-flux protocols. ET estimates along with other data--latent-heat flux, sensible-heat flux, rainfall, air temperature, wind speed and direction, solar irradiance, net radiation, soil-heat flux and relative humidity--can be used to aid in the development of water management policies and regulations. Currently, many financial institutions have adopted an understanding about baseline environmental monitoring. The “Equator Principle” is an example of a voluntary standard for managing social and environmental risk in project financing and has changed the way in which projects are financed.

  20. Monitoring and Forecasting Reference Evapotranspiration for Food Security Assessments

    Science.gov (United States)

    Shukla, S.; Hobbins, M.; McEvoy, D.; Husak, G. J.; Dewes, C.; McNally, A.; Huntington, J. L.; Funk, C. C.; Verdin, J. P.

    2016-12-01

    Reference evapotranspiration (Ref ET; driven by temperature, humidity, wind speed, and solar radiation) and precipitation are the two most important climatic drivers of seasonal crop yields, which are directly associated with food security in several parts of the globe. In the last decade or so, significant strides have been made by the Famine Early Warning Systems Network (FEWS NET) team and collaborators, towards improving precipitation monitoring. However, efforts to improve Ref ET monitoring and forecasting have thus far lagged by comparison. This presentation describes ongoing activities of the FEWS NET team and collaborators towards the development and implementation of a near-real time Ref ET monitoring and forecasting system, focusing primarily on the food-insecure FEWS NET countries. Due to a lack of in situ observations of meteorological forcings, the Ref ET monitoring dataset, which is calculated using the Penman-Monteith formulation of the ASCE Standardized Reference ET, uses NASA's MERRA-2 atmospheric forcings and is spatially downscaled using a finer resolution climatology of the International Water Management Institute global PET dataset. Ref ET forecasts (up to 6 months lead time) are calculated using seasonal climate forecasts from NCEP's CFSv2 and NASA's GEOS-5 models. Long-term (since early 1980s through 2015) evaluation of Ref ET monitoring and forecast datasets and the approach to provide operational updates of both datasets in near-real time, are summarized in this presentation. As a case study, the influence of improved Ref ET monitoring and Ref ET forecasts on crop yield estimates and food security outlooks in East Africa is also examined using the Water Requirement Satisfaction Index model. In summary, this presentation highlights the importance of monitoring and forecasting Ref ET for food security assessments and early warning.

  1. Measuring surface energy and evapotranspiration across Caribbean mangrove forests

    Science.gov (United States)

    Lagomasino, D.; Fatoyinbo, T. E.; Price, R.

    2014-12-01

    Coastal mangroves lose large amounts of water through evapotranspiration (ET) that can be equivalent to the amount of annual rainfall in certain years. Satellite remote sensing has been used to estimate surface energy and ET variability in many forested ecosystems, yet has been widely overlooked in mangrove forests. Using a combination of long-term datasets (30-year) acquired from the NASA Landsat 5 and 7 satellite databases, the present study investigated ET and surface energy balance variability between two mangrove forest sites in the Caribbean: 1) Everglades National Park (ENP; Florida, USA) and 2) Sian Ka'an Biosphere Reserve (SKBR; Quintana Roo, Mexico). A satellite-derived surface energy balance model was used to estimate ET in tall and scrub mangroves environments at ENP and SKBR. Results identified significant differences in soil heat flux measurements and ET between the tall and scrub mangrove environments. Scrub mangroves exhibited the highest soil heat flux coincident with the lowest biophysical indices (i.e., Fractional Vegetation Cover, Normalized Difference Vegetation Index, and Soil-Adjusted Vegetation Index) and ET rates. Mangrove damage and mortality was observed on the satellite images following strong tropical storms and associated with anthropogenic modifications and resulted in low values in spectral vegetation indices, higher soil heat flux, and higher ET. Recovery of the spectral characteristics, soil heat flux and ET was within 1-2 years following hurricane disturbance while, degradation caused by human disturbance persisted for many years. Remotely sensed ET of mangrove forests can provide estimates over a few decades and provide us with some understanding of how these environments respond to disturbances to the landscape in periods where no ground data exists or in locations that are difficult to access. Moreover, relationships between energy and water balance components developed for the coastal mangroves of Florida and Mexico could be

  2. Estimation of evapotranspiration in the Mu Us Sandland of China

    Directory of Open Access Journals (Sweden)

    S. Liu

    2010-03-01

    Full Text Available Evapotranspiration (ET was estimated from 1981–2005 over Wushen County located in the Mu Us Sandland, China, by applying the Advection-Aridity model, which is based on the complementary relationship hypothesis. We used National Oceanic and Atmospheric Administration (NOAA Advanced Very High Resolution Radiometer (AVHRR, Moderate Resolution Imaging Spectroradiometer (MODIS, and meteorological data. Our results show that the estimated daily ET was about 4.5% higher than measurements using an Eddy Covariance (EC system after forcing energy balance closure over an alfalfa field from 22 July 2004 to 23 August 2004. At a regional scale, the estimated monthly ET was about 8.7% lower than measurements using the EC system after forcing energy balance closure over an alfalfa field in August 2004. These results were about 3.0% higher than ET measurements by microlysimeter over sand dunes during June 1988. From 1981 to 2005, the average annual ET and precipitation levels were 287 mm and 336 mm, respectively, in Wushen County. The average annual ET varied from 230 mm in western parts of Wushen County to 350 mm in eastern parts of the county. Both inter-annual and seasonal variations in ET were substantial in Wushen County. The annual ET was 200–400 mm from 1981–2005, and the seasonal pattern of ET showed a single peak distribution. The cumulative ET during the June–September 2004 period was 250 mm, which was 87% of the total annual ET. The annual ET, precipitation, and the maximum Normalized Difference Vegetation Index (NDVImax showed positive correlations temporally and spatially.

  3. Reference evapotranspiration variability and trends in Spain, 1961-2011

    Science.gov (United States)

    Vicente-Serrano, Sergio M.; Azorin-Molina, Cesar; Sanchez-Lorenzo, Arturo; Revuelto, Jesús; López-Moreno, Juan I.; González-Hidalgo, José C.; Moran-Tejeda, Enrique; Espejo, Francisco

    2014-10-01

    In this study we analyzed the spatial distribution, temporal variability and trends in reference evapotranspiration (ET0) in Spain from 1961 to 2011. Twelve methods were analyzed to quantify ET0 from quality controlled and homogeneous series of various meteorological variables measured at 46 meteorological stations. Some of the models used are temperature based (e.g., Thornthwaite, Hargreaves, Linacre), whereas others are more complex and require more meteorological variables for calculation (e.g., Priestley-Taylor, Papadakis, FAO-Blaney-Criddle). The Penman-Monteith equation was used as a reference to quantify ET0, and for comparison among the other methods applied in the study. No major differences in the spatial distribution of the average ET0 were evident among the various methods. At annual and seasonal scales some of the ET0 methods requiring only temperature data for calculation provided better results than more complex methods requiring more variables. Among them the Hargreaves (HG) equation provided the best results, at both the annual and seasonal scales. The analysis of the temporal variability and trends in the magnitude of ET0 indicated that all methods show a marked increase in ET0 at the seasonal and annual time scales. Nevertheless, results obtained suggested substantial uncertainties among the methods assessed to determine ET0 changes, due to differences in temporal variability of the resulting time series, but mainly for the differences in the magnitude of change of ET0 and its spatial distribution. This suggests that ET0 trends obtained by means of methods that only require temperature data for ET0 calculations should be evaluated carefully under the current global warming scenario.

  4. Reconstruction of temporal variations of evapotranspiration using instantaneous estimates at the time of satellite overpass

    Directory of Open Access Journals (Sweden)

    E. Delogu

    2012-08-01

    Full Text Available Evapotranspiration estimates can be derived from remote sensing data and ancillary, mostly meterorological, information. For this purpose, two types of methods are classically used: the first type estimates a potential evapotranspiration rate from vegetation indices, and adjusts this rate according to water availability derived from either a surface temperature index or a first guess obtained from a rough estimate of the water budget, while the second family of methods relies on the link between the surface temperature and the latent heat flux through the surface energy budget. The latter provides an instantaneous estimate at the time of satellite overpass. In order to compute daily evapotranspiration, one needs an extrapolation algorithm. Since no image is acquired during cloudy conditions, these methods can only be applied during clear sky days. In order to derive seasonal evapotranspiration, one needs an interpolation method. Two combined interpolation/extrapolation methods based on the self preservation of evaporative fraction and the stress factor are compared to reconstruct seasonal evapotranspiration from instantaneous measurements acquired in clear sky conditions. Those measurements are taken from instantaneous latent heat flux from 11 datasets in Southern France and Morocco. Results show that both methods have comparable performances with a clear advantage for the evaporative fraction for datasets with several water stress events. Both interpolation algorithms tend to underestimate evapotranspiration due to the energy limiting conditions that prevail during cloudy days. Taking into account the diurnal variations of the evaporative fraction according to an empirical relationship derived from a previous study improved the performance of the extrapolation algorithm and therefore the retrieval of the seasonal evapotranspiration for all but one datasets.

  5. Estimation of land surface evapotranspiration with A satellite remote sensing procedure

    Science.gov (United States)

    Irmak, A.; Ratcliffe, I.; Ranade, P.; Hubbard, K.G.; Singh, R.K.; Kamble, B.; Kjaersgaard, J.

    2011-01-01

    There are various methods available for estimating magnitude and trends of evapotranspiration. Bowen ratio energy balance system and eddy correlation techniques offer powerful alternatives for measuring land surface evapotranspiration. In spite of the elegance, high accuracy, and theoretical attractions of these techniques for measuring evapotranspiration, their practical use over large areas can be limited due to the number of sites needed and the related expense. Application of evapotranspiration mapping from satellite measurements can overcome the limitations. The objective of this study was to utilize the METRICTM (Mapping Evapotranspiration at High Resolution using Internalized Calibration) model in Great Plains environmental settings to understand water use in managed ecosystems on a regional scale. We investigated spatiotemporal distribution of a fraction of reference evapotranspiration (ETrF) using eight Landsat 5 images during the 2005 and 2006 growing season for path 29, row 32. The ETrF maps generated by METRICTM allowed us to follow the magnitude and trend in ETrF for major land-use classes during the growing season. The ETrF was lower early in the growing season for agricultural crops and gradually increased as the normalized difference vegetation index of crops increased, thus presenting more surface area over which water could transpire toward the midseason. Comparison of predictions with Bowen ratio energy balance system measurements at Clay Center, NE, showed that METRICTM performed well at the field scale for predicting evapotranspiration from a cornfield. If calibrated properly, the model could be a viable tool to estimate water use in managed ecosystems in subhumid climates at a large scale.

  6. Improving evapotranspiration in a land surface model using biophysical variables derived from MSG/SEVIRI satellite

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    N. Ghilain

    2012-08-01

    Full Text Available Monitoring evapotranspiration over land is highly dependent on the surface state and vegetation dynamics. Data from spaceborn platforms are desirable to complement estimations from land surface models. The success of daily evapotranspiration monitoring at continental scale relies on the availability, quality and continuity of such data. The biophysical variables derived from SEVIRI on board the geostationary satellite Meteosat Second Generation (MSG and distributed by the Satellite Application Facility on Land surface Analysis (LSA-SAF are particularly interesting for such applications, as they aimed at providing continuous and consistent daily time series in near-real time over Africa, Europe and South America. In this paper, we compare them to monthly vegetation parameters from a database commonly used in numerical weather predictions (ECOCLIMAP-I, showing the benefits of the new daily products in detecting the spatial and temporal (seasonal and inter-annual variability of the vegetation, especially relevant over Africa. We propose a method to handle Leaf Area Index (LAI and Fractional Vegetation Cover (FVC products for evapotranspiration monitoring with a land surface model at 3–5 km spatial resolution. The method is conceived to be applicable for near-real time processes at continental scale and relies on the use of a land cover map. We assess the impact of using LSA-SAF biophysical variables compared to ECOCLIMAP-I on evapotranspiration estimated by the land surface model H-TESSEL. Comparison with in-situ observations in Europe and Africa shows an improved estimation of the evapotranspiration, especially in semi-arid climates. Finally, the impact on the land surface modelled evapotranspiration is compared over a north–south transect with a large gradient of vegetation and climate in Western Africa using LSA-SAF radiation forcing derived from remote sensing. Differences are highlighted. An evaluation against remote sensing derived land

  7. Estimating groundwater recharge in the dry zone of Sri Lanka using weekly, 10-daily or monthly evapotranspiration data

    OpenAIRE

    Silva, RP

    1999-01-01

    Howard and Lloyd (1979) have shown that daily values for rainfall and potential evapotranspiration are required in estimating recharge with a soil water balance model. However, available data may not be daily but weekly or even monthly. This is true for potential evapotranspiration data which are usually derived from pan evaporation data. This paper examines the effect of using distributed weekly, 10-daily or monthly potential evapotranspiration values rather than the actual daily values in e...

  8. Evaluation of evapotranspiration methods for model validation in a semi-arid watershed in northern China

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    K. Schneider

    2007-05-01

    Full Text Available This study evaluates the performance of four evapotranspiration methods (Priestley-Taylor, Penman-Monteith, Hargreaves and Makkink of differing complexity in a semi-arid environment in north China. The results are compared to observed water vapour fluxes derived from eddy flux measurements. The analysis became necessary after discharge simulations using an automatically calibrated version of the Soil and Water Assessment Tool (SWAT failed to reproduce runoff measurements. Although the study area receives most of the annual rainfall during the vegetation period, high temperatures can cause water scarcity. We investigate which evapotranspiration method is most suitable for this environment and whether the model performance of SWAT can be improved with the most adequate evapotranspiration method.

    The evapotranspiration models were tested in two consecutive years with different rainfall amounts. In general, the simple Hargreaves and Makkink equations outmatch the more complex Priestley-Taylor and Penman-Monteith methods, although their performance depended on water availability. Effects on the quality of SWAT runoff simulations, however, remained minor. Although evapotranspiration is an important process in the hydrology of this steppe environment, our analysis indicates that other driving factors still need to be identified to improve SWAT simulations.

  9. Using the Priestley-Taylor expression for estimating actual evapotranspiration from satellite Landsat ETM + data

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    A. Khaldi

    2014-09-01

    Full Text Available The quantification of evapotranspiration from irrigated areas is important for agriculture water management, especially in arid and semi-arid regions where water deficiency is becoming a major constraint in economic welfare and sustainable development. Conventional methods that use point measurements to estimate evapotranspiration are representative only of local areas and cannot be extended to large areas because of landscape heterogeneity. Remote sensing-based energy balance models are presently most suited for estimating evapotranspiration at both field and regional scales. In this study, we aim to develop a methodology based on the triangle concept, allowing estimation of evapotranspiration through the classical equation of Priestley and Taylor (1972 where the proportional coefficient α in this equation is ranged using a linear interpolation between surface temperature and Normalized Difference Vegetation Index (NDVI values. Preliminary results using remotely sensed data sets from Landsat ETM+ over the Habra Plains in west Algeria are in good agreement with ground measurements. The proposed approach appears to be more reliable and easily applicable for operational estimation of evapotranspiration over large areas.

  10. Time series analysis of reference crop evapotranspiration for Bokaro District, Jharkhand, India

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    Gautam Ratnesh

    2016-09-01

    Full Text Available Evapotranspiration is the one of the major role playing element in water cycle. More accurate measurement and forecasting of Evapotranspiration would enable more efficient water resources management. This study, is therefore, particularly focused on evapotranspiration modelling and forecasting, since forecasting would provide better information for optimal water resources management. There are numerous techniques of evapotranspiration forecasting that include autoregressive (AR and moving average (MA, autoregressive moving average (ARMA, autoregressive integrated moving average (ARIMA, Thomas Feiring, etc. Out of these models ARIMA model has been found to be more suitable for analysis and forecasting of hydrological events. Therefore, in this study ARIMA models have been used for forecasting of mean monthly reference crop evapotranspiration by stochastic analysis. The data series of 102 years i.e. 1224 months of Bokaro District were used for analysis and forecasting. Different order of ARIMA model was selected on the basis of autocorrelation function (ACF and partial autocorrelation (PACF of data series. Maximum likelihood method was used for determining the parameters of the models. To see the statistical parameter of model, best fitted model is ARIMA (0, 1, 4 (0, 1, 112.

  11. NOAA Introduces its First-Generation Reference Evapotranspiration Product

    Science.gov (United States)

    Hobbins, M.; Geli, H. M.; Lewis, C.; Senay, G. B.; Verdin, J. P.

    2013-12-01

    NOAA is producing daily, gridded operational, long-term, reference evapotranspiration (ETo) data for the National Water Census (NWC). The NWC is a congressional mandate to provide water managers with accurate, up-to-date, scientifically defensible reporting on the national water cycle; as such, it requires a high-quality record of actual ET, which we derive as a fraction of NOAA's land-based ETo a fraction determined by remotely sensed (RS) LST and/or surface reflectance in an operational version of the Simplified Surface Energy Balance (SSEBop). This methodology permits mapping of ET on a routine basis with a high degree of consistency at multiple spatial scales. This presentation addresses the ETo input to this process. NOAA's ETo dataset is generated from the American Society of Civil Engineers Standardized Penman-Monteith equation driven by hourly, 0.125-degree (~12-km) data from the North American Land Data Assimilation System (NLDAS). Coverage is CONUS-wide from Jan 1, 1979, to within five days of the present. The ETo is verified against agro-meteorological stations in western CONUS networks, while a first-order, second-moment uncertainty analysis indicates when, where, and to what extent each driver contributes to ETo variability (and so potentially require the most attention). As the NWC's mandate requires a nationwide coverage, the ETo dataset must also be verified outside of the measure's traditional, agricultural/irrigated areas of application. In this presentation, we summarize the verification of the gridded ETo product and demonstrate the drivers of ETo variability in space and time across CONUS. Beyond its primary use as a component of ET in the NWC, we further explore potential uses of the ETo product as an input to drought models and as a stand-alone index of fast-developing agricultural drought, or 'flash drought.' NOAA's product is the first consistently modeled, daily, continent-wide ETo dataset that is both up-to-date and as temporally

  12. Regional simulation of urban evapotranspiration over Helsinki, Finland in 2008

    Science.gov (United States)

    Falk, M.; Spano, D.; Snyder, R. L.; Paw U, K.; Marras, S.; Pyles, D.

    2012-12-01

    The number of urban metabolism studies has increased in recent years, due to the important impact that energy, water and carbon exchange over urban areas have on climate change. Urban modeling is therefore crucial in the future design and management of cities. This study presents the ACASA model coupled to the Weather Research and Forecasting (WRF-ARW) mesoscale model to simulate urban area evapotranspiration, surface energy budget terms, and carbon exchange estimates at a horizontal resolution of 600 meters for urban areas of roughly 20 by 20 km. As part of the European Project "BRIDGE", these regional simulations were used in combination with remotely sensed data to provide constraints on the land surface types and mass and energy exchange of urban centers. Land surface-atmosphere mass and energy exchanges LE were simulated using the Advanced Canopy Atmosphere Soil Algorithm (ACASA). The WRF-ACASA coupled model was used to scale up to a regional domain to better simulate the evolution of the urban atmosphere exchange at regional scale: we used a sequence of 6 nested domains with feedback for WRF-ACASA (dx = 48.6, 16.4, 5.2, 1.8, and 0.6 km) using NNRP reanalysis data in combination with CLC land cover data. Our results show that the model performed well compared with the observations both for the surface energy fluxes as well as the surface carbon exchange. The model can generally account for 45-72% of half-hourly variations of observed fluxes. Generally the partitioning of energy fluxes was on par with other urban model performances. On a biweekly time scale we compared the average diurnal course of LE (latent energy flux) of the model against observations. The model was able to resolve 91-92% of the variation of observed fluxes on this aggregate scale with a slope of the linear regression of 0.92 for LE. Simulations yielded spatially consistent results according to land use distribution and location of the urban center. Keywords: Urban metabolism, surface

  13. Artificial neural networks employment in the prediction of evapotranspiration of greenhouse-grown sweet pepper

    Directory of Open Access Journals (Sweden)

    Héliton Pandorfi

    2016-06-01

    Full Text Available ABSTRACT This study aimed to investigate the applicability of artificial neural networks (ANNs in the prediction of evapotranspiration of sweet pepper cultivated in a greenhouse. The used data encompass the second crop cycle, from September 2013 to February 2014, constituting 135 days of daily meteorological data, referring to the following variables: temperature and relative air humidity, wind speed and solar radiation (input variables, as well as evapotranspiration (output variable, determined using data obtained by load-cell weighing lysimeter. The recorded data were divided into three sets for training, testing and validation. The ANN learning model recognized the evapotranspiration patterns with acceptable accuracy, with mean square error of 0.005, in comparison to the data recorded in the lysimeter, with coefficient of determination of 0.87, demonstrating the best approximation for the 4-21-1 network architecture, with multilayers, error back-propagation learning algorithm and learning rate of 0.01.

  14. Improving evapotranspiration processes in distrubing hydrological models using Remote Sensing derived ET products.

    Science.gov (United States)

    Abitew, T. A.; van Griensven, A.; Bauwens, W.

    2015-12-01

    Evapotranspiration is the main process in hydrology (on average around 60%), though has not received as much attention in the evaluation and calibration of hydrological models. In this study, Remote Sensing (RS) derived Evapotranspiration (ET) is used to improve the spatially distributed processes of ET of SWAT model application in the upper Mara basin (Kenya) and the Blue Nile basin (Ethiopia). The RS derived ET data is obtained from recently compiled global datasets (continuously monthly data at 1 km resolution from MOD16NBI,SSEBop,ALEXI,CMRSET models) and from regionally applied Energy Balance Models (for several cloud free days). The RS-RT data is used in different forms: Method 1) to evaluate spatially distributed evapotransiration model resultsMethod 2) to calibrate the evotranspiration processes in hydrological modelMethod 3) to bias-correct the evapotranpiration in hydrological model during simulation after changing the SWAT codesAn inter-comparison of the RS-ET products shows that at present there is a significant bias, but at the same time an agreement on the spatial variability of ET. The ensemble mean of different ET products seems the most realistic estimation and was further used in this study.The results show that:Method 1) the spatially mapped evapotranspiration of hydrological models shows clear differences when compared to RS derived evapotranspiration (low correlations). Especially evapotranspiration in forested areas is strongly underestimated compared to other land covers.Method 2) Calibration allows to improve the correlations between the RS and hydrological model results to some extent.Method 3) Bias-corrections are efficient in producing (sesonal or annual) evapotranspiration maps from hydrological models which are very similar to the patterns obtained from RS data.Though the bias-correction is very efficient, it is advised to improve the model results by better representing the ET processes by improved plant/crop computations, improved

  15. Dominant effect of increasing forest biomass on evapotranspiration: interpretations of movement in Budyko space

    Science.gov (United States)

    Jaramillo, Fernando; Cory, Neil; Arheimer, Berit; Laudon, Hjalmar; van der Velde, Ype; Hasper, Thomas B.; Teutschbein, Claudia; Uddling, Johan

    2018-01-01

    During the last 6 decades, forest biomass has increased in Sweden mainly due to forest management, with a possible increasing effect on evapotranspiration. However, increasing global CO2 concentrations may also trigger physiological water-saving responses in broadleaf tree species, and to a lesser degree in some needleleaf conifer species, inducing an opposite effect. Additionally, changes in other forest attributes may also affect evapotranspiration. In this study, we aimed to detect the dominating effect(s) of forest change on evapotranspiration by studying changes in the ratio of actual evapotranspiration to precipitation, known as the evaporative ratio, during the period 1961-2012. We first used the Budyko framework of water and energy availability at the basin scale to study the hydroclimatic movements in Budyko space of 65 temperate and boreal basins during this period. We found that movements in Budyko space could not be explained by climatic changes in precipitation and potential evapotranspiration in 60 % of these basins, suggesting the existence of other dominant drivers of hydroclimatic change. In both the temperate and boreal basin groups studied, a negative climatic effect on the evaporative ratio was counteracted by a positive residual effect. The positive residual effect occurred along with increasing standing forest biomass in the temperate and boreal basin groups, increasing forest cover in the temperate basin group and no apparent changes in forest species composition in any group. From the three forest attributes, standing forest biomass was the one that could explain most of the variance of the residual effect in both basin groups. These results further suggest that the water-saving response to increasing CO2 in these forests is either negligible or overridden by the opposite effect of the increasing forest biomass. Thus, we conclude that increasing standing forest biomass is the dominant driver of long-term and large-scale evapotranspiration

  16. Dominant effect of increasing forest biomass on evapotranspiration: interpretations of movement in Budyko space

    Directory of Open Access Journals (Sweden)

    F. Jaramillo

    2018-01-01

    Full Text Available During the last 6 decades, forest biomass has increased in Sweden mainly due to forest management, with a possible increasing effect on evapotranspiration. However, increasing global CO2 concentrations may also trigger physiological water-saving responses in broadleaf tree species, and to a lesser degree in some needleleaf conifer species, inducing an opposite effect. Additionally, changes in other forest attributes may also affect evapotranspiration. In this study, we aimed to detect the dominating effect(s of forest change on evapotranspiration by studying changes in the ratio of actual evapotranspiration to precipitation, known as the evaporative ratio, during the period 1961–2012. We first used the Budyko framework of water and energy availability at the basin scale to study the hydroclimatic movements in Budyko space of 65 temperate and boreal basins during this period. We found that movements in Budyko space could not be explained by climatic changes in precipitation and potential evapotranspiration in 60 % of these basins, suggesting the existence of other dominant drivers of hydroclimatic change. In both the temperate and boreal basin groups studied, a negative climatic effect on the evaporative ratio was counteracted by a positive residual effect. The positive residual effect occurred along with increasing standing forest biomass in the temperate and boreal basin groups, increasing forest cover in the temperate basin group and no apparent changes in forest species composition in any group. From the three forest attributes, standing forest biomass was the one that could explain most of the variance of the residual effect in both basin groups. These results further suggest that the water-saving response to increasing CO2 in these forests is either negligible or overridden by the opposite effect of the increasing forest biomass. Thus, we conclude that increasing standing forest biomass is the dominant driver of long-term and large

  17. Combining the triangle method with thermal inertia to estimate regional evapotranspiration

    DEFF Research Database (Denmark)

    Stisen, Simon; Sandholt, Inge; Nørgaard, Anette

    2008-01-01

    Spatially distributed estimates of evaporative fraction and actual evapotranspiration are pursued using a simple remote sensing technique based on a remotely sensed vegetation index (NDVI) and diurnal changes in land surface temperature. The technique, known as the triangle method, is improved...... in surface temperature, dTs with an interpretation of the triangular shaped dTs-NDVI space allows for a direct estimation of evaporative fraction. The mean daytime energy available for evapotranspiration (Rn-G) is estimated using several remote sensors and limited ancillary data. Finally regional estimates...

  18. Spatial modelling of evapotranspiration in the Luquillo experimental forest of Puerto Rico using remotely-sensed data.

    Science.gov (United States)

    Wei Wu; Charles A.S. Hall; Frederick N. Scatena; Lindi J. Quackenbush

    2006-01-01

    Summary Actual evapotranspiration (aET) and related processes in tropical forests can explain 70% of the lateral global energy transport through latent heat, and therefore are very important in the redistribution of water on the Earth’s surface [Mauser, M., Scha¨dlich, S., 1998. Modelling the spatial distribution of evapotranspiration on different scales using remote...

  19. Evapotranspiration modules for crop growth simulation. Implementation of the algorithms from Penman, Makkink and Priestley-Taylor

    NARCIS (Netherlands)

    Kraalingen, van D.W.G.; Stol, W.

    1997-01-01

    Calculation of evapotranspiration is essential for the estimation of crop water use or for studying the effect of drought stress on crop performance with simulation models. Several methods are available for calculation of evapotranspiration. This report describes three different methods : the Penman

  20. Regional estimation of daily to annual regional evapotranspiration with MODIS data in the Yellow River Delta wetland

    NARCIS (Netherlands)

    Jia, L.; Xi, G.; Liu, S.; Huang, C.; Yan, Y.; Liu, G.

    2009-01-01

    Evapotranspiration (ET) from the wetland of the Yellow River Delta (YRD) is one of the important components in the water cycle, which represents the water consumption by the plants and evaporation from the water and the non-vegetated surfaces. Reliable estimates of the total evapotranspiration from

  1. Modeling potential evapotranspiration of two forested watersheds in the southern Appalachians

    Science.gov (United States)

    L.Y. Rao; G. Sun; C.R. Ford; J.M. Vose

    2011-01-01

    Global climate change has direct impacts on watershed hydrology through altering evapotranspiration (ET) processes at multiple scales. There are many methods to estimate forest ET with models, but the most practical and the most popular one is the potential ET (PET) based method. However, the choice of PET methods for AET estimation remains challenging. This study...

  2. Benchmark products for land evapotranspiration: LandFlux-EVAL multi-data set synthesis

    NARCIS (Netherlands)

    Mueller, B.; Hirschi, M.; Jimenez, C.; Ciais, P.; Dirmeyer, P.A.; Dolman, A.J.; Fisher, J.B.; Jung, M.; Ludwig, F.; Maignan, F.

    2013-01-01

    Land evapotranspiration (ET) estimates are available from several global datasets. Here, monthly global land ET synthesis products, merged from these individual datasets over the time periods 1989–1995 (7 yr) and 1989–2005 (17 yr), are presented. The 5 merged synthesis products over the shorter

  3. 1:1,000,000-scale areas of evapotranspiration in the Great Basin

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This data set consists of 1:1,000,000-scale areas where shallow ground water is consumed by evapotranspiration (ET) in the Great Basin. The source of this data set...

  4. CONTROLLING FACTORS OF POTENTIAL EVAPOTRANSPIRATION ABOVE GRASSLAND IN HUMID AND ARID AREA

    Directory of Open Access Journals (Sweden)

    . Yanto

    2013-05-01

    Full Text Available Potential evapotranspiration (PET is an importance process in water balance studies controlled by a number of meteorological factors such as temperature, wind speed, atmospheric pressure, solar radiation, vapor pressure gradient, relative humidity and biological factors such as vegetation type, canopy height and plant density that varied in time-scale and in spatial scale. Of all those variables, determining the most controlling factors of evapotranspiration in humid and arid area is of interest of this paper. Two sites representing humid and arid area i.e. Fermi Prairie site in Illinois and Audubon Research Ranch in Arizona respectively were investigated in this study.  The flux data employed in this study was acquired from Ameriflux Netwotk. Penmann-Monteith formula is employed in to estimate evapotranspiration rate in both sites. The result shows that the PET is in dependence on the considered meteorological factor such as shortwave radiation, vapor pressure, air temperature, wind speed, net radiation and vapor pressure deficit. It is also can be inferred from the analysis that PET is also strongly controlled by vegetation factors represented as stomatal resistance. Keywords: Potential evapotranspiration, Penmann-Monteith, humid, arid.

  5. A comparison of two downscaling procedures to increase the spatial resolution of mapping actual evapotranspiration

    NARCIS (Netherlands)

    Mahour, M.; Tolpekin, V.A.; Stein, A.; Sharifi, M.A.

    2017-01-01

    This research addressed the effects of downscaling cokriging Land Surface Temperature (LST) on estimation of Actual Evapotranspiration (AET) from remote sensing images. Two procedures were followed. We first applied downscaling cokriging to a coarse resolution LST product of MODIS at 1000 m. With

  6. Simple models to predict grassland ecosystem C exchange and actual evapotranspiration using NDVI and environmental variables

    Science.gov (United States)

    Semiarid grasslands contribute significantly to net terrestrial carbon flux as plant productivity and heterotrophic respiration in these moisture-limited systems are correlated with metrics related to water availability (e.g., precipitation, Actual EvapoTranspiration or AET). These variables are als...

  7. Analyses of Spring Barley Evapotranspiration Rates Based on Gradient Measurements and Dual Crop Coefficient Model

    Czech Academy of Sciences Publication Activity Database

    Pozníková, Gabriela; Fischer, Milan; Pohanková, Eva; Trnka, Miroslav

    2014-01-01

    Roč. 62, č. 5 (2014), s. 1079-1086 ISSN 1211-8516 R&D Projects: GA MŠk LH12037; GA MŠk(CZ) EE2.3.20.0248 Institutional support: RVO:67179843 Keywords : evapotranspiration * dual crop coefficient model * Bowen ratio/energy balance method * transpiration * soil evaporation * spring barley Subject RIV: EH - Ecology, Behaviour

  8. Evapotranspiration and soil moisture dynamics in a temperate grassland ecosystem in Inner Mongolia China

    Science.gov (United States)

    L. Hao; Ge Sun; Yongqiang Liu; G. S. Zhou; J. H.   Wan;  L. B. Zhang; J. L. Niu; Y. H. Sang;  J. J He

    2015-01-01

    Precipitation, evapotranspiration (ET), and soil moisture are the key controls for the productivity and functioning of temperate grassland ecosystems in Inner Mongolia, northern China. Quantifying the soil moisture dynamics and water balances in the grasslands is essential to sustainable grassland management under global climate change. We...

  9. Evaluation of an urban canopy model in a tropical city: the role of tree evapotranspiration

    Science.gov (United States)

    Liu, Xuan; Li, Xian-Xiang; Harshan, Suraj; Roth, Matthias; Velasco, Erik

    2017-09-01

    A single layer urban canopy model (SLUCM) with enhanced hydrologic processes, is evaluated in a tropical city, Singapore. The evaluation was performed using an 11 month offline simulation with the coupled Noah land surface model/SLUCM over a compact low-rise residential area. Various hydrological processes are considered, including anthropogenic latent heat release, and evaporation from impervious urban facets. Results show that the prediction of energy fluxes, in particular latent heat flux, is improved when these processes were included. However, the simulated latent heat flux is still underestimated by ∼40%. Considering Singapore’s high green cover ratio, the tree evapotranspiration process is introduced into the model, which significantly improves the simulated latent heat flux. In particular, the systematic error of the model is greatly reduced, and becomes lower than the unsystematic error in some seasons. The effect of tree evapotranspiration on the urban surface energy balance is further demonstrated during an unusual dry spell. The present study demonstrates that even at sites with relatively low (11%) tree coverage, ignoring evapotranspiration from trees may cause serious underestimation of the latent heat flux and atmospheric humidity. The improved model is also transferable to other tropical or temperate regions to study the impact of tree evapotranspiration on urban climate.

  10. Model Simulation of Urban Evapotranspiration Rates Given Spatial Changes in Land Cover and Elevation

    Science.gov (United States)

    Yang, Y.; Endreny, T. A.

    2009-05-01

    Urban heat islands (UHI) emerge due to changes in albedo and imperviousness as compared with surrounding countryside, and UHI mitigation plans have focused on increasing urban tree cover. Trees can cool urban areas by direct shading and indirect evapotranspiration. Our goal is to create spatially distributed estimates of tree evapotranspiration during the growing season, to use in human thermal comfort models and other UHI simulations. We are modifying tree anatomy and growth functions in the USDA Forest Service Urban Forest Effects (UFORE) model. Modification represents the spatial variation of soil moisture and canopy radiation, which regulate evapotranspiration. Surface elevation derived topographic indices and land cover maps, including NLCD and aerial photographs, are used to adjust weather station estimates of radiation and soil moisture. Tree species and initial anatomy were selected from data gathered by the USDA Forest Service from plots in Syracuse, New York. Model estimates of evapotranspiration were generated for 30m by 30m pixels, and represented soil water and radiation constraints by modifying parameters in the Penman Monteith equations. Future work involves incorporating land cover and topographic data uncertainty into soil moisture and radiation constraints, which would be represented through Monte Carlo simulations. Applications of this research will be considered for the UFORE model in managing urban forest tree plantings to mitigate UHI impacts.

  11. Intercomparison of Evapotranspiration Over the Savannah Volta Basin in West Africa Using Remote Sensing Data.

    Science.gov (United States)

    Opoku-Duah, S; Donoghue, D N M; Burt, T P

    2008-04-17

    This paper compares evapotranspiration estimates from two complementary satellite sensors - NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) and ESA's ENVISAT Advanced Along-Track Scanning Radiometer (AATSR) over the savannah area of the Volta basin in West Africa. This was achieved through solving for evapotranspiration on the basis of the regional energy balance equation, which was computationally-driven by the Surface Energy Balance Algorithm for Land algorithm (SEBAL). The results showed that both sensors are potentially good sources of evapotranspiration estimates over large heterogeneous landscapes. The MODIS sensor measured daily evapotranspiration reasonably well with a strong spatial correlation (R²=0.71) with Landsat ETM+ but underperformed with deviations up to ~2.0 mm day -1 , when compared with local eddy correlation observations and the Penman-Monteith method mainly because of scale mismatch. The AATSR sensor produced much poorer correlations (R²=0.13) with Landsat ETM+ and conventional ET methods also because of differences in atmospheric correction and sensor calibration over land.

  12. Intercomparison of Evapotranspiration Over the Savannah Volta Basin in West Africa Using Remote Sensing Data

    Directory of Open Access Journals (Sweden)

    T. P. Burt

    2008-04-01

    Full Text Available This paper compares evapotranspiration estimates from two complementary satellite sensors – NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS and ESA’s ENVISAT Advanced Along-Track Scanning Radiometer (AATSR over the savannah area of the Volta basin in West Africa. This was achieved through solving for evapotranspiration on the basis of the regional energy balance equation, which was computationally-driven by the Surface Energy Balance Algorithm for Land algorithm (SEBAL. The results showed that both sensors are potentially good sources of evapotranspiration estimates over large heterogeneous landscapes. The MODIS sensor measured daily evapotranspiration reasonably well with a strong spatial correlation (R2=0.71 with Landsat ETM+ but underperformed with deviations up to ~2.0 mm day-1, when compared with local eddy correlation observations and the Penman-Monteith method mainly because of scale mismatch. The AATSR sensor produced much poorer correlations (R2=0.13 with Landsat ETM+ and conventional ET methods also because of differences in atmospheric correction and sensor calibration over land.

  13. An Integrated Model for Simulating Regional Water Resources Based on Total Evapotranspiration Control Approach

    Directory of Open Access Journals (Sweden)

    Jianhua Wang

    2014-01-01

    Full Text Available Total evapotranspiration and water consumption (ET control is considered an efficient method for water management. In this study, we developed a water allocation and simulation (WAS model, which can simulate the water cycle and output different ET values for natural and artificial water use, such as crop evapotranspiration, grass evapotranspiration, forest evapotranspiration, living water consumption, and industry water consumption. In the calibration and validation periods, a “piece-by-piece” approach was used to evaluate the model from runoff to ET data, including the remote sensing ET data and regional measured ET data, which differ from the data from the traditional hydrology method. We applied the model to Tianjin City, China. The Nash-Sutcliffe efficiency (Ens of the runoff simulation was 0.82, and its regression coefficient R2 was 0.92. The Nash-Sutcliffe Efficiency (Ens of regional total ET simulation was 0.93, and its regression coefficient R2 was 0.98. These results demonstrate that ET of irrigation lands is the dominant part, which accounts for 53% of the total ET. The latter is also a priority in ET control for water management.

  14. Estimating evapotranspiration from a reed bed using the Bowen ratio energy balance method

    Science.gov (United States)

    Peacock, C. E.; Hess, T. M.

    2004-02-01

    An increase in demand for water for agricultural and domestic use, combined with new legislation regarding the water needs of natural habitats, has led to an increased requirement for accurate calculations of hydrological fluxes through wetlands. Evapotranspiration is one of the most important but least well understood fluxes in wetland hydrology. Research has been carried out on Stodmarsh National Nature Reserve in Kent, UK, a Ramsar site containing the largest reed beds in southern England. The objective was to quantify water loss through evapotranspiration on the site to allow more effective management of water levels and maintenance of maximum conservation potential for bird life. The Bowen ratio energy balance approach was employed, which is one of the most accurate ways of measuring evapotranspiration but has been rarely used on reed beds. These measurements were used with Penman-Monteith reference evapotranspiration in order to create crop coefficients. It was found that crop coefficients were inconsistent from day to day but were generally less than unity. The inconsistency was thought to be caused by variations in meteorological conditions: e.g. significant differences in crop coefficients were found between days with high radiation and a dry canopy, compared with days with low radiation and a wet canopy. Canopy interception of precipitation was particularly important, with crop coefficients being significantly higher on wet days, possibly due to the higher rates of evaporation of intercepted water due to the lack of stomatal resistance.

  15. Infrared thermometry and stress monitoring of corn, and sensitivity analysis of reference evapotranspiration to sensor accuracy

    Science.gov (United States)

    Abstract for SOCR seminar: The USDA-ARS Water Management Research Unit in Fort Collins, CO is tasked with maintaining high crop yields under limited water. One focus of this project is to quantify evapotranspiration (ET) and water stress. Canopy temperature methods have been used for decades to quan...

  16. Daily reference evapotranspiration modeling by using genetic programming approach in the Basque Country (Northern Spain)

    NARCIS (Netherlands)

    Shiri, J.; Kisi, O.; Landeras, G.; Lopez, J.J.; Nazemi, A.H.; Stuyt, L.C.P.M.

    2012-01-01

    Evapotranspiration, as a major component of the hydrological cycle, is of importance for water resources management and development, as well as for estimating the water budget of irrigation schemes. This study presents a Gene Expression Programming (GEP) approach, for estimating daily reference

  17. An overview of the Central Queensland University self-contained evapotranspiration beds.

    Science.gov (United States)

    Kele, B; Midmore, D J; Harrower, K; McKennariey, B J; Hood, B

    2005-01-01

    The Central Queensland University (CQU) has championed a self-contained concrete lined evapotranspiration channel. Any non-transpired effluent returns to a holding tank and is recirculated through the evapotranspiration channel until it is used. This paper examines the results from the Rockhampton trial site. Nutrient ions in the effluent were quantified over time and found not to accumulate in solution. Microbial analysis of the treated effluent was performed and was found to be within the ranges required by the relevant legislative codes. Citrus fruit grown in the evapotranspiration channel were sampled and no elevated levels of faecal coliforms were recorded. Macronutrients and micronutrients of the soil in the channels were measured over a 5-year period. No toxic accumulations or nutrient deficiencies in the soil occurred. Levels of salinity and sodicity in the evapotranspiration channel soil were quantified. Salinity rose slightly, as did sodium. Concentrations of salts and sodium did not reach unsustainable levels. The aim of the trial was to develop an on-site treatment and reuse system that is sustainable and protects public and environmental health.

  18. Exceedance probability of the standardized precipitation-evapotranspiration index in the Texas High Plains

    Science.gov (United States)

    Drought is a common occurrence in many arid and semi-arid regions that can have large negative impacts on water resources and agricultural production. Since agricultural drought is affected by both water supply and demand (precipitation and evapotranspiration), it is beneficial to include both in a...

  19. Estimating forest ecosystem evapotranspiration at multiple temporal scales with a dimension analysis approach

    Science.gov (United States)

    Guoyi Zhou; Ge Sun; Xu Wang; Chuanyan Zhou; Steven G. McNulty; James M. Vose; Devendra M. Amatya

    2008-01-01

    It is critical that evapotranspiration (ET) be quantified accurately so that scientists can evaluate the effects of land management and global change on water availability, streamflow, nutrient and sediment loading, and ecosystem productivity in watersheds. The objective of this study was to derive a new semi-empirical ET modeled using a dimension analysis method that...

  20. Influence of potential evapotranspiration on the water balance of sugarcane fields in Maui, Hawaii

    Science.gov (United States)

    The year-long warm temperatures and other climatic characteristics of the Pacific Ocean Islands have made Hawaii an optimum place for growing sugarcane; however, irrigation is essential to satisfy the large water demand of sugarcane. Under the Hawaiian tropical weather, actual evapotranspiration (A...

  1. Accuracy assessment of NOAA gridded daily reference evapotranspiration for the Texas High Plains

    Science.gov (United States)

    The National Oceanic and Atmospheric Administration (NOAA) provides daily reference evapotranspiration (ETref) maps for the contiguous United States using climatic data from North American Land Data Assimilation System (NLDAS). This data provides large-scale spatial representation of ETref, which i...

  2. Evapotranspiration estimates derived using multi-platform remote sensing in a semiarid region

    Science.gov (United States)

    Evapotranspiration (ET) is a key component of the water balance, especially in arid and semiarid regions. The current study takes advantage of spatially-distributed, near real-time information provided by satellite remote sensing to develop a regional scale ET product derived from remotely-sensed ob...

  3. Testing DRAINMOD-FOREST for predicting evapotranspiration in a mid-rotation pine plantation

    Science.gov (United States)

    Shiying Tian; Mohamed A. Youssef; Ge Sun; George M. Chescheir; Asko Noormets; Devendra M. Amatya; R. Wayne Skaggs; John S. King; Steve McNulty; Michael Gavazzi; Guofang Miao; Jean-Christophe Domec

    2015-01-01

    Evapotranspiration (ET) is a key component of the hydrologic cycle in terrestrial ecosystems and accurate description of ET processes is essential for developing reliable ecohydrological models. This study investigated the accuracy of ET prediction by the DRAINMOD-FOREST after its calibration/validation for predicting commonly measured hydrological variables. The model...

  4. Daily evapotranspiration over cotton by assimilating remotely sensed data with ground-based radiometers

    Science.gov (United States)

    Estimation of spatially distributed evapotranspiration (ET) with remote sensing could be especially valuable for developing water management tools in arid lands. For decision support over irrigated crops, these spatial ET estimates also depend upon good spatial resolution ($<$30 m)at timely interval...

  5. Carbon fluxes, evapotranspiration, and water use efficiency of terrestrial ecosystems in China

    Science.gov (United States)

    Jingfeng Xiao; Ge Sun; Jiquan Chen; Hui Chen; Shiping Chen; Gang Dong

    2013-01-01

    The magnitude, spatial patterns, and controlling factors of the carbon and water fluxes of terrestrial ecosystems in China are not well understood due to the lack of ecosystem-level flux observations. We synthesized flux and micrometeorological observations from 22 eddy covariance flux sites across China,and examined the carbon fluxes, evapotranspiration (ET), and...

  6. Merging raster meteorological data with low resolution satellite images for improved estimation of actual evapotranspiration

    Science.gov (United States)

    Cherif, Ines; Alexandridis, Thomas; Chambel Leitao, Pedro; Jauch, Eduardo; Stavridou, Domna; Iordanidis, Charalampos; Silleos, Nikolaos; Misopolinos, Nikolaos; Neves, Ramiro; Safara Araujo, Antonio

    2013-04-01

    Actual evapotranspiration (ETa) can be estimated using Energy Balance models and remotely sensed data. In particular, satellite images acquired in visible, near and thermal infrared parts of the spectrum have been used with the Surface Energy Balance Algorithm for Land (SEBAL) to estimate actual evapotranspiration. This algorithm is solving the Energy Balance Equation using data from a meteorological station present in the vicinity, and assumes the meteorological conditions homogeneous over the study area. Most often, data from a representative weather station are used. This assumption may lead to substantial errors in areas with high spatial variability in weather parameters. In this paper, the ITA-MyWater algorithms (Integrated Thermodynamic Algorithms for MyWater project), an adaptation of SEBAL was merged together with spatially distributed meteorological data to increase the accuracy of ETa estimations at regional scale using MODIS satellite images. The major changes introduced to migrate from point to raster are that (i) air temperature and relative humidity maps are used for the estimation of the Energy Balance terms, including instantaneous net radiation and soil heat flux and (ii) the variability of wind speed is taken into account to generate maps of the aerodynamic resistance, sensible heat flux and difference between soil and air temperature at the boundary conditions (at dry and wet pixels). The approach was applied in the river basin of Tamega in Portugal, where actual evapotranspiration was estimated for several MODIS 8-day periods from spring to winter of the same year. The raster meteorological maps were produced by the MM5 weather forecast model. Daily reference evapotranspiration was calculated with MOHID LAND model. Using a temporal integration technique and the daily reference evapotranspiration maps, the cumulative evapotranspiration over the MODIS 8-day period was estimated and compared to the global evapotranspiration MODIS product (MOD16A2

  7. Epistemic Uncertainty in Evalustion of Evapotranspiration and Net Infiltration Using Analogue Meteorological Data

    Energy Technology Data Exchange (ETDEWEB)

    B. Faybishenko

    2006-09-01

    Uncertainty is typically defined as a potential deficiency in the modeling of a physical process, owing to a lack of knowledge. Uncertainty can be categorized as aleatoric (inherent uncertainty caused by the intrinsic randomness of the system) or epistemic (uncertainty caused by using various model simplifications and their parameters). One of the main reasons for model simplifications is a limited amount of meteorological data. This paper is devoted to the epistemic uncertainty quantification involved in two components of the hydrologic balance-evapotranspiration and net infiltration for interglacial (present day), and future monsoon, glacial transition, and glacial climates at Yucca Mountain, using the data from analogue meteorological stations. In particular, the author analyzes semi-empirical models used for evaluating (1) reference-surface potential evapotranspiration, including temperature-based models (Hargreaves-Samani, Thornthwaite, Hamon, Jensen-Haise, and Turc) and radiation-based models (Priestly-Taylor and Penman), and (2) surface-dependent potential evapotranspiration (Penman-Monteith and Shuttleworth-Wallace models). Evapotranspiration predictions are then used as inputs for the evaluation of net infiltration using the semi-empirical models of Budyko, Fu, Milly, Turc-Pike, and Zhang. Results show that net infiltration ranges are expected to generally increase from the present-day climate to monsoon climate, to glacial transition climate, and then to the glacial climate. The propagation of uncertainties through model predictions for different climates is characterized using statistical measures. Predicted evapotranspiration ranges are reasonably corroborated against the data from Class A pan evaporometers (taking into account evaporation-pan adjustment coefficients), and ranges of net infiltration predictions are corroborated against the geochemical and temperature-based estimates of groundwater recharge and percolation rates through the unsaturated

  8. Evapotranspiration simulated by CRITERIA and AquaCrop models in stony soils

    Directory of Open Access Journals (Sweden)

    Pasquale Campi

    2015-06-01

    Full Text Available The performance of a water balance model is also based on the ability to correctly perform simulations in heterogeneous soils. The objective of this paper is to test CRITERIA and AquaCrop models in order to evaluate their suitability in estimating evapotranspiration at the field scale in two types of soil in the Mediterranean region: non-stony and stony soil. The first step of the work was to calibrate both models under the non-stony conditions. The models were calibrated by using observations on wheat crop (leaf area index or canopy cover, and phenological stages as a function of degree days and pedo-climatic measurements. The second step consisted in the analysing the impact of the soil type on the models performances by comparing simulated and measured values. The outputs retained in the analysis were soil water content (at the daily scale and crop evapotranspiration (at two time scales: daily and crop season. The model performances were evaluated through four statistical tests: normalised difference (D% at the seasonal time scale; and relative root mean square error (RRMSE, efficiency index (EF, coefficient of determination (r2 at the daily scale. At the seasonal scale, values of D% were less than 15% in stony and on-stony soils, indicating a good performance attained by both models. At the daily scale, the RRMSE values (<30% indicate that the evapotranspiration simulated by CRITERIA is acceptable in both soil types. In the stony soil conditions, 3 out 4 statistical tests (RRMSE, EF, r2 indicate the inadequacy of AquaCrop to simulate correctly daily evapotranspiration. The higher performance of CRITERIA model to simulate daily evapotranspiration in stony soils, is due to the soil submodel, which requires the percentage skeleton as an input, while AquaCrop model takes into account the presence of skeleton by reducing the soil volume.

  9. Comparison of estimates of evapotranspiration and consumptive use in Palo Verde Valley, California

    Science.gov (United States)

    Raymond, Lee H.; Owen-Joyce, Sandra J.

    1987-01-01

    Estimates of evapotranspiration and consumptive use by vegetation in Palo Verde Valley, California, were compared for calendar years 1981 to 1984. Vegetation types were classified, and the areas covered by each type were computed from Landsat satellite digital-image analysis. Evapotranspiration was calculated by multiplying the area of each vegetation type by a corresponding water use rate adjusted for year-to-year variations in climate. The vegetation classification slightly underestimates the total vegetated area when compared to crop reports, because not all multiple cropping could be identified. The accuracy of evapotranspiration calculated from vegetation classification depends primarily on the correct classification of alfalfa and cotton because alfalfa and cotton have larger acreages and use more water/acre than the other crops in the valley. Consumptive use was calculated using a water budget for each of the 4 years. Estimates of evapotranspiration and consumptive use by vegetation, respectively, were: (1) 439,400 and 483,500 acre-ft in 1981, (2) 430,700 and 452,700 acre-ft in 1982, (3) 402,000 and 364,400 acre-ft in 1983, and (4) 406,700 and 373,800 acre-ft in 1984. Evapotranspiration estimates were lower than consumptive use estimates in 1981 and 1982 and higher in 1983 and 1984. Both estimates were lower in 1983 and 1984 than in 1981 and 1982. Yearly differences in estimates correspond most closely to significant changes in stage of the lower Colorado River caused by flood control releases in 1983 and 1984 and to changes in cropping practices. (Author 's abstract)

  10. [Spatiotemporal variation characteristics and related affecting factors of actual evapotranspiration in the Hun-Taizi River Basin, Northeast China].

    Science.gov (United States)

    Feng, Xue; Cai, Yan-Cong; Guan, De-Xin; Jin, Chang-Jie; Wang, An-Zhi; Wu, Jia-Bing; Yuan, Feng-Hui

    2014-10-01

    Based on the meteorological and hydrological data from 1970 to 2006, the advection-aridity (AA) model with calibrated parameters was used to calculate evapotranspiration in the Hun-Taizi River Basin in Northeast China. The original parameter of the AA model was tuned according to the water balance method and then four subbasins were selected to validate. Spatiotemporal variation characteristics of evapotranspiration and related affecting factors were analyzed using the methods of linear trend analysis, moving average, kriging interpolation and sensitivity analysis. The results showed that the empirical parameter value of 0.75 of AA model was suitable for the Hun-Taizi River Basin with an error of 11.4%. In the Hun-Taizi River Basin, the average annual actual evapotranspiration was 347.4 mm, which had a slightly upward trend with a rate of 1.58 mm · (10 a(-1)), but did not change significantly. It also indicated that the annual actual evapotranspiration presented a single-peaked pattern and its peak value occurred in July; the evapotranspiration in summer was higher than in spring and autumn, and it was the smallest in winter. The annual average evapotranspiration showed a decreasing trend from the northwest to the southeast in the Hun-Taizi River Basin from 1970 to 2006 with minor differences. Net radiation was largely responsible for the change of actual evapotranspiration in the Hun-Taizi River Basin.

  11. Automated calculation of the evapotranspiration and crop coefficients for a large number of peatland sites using diurnal groundwater table fluctuations

    Science.gov (United States)

    Maurer, Eike; Bechtold, Michel; Dettmann, Ullrich; Tiemeyer, Bärbel

    2014-05-01

    Evapotranspiration is one of the main processes controlling peatland hydrology. Greenhouse gas (GHG) emissions from peatlands are in turn strongly controlled by the groundwater table. Through the increasing political and scientific interest to reduce GHG emissions, monitoring and modelling strategies to optimize re-wetting strategies and to quantify GHG emissions are needed. To achieve these aims, an accurate determination of the evapotranspiration as an essential part of the water balance is required. Many different approaches are known to determine the evapotranspiration. They are mostly either expensive or hard to parameterize. Plant specific crop coefficients (Kc-values) are an option to calculate plant-specific evapotranspiration but due to the lack of Kc-values for typical peatland vegetation types more data on evapotranspiration from peatlands in the temperate zone are required. Furthermore, simple methods to estimate evapotranspiration are needed especially for monitoring projects. Diurnal groundwater table fluctuations caused by root water uptake and groundwater inflow can be used to calculate daily evapotranspiration rates. This approach was first described by White (1932) who compared groundwater recovery rates at night to the decline during daytime. Besides the groundwater table data only the specific yield (Sy) is needed to calculate evapotranspiration. However, the method has some limitations because not all days can be evaluated which leads to data gaps during rainy and very dry or very wet periods. This study presents an automated method to calculate the specific yield, evapotranspiration and crop coefficients for a large number of sites covering all major peatland types and their typical land uses in Germany. As an input for our method, only groundwater level, precipitation and grass reference evapotranspiration (ET0) data is required. In a first step, the groundwater level data was smoothed by a LOESS function. In a second step, site-specific SY

  12. Dynamic evapotranspiration in tree-resolving LES - The ED2RAFLES model

    Science.gov (United States)

    Bohrer, G.; Medvigy, D.

    2010-12-01

    How evapotranspiration scales from individual plants to a landscape is a critical problem in hydrology. To investigate this problem, we developed a version of the RAMS-Based Forest Large Eddy Simulations (RAFLES) which includes a dynamic, multi-layered evapotranspiration and CO2 uptake. RAFLES resolves vegetation as a heterogeneous 3D field. It can run at resolutions down to 1 m^3 and can incorporate explicit canopy representations derived from lidar. The canopy influences dynamics through a drag term, proportional to the leaf density at each numerical cell, and as a solid volume, which blocks some of the volume and apertures inside the canopy space. To calculate the exchange of scalar fluxes between the canopy and the air, the Ecosystem Demography version 2 (ED2) was coupled with RAFLES. ED2RAFLES dynamically resolves sensible heat fluxes, evapotranspiration, radiative transfer, and carbon fluxes. The surface energy budget is solved at vertical levels inside the canopy to find the skin temperature of the leaves and soil surface, and evapotranspiration rates. Evapotranspiration is also driven by frictional velocity near the leaves and is further restricted by stomatal conductance, parameterized using a Ball-Berry scheme, and by soil water availability. We tested the sensitivity of modeled evapotranspiration to the dynamic representation for a virtual canopy domain, based on the spatial structure of the forest around the Ameriflux eddy-flux tower, at the University of Michigan Biological Station (UMBS). A “test” simulation used the dynamic ED2-driven evaporation. A “control” simulation prescribed sensible and latent heat fluxes as a function of LAI and light attenuation at a rate equal to the mean heat flux from the test simulation. The simulation differed in the degree of spatial heterogeneity of fluxes across the domains and in the coherency between canopy structure and evaporation. Quantifying this coherency is important to our understanding of the

  13. Assessment of the EUMETSAT LSA-SAF evapotranspiration product for drought monitoring in Europe

    Science.gov (United States)

    Sepulcre-Canto, Guadalupe; Vogt, Jürgen; Arboleda, Alirio; Antofie, Tiberiu

    2014-08-01

    Evapotranspiration is a key parameter for water stress assessment as it is directly related to the moisture status of the soil-vegetation system and describes the moisture transfer from the surface to the atmosphere. With the launch of the Meteosat Second Generation geostationary satellites and the setup of the Satellite Application Facilities, it became possible to operationally produce evapotranspiration data with high spatial and temporal evolution over the entire continents of Europe and Africa. In the frame of this study we present an evaluation of the potential of the evapotranspiration (ET) product from the EUMETSAT Satellite Application Facility on Land Surface Analysis (LSA-SAF) for drought assessment and monitoring in Europe. To assess the potential of this product, the LSA-SAF ET was used as input for the ratio of ET to reference evapotranspiration (ET0), the latter estimated from the ECMWF interim reanalysis. In the analysis two case studies were considered corresponding to the drought episodes of spring/summer 2007 and 2011. For these case studies, the ratio ET/ET0 was compared with meteorological drought indices (SPI, SPEI and Sc-PDSI for 2007 and SPI for 2011) as well as with the anomalies of the fraction of absorbed photosynthetic active radiation (fAPAR) derived from remote sensing data. The meteorological and remote sensing indicators were taken from the European Drought Observatory (EDO) and the CARPATCLIM climatological atlas. Results show the potential of ET/ET0 to characterize soil moisture variability, and to give additional information to fAPAR and to precipitation distribution for drought assessment. The main limitations of the proposed ratio for drought characterization are discussed, including options to overcome them. These options include the use of filters to discriminate areas with a low percentage vegetation cover or areas that are not in their growing period and the use of evapotranspiration without water restriction (ETwwr

  14. Estimation of reference evapotranspiration using multivariate fractional polynomial, Bayesian regression, and robust regression models in three arid environments

    Science.gov (United States)

    Khoshravesh, Mojtaba; Sefidkouhi, Mohammad Ali Gholami; Valipour, Mohammad

    2017-07-01

    The proper evaluation of evapotranspiration is essential in food security investigation, farm management, pollution detection, irrigation scheduling, nutrient flows, carbon balance as well as hydrologic modeling, especially in arid environments. To achieve sustainable development and to ensure water supply, especially in arid environments, irrigation experts need tools to estimate reference evapotranspiration on a large scale. In this study, the monthly reference evapotranspiration was estimated by three different regression models including the multivariate fractional polynomial (MFP), robust regression, and Bayesian regression in Ardestan, Esfahan, and Kashan. The results were compared with Food and Agriculture Organization (FAO)-Penman-Monteith (FAO-PM) to select the best model. The results show that at a monthly scale, all models provided a closer agreement with the calculated values for FAO-PM ( R 2 > 0.95 and RMSE < 12.07 mm month-1). However, the MFP model gives better estimates than the other two models for estimating reference evapotranspiration at all stations.

  15. Spatially Distributed Assimilation of Remotely Sensed Leaf Area Index and Potential Evapotranspiration for Hydrologic Modeling in Wetland Landscapes

    Science.gov (United States)

    Evapotranspiration (ET), a highly dynamic flux in wetland landscapes, regulates the accuracy of surface/sub-surface runoff simulation in a hydrologic model. However, considerable uncertainty in simulating ET-related processes remains, including our limited ability to incorporate ...

  16. Reference crop evapotranspiration estimate using high-resolution meteorological network's data

    Directory of Open Access Journals (Sweden)

    C. Lussana

    2009-10-01

    Full Text Available Water management authorities need detailed information about each component of the hydrological balance. This document presents a method to estimate the evapotranspiration rate, initialized in order to obtain the reference crop evapotranspiration rate (ET0. By using an Optimal Interpolation (OI scheme, the hourly observations of several meteorological variables, measured by a high-resolution local meteorological network, are interpolated over a regular grid. The analysed meteorological fields, containing detailed meteorological information, enter a model for turbulent heat fluxes estimation based on Monin-Obukhov surface layer similarity theory. The obtained ET0 fields are then post-processed and disseminated to the users.

  17. Evapotranspiration Calculation on the Basis of the Riparian Zone Water Balance

    Directory of Open Access Journals (Sweden)

    SZILÁGYI, József

    2008-01-01

    Full Text Available Riparian forests have a strong influence on groundwater levels and groundwater sustainedstream baseflow. An empirical and a hydraulic version of a new method were developed to calculateevapotranspiration values from riparian zone groundwater levels. The new technique was tested on thehydrometeorological data set of the Hidegvíz Valley (located in Sopron Hills at the eastern foothills ofthe Alps experimental catchment. Evapotranspiration values of this new method were compared tothe Penman-Monteith evapotranspiration values on a half hourly scale and to the White methodevapotranspiration values on a daily scale. Sensitivity analysis showed that the more reliable hydraulicversion of our ET estimation technique is most sensitive (i.e., linearly to the values of the saturatedhydraulic conductivity and specific yield taken from the riparian zone.

  18. Growth of soybean at future tropospheric ozone concentrations decreases canopy evapotranspiration and soil water depletion.

    Science.gov (United States)

    Bernacchi, Carl J; Leakey, Andrew D B; Kimball, Bruce A; Ort, Donald R

    2011-06-01

    Tropospheric ozone is increasing in many agricultural regions resulting in decreased stomatal conductance and overall biomass of sensitive crop species. These physiological effects of ozone forecast changes in evapotranspiration and thus in the terrestrial hydrological cycle, particularly in intercontinental interiors. Soybean plots were fumigated with ozone to achieve concentrations above ambient levels over five growing seasons in open-air field conditions. Mean season increases in ozone concentrations ([O₃]) varied between growing seasons from 22 to 37% above background concentrations. The objective of this experiment was to examine the effects of future [O₃] on crop ecosystem energy fluxes and water use. Elevated [O₃] caused decreases in canopy evapotranspiration resulting in decreased water use by as much as 15% in high ozone years and decreased soil water removal. In addition, ozone treatment resulted in increased sensible heat flux in all years indicative of day-time increase in canopy temperature of up to 0.7 °C. Published by Elsevier Ltd.

  19. Evapotranspiration trends over the eastern United States during the 20th century

    Science.gov (United States)

    Kramer, Ryan J.; Bounoua, Lahouari; Zhang, Ping; Wolfe, Robert E.; Huntington, Thomas G.; Imhoff, Marc L.; Thome, Kurtis; Noyce, Genevieve L.

    2015-01-01

    Most models evaluated by the Intergovernmental Panel for Climate change estimate projected increases in temperature and precipitation with rising atmospheric CO2 levels. Researchers have suggested that increases in CO2 and associated increases in temperature and precipitation may stimulate vegetation growth and increase evapotranspiration (ET), which acts as a cooling mechanism, and on a global scale, may slow the climate-warming trend. This hypothesis has been modeled under increased CO2 conditions with models of different vegetation-climate dynamics. The significance of this vegetation negative feedback, however, has varied between models. Here we conduct a century-scale observational analysis of the Eastern US water balance to determine historical evapotranspiration trends and whether vegetation greening has affected these trends. We show that precipitation has increased significantly over the twentieth century while runoff has not. We also show that ET has increased and vegetation growth is partially responsible.

  20. Evapotranspiration modules for crop growth simulation. Implementation of the algorithms from Penman, Makkink and Priestley-Taylor

    OpenAIRE

    Kraalingen, van, D.W.G.; Stol, W.

    1997-01-01

    Calculation of evapotranspiration is essential for the estimation of crop water use or for studying the effect of drought stress on crop performance with simulation models. Several methods are available for calculation of evapotranspiration. This report describes three different methods : the Penman method (1948) and the approaches of Makkink (1957) and Priestley -Taylor (1972). The modules described in this report are developed for use in general crop growth models for water-limited conditio...

  1. Irrigation scheduling of grapefruit trees in a Mediterranean environment throughout evaluation of plant water status and evapotranspiration

    OpenAIRE

    ÜNLÜ, Mustafa; KANBER, Rıza; KOÇ, D. Levent; ÖZEKİCİ, Bülent; KEKEÇ, Uğur

    2014-01-01

    In this study, 1 full irrigation regime (100% of crop evapotranspiration, I100) and 2 deficit irrigation regimes (70%, I70, and 50%, I50) were evaluated in a Rio Red grapefruit (Citrus paradisi Macfad. 'Rio Red') orchard in Adana, Turkey. Fruit yield, leaf water potential (LWP), and soil water depletion (SWD) were measured among trees from each treatment. Actual evapotranspiration was calculated in 3 ways, using 2 energy balance methods (eddy correlation and Bowen&am...

  2. A Multiscalar Drought Index Sensitive to Global Warming: The Standardized Precipitation Evapotranspiration Index

    OpenAIRE

    Vicente-Serrano, Sergio M.; Begueria, Santiago; Lopez-Moreno, Juan I.

    2010-01-01

    We propose a new climatic drought index: the Standardized Precipitation Evapotranspiration Index (SPEI). The SPEI is based on precipitation and temperature data, and has the advantage of combining a multi-scalar character with the capacity to include the effects of temperature variability on drought assessment. The procedure to calculate the index is detailed, and involves a climatic water balance, the accumulation of deficit/surplus at different time scales, and adjustment to a Log-logistic ...

  3. On the hydrologic adjustment of climate-model projections: The potential pitfall of potential evapotranspiration

    Science.gov (United States)

    Milly, P.C.D.; Dunne, K.A.

    2011-01-01

    Hydrologic models often are applied to adjust projections of hydroclimatic change that come from climate models. Such adjustment includes climate-bias correction, spatial refinement ("downscaling"), and consideration of the roles of hydrologic processes that were neglected in the climate model. Described herein is a quantitative analysis of the effects of hydrologic adjustment on the projections of runoff change associated with projected twenty-first-century climate change. In a case study including three climate models and 10 river basins in the contiguous United States, the authors find that relative (i.e., fractional or percentage) runoff change computed with hydrologic adjustment more often than not was less positive (or, equivalently, more negative) than what was projected by the climate models. The dominant contributor to this decrease in runoff was a ubiquitous change in runoff (median 211%) caused by the hydrologic model's apparent amplification of the climate-model-implied growth in potential evapotranspiration. Analysis suggests that the hydrologic model, on the basis of the empirical, temperature-based modified Jensen-Haise formula, calculates a change in potential evapotranspiration that is typically 3 times the change implied by the climate models, which explicitly track surface energy budgets. In comparison with the amplification of potential evapotranspiration, central tendencies of other contributions from hydrologic adjustment (spatial refinement, climate-bias adjustment, and process refinement) were relatively small. The authors' findings highlight the need for caution when projecting changes in potential evapotranspiration for use in hydrologic models or drought indices to evaluate climatechange impacts on water. Copyright ?? 2011, Paper 15-001; 35,952 words, 3 Figures, 0 Animations, 1 Tables.

  4. An improved constant evaporative fraction method for estimating daily evapotranspiration from remotely sensed instantaneous observations

    Science.gov (United States)

    Tang, Ronglin; Li, Zhao-Liang

    2017-03-01

    Evapotranspiration (ET) is a primary mechanism for water and heat transfer between land and the atmosphere. One approach to estimate ET is from instantaneous remotely sensed data. The constant evaporative fraction (EF) method is then usually used to estimate integrated daily fluxes, which are typically underestimated values. Here we present a theoretical improvement to the conventional EF. The improved EF is shown to be robust and superior to the conventional approach, and it significantly reduces the underestimation bias.

  5. Climatic Characteristics of Reference Evapotranspiration in the Hai River Basin and Their Attribution

    Directory of Open Access Journals (Sweden)

    Lingling Zhao

    2014-05-01

    Full Text Available Based on the meteorological data from 46 stations in the Hai River Basin (HRB from 1961–2010, the annual and seasonal variation of reference evapotranspiration was analyzed. The sensitivity coefficients combined with the detrend method were used to discuss the dominant factor affecting the reference evapotranspiration (ETo. The obtained results indicate that the annual reference evapotranspiration is dominated by the decreasing trends at the confidence level of 95% in the southern and eastern parts of the HRB. The sensitivity order of climatic variables to ETo from strong to weak is: relativity humidity, temperature, shortwave radiation and wind speed, respectively. However, comprehensively considering the sensitivity and its variation strength, the detrend analysis indicates that the decreasing trends of ETo in eastern and southern HRB may be caused mainly by the decreasing wind speed and shortwave radiation. As for the relationship between human activity and the trend of ETo, we found that ETo decreased more significantly on the plains than in the mountains. By contrast, the population density increased more considerably from 2000 to 2010 on the plains than in the mountains. Therefore, in this paper, the correlation of the spatial variation pattern between ETo and population was further analyzed. The spatial correlation coefficient between population and the trend of ETo is −0.132, while the spatial correlation coefficient between the trend of ETo and elevation, temperature, shortwave radiation and wind speed is 0.667, 0.668, 0.749 and 0.416, respectively. This suggests that human activity has a certain influence on the spatial variation of ETo, while natural factors play a decisive role in the spatial variation of reference evapotranspiration in this area.

  6. Crop evapotranspiration estimation using remote sensing and the existing network of meteorological stations in Cyprus

    Science.gov (United States)

    Papadavid, G.; Hadjimitsis, D.; Michaelides, S.; Nisantzi, A.

    2011-05-01

    Cyprus is frequently confronted with severe droughts and the need for accurate and systematic data on crop evapotranspiration (ETc) is essential for decision making, regarding water irrigation management and scheduling. The aim of this paper is to highlight how data from meteorological stations in Cyprus can be used for monitoring and determining the country's irrigation demands. This paper shows how daily ETc can be estimated using FAO Penman-Monteith method adapted to satellite data and auxiliary meteorological parameters. This method is widely used in many countries for estimating crop evapotranspiration using auxiliary meteorological data (maximum and minimum temperatures, relative humidity, wind speed) as inputs. Two case studies were selected in order to determine evapotranspiration using meteorological and low resolution satellite data (MODIS - TERRA) and to compare it with the results of the reference method (FAO-56) which estimates the reference evapotranspiration (ETo) by using only meteorological data. The first approach corresponds to the FAO Penman-Monteith method adapted for using both meteorological and remotely sensed data. Furthermore, main automatic meteorological stations in Cyprus were mapped using Geographical Information System (GIS). All the agricultural areas of the island were categorized according to the nearest meteorological station which is considered as "representative" of the area. Thiessen polygons methodology was used for this purpose. The intended goal was to illustrate what can happen to a crop, in terms of water requirements, if meteorological data are retrieved from other than the representative stations. The use of inaccurate data can result in low yields or excessive irrigation which both lead to profit reduction. The results have shown that if inappropriate meteorological data are utilized, then deviations from correct ETc might be obtained, leading to water losses or crop water stress.

  7. Partitioning evapotranspiration into green and blue water sources in the conterminous United States

    Science.gov (United States)

    Velpuri, Naga Manohar; Senay, Gabriel

    2017-01-01

    In this study, we combined two actual evapotranspiration datasets (ET), one obtained from a root zone water balance model and another from an energy balance model, to partition annual ET into green (rainfall-based) and blue (surface/groundwater) water sources. Time series maps of green water ET (GWET) and blue water ET (BWET) are produced for the conterminous United States (CONUS) over 2001–2015.

  8. Evaluating biological and physical drivers of evapotranspiration trends at northeastern US watersheds

    Science.gov (United States)

    John L. Campbell; Matthew A. Vadeboncoeur; Heidi Asbjornsen; Mark B. Green; Mary Beth Adams; Elizabeth W. Boyer

    2016-01-01

    Despite a general consensus that the Earth’s hydrologic cycle is intensifying as a result of anthropogenic climate forcing (e.g. Huntington 2006), there remains substantial uncertainty over the consequences of this intensification for terrestrial evapotranspiration (ET; e.g., Hobbins and others 2004, Walter and others 2004, van Heerwaarden and others 2010). Most models...

  9. Near Real-Time Monitoring of Global Evapotranspiration and its Application to Water Resource Management

    Science.gov (United States)

    Halverson, G. H.; Fisher, J.; Jewell, L. A.; Moore, G.; Verma, M.; McDonald, T.; Kim, S.; Muniz, A.

    2016-12-01

    Water scarcity and its impact on agriculture is a pressing world concern. At the heart of this crisis is the balance of water exchange between the land and the atmosphere. The ability to monitor evapotranspiration provides a solution by enabling sustainable irrigation practices. The Priestley-Taylor Jet Propulsion Laboratory model of evapotranspiration has been implemented to meet this need as a daily MODIS product with 1 to 5 km resolution. An automated data pipeline for this model implementation provides daily data with global coverage and near real-time latency using the Geospatial Data Abstraction Library. An interactive map providing on-demand statistical analysis enables water resource managers to monitor rates of water loss. To demonstrate the application of remotely-sensed evapotranspiration to water resource management, a partnership has been arranged with the New Mexico Office of the State Engineer (NMOSE). The online water research management tool was developed to meet the specifications of NMOSE using the Leaflet, GeoServer, and Django frameworks. NMOSE will utilize this tool to monitor drought and fire risk and manage irrigation. Through this test-case, it is hoped that real-time, user-friendly remote sensing tools will be adopted globally to make resource management decisions informed by the NASA Earth Observation System.

  10. Estimating evapotranspiration and drought stress with ground-based thermal remote sensing in agriculture: a review.

    Science.gov (United States)

    Maes, W H; Steppe, K

    2012-08-01

    As evaporation of water is an energy-demanding process, increasing evapotranspiration rates decrease the surface temperature (Ts) of leaves and plants. Based on this principle, ground-based thermal remote sensing has become one of the most important methods for estimating evapotranspiration and drought stress and for irrigation. This paper reviews its application in agriculture. The review consists of four parts. First, the basics of thermal remote sensing are briefly reviewed. Second, the theoretical relation between Ts and the sensible and latent heat flux is elaborated. A modelling approach was used to evaluate the effect of weather conditions and leaf or vegetation properties on leaf and canopy temperature. Ts increases with increasing air temperature and incoming radiation and with decreasing wind speed and relative humidity. At the leaf level, the leaf angle and leaf dimension have a large influence on Ts; at the vegetation level, Ts is strongly impacted by the roughness length; hence, by canopy height and structure. In the third part, an overview of the different ground-based thermal remote sensing techniques and approaches used to estimate drought stress or evapotranspiration in agriculture is provided. Among other methods, stress time, stress degree day, crop water stress index (CWSI), and stomatal conductance index are discussed. The theoretical models are used to evaluate the performance and sensitivity of the most important methods, corroborating the literature data. In the fourth and final part, a critical view on the future and remaining challenges of ground-based thermal remote sensing is presented.

  11. Global cross-station assessment of neuro-fuzzy models for estimating daily reference evapotranspiration

    Science.gov (United States)

    Shiri, Jalal; Nazemi, Amir Hossein; Sadraddini, Ali Ashraf; Landeras, Gorka; Kisi, Ozgur; Fard, Ahmad Fakheri; Marti, Pau

    2013-02-01

    SummaryAccurate estimation of reference evapotranspiration is important for irrigation scheduling, water resources management and planning and other agricultural water management issues. In the present paper, the capabilities of generalized neuro-fuzzy models were evaluated for estimating reference evapotranspiration using two separate sets of weather data from humid and non-humid regions of Spain and Iran. In this way, the data from some weather stations in the Basque Country and Valencia region (Spain) were used for training the neuro-fuzzy models [in humid and non-humid regions, respectively] and subsequently, the data from these regions were pooled to evaluate the generalization capability of a general neuro-fuzzy model in humid and non-humid regions. The developed models were tested in stations of Iran, located in humid and non-humid regions. The obtained results showed the capabilities of generalized neuro-fuzzy model in estimating reference evapotranspiration in different climatic zones. Global GNF models calibrated using both non-humid and humid data were found to successfully estimate ET0 in both non-humid and humid regions of Iran (the lowest MAE values are about 0.23 mm for non-humid Iranian regions and 0.12 mm for humid regions). non-humid GNF models calibrated using non-humid data performed much better than the humid GNF models calibrated using humid data in non-humid region while the humid GNF model gave better estimates in humid region.

  12. Upflow Evapotranspiration System for the Treatment of On-Site Wastewater Effluent

    Directory of Open Access Journals (Sweden)

    Sean Curneen

    2015-05-01

    Full Text Available Full-scale willow evapotranspiration systems fed from the base with septic tank or secondary treated domestic effluent from single houses have been constructed and instrumented in Ireland in order to investigate whether the technology could provide a solution to the problem of on-site effluent disposal in areas with low permeability subsoils. Continuous monitoring of rainfall, reference evapotranspiration, effluent flows and water level in the sealed systems revealed varying evapotranspiration rates across the different seasons. No system managed to achieve zero discharge in any year remaining at maximum levels for much of the winter months, indicating some loss of water by lateral exfiltration at the surface. Water sampling and analysis however, showed that the quality of any surface overflow from the systems was similar to rainfall runoff. The performance results have then been used to formulate design guidelines for such systems in Ireland’s temperate maritime climate. The effect of varying different combinations of design parameters (plan area, soil depth, etc. has been evaluated with respect to the simulated number of overflow days over a five-year period using a water balance model. Design guidelines have then been based upon minimising the amount of runoff, in conjunction with other practical and financial considerations.

  13. Satellite NDVI Assisted Monitoring of Vegetable Crop Evapotranspiration in California’s San Joaquin Valley

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    Thomas J. Trout

    2012-02-01

    Full Text Available Reflective bands of Landsat-5 Thematic Mapper satellite imagery were used to facilitate the estimation of basal crop evapotranspiration (ETcb, or potential crop water use, in San Joaquin Valley fields during 2008. A ground-based digital camera measured green fractional cover (Fc of 49 commercial fields planted to 18 different crop types (row crops, grains, orchard, vineyard of varying maturity over 11 Landsat overpass dates. Landsat L1T terrain-corrected images were transformed to surface reflectance and converted to normalized difference vegetation index (NDVI. A strong linear relationship between NDVI and Fc was observed (r2 = 0.96, RMSE = 0.062. The resulting regression equation was used to estimate Fc for crop cycles of broccoli, bellpepper, head lettuce, and garlic on nominal 7–9 day intervals for several study fields. Prior relationships developed by weighing lysimeter were used to transform Fc to fraction of reference evapotranspiration, also known as basal crop coefficient (Kcb. Measurements of grass reference evapotranspiration from the California Irrigation Management Information System were then used to calculate ETcb for each overpass date. Temporal profiles of Fc, Kcb, and ETcb were thus developed for the study fields, along with estimates of seasonal water use. Daily ETcb retrieval uncertainty resulting from error in satellite-based Fc estimation was < 0.5 mm/d, with seasonal uncertainty of 6–10%. Results were compared with FAO-56 irrigation guidelines and prior lysimeter observations for reference.

  14. A process-based evapotranspiration model incorporating coupled soil water-atmospheric controls

    Science.gov (United States)

    Haghighi, Erfan; Kirchner, James

    2016-04-01

    Despite many efforts to develop evapotranspiration models (in the framework of the Penman-Monteith equation) with improved parametrizations of various resistance terms to water vapor transfer into the atmosphere, evidence suggests that estimates of evapotranspiration and its partitioning are prone to bias. Much of this bias could arise from the exclusion of surface hydro-thermal properties and of physical interactions close to the surface where heat and water vapor fluxes originate. Recent progress has been made in mechanistic modeling of surface-turbulence interactions, accounting for localized heat and mass exchange rates from bare soil surfaces covered by protruding obstacles. We seek to extend these results partially vegetated surfaces, to improve predictive capabilities and accuracy of remote sensing techniques quantifying evapotranspiration fluxes. The governing equations of liquid water, water vapor, and energy transport dynamics in the soil-plant-atmosphere system are coupled to resolve diffusive vapor fluxes from isolated pores (plant stomata and soil pores) across a near-surface viscous sublayer, explicitly accounting for pore-scale transport mechanisms and environmental forcing. Preliminary results suggest that this approach offers unique opportunities for directly linking transport properties in plants and adjacent bare soil with resulting plant transpiration and localized bare soil evaporation rates. It thus provides an essential building block for interpreting and upscaling results to field and landscape scales for a range of vegetation cover and atmospheric conditions.

  15. Reliability of MODIS Evapotranspiration Products for Heterogeneous Dry Forest: A Study Case of Caatinga

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    Rodrigo de Queiroga Miranda

    2017-01-01

    Full Text Available Evapotranspiration (ET is normally considered as the sum of all water that evaporates from the soil and transpires from plants. However, accurately estimating ET from complex landscapes can be difficult because of its high spatial heterogeneity and diversity of driver factors, which make extrapolation of data from a point to a larger area quite inaccurate. In this paper, we hypothesize that MODIS products can be of use to estimate ET in areas of Caatinga vegetation, the hydrology of which has not been adequately studied. The experiment was conducted in a preserved level area of Caatinga in which meteorological and water flux measures were taken throughout 2012 by eddy covariance. Evapotranspiration estimates from eddy covariance were compared with remotely sensed evapotranspiration estimates from MOD16A2 and SAFER products. Correlations were performed at monthly, 8-day, and daily scales; and produced r2 values of monthly scale = 0.92, 8-day scale = 0.88, and daily scale = 0.85 for the SAFER algorithm. Monthly MOD16A2 data produced a value of r2=0.82, and they may be useful because they are free, downloadable, and easy to use by researchers and governments.

  16. Application of Riparian Evapotranspiration Package in MODFLOW for Riparian Vegetation Restoration

    Science.gov (United States)

    Ajami, H.; Maddock, T., III

    2009-04-01

    Quantifying spatial and temporal variability of riparian evapotranspiration (ET) is essential in water resources management especially in management and restoration of riparian ecosystems where multiple agricultural, industrial, and domestic users may exist. To enhance riparian evapotranspiration estimation in a MODFLOW groundwater model, RIPGIS-NET, an ArcGIS custom application, was developed to derive parameters and visualize results of spatially explicit riparian evapotranspiration in groundwater flow models for ecohydrology, riparian ecosystem management, stream restoration and water resources applications. RIPGIS-NET works with RIP-ET, a modeling package for MODFLOW. RIP-ET improves riparian ET simulations by using a set of eco-physiologically based ET curves for plant functional subgroups (PFSG), and is able to separate ground evaporation and plant transpiration processes. To evaluate impact of riparian restoration scenarios on groundwater resources, the above packages were applied to MODFLOW model of hypothetical Dry Alkaline Valley area. Using riparian ET curve files which show the relation between the groundwater level and ET, aerial extent of riparian vegetation in each season and a digital elevation map, RIPGIS-NET derived RIP-ET model parameters for each season. After running MODFLOW, groundwater head dynamics and spatial variability of riparian ET were visualized in GIS environment for each restoration scenario. This study provided useful information for riparian restoration planning in this area. It further highlighted the advantage of using spatially explicit models and datasets for riparian restoration planning.

  17. Investigating the Effect of Soil Texture and Fertility on Evapotranspiration and Crop Coefficient of Maize Forage

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    M. Ghorbanian Kerdabadi

    2017-02-01

    Full Text Available Introduction: Crop coefficient varies in different environmental conditions, such as deficit irrigation, salinity and intercropping. The effect of soil fertility and texture of crop coefficient and evapotranspiration of maize was investigated in this study. Low soil fertility and food shortages as a stressful environment for plants that makes it different evapotranspiration rates of evapotranspiration calculation is based on the FAO publication 56. Razzaghi et al. (2012 investigate the effect of soil type and soil-drying during the seed-filling phase on N-uptake, yield and water use, a Danish-bred cultivar (CV. Titicaca was grown in field lysimeters with sand, sandy loam and sandy clay loam soil. Zhang et al (2014 were investigated the Effect of adding different amounts of nitrogen during three years (from 2010 to 2012 on water use efficiency and crop evapotranspiration two varieties of winter wheat. The results of their study showed. The results indicated the following: (1 in this dry land farming system, increased N fertilization could raise wheat yield, and the drought-tolerant Changhan No. 58 showed a yield advantage in drought environments with high N fertilizer rates; (2 N application affected water consumption in different soil layers, and promoted wheat absorbing deeper soil water and so increased utilization of soil water; and (3 comprehensive consideration of yield and WUE of wheat indicated that the N rate of 270 kg/ha for Changhan No. 58 was better to avoid the risk of reduced production reduction due to lack of precipitation; however, under conditions of better soil moisture, the N rate of 180 kg/ha was more economic. Materials and Methods: The study was a factorial experiment in a completely randomized design with three soil texture treatment, including silty clay loam, loam and sandy-loam soil and three fertility treatment, including without fertilizer, one and two percent fertilizer( It was conducted at the experimental farm in

  18. Groundwater discharge by evapotranspiration, Dixie Valley, west-central Nevada, March 2009-September 2011

    Science.gov (United States)

    Garcia, C. Amanda; Huntington, Jena M; Buto, Susan G.; Moreo, Michael T.; Smith, J. LaRue; Andraski, Brian J.

    2014-01-01

    With increasing population growth and land-use change, urban communities in the desert Southwest are progressively looking toward remote basins to supplement existing water supplies. Pending applications by Churchill County for groundwater appropriations from Dixie Valley, Nevada, a primarily undeveloped basin east of the Carson Desert, have prompted a reevaluation of the quantity of naturally discharging groundwater. The objective of this study was to develop a revised, independent estimate of groundwater discharge by evapotranspiration (ETg) from Dixie Valley using a combination of eddy-covariance evapotranspiration (ET) measurements and multispectral satellite imagery. Mean annual ETg was estimated during water years 2010 and 2011 at four eddy-covariance sites. Two sites were in phreatophytic shrubland dominated by greasewood, and two sites were on a playa. Estimates of total ET and ETg were supported with vegetation cover mapping, soil physics considerations, water‑level measurements from wells, and isotopic water sourcing analyses to allow partitioning of ETg into evaporation and transpiration components. Site-based ETg estimates were scaled to the basin level by combining remotely sensed imagery with field reconnaissance. Enhanced vegetation index and brightness temperature data were compared with mapped vegetation cover to partition Dixie Valley into five discharging ET units and compute basin-scale ETg. Evapotranspiration units were defined within a delineated groundwater discharge area and were partitioned as (1) playa lake, (2) playa, (3) sparse shrubland, (4) moderate-to-dense shrubland, and (5) grassland.

  19. Regional probability distribution of the annual reference evapotranspiration and its effective parameters in Iran

    Science.gov (United States)

    Khanmohammadi, Neda; Rezaie, Hossein; Montaseri, Majid; Behmanesh, Javad

    2017-10-01

    The reference evapotranspiration (ET0) plays an important role in water management plans in arid or semi-arid countries such as Iran. For this reason, the regional analysis of this parameter is important. But, ET0 process is affected by several meteorological parameters such as wind speed, solar radiation, temperature and relative humidity. Therefore, the effect of distribution type of effective meteorological variables on ET0 distribution was analyzed. For this purpose, the regional probability distribution of the annual ET0 and its effective parameters were selected. Used data in this research was recorded data at 30 synoptic stations of Iran during 1960-2014. Using the probability plot correlation coefficient (PPCC) test and the L-moment method, five common distributions were compared and the best distribution was selected. The results of PPCC test and L-moment diagram indicated that the Pearson type III distribution was the best probability distribution for fitting annual ET0 and its four effective parameters. The results of RMSE showed that the ability of the PPCC test and L-moment method for regional analysis of reference evapotranspiration and its effective parameters was similar. The results also showed that the distribution type of the parameters which affected ET0 values can affect the distribution of reference evapotranspiration.

  20. Estimatation of evapotranspiration and crop coefficient of melon cultivated in protected environment

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    Cláudia S. Lozano

    Full Text Available ABSTRACT The objective of this work was to determine the water consumption and the crop coefficient of melon in a protected environment. The experiment was conducted in a greenhouse at the Technical Center of Irrigation of the State University of Maringá, in Maringá, PR. The melon hybrid used was Sunrise and the irrigations were performed daily by drip irrigation. Crop water requirement was quantified based on its evapotranspiration directly measured through constant water table lysimeters. Weather information was collected in an automatic weather station, installed inside the protected environment, which allowed to calculate the reference evapotranspiration by the Penman-Monteith method. The total water consumption of the melon crop was 295 mm, reaching maximum crop evapotranspiration of 5.16 mm d-1. The phenological stages were shorter in the initial, growth and intermediate phases, compared with the data from FAO. The determined crop coefficients were 0.87, 1.15 and 0.64 for the initial, intermediate and final stages, respectively

  1. Geospatial interpolation of reference evapotranspiration (ETo in areas with scarce data: case study in the South of Minas Gerais, Brazil

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    Silvio Jorge Coelho Simões

    2012-08-01

    Full Text Available The reference evapotranspiration is an important hydrometeorological variable; its measurement is scarce in large portions of the Brazilian territory, what demands the search for alternative methods and techniques for its quantification. In this sense, the present work investigated a method for the spatialization of the reference evapotranspiration using the geostatistical method of kriging, in regions with limited data and hydrometeorological stations. The monthly average reference evapotranspiration was calculated by the Penman-Monteith-FAO equation, based on data from three weather stations located in southern Minas Gerais (Itajubá, Lavras and Poços de Caldas, and subsequently interpolated by ordinary point kriging using the approach "calculate and interpolate." The meteorological data for a fourth station (Três Corações located within the area of interpolation were used to validate the reference evapotranspiration interpolated spatially. Due to the reduced number of stations and the consequent impossibility of carrying variographic analyzes, correlation coefficient (r, index of agreement (d, medium bias error (MBE, root mean square error (RMSE and t-test were used for comparison between the calculated and interpolated reference evapotranspiration for the Três Corações station. The results of this comparison indicated that the spatial kriging procedure, even using a few stations, allows to interpolate satisfactorily the reference evapotranspiration, therefore, it is an important tool for agricultural and hydrological applications in regions with lack of data.

  2. Evapotranspiration and Surface Energy Fluxes Estimation Using the Landsat-7 Enhanced Thematic Mapper Plus Image over a Semiarid Agrosystem in the North-West of Algeria

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    Nehal Laounia

    Full Text Available Abstract Monitoring evapotranspiration and surface energy fluxes over a range of spatial and temporal scales is crucial for many agroenvironmental applications. Different remote sensing based energy balance models have been developed, to estimate evapotranspiration at both field and regional scales. In this contribution, METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration, has been applied for the estimation of actual evapotranspiration in the Ghriss plain in Mascara (western Algeria, a semiarid region with heterogeneous surface conditions. Four images acquired during 2001 and 2002 by the Landsat-7 satellite were used. The METRIC model followed an energy balance approach, where evapotranspiration is estimated as the residual term when net radiation, sensible and soil heat fluxes are known. Different moisture indicators derived from the evapotranspiration were then calculated: reference evapotranspiration fraction, Priestley-Taylor parameter and surface resistance to evaporation. The evaluation of evapotranspiration and surface energy fluxes are accurate enough for the spatial variations of evapotranspiration rather satisfactory than sophisticated models without having to introduce an important number of parameters in input with difficult accessibility in routine. In conclusion, the results suggest that METRIC can be considered as an operational approach to predict actual evapotranspiration from agricultural areas having limited amount of ground information.

  3. Estimation of Actual Evapotranspiration Using an Agro-Hydrological Model and Remote Sensing Techniques

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    mostafa yaghoobzadeh

    2017-02-01

    Full Text Available Introduction: Accurate estimation of evapotranspiration plays an important role in quantification of water balance at awatershed, plain and regional scale. Moreover, it is important in terms ofmanaging water resources such as water allocation, irrigation management, and evaluating the effects of changing land use on water yields. Different methods are available for ET estimation including Bowen ratio energy balance systems, eddy correlation systems, weighing lysimeters.Water balance techniques offer powerful alternatives for measuring ET and other surface energy fluxes. In spite of the elegance, high accuracy and theoretical attractions of these techniques for measuring ET, their practical use over large areas might be limited. They can be very expensive for practical applications at regional scales under heterogeneous terrains composed of different agro-ecosystems. To overcome aforementioned limitations by use of satellite measurements are appropriate approach. The feasibility of using remotely sensed crop parameters in combination of agro-hydrological models has been investigated in recent studies. The aim of the present study was to determine evapotranspiration by two methods, remote sensing and soil, water, atmosphere, and plant (SWAP model for wheat fields located in Neishabour plain. The output of SWAP has been validated by means of soil water content measurements. Furthermore, the actual evapotranspiration estimated by SWAP has been considered as the “reference” in the comparison between SEBAL energy balance models. Materials and Methods: Surface Energy Balance Algorithm for Land (SEBAL was used to estimate actual ET fluxes from Modis satellite images. SEBAL is a one-layer energy balance model that estimates latent heat flux and other energy balance components without information on soil, crop, and management practices. The near surface energy balance equation can be approximated as: Rn = G + H + λET Where Rn: net radiation (Wm2; G

  4. Partitioning understory evapotranspiration in semi-arid ecosystems in Namibia using the isotopic composition of water vapour

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    de Blécourt, Marleen; Gaj, Marcel; Holtorf, Kim-Kirsten; Gröngröft, Alexander; Brokate, Ralph; Himmelsbach, Thomas; Eschenbach, Annette

    2016-04-01

    In dry environments with a sparse vegetation cover, understory evapotranspiration is a major component of the ecosystem water balance. Consequently, knowledge on the size of evapotranspiration fluxes and the driving factors is important for our understanding of the hydrological cycle. Understory evapotranspiration is made up of soil evaporation and plant transpiration. Soil evaporation can be measured directly from patches free of vegetation. However, when understory vegetation is present distinguishing between soil evaporation and plant transpiration is challenging. In this study, we aim to partition understory evapotranspiration based on an approach that combines the measurements of water-vapour fluxes using the closed chamber method with measurements of the isotopic composition of water vapour. The measurements were done in the framework of SASSCAL (Southern African Science Service Centre for Climate Change and Adaptive Land Management). The study sites were located in three different semi-arid ecosystems in Namibia: thornbush savanna, Baikiaea woodland and shrubland. At each site measurements were done under tree canopies as well as at unshaded areas between the canopies. We measured evaporation from the bare soil and evapotranspiration from patches covered with herbaceous species and shrubs using a transparent chamber connected with an infrared gas analyser (LI-8100A, LICOR Inc.). The stable isotope composition of water vapour inside the chamber and depth profiles of soil water stable isotopes were determined in-situ using a tuneable off-axis integrated cavity output spectroscope (OA-ICOS, Los Gatos Research, DLT 100). Xylem samples were extracted using the cryogenic vacuum extraction method and the isotopic composition of the extracted water was measured subsequently with a cavity-ring-down spectrometer (CRDS L2120-i, Picarro Inc.). We will present the quantified fluxes of understory evapotranspiration measured in the three different ecosystems, show the

  5. Evapotranspiration of rubber ( Hevea brasiliensis ) cultivated at two plantation sites in Southeast Asia: RUBBER EVAPOTRANSPIRATION IN SE ASIA

    Energy Technology Data Exchange (ETDEWEB)

    Giambelluca, Thomas W. [Department of Geography, University of Hawai' i at Mānoa, Honolulu Hawai' i USA; Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya Japan; Mudd, Ryan G. [Department of Geography, University of Hawai' i at Mānoa, Honolulu Hawai' i USA; Liu, Wen [Department of Geography, University of Hawai' i at Mānoa, Honolulu Hawai' i USA; Ziegler, Alan D. [Department of Geography, National University of Singapore, Singapore Singapore; Kobayashi, Nakako [Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya Japan; Kumagai, Tomo' omi [Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya Japan; Miyazawa, Yoshiyuki [Department of Geography, University of Hawai' i at Mānoa, Honolulu Hawai' i USA; Research Institute of East Asia Environments, Kyushu University, Fukuoka Japan; Lim, Tiva Khan [Cambodian Rubber Research Institute, Phnom Penh Cambodia; Huang, Maoyi [Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland Washington USA; Fox, Jefferson [East-West Center, Honolulu Hawai' i USA; Yin, Song [Cambodian Rubber Research Institute, Phnom Penh Cambodia; Mak, Sophea Veasna [Cambodian Rubber Research Institute, Phnom Penh Cambodia; Kasemsap, Poonpipope [Department of Horticulture, Kasetsart University, Bangkok Thailand

    2016-02-01

    The expansion of rubber (Hevea brasiliensis) cultivation to higher latitudes and higher elevations in southeast Asia is part of a dramatic shift in the direction of rural land cover change in the region toward more tree covered landscapes. To investigate the possible effects of increasing rubber cultivation in the region on ecosystem services including water cycling, eddy covariance towers were established to measure ecosystem fluxes within two rubber plantations, one each in Bueng Kan, northeastern Thailand, and Kampong Cham, central Cambodia. The results show that evapotranspiration (ET) at both sites is strongly related to variations in available energy and leaf area, and moderately controlled by soil moisture. Measured mean annual ET was 1128 and 1272 mm for the Thailand and Cambodia sites, respectively. After adjustment for energy closure, mean annual was estimated to be 1211 and 1459 mm yr at the Thailand and Cambodia sites, respectively. Based on these estimates and that of another site in Xishuangbanna, southwestern China, it appears that of rubber is higher than that of other tree dominated land covers in the region, including forest. While measurements by others in non rubber tropical ecosystems indicate that at high net radiation sites is at most only slightly higher than for sites with lower net radiation, mean annual rubber increases strongl with increasing net radiation across the three available rubber plantation observation sites. With the continued expansion of tree dominated land covers, including rubber cultivation, in southeast Asia, the possible association between commercially viable, fast growing tree crop species Giambelluca et al. Evapotranspiration of rubber (Havea brasiliensis) cultivated at two sites in southeast Asia and their relatively high water use raises concerns about potential effects on water and food security.

  6. Evapotranspiration estimate in the Mediterranean: the comparison between different methods and possible impacts of climate change

    Science.gov (United States)

    Todorovic, Mladen; Karic, Biljana; Santos Pereira, Luis; Lionello, Piero

    2015-04-01

    This work focused on the performances of different methods to estimate evapotranspiration (ET) across the Mediterranean climates. Two types of monthly weather data were used in the analysis: CLIMWAT historical database for 577 meteorological stations located in the Mediterranean countries and data derived from the ENSEMBLES project (EC-FP6-ENV) Regional Circulation Model (RCM) simulations. The performance of two temperature based approaches for the estimation of reference evapotranspiration (Hargreaves-Samani - HS and the FAO Penman-Monteith with temperature data only - PMT) was assessed against the Penman-Monteith approach (PM) using a full input climate data. Data were grouped according to climate: hyper-arid, arid, semi-arid, dry sub-humid, moist sub-humid and humid zones. For almost all zones, the statistical parameters indicate slightly better performance of PMT than HS method. Both methods tend to underestimate ETo in hyper arid areas and to overestimate ETo in humid areas. The reduction of either minimum air temperature or dew temperature by 2°C under arid conditions (when the ratio between precipitation and ETo is smaller than 0.4) improves ETo estimation especially for interior locations and in hyper-arid and arid regions. The analysis performed for the future referred to the A1B SRES scenario for the period 2036-2065 using the results of RACMO2 driven by ECHAM5. The overall results indicated the redistribution of climatic zone over the Mediterranean with the further extension of arid zones towards higher altitudes. Accordingly, the variation in the performances of ET models was observed. Moreover, the climate change had an impact of the peak monthly evapotranspiration of Mediterranean crops which, in turn, affected the climatic water balance over the whole region.

  7. Analyzing Land Surface Evapotranspiration in Semi-Arid Regions Using A Modified Triangle Method

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    Zhang, H.; Gorelick, S.; Avisse, N.; Tilmant, A.; Rajsekhar, D.; Yoon, J.

    2016-12-01

    Difficulty in estimating spatially variable actual evapotranspiration continues to pose an obstacle to regional water resources planning and management. The widely-used satellite-based triangle methods require similar elevations across the domain, an assumption that is often doubtful at the regional scale. This study presents a modified triangle method based on the discretization of digital elevation models. It disaggregates the domain into a number of overlapping elevation zones and constructs a temperature-vegetation triangle for each elevation zone. The wet edge is determined using a linear temperature lapse rate derived from annual average air temperature observations across weather stations at different elevations. Dry and wet edges are extended to a hypothetical "fully-vegetated" pixel, and evapotranspiration capacity varies on both edges. This method addresses elevation variation and water stress in semi-arid environments, without altering land surface temperature and elevation data. We demonstrate this method in northwestern Jordan with MODIS data from 2009. Results show that this method is an effective approach to correct overestimation by a traditional triangle method and underestimation by the MODIS evapotranspiration product over both natural vegetated and irrigated areas. In contrast to previous triangle algorithms in which the domain-wide lump temperature and NDVI data could mask the underlying signal and efficacy of triangle methods, this method represents a semi-distributed scheme to discretize the altitude effects on triangle methods and provides a template to address the heterogeneity of other physical factors. It constitutes an essential step towards the satellite-based quantification of irrigation water use and effective water resources management in Jordan as well as other semi-arid regions with high freshwater vulnerability.

  8. Using SEBAL to Investigate How Variations in Climate Impact on Crop Evapotranspiration

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    Giorgos Papadavid

    2017-07-01

    Full Text Available Water allocation to crops, and especially to the most water intensive ones, has always been of great importance in agricultural processes. Deficit or excessive irrigation could create either crop health-related problems or water over-consumption, respectively. The latter could lead to groundwater depletion and deterioration of its quality through deep percolation of agrichemical residuals. In this context, and under the current conditions where Cyprus is facing effects of possible climate changes, the purpose of this study seeks to estimate the needed crop water requirements of the past (1995–2004 and the corresponding ones of the present (2005–2015 in order to test if there were any significant changes regarding the crop water requirements of the most water-intensive trees in Cyprus. The Mediterranean region has been identified as the region that will suffer the most from variations of climate. Thus the paper refers to effects of these variations on crop evapotranspiration (ETc using remotely-sensed data from Landsat TM/ETM+/OLI employing a sound methodology used worldwide, the Surface Energy Balance Algorithm for Land (SEBAL. Though the general feeling is that of changes on climate will consequently affect ETc, our results indicate that there is no significant effect of climate variation on crop evapotranspiration, despite the fact that some climatic factors have changed. Applying Student’s t-test, the mean values for the most water-intensive trees in Cyprus of the 1994–2004 decade have shown no statistical difference from the mean values of 2005–2015 for all the cases, concluding that the climate change taking place in the past decades in Cyprus have either not affected the crop evapotranspiration or the crops have managed to adapt to the new environmental conditions through time.

  9. Climate trends and behaviour of drought indices based on precipitation and evapotranspiration in Portugal

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    A. A. Paulo

    2012-05-01

    Full Text Available Distinction between drought and aridity is crucial to understand water scarcity processes. Drought indices are used for drought identification and drought severity characterisation. The Standardised Precipitation Index (SPI and the Palmer Drought Severity Index (PDSI are the most known drought indices. In this study, they are compared with the modified PDSI for Mediterranean conditions (MedPDSI and the Standardised Precipitation Evapotranspiration Index (SPEI. MedPDSI results from the soil water balance of an olive crop, thus real evapotranspiration is considered, while SPEI uses potential (climatic evapotranspiration. Similarly to the SPI, SPEI can be computed at various time scales. Aiming at understanding possible impacts of climate change, prior to compare the drought indices, a trend analysis relative to precipitation and temperature in 27 weather stations of Portugal was performed for the period 1941 to 2006. A trend for temperature increase was observed for some weather stations and trends for decreasing precipitation in March and increasing in October were also observed for some locations. Comparisons of the SPI and SPEI at 9- and 12-month time scales, the PDSI and MedPDSI were performed for the same stations and period. SPI and SPEI produce similar results for the same time scales concerning drought occurrence and severity. PDSI and MedPDSI correlate well between them and the same happened for SPI and SPEI. PDSI and MedPDSI identify more severe droughts than SPI or SPEI and identify drought occurrence earlier than these indices. This behaviour is likely to be related with the fact that a water balance is performed with PDSI and MedPDSI, which better approaches the supply-demand balance.

  10. Climate trends and behaviour of drought indices based on precipitation and evapotranspiration in Portugal

    Science.gov (United States)

    Paulo, A. A.; Rosa, R. D.; Pereira, L. S.

    2012-05-01

    Distinction between drought and aridity is crucial to understand water scarcity processes. Drought indices are used for drought identification and drought severity characterisation. The Standardised Precipitation Index (SPI) and the Palmer Drought Severity Index (PDSI) are the most known drought indices. In this study, they are compared with the modified PDSI for Mediterranean conditions (MedPDSI) and the Standardised Precipitation Evapotranspiration Index (SPEI). MedPDSI results from the soil water balance of an olive crop, thus real evapotranspiration is considered, while SPEI uses potential (climatic) evapotranspiration. Similarly to the SPI, SPEI can be computed at various time scales. Aiming at understanding possible impacts of climate change, prior to compare the drought indices, a trend analysis relative to precipitation and temperature in 27 weather stations of Portugal was performed for the period 1941 to 2006. A trend for temperature increase was observed for some weather stations and trends for decreasing precipitation in March and increasing in October were also observed for some locations. Comparisons of the SPI and SPEI at 9- and 12-month time scales, the PDSI and MedPDSI were performed for the same stations and period. SPI and SPEI produce similar results for the same time scales concerning drought occurrence and severity. PDSI and MedPDSI correlate well between them and the same happened for SPI and SPEI. PDSI and MedPDSI identify more severe droughts than SPI or SPEI and identify drought occurrence earlier than these indices. This behaviour is likely to be related with the fact that a water balance is performed with PDSI and MedPDSI, which better approaches the supply-demand balance.

  11. Evaluating Soil Health Using Remotely Sensed Evapotranspiration on the Benchmark Barnes Soils of North Dakota

    Science.gov (United States)

    Bohn, Meyer; Hopkins, David; Steele, Dean; Tuscherer, Sheldon

    2017-04-01

    The benchmark Barnes soil series is an extensive upland Hapludoll of the northern Great Plains that is both economically and ecologically vital to the region. Effects of tillage erosion coupled with wind and water erosion have degraded Barnes soil quality, but with unknown extent, distribution, or severity. Evidence of soil degradation documented for a half century warrants that the assumption of productivity be tested. Soil resilience is linked to several dynamic soil properties and National Cooperative Soil Survey initiatives are now focused on identifying those properties for benchmark soils. Quantification of soil degradation is dependent on a reliable method for broad-scale evaluation. The soil survey community is currently developing rapid and widespread soil property assessment technologies. Improvements in satellite based remote-sensing and image analysis software have stimulated the application of broad-scale resource assessment. Furthermore, these technologies have fostered refinement of land-based surface energy balance algorithms, i.e. Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC) algorithm for evapotranspiration (ET) mapping. The hypothesis of this study is that ET mapping technology can differentiate soil function on extensive landscapes and identify degraded areas. A recent soil change study in eastern North Dakota resampled legacy Barnes pedons sampled prior to 1960 and found significant decreases in organic carbon. An ancillary study showed that evapotranspiration (ET) estimates from METRIC decreased with Barnes erosion class severity. An ET raster map has been developed for three eastern North Dakota counties using METRIC and Landsat 5 imagery. ET pixel candidates on major Barnes soil map units were stratified into tertiles and classified as ranked ET subdivisions. A sampling population of randomly selected points stratified by ET class and county proportion was established. Morphologic and chemical data will

  12. Evapotranspiration estimates using remote-sensing data, Parker and Palo Verde valleys, Arizona and California

    Science.gov (United States)

    Raymond, Lee H.; Rezin, Kelly V.

    1989-01-01

    In 1981 the U.S. Geological Survey established an experimental project to assess the possible and practical use of remote-sensing data to estimate evapotranspiration as an approximation of consumptive use of water in the lower Colorado River flood plain. The project area was in Parker Valley, Arizona. The approach selected was to measure the areas covered by each type of vegetation, using remote-sensing data in various types of analyses, and to multiply each area by a predetermined water-use rate. Two calibration and six remote-sensing methods of classifying crop types were compared for cost, accuracy, consistency, and labor requirements. Included were one method each for field reconnaissance using 1982 data, low-altitude (less than 5,000 feet) aerial photography using 1982 data, and visual photointerpretation of Landsat satellite images using 1981 and 1982 data; two methods for medium-altitude (15,000-18,000 feet) aerial photography using 1982 data; and three methods for digital Landsat satellite images using 1981 data. A test of the most promising digital-processing method, which used three image dates, was made in part of Palo Verde Valley, California, where 1981 crop data were more complete than in Parker Valley. Of the eight methods studied, the two-date digital-processing method was the most consistent and least labor intensive for identifying two or three major crops; visual photointerpretation of Landsat images was the least expensive. Evapotranspiration estimates from crop classifications by all methods differed by a maximum of 6 percent. Total evapotranspiration calculated from crop data and phreatophyte maps in 1981 ranged from 11 percent lower in Palo Verde Valley to 17 percent lower in Parker Valley than consumptive use calculated by water budgets. The difference was greater in Parker Valley because the winter crop data were not included.

  13. Ecohydrology of Graciosa semi-natural grasslands: water use and evapotranspiration partition

    Science.gov (United States)

    Paço, Teresa A.; Paredes, Paula; Azevedo, Eduardo B.; Madruga, João S.; Pereira, Luís S.

    2016-04-01

    Semi-natural grasslands are a main landscape of Graciosa and other Islands of Azores. The present study aims at calibrate and validate the soil water balance model SIMDualKc for those grasslands aiming at assessing the dynamics of soil water and evapotranspiration. This objective relates with the need to improve knowledge on the ecohydrology of grasslands established in (volcanic) Andosols. This model adopts the dual crop coefficient approach to compute daily crop evapotranspiration (ETc) and to perform its partition into transpiration (T) and soil evaporation (Es). The application refers to a semi-natural grassland sporadically sowed with ryegrass (Lolium multiflorum Lam.). Model calibration and validation were performed comparing simulated against observed grassland evapotranspiration throughout two periods in consecutive years. Daily ET values were derived from eddy covariance data collected at the Eastern North Atlantic (ENA) facility of the ARM programme (established and supported by the U.S. Department of Energy with the collaboration of the local government and University of the Azores), at Graciosa, Azores (Portugal). Various statistical performance indicators were used to assess model accuracy and results show a good adequacy of the model for predicting vegetation ET in such conditions. Surface flux energy balance was also evaluated throughout the observation period (2014-2016). The ratio Es/ET shows that soil evaporation is much small than T/ET due to high soil cover by vegetation. The model was then applied to contrasting climatic conditions (dry vs. wet years) to assess related impacts on water balance components and grassland transpiration.

  14. Evapotranspiration from agricultural plant communities in the high rainfall zone of the southwest of Western Australia

    Science.gov (United States)

    Scott, P. R.; Sudmeyer, R. A.

    1993-06-01

    The clearing of native vegetation and its replacement with shallow rooted, annual crops and pastures has resulted in rising groundwater levels and concentration of salts in the surface soils of resulting groundwater discharge areas in the southwest of Western Australia. The potential to manipulate the recharge rates to groundwaters by using agronomic techniques to change catchment evapotranspiration ( Et), has been the subject of much discussion. From 1986 to 1989, annual Et was estimated from daytime measurements of Et from annual pasture (existing pasture, subterranean clover, Medicago murex), crops (lupins, oats, rape, barley and wheat) and two perennial pastures (lucerne and phalaris) at a site near Collie in the southwest of Western Australia. The ventilated chamber technique was used to measure Et rates, together with ancillary measurements of above ground biomass and rooting depth. Seasonal values of Et are presented and combined to allow a boundary analysis of annual Et for each species. Et was found to be influenced by the amount and timing of biomass production, and by the rooting depth. The median annual evapotranspiration of annual pasture was shown to be the least (339 mm), and lupins the most (471 mm). The site environment combined high rainfall and low evaporative demand in winter, and low moisture-holding capacity of duplex soils with preferred pathways through subsoil clays. In this context, the potential of deeper rooted, perennial species to use more water, was apparent. It is argued that the smaller the difference in annual evapotranspiration between alternative and current agricultural practice (annual pasture), the larger the proportion of a catchment likely to be required for treatment to affect groundwater levels. Recharge manipulation alone, using the species tested, may not be sufficient for catchment salinity control. A wide range of other strategies exist; a combination of these, to suit the practical and economic constraints of the

  15. Evapotranspiration (ET) data at Immokalee row crop site, Collier County, Florida, September 22, 2008 - January 8, 2009

    Science.gov (United States)

    Swancar, Amy

    2017-01-01

    This U.S. Geological Survey (USGS) data release consists of evapotranspiration measurements made at the USGS Immokalee row crop climate station beginning September 22, 2008 and ending January 8, 2009. Daily evapotranspiration rates corrected to a near-surface energy-budget varied from 0.1 millimeter (9/28/2008) to 3.3 millimeters (9/24/2008). The eddy-covariance method was used, with high-frequency sensors installed above an experimental field planted in green peppers to measure sensible and latent heat fluxes. Ancillary meteorological data are also included in the data set: net radiation, soil temperature and moisture, air temperature, relative humidity, wind speed and direction, and ground-water level. Data were collected at 30-minute resolution, with evapotranspiration corrected to the near-surface energy-budget at that timescale. The study was conducted at an experimental field on the University of Florida Southwest Florida Research and Education Center (SWFREC) in Immokalee, Florida (Latitude 26 27 40 North Longitude 81 26 24 West, in degrees minutes seconds, North American Datum 83, Section 20, Township 46S, Range 29E). The full data release associated with this site consists of: 1.  Immokalee row crop evapotranspiration, 30-minute data, from September 22, 2008 through January 8, 2009 (comma delimited text format) 2. Immokalee row crop evapotranspiration, daily data, from September 23, 2008 through January 7, 2009 (comma delimited text format) including an ancillary file: Vegetation and equipment photographs (zipped jpeg files).

  16. Projections of changes of areal evapotranspiration for different land-use units in the Wielkopolska Region (Poland)

    Science.gov (United States)

    Szwed, Małgorzata

    2017-10-01

    Strong global warming has been observed in the last three decades. Central Europe, including Poland, is not an exception. Moreover, climate projections for Poland foresee further warming as well as changes in the quantity as well as spatial and seasonal distribution of precipitation. This will result in changes in all elements of the water balance, including the areal evapotranspiration. For estimating the areal evapotranspiration, the heat balance method (HBM) is used in this paper for the growing season (March-October), whereas for the remaining months (November-February), evaporation is calculated according to the Ivanov equation. Values of areal evapotranspiration from selected land units are examined and compared for the average conditions in two time horizons, i.e. 1961-1990 (control period) and 2061-2090 (projection horizon) over the Wielkopolska Region in Poland, based on multi-model ensemble climate projections. Projections for the future, based on the MPI-M-REMO model, indicate that the regional average increases of the annual sum of areal evapotranspiration (connected mainly with an increase of air temperature) is equal to 45 mm, with the biggest changes during winter. In the growing season, the highest increases are expected to appear in July and June. As regards the spatial distribution, the highest increases are projected for the areas with presently highest evapotranspiration, e.g. the southwestern parts of the region.

  17. Estimation of Actual Evapotranspiration by Remote Sensing: Application in Thessaly Plain, Greece

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    Nikos Mamassis

    2008-06-01

    Full Text Available Remote sensing can assist in improving the estimation of the geographical distribution of evapotranspiration, and consequently water demand in large cultivated areas for irrigation purposes and sustainable water resources management. In the direction of these objectives, the daily actual evapotranspiration was calculated in this study during the summer season of 2001 over the Thessaly plain in Greece, a wide irrigated area of great agricultural importance. Three different methods were adapted and applied: the remotesensing methods by Granger (2000 and Carlson and Buffum (1989 that use satellite data in conjunction with ground meteorological measurements and an adapted FAO (Food and Agriculture Organisation Penman-Monteith method (Allen at al. 1998, which was selected to be the reference method. The satellite data were used in conjunction with ground data collected on the three closest meteorological stations. All three methods, exploit visible channels 1 and 2 and infrared channels 4 and 5 of NOAA-AVHRR (National Oceanic and Atmospheric Administration - Advanced Very High Resolution Radiometer sensor images to calculate albedo and NDVI (Normalised Difference Vegetation Index, as well as surface temperatures. The FAO Penman-Monteith and the Granger method have used exclusively NOAA-15 satellite images to obtain mean surface temperatures. For the Carlson-Buffum method a combination of NOAA-14 and ΝΟΑΑ-15 satellite images was used, since the average rate of surface temperature rise during the morning was required. The resulting estimations show that both the Carlson-Buffum and Granger methods follow in general the variations of the reference FAO Penman-Monteith method. Both methods have potential for estimating the spatial distribution of evapotranspiration, whereby the degree of the relative agreement with the reference FAO Penman-Monteith method depends on the crop growth stage. In particular, the Carlson- Buffum

  18. Simulating Crop Evapotranspiration Response under Different Planting Scenarios by Modified SWAT Model in an Irrigation District, Northwest China.

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    Xin Liu

    Full Text Available Modelling crop evapotranspiration (ET response to different planting scenarios in an irrigation district plays a significant role in optimizing crop planting patterns, resolving agricultural water scarcity and facilitating the sustainable use of water resources. In this study, the SWAT model was improved by transforming the evapotranspiration module. Then, the improved model was applied in Qingyuan Irrigation District of northwest China as a case study. Land use, soil, meteorology, irrigation scheduling and crop coefficient were considered as input data, and the irrigation district was divided into subdivisions based on the DEM and local canal systems. On the basis of model calibration and verification, the improved model showed better simulation efficiency than did the original model. Therefore, the improved model was used to simulate the crop evapotranspiration response under different planting scenarios in the irrigation district. Results indicated that crop evapotranspiration decreased by 2.94% and 6.01% under the scenarios of reducing the planting proportion of spring wheat (scenario 1 and summer maize (scenario 2 by keeping the total cultivated area unchanged. However, the total net output values presented an opposite trend under different scenarios. The values decreased by 3.28% under scenario 1, while it increased by 7.79% under scenario 2, compared with the current situation. This study presents a novel method to estimate crop evapotranspiration response under different planting scenarios using the SWAT model, and makes recommendations for strategic agricultural water management planning for the rational utilization of water resources and development of local economy by studying the impact of planting scenario changes on crop evapotranspiration and output values in the irrigation district of northwest China.

  19. Operational Actual Wetland Evapotranspiration Estimation for South Florida Using MODIS Imagery

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    Cristobal N. Ceron

    2015-03-01

    Full Text Available Evapotranspiration is a reliable indicator of wetland health. Wetlands are an important and valuable ecosystem on the South Florida landscape. Accurate wetland Actual Evapotranspiration (AET data can be used to evaluate the performance of South Florida’s Everglades restoration programs. However, reliable AET measurements rely on scattered point measurements restricting applications over a larger area. The objective of this study was to validate the ability of the Simplified Surface Energy Balance (SSEB approach and the Simple Method (also called the Abtew Method to provide large area AET estimates for wetland recovery efforts. The study used Moderate Resolution Imaging Spectroradiometer (MODIS sensor spectral data and South Florida Water Management District (SFWMD solar radiation data to derive weekly AET values for South Florida. The SSEB-Simple Method approach provided acceptable results with good agreement with observed values during the critical dry season period, when cloud cover was low (rave (n = 59 = 0.700, pave < 0.0005, but requires further refinement to be viable for yearly estimates because of poor performance during wet season months, mainly because of cloud contamination. The approach can be useful for short-term wetland recovery assessment projects that occur during the dry season and/or long term projects that compare site AET rates from dry season to dry season.

  20. Comparative Analysis of METRIC Model and Atmometer Methods for Estimating Actual Evapotranspiration

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    Arturo Reyes-González

    2017-01-01

    Full Text Available Accurate estimation of crop evapotranspiration (ET is a key factor in agricultural water management including irrigated agriculture. The objective of this study was to compare ET estimated from the satellite-based remote sensing METRIC model to in situ atmometer readings. Atmometer readings were recorded from three sites in eastern South Dakota every morning between 8:15 and 8:30 AM for the duration of the 2016 growing season. Seven corresponding clear sky images from Landsat 7 and Landsat 8 (Path 29, Row 29 were processed and used for comparison. Three corn fields in three sites were used to compare actual evapotranspiration (ETa. The results showed a good relationship between ETa estimated by the METRIC model (ETa-METRIC and ETa estimated with atmometer (ETa-atm (r2 = 0.87, index of agreement of 0.84, and RMSE = 0.65 mm day−1. However, ETa-atm values were consistently lower than ETa-METRIC values. The differences in daily ETa between the two methods increase with high wind speed values (>4 m s−1. Results from this study are useful for improving irrigation water management at local and field scales.

  1. Soil water dynamics and evapotranspiration of forage cactus clones under rainfed conditions

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    Thieres George Freire da Silva

    2015-07-01

    Full Text Available Abstract: The objective of this work was to evaluate soil water dynamics in areas cultivated with forage cactus clones and to determine how environmental conditions and crop growth affect evapotranspiration. The study was conducted in the municipality of Serra Talhada, in the state of Pernambuco, Brazil. Crop growth was monitored through changes in the cladode area index (CAI and through the soil cover fraction, calculated at the end of the cycle. Real evapotranspiration (ET of the three evaluated clones was obtained as the residual term in the soil water balance method. No difference was observed between soil water balance components, even though the evaluated clones were of different genus and had different CAI increments. Accumulated ET was of 1,173 mm during the 499 days of the experiment, resulting in daily average of 2.35 mm. The CAI increases the water consumption of the Orelha de Elefante Mexicana clone. In dry conditions, the water consumption of the Miúda clone responds more slowly to variation in soil water availability. The lower evolution of the CAI of the IPA Sertânia clone, during the rainy season, leads to a higher contribution of the evaporation component in ET. The atmospheric demand controls the ET of clones only when there is higher soil water availability; in this condition, the water consumption of the Miúda clone decreases more rapidly with the increase of atmospheric demand.

  2. Three decades of reference evapotranspiration estimates for a tropical watershed in the eastern Amazon

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    RENATO O. DA SILVA JÚNIOR

    2017-10-01

    Full Text Available ABSTRACT This study estimated the reference evapotranspiration rate (ETo for the Itacaiúnas River Watershed (IRW, Eastern Amazonia, and measured the accuracy of eight empirical equations: Penman-Monteith (PM, Priestley-Taylor (PT, Hargreaves and Samani (HS, Camargo (CAM, Thornthwaite (TH, Hamon (HM, Kharrufa (KF and Turc (TC using monthly data from 1980 to 2013. In addition, it verifies the regional applicability to the IRW using a for the Marabá-PA station. The methods TC and PM (FAO56 presented the best results, which demonstrate that radiation and higher temperatures are the dominant drivers in the Evapotranspiration process, while relative humidity and wind speed have a much smaller impact. The temporal and spatial variability of ETo for IRW show has strong seasonality, increasing during the dry season and decreasing during the rainy season. The statistical analyses at 1% level of significance, indicates that there is no correlation of the residuals between the dry and rainy seasons, and test of the physical parameters such as mean temperature, solar radiation and relative air humidity explains the variations of ETo.

  3. Identification of trend in long term precipitation and reference evapotranspiration over Narmada river basin (India)

    Science.gov (United States)

    Pandey, Brij Kishor; Khare, Deepak

    2018-02-01

    Precipitation and reference evapotranspiration are key parameters in hydro-meteorological studies and used for agricultural planning, irrigation system design and management. Precipitation and evaporative demand are expected to be alter under climate change and affect the sustainable development. In this article, spatial variability and temporal trend of precipitation and reference evapotranspiration (ETo) were investigated over Narmada river basin (India), a humid tropical climatic region. In the present study, 12 and 28 observatory stations were selected for precipitation and ETo, respectively of 102-years period (1901-2002). A rigorous analysis for trend detection was carried out using non parametric tests such as Mann-Kendall (MK) and Spearman Rho (SR). Sen's slope estimator was used to analyze the rate of change in long term series. Moreover, all the stations of basin exhibit positive trend for annual ETo, while 8% stations indicate significant negative trend for mean annual precipitation, respectively. Change points of annual precipitation were identified around the year 1962 applying Buishand's and Pettit's test. Annual mean precipitation reduced by 9% in upper part while increased maximum by 5% in lower part of the basin due temporal changes. Although annual mean ETo increase by 4-12% in most of the region. Moreover, results of the study are very helpful in planning and development of agricultural water resources.

  4. Verification SEBAL and Hargreaves –Samani Models to Estimate Evapotranspiration by Lysimeter Data

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    Ali Morshedi

    2017-02-01

    Full Text Available Introduction: Evapotranspiration (ET is an important component of the hydrological cycle, energy equations at the surface and water balance. ET estimation is needed in various fields of science, such as hydrology, agriculture, forestry and pasture, and water resources management. Conventional methods used to estimate evapotranspiration from point measurements. Remote sensing models have the capability to estimate ET using surface albedo, surface temperature and vegetation indices in larger scales. Surface Energy Balance Algorithm for Land (SEBAL estimate ET at the moment of satellite path as a residual of energy balance equation for each pixel. In this study Hargreaves-Samani (HS and SEBAL models ET compared to an alfalfa lysimeter data’s, located in Shahrekord plain within the Karun basin. Satellite imageries were based on Landsat 7 ETM+ sensor data’s in seven satellite passes for path 164 and row 38 in the World Reference System, similar to lysimeter sampling data period, from April to October 2011. SEBAL uses the energy balance equation to estimate evapotranspiration. Equation No. 1 shows the energy balance equation for an evaporative surface: λET=Rn–G–H [1] In this equation Rn, H, G and λET represent the net radiation flux input to the surface (W/m2, Sensible heat flux (W/m2, soil heat flux (W/m2, and latent heat of vaporization (W/m2, respectively. In this equation the vertical flux considered and the horizontal fluxes of energy are neglected. The above equation must be used for large surfaces and uniformly full cover plant area. SEBAL is provided for estimating ET, using the minimum data measured by ground equipment. This model is applied and tested in more than 30 countries with an accuracy of about 85% at field scale, and 95 percent in the daily and seasonal scales. In Borkhar watershed (East of Isfahan, IRAN ASTER and MODIS satellite imageries were used for SEBAL to compare Penman-Monteith model. Results showed that estimated

  5. Ecological restoration of groundwater-dependent vegetation in the arid Ejina Delta: evidences from satellite evapotranspiration

    Science.gov (United States)

    Kai, Lu; Garcia, Monica; Yu, Jingjie; Zhang, Yichi; Wang, Ping; Wang, Sheng; Liu, Xiao

    2017-04-01

    The ecological water conveyance project (EWCP) in the Ejina delta, a typical hyper-arid area of China, aimed to restore degraded phreatophytic ecosystems. We assessed the degree of ecosystem recovery using as an ecohydrological indicator a ratio between actual and potential evapotranspiration derived from MODIS since the beginning of the project in 2001. The selected indicator was the Temperature Vegetation Dryness Index (TVDI) which was validated with Eddy covariance (EC) data confirming its applicability to monitor groundwater dependent vegetation. The spatial analyses of the evapotranspiration ratio show drying trends (2000-2015) which are stronger and also cover larger extensions than the wetting trends. Thus, the condition of key riparian areas relying mostly on surface water improved since the project began. However, groundwater dependent ecosystems located in lower river Xihe reaches present drying trends. It seems that despite of the runoff supplemented by the EWCP project, there is nowadays more inequality in the access to water by groundwater dependent ecosystems in the Ejina Delta. The study shows that energy-evaporation indices, relying on radiometric satellite temperature like the TVDI, can detect degradation signals that otherwise might go undetected by NDVI analyses especially in arid regions, where vegetation indices are greatly affected by the soil background signals. Additionally, they can provide timely information to water managers on how much water to allocate for a sustainable restoration program.

  6. Comparison of different methods in estimating potential evapotranspiration at Muda Irrigation Scheme of Malaysia

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    Sobri Harun

    2012-04-01

    Full Text Available Evapotranspiration (ET is a complex process in the hydrological cycle that influences the quantity of runoff and thus the irrigation water requirements. Numerous methods have been developed to estimate potential evapotranspiration (PET. Unfortunately, most of the reliable PET methods are parameter rich models and therefore, not feasible for application in data scarce regions. On the other hand, accuracy and reliability of simple PET models vary widely according to regional climate conditions. The objective of the present study was to evaluate the performance of three temperature-based and three radiation-based simple ET methods in estimating historical ET and projecting future ET at Muda Irrigation Scheme at Kedah, Malaysia. The performance was measured by comparing those methods with the parameter intensive Penman-Monteith Method. It was found that radiation based methods gave better performance compared to temperature-based methods in estimation of ET in the study area. Future ET simulated from projected climate data obtained through statistical downscaling technique also showed that radiation-based methods can project closer ET values to that projected by Penman-Monteith Method. It is expected that the study will guide in selecting suitable methods for estimating and projecting ET in accordance to availability of meteorological data.

  7. Satellite-Derived Spatiotemporal Variations in Evapotranspiration over Northeast China during 1982–2010

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    Lilin Zhang

    2017-11-01

    Full Text Available Evapotranspiration (ET is a critical process for the climate system and water cycles. However, the spatiotemporal variations in terrestrial ET over Northeast China over the past three decades calculated from sparse meteorological point-based data remain large uncertain. In this paper, a recently proposed modified satellite-based Priestley–Taylor (MS–PT algorithm was applied to estimate ET of Northeast China during 1982–2010. Validation results show that the square of the correlation coefficients (R2 for the six flux tower sites varies from 0.55 to 0.88 (p < 0.01, and the mean root mean square error (RMSE is 0.92 mm/d. The ET estimated by MS–PT has an annual mean of 441.14 ± 18 mm/year in Northeast China, with a decreasing trend from southeast coast to northwest inland. The ET also shows in both annual and seasonal linear trends over Northeast China during 1982–2010, although this trend seems to have ceased after 1998, which increased on average by 12.3 mm per decade pre-1998 (p < 0.1 and decreased with large interannual fluctuations post-1998. Importantly, our analysis on ET trends highlights a large difference from previous studies that the change of potential evapotranspiration (PET plays a key role for the change of ET over Northeast China. Only in the western part of Northeast China does precipitation appear to be a major controlling influence on ET.

  8. Evaluation of evapotranspiration in small on-site HSF constructed wetlands.

    Science.gov (United States)

    Papaevangelou, Vassiliki A; Gikas, Georgios D; Tsihrintzis, Vassilios A

    2012-01-01

    Experimental results on evapotranspiration (ET), relevant to small on-site facilities are presented, derived from one-year controlled experiments in five pilot-scale horizontal subsurface flow (HSF) constructed wetlands (CW) used as lysimeters. The CW units operated in Northern Greece. They were rectangular tanks made of steel, with dimensions 3m long, 0.75m wide and 1m deep. Three different porous media were used, i.e., medium gravel, fine gravel and cobbles. Two plants were used, namely common reed (R, Phragmites australis) and cattails (C, Typha latifolia). One unit was unplanted. ET was estimated based on the water budget method. Conclusions were drawn on its relation to season and vegetation density. Furthermore, Pearson correlation coefficient analysis identified the main factors affecting wetland plant ET. Seven well-known ET empirical methods were applied to estimate ET using the measured meteorological and wetland data. ET estimated by the empirical methods were multiplied with appropriate correction coefficients to match measured ET, providing this way appropriate plant coefficient (K(c)) values, and equations for predicting HSF CW evapotranspiration. The suitability of these methods for the particular constructed wetland type is discussed through comparison with the measured data. The Blaney-Criddle method was found as best. Furthermore, stepwise multiple linear regression analysis was used with the measured ET and meteorological data to produce simple empirical equations to predict ET rates according to meteorological factors, plant and substrate material.

  9. FAO-56 Dual Model Combined with Multi-Sensor Remote Sensing for Regional Evapotranspiration Estimations

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    Rim Amri

    2014-06-01

    Full Text Available The main goal of this study is to evaluate the potential of the FAO-56 dual technique for the estimation of regional evapotranspiration (ET and its constituent components (crop transpiration and soil evaporation, for two classes of vegetation (olives trees and cereals in the semi-arid region of the Kairouan plain in central Tunisia. The proposed approach combines the FAO-56 technique with remote sensing (optical and microwave, not only for vegetation characterization, as proposed in other studies but also for the estimation of soil evaporation, through the use of satellite moisture products. Since it is difficult to use ground flux measurements to validate remotely sensed data at regional scales, comparisons were made with the land surface model ISBA-A-gs which is a physical SVAT (Soil–Vegetation–Atmosphere Transfer model, an operational tool developed by Météo-France. It is thus shown that good results can be obtained with this relatively simple approach, based on the FAO-56 technique combined with remote sensing, to retrieve temporal variations of ET. The approach proposed for the daily mapping of evapotranspiration at 1 km resolution is approved in two steps, for the period between 1991 and 2007. In an initial step, the ISBA-A-gs soil moisture outputs are compared with ERS/WSC products. Then, the output of the FAO-56 technique is compared with the output generated by the SVAT ISBA-A-gs model.

  10. Accuracy assessment of NOAA gridded daily reference evapotranspiration for the Texas High Plains

    Science.gov (United States)

    Moorhead, Jerry; Gowda, Prasanna H.; Hobbins, Michael; Senay, Gabriel; Paul, George; Marek, Thomas; Porter, Dana

    2015-01-01

    The National Oceanic and Atmospheric Administration (NOAA) provides daily reference evapotranspiration (ETref) maps for the contiguous United States using climatic data from North American Land Data Assimilation System (NLDAS). This data provides large-scale spatial representation of ETref, which is essential for regional scale water resources management. Data used in the development of NOAA daily ETref maps are derived from observations over surfaces that are different from short (grass — ETos) or tall (alfalfa — ETrs) reference crops, often in nonagricultural settings, which carries an unknown discrepancy between assumed and actual conditions. In this study, NOAA daily ETos and ETrs maps were evaluated for accuracy, using observed data from the Texas High Plains Evapotranspiration (TXHPET) network. Daily ETos, ETrs and the climatic data (air temperature, wind speed, and solar radiation) used for calculating ETref were extracted from the NOAA maps for TXHPET locations and compared against ground measurements on reference grass surfaces. NOAA ETrefmaps generally overestimated the TXHPET observations (1.4 and 2.2 mm/day ETos and ETrs, respectively), which may be attributed to errors in the NLDAS modeled air temperature and wind speed, to which reference ETref is most sensitive. Therefore, a bias correction to NLDAS modeled air temperature and wind speed data, or adjustment to the resulting NOAA ETref, may be needed to improve the accuracy of NOAA ETref maps.

  11. Comparison of four different energy balance models for estimating evapotranspiration in the Midwestern United States

    Science.gov (United States)

    Singh, Ramesh K.; Senay, Gabriel B.

    2016-01-01

    The development of different energy balance models has allowed users to choose a model based on its suitability in a region. We compared four commonly used models—Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC) model, Surface Energy Balance Algorithm for Land (SEBAL) model, Surface Energy Balance System (SEBS) model, and the Operational Simplified Surface Energy Balance (SSEBop) model—using Landsat images to estimate evapotranspiration (ET) in the Midwestern United States. Our models validation using three AmeriFlux cropland sites at Mead, Nebraska, showed that all four models captured the spatial and temporal variation of ET reasonably well with an R2 of more than 0.81. Both the METRIC and SSEBop models showed a low root mean square error (0.80), whereas the SEBAL and SEBS models resulted in relatively higher bias for estimating daily ET. The empirical equation of daily average net radiation used in the SEBAL and SEBS models for upscaling instantaneous ET to daily ET resulted in underestimation of daily ET, particularly when the daily average net radiation was more than 100 W·m−2. Estimated daily ET for both cropland and grassland had some degree of linearity with METRIC, SEBAL, and SEBS, but linearity was stronger for evaporative fraction. Thus, these ET models have strengths and limitations for applications in water resource management.

  12. Surface Energy Balance Based Evapotranspiration Mapping in the Texas High Plains.

    Science.gov (United States)

    Gowda, Prasanna H; Chávez, José L; Howell, Terry A; Marek, Thomas H; New, Leon L

    2008-08-28

    Agriculture on the Texas High Plains (THP) uses approximately 89% of groundwater withdrawals from the Ogallala Aquifer. Consequently, groundwater levels are declining faster than the recharge rate. Therefore, efficient agricultural water use is essential for economic viability and sustainability of the THP. Accurate regional evapotranspiration (ET) maps would provide valuable information on actual crop water use. In this study, METRIC (Mapping Evapotranspiration at High Resolution using Internalized Calibration), a remote sensing based ET algorithm, was evaluated for mapping ET in the THP. Two Landsat 5 Thematic Mapper images acquired on 27 June (DOY 178) and 29 July (DOY 210) 2005 were used for this purpose. The performance of the ET model was evaluated by comparing the predicted daily ET with values derived from soil moisture budget at four commercial agricultural fields. Daily ET estimates resulted with a prediction error of 12.7±8.1% (mean bias error ± root mean square error) on DOY 178 and -4.7±9.4% on DOY 210 when compared with ET derived from measured soil moisture through the soil water balance. These results are good considering the prevailing advective conditions in the THP. METRIC have the potential to be used for mapping regional ET in the THP region. However, more evaluation is needed under different agroclimatological conditions.

  13. An Interactive Real-time Decision Support System for Leachate Irrigation on Evapotranspiration Landfill Covers

    Science.gov (United States)

    Wang, Y.

    2015-12-01

    Landfill disposal is still the most common and economical practice for municipal solid waste in most countries. However, heavily polluted leachate generated by excess rainwater percolating through the landfill waste is the major drawback of this practice. Evapotranspiration (ET) cover systems are increasingly being used as alternative cover systems to minimize percolation by evapotranspiration. Leachate recirculation is one of the least expensive options for leachate treatment. The combination of ET cover systems and leachate recirculation can be an economical and environment-friendly practice for landfill leachate management. An interactive real-time decision support system is being developed to better manage leachate irrigation using historical and forecasting weather data, and real time soil moisture data. The main frame of this system includes soil water modules, and plant-soil modules. An inverse simulation module is also included to calibrate certain parameters based on observed data when necessary. It would be an objectives-oriented irrigation management tool to minimize landfill operation costs and negative environmental impacts.

  14. Estimating root-zone moisture and evapotranspiration with AVHRR data[Advanced Very High Resolution Radiometer

    Energy Technology Data Exchange (ETDEWEB)

    Song, J.; Wesely, M. L.

    1999-10-08

    The parameterized subgrid-scale surface fluxes (PASS) model uses satellite data and limited surface observations to infer root-zone available moisture content and evapotranspiration rate with moderate spatial resolution over extended terrestrial areas. The ultimate goal of this work is to produce estimates of water loss by evapotranspiration, for application in hydrological models. The major advantage to the method is that it can be applied to areas having diverse surface characteristics where direct surface flux measurements either do not exist or are not feasible and where meteorological data are available from only a limited number of ground stations. The emphasis of this work with the PASS model is on improving (1) methods of using satellite remote sensing data to derive the essential parameters for individual types of surfaces over large areas, (2) algorithms for describing the interactions of near-surface atmospheric conditions with surface processes, and (3) algorithms for computing surface energy and water vapor flux at a scale close to the size of a satellite-derived image pixel. The PASS approach is being developed and tested further with observations from the 1997 Cooperative Atmosphere-Surface Exchange Study (CASES-97) at the Atmospheric Boundary Layer Experiments (ABLE) site in the Walnut River Watershed (WRW), an area of about 5,000 km{sup 2} in southern Kansas. Here the authors describe some of the progress made since the previous report.

  15. Comparison of Four Different Energy Balance Models for Estimating Evapotranspiration in the Midwestern United States

    Directory of Open Access Journals (Sweden)

    Ramesh K. Singh

    2015-12-01

    Full Text Available The development of different energy balance models has allowed users to choose a model based on its suitability in a region. We compared four commonly used models—Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC model, Surface Energy Balance Algorithm for Land (SEBAL model, Surface Energy Balance System (SEBS model, and the Operational Simplified Surface Energy Balance (SSEBop model—using Landsat images to estimate evapotranspiration (ET in the Midwestern United States. Our models validation using three AmeriFlux cropland sites at Mead, Nebraska, showed that all four models captured the spatial and temporal variation of ET reasonably well with an R2 of more than 0.81. Both the METRIC and SSEBop models showed a low root mean square error (<0.93 mm·day−1 and a high Nash–Sutcliffe coefficient of efficiency (>0.80, whereas the SEBAL and SEBS models resulted in relatively higher bias for estimating daily ET. The empirical equation of daily average net radiation used in the SEBAL and SEBS models for upscaling instantaneous ET to daily ET resulted in underestimation of daily ET, particularly when the daily average net radiation was more than 100 W·m−2. Estimated daily ET for both cropland and grassland had some degree of linearity with METRIC, SEBAL, and SEBS, but linearity was stronger for evaporative fraction. Thus, these ET models have strengths and limitations for applications in water resource management.

  16. REMOTE SENSING AND SURFACE ENERGY FLUX MODELS TO DERIVE EVAPOTRANSPIRATION AND CROP COEFFICIENT

    Directory of Open Access Journals (Sweden)

    Salvatore Barbagallo

    2008-06-01

    Full Text Available Remote sensing techniques using high resolution satellite images provide opportunities to evaluate daily crop water use and its spatial and temporal distribution on a field by field basis. Mapping this indicator with pixels of few meters of size on extend areas allows to characterize different processes and parameters. Satellite data on vegetation reflectance, integrated with in field measurements of canopy coverage features and the monitoring of energy fluxes through the soil-plant-atmosphere system, allow to estimate conventional irrigation components (ET, Kc thus improving irrigation strategies. In the study, satellite potential evapotranspiration (ETp and crop coefficient (Kc maps of orange orchards are derived using semi-empirical approaches between reflectance data from IKONOS imagery and ground measurements of vegetation features. The monitoring of energy fluxes through the orchard allows to estimate actual crop evapotranspiration (ETa using energy balance and the Surface Renewal theory. The approach indicates substantial promise as an efficient, accurate and relatively inexpensive procedure to predict actual ET fluxes and Kc from irrigated lands.

  17. Benchmarking NLDAS-2 Soil Moisture and Evapotranspiration to Separate Uncertainty Contributions

    Science.gov (United States)

    Nearing, Grey S.; Mocko, David M.; Peters-Lidard, Christa D.; Kumar, Sujay V.; Xia, Youlong

    2016-01-01

    Model benchmarking allows us to separate uncertainty in model predictions caused 1 by model inputs from uncertainty due to model structural error. We extend this method with a large-sample approach (using data from multiple field sites) to measure prediction uncertainty caused by errors in (i) forcing data, (ii) model parameters, and (iii) model structure, and use it to compare the efficiency of soil moisture state and evapotranspiration flux predictions made by the four land surface models in the North American Land Data Assimilation System Phase 2 (NLDAS-2). Parameters dominated uncertainty in soil moisture estimates and forcing data dominated uncertainty in evapotranspiration estimates; however, the models themselves used only a fraction of the information available to them. This means that there is significant potential to improve all three components of the NLDAS-2 system. In particular, continued work toward refining the parameter maps and look-up tables, the forcing data measurement and processing, and also the land surface models themselves, has potential to result in improved estimates of surface mass and energy balances.

  18. Sensitivity of MODIS evapotranspiration algorithm (MOD16) to the acuracy of meteorological data and land use and land cover parameterization

    Science.gov (United States)

    Ruhoff, Anderson; Santini Adamatti, Daniela

    2017-04-01

    MODIS evapotranspiration (MOD16) is currently available with 1 km of spatial resolution over 109.03 Million km2 of vegetated land surface areas and this information is widely used to evaluate the linkages between hydrological, energy and carbon cycles. The algorithm is driven by meteorological reanalysis data and MODIS remotely-sensed data, which include land use and land cover classification (MCD12Q1), leaf area index (LAI) and fraction of absorbed photosynthetically active radiation (FPAR) (MOD15A2) and albedo (MOD43b3). For calibration and parameterization, the algorithm uses a Biome Property Look-up Table (BPLUT) based on MCD12Q1 land cover classification. Several studies evaluated MOD16 accuracy using evapotranspiration measurements and water balance analysis, showing that this product can reproduce global evapotranspiration effectively under a variety climate condition, from local to wide-basin scale, with uncertainties up to 25%. In this study, we evaluated the sensitivity of MOD16 algorithm to land use and land cover parameterization and to meteorological data. Considering that MCD12Q1 has an accuracy between 70 and 85% at continental scale, we changed land cover parametererization to understand the influence of land use and land cover classification on MOD16 evapotranspiration estimations. Knowing that meteorological reanalysis data also have uncertainties (mostly related to the coarse spatial resolution), we compared MOD16 evapotranspiration driven by observed meteorological data to those driven by the reanalysis data. Our analysis were carried in South America, with evapotranspiration and meteorological measurements from the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) at 8 different sites, including tropical rainforest, tropical dry forest, selective logged forest, seasonal flooded forest and pasture/agriculture. Our results indicate that land use and land cover classification has a strong influence on MOD16 algorithm. The use of

  19. Accuracy of the Temperature-Vegetation Dryness Index using MODIS under water-limited vs. energy-limited evapotranspiration conditions

    DEFF Research Database (Denmark)

    Garcia, Monica; Fernández, N.; Villagarcía, L.

    2014-01-01

    Water deficit indices based on the spatial relationship between surface temperature (Ts) and NDVI, known as triangle approaches, are widely used for drought monitoring. However, their application has been recently questioned when the main factor limiting evapotranspiration is energy. Even though...... water is the main control in dryland ecosystems, these can also undergo periods of energy and temperature limitation. In this paper we aimed to: (i) evaluate the TVDI (Temperature-Vegetation Dryness Index) to estimate water deficits (e.g. ratio between actual and potential evapotranspiration), and heat...

  20. Assessing the suitability of American National Aeronautics and Space Administration (NASA) agro-climatology archive to predict daily meteorological variables and reference evapotranspiration in Sicily, Italy

    Science.gov (United States)

    For decades, the importance of evapotranspiration processes has been recognized in many disciplines, including hydrologic and drainage studies, irrigation systems design and management. A wide number of equations have been proposed to estimate crop reference evapotranspiration, ET0, based on the var...

  1. Plants Growth Rate in Evapotranspiration continuous system reactors as the 2nd Treatment at Anaerobic-evapotranspiration system with High Strength Ammonium in Leachate Influent

    Directory of Open Access Journals (Sweden)

    Badrus Zaman

    2014-05-01

    Full Text Available Ammonium is one of parameter which responsible to leachate toxicity. Preliminary research was shown that the Fimbristylis globulosa (water plant, Alocasia macrorrhiza (terrestrial plant and Eleusine indica (terrestrial grass were potential plants for used as object in evaporation reactor system with high strength ammonium  concentration in leachate treatment. This research was integrated of anaerobic system with evapotranspiration system with continuous influent using ammonium concentration in leachate was 2000 mg/l NH4-N. Plants growth rate was analyzed for 25 days operated. The result shown that average of thallus growth rate of Fimbristylis globulosa was 17,5 cm d-1. The average of leaf and thallus growth rate of Alocasia macrorrhiza was 18,1 cm d-1 and 3,2 cm d-1 respectively. The average of blade and thallus of Eleusine indica were same that was 4,7 cm d-1.This research conclude that integration system of anaerobic and evpotranspiration was be potential used for high strength ammonium in leachate treatment.

  2. Assessing the performance of two models on calculating maize actual evapotranspiration in a semi-humid and drought-prone region of China

    Science.gov (United States)

    Wang, J.; Wang, J. L.; Zhao, C. X.; McGiffen, M. E.; Liu, J. B.; Wang, G. D.

    2017-01-01

    The two-step and one-step models for calculating evapotranspiration of maize were evaluated in a semi-humid and drought-prone region of northern China. Data were collected in the summers of 2013 and 2014 to determine relative model accuracy in calculating maize evaopotranspiration. The two-step model predicted daily evaoptranspiration with crop coefficients proposed by FAO and crop coefficient calibrated by local field data; the one-step model predicted daily evapotranspiration with coefficients derived by other researcher and coefficients calibrated by local field data. The predicted daily evapotranspiration in 2013 and 2014 growing seasons with the above two different models was both compared with the observed evapotranspiration with eddy covariance method. Furthermore, evapotranspiration in different growth stages of 2013 and 2014 maize growing seasons was predicted using the models with the local calibrated coefficients. The results indicated that calibration of models was necessary before using them to predict daily evapotranspiration. The model with the calibrated coefficients performed better with higher coefficient of determination and index of agreement and lower mean absolute error and root mean square error than before. And the two-step model better predicted daily evapotranspiration than the one-step model in our experimental field. Nevertheless, as to prediction ET of different growth stages, there still had some uncertainty when predicting evapotranspiration in different year. So the comparisons suggested that model prediction of crop evapotranspiration was practical, but requires calibration and validation with more data. Thus, considerable improvement is needed for these two models to be practical in predicting evapotranspiration for maize and other crops, more field data need to be measured, and an in-depth study still needs to be continued.

  3. Evaluating the role of evapotranspiration remote sensing data in improving hydrological modeling predictability

    Science.gov (United States)

    Herman, Matthew R.; Nejadhashemi, A. Pouyan; Abouali, Mohammad; Hernandez-Suarez, Juan Sebastian; Daneshvar, Fariborz; Zhang, Zhen; Anderson, Martha C.; Sadeghi, Ali M.; Hain, Christopher R.; Sharifi, Amirreza

    2018-01-01

    As the global demands for the use of freshwater resources continues to rise, it has become increasingly important to insure the sustainability of this resources. This is accomplished through the use of management strategies that often utilize monitoring and the use of hydrological models. However, monitoring at large scales is not feasible and therefore model applications are becoming challenging, especially when spatially distributed datasets, such as evapotranspiration, are needed to understand the model performances. Due to these limitations, most of the hydrological models are only calibrated for data obtained from site/point observations, such as streamflow. Therefore, the main focus of this paper is to examine whether the incorporation of remotely sensed and spatially distributed datasets can improve the overall performance of the model. In this study, actual evapotranspiration (ETa) data was obtained from the two different sets of satellite based remote sensing data. One dataset estimates ETa based on the Simplified Surface Energy Balance (SSEBop) model while the other one estimates ETa based on the Atmosphere-Land Exchange Inverse (ALEXI) model. The hydrological model used in this study is the Soil and Water Assessment Tool (SWAT), which was calibrated against spatially distributed ETa and single point streamflow records for the Honeyoey Creek-Pine Creek Watershed, located in Michigan, USA. Two different techniques, multi-variable and genetic algorithm, were used to calibrate the SWAT model. Using the aforementioned datasets, the performance of the hydrological model in estimating ETa was improved using both calibration techniques by achieving Nash-Sutcliffe efficiency (NSE) values >0.5 (0.73-0.85), percent bias (PBIAS) values within ±25% (±21.73%), and root mean squared error - observations standard deviation ratio (RSR) values model performance for estimating the streamflow (NSE: 0.32-0.52, PBIAS: ±32.73%, and RSR: 0.63-0.82). Meanwhile, using the

  4. Evapotranspiration and water use efficiency in maize-soybean crops in the US Midwest

    Science.gov (United States)

    Hussain, M. Z.; Hamilton, S. K.; Bhardwaj, A. K.; Basso, B.; Thelen, K.; Robertson, P.

    2015-12-01

    Evapotranspiration from maize and soybean crops is an important component of terrestrial water balance in the US Midwest. In this study we examine water use in continuous maize (corn) vs. maize-soybean rotations, with cover crops planted in some years. From 2010-14, we continuously measured growing season evapotranspiration (ET) based on daily drawdown of soil moisture content using TDR (time-domain reflectometry) probes installed throughout the root zone. Treatments included continuous maize (CM), continuous maize with cover crops (CMC) and maize-soybean rotation with cover crops (MSC), all grown without irrigation in a temperate humid climate (Michigan, USA). Cover crops were planted in the autumn after harvest of the main crop and harvested in spring prior to planting of the next main crop during 2012-2013 (2013) and 2013-2014 (2014). Four study years (2010, 2011, 2013 and 2014) had normal growing season rainfall (568, 555, 445, and 472 mm) while 2012 was an extreme drought season with a growing-season rainfall deficit of ~50% (210 mm below average). Growing season ET in CM, CMC and MSC during years of normal rainfall averaged 517, 433, and 443 mm, respectively, compared to 455, 374 and 304 mm in the 2012 drought year. Cover crop ET was inconsequential to the subsequent main crops due to abundant rainfall in the spring periods; soils held as much water as they could at the transition from cover crops to main crops. Grain yield in years of normal rainfall for CM, CMC and MSC averaged 12.6, 8.4 and 7.8 Mg ha-1, respectively, compared to 4.9, 4.0, and 4.0 Mg ha-1 in the 2012 drought year. Maximum biomass in years of normal rainfall averaged 38, 30 and 21 Mg ha-1 compared to 19, 13, and 13 Mg ha-1 in the drought year. Water use efficiencies, defined as ratio of maximum standing-stock biomass to growing season evapotranspiration, were 74, 69, and 47 kg ha-1 mm-1 for CM, CMC and MSC in years of normal rainfall, while values in the drought year were 41, 34 and 46 kg ha

  5. Determining suitability of Large Aperture Scintillometer for validating remote sensing based evapotranspiration maps

    Science.gov (United States)

    Paul, G.; Gowda, P. H.; Howell, T. A.; Basu, S.; Colaizzi, P. D.; Marek, T.

    2013-12-01

    Scintillation method is a relatively new technique for measuring the sensible heat and water fluxes over land surfaces. Path integrating capabilities of scintillometer over heterogeneous landscapes make it a potential tool for comparing the energy fluxes derived from remote sensing based energy balance algorithms. For this reason, scintillometer-derived evapotranspiration (ET) fluxes are being used to evaluate remote sensing based energy balance algorithms for their ability to estimate ET fluxes. However, LAS' (Large Aperture Scintillometer) ability to derive ET fluxes is not thoroughly tested. The objective of this study was to evaluate LAS- and Surface Energy Balance System (SEBS)-derived fluxes against lysimetric data to determine LAS' suitability for validating remote sensing based evapotranspiration (ET) maps. The study was conducted during the Bushland Evapotranspiration and Agricultural Remote sensing EXperiment - 2008 (BEAREX-08) at the USDA-ARS Conservation and Production Research Laboratory (CPRL), Bushland, Texas. SEBS was coded in a GIS environment to retrieve ET fluxes from the high resolution imageries acquired using airborne multispectral sensors. The CPRL has four large weighing lysimeters (3 m long x 3 m wide x 2.4 m deep), each located in the middle of approximately 5 ha fields, arranged in a block pattern. The two lysimeter fields located on the east (NE and SE) were managed under irrigated conditions, and the other two lysimeters on the west (NW and SW) were under dryland management. Each lysimeter field was equipped with an automated weather station that provided measurements for net radiation (Rn), Ts, soil heat flux (Go), Ta, relative humidity, and wind speed. During BEAREX08, the NE and SE fields were planted to cotton on May 21, and the NW and SW dryland lysimeters fields were planted to cotton on June 5. One LAS each was deployed across two large dryland lysimeter fields (NW and SW) and two large irrigated lysimeter fields (NE and SE). The

  6. Daily Landsat-scale evapotranspiration estimation over a forested landscape in North Carolina, USA, using multi-satellite data fusion

    Science.gov (United States)

    Yun Yang; Martha C. Anderson; Feng Gao; Christopher R. Hain; Kathryn A. Semmens; William P. Kustas; Asko Noormets; Randolph H. Wynne; Valerie A. Thomas; Ge Sun

    2017-01-01

    As a primary flux in the global water cycle, evapotranspiration (ET) connects hydrologic and biological processes and is directly affected by water and land management, land use change and climate variability. Satellite remote sensing provides an effective means for diagnosing ET patterns over heterogeneous landscapes; however, limitations on the spatial and temporal...

  7. Estimating daily Landsat-scale evapotranspiration over a managed pine plantation in North Carolina, USA using a data fusion method

    Science.gov (United States)

    As a primary flux in the global water cycle, evapotranspiration (ET) connects hydrologic and biological processes and is directly affected by water management, land use change and climate change. The two source energy balance (TSEB) model has been widely applied to quantify field scale ET using sate...

  8. Monthly land cover-specific evapotranspiration models derived from global eddy flux measurements and remote sensing data

    Science.gov (United States)

    Yuan Fang; Ge Sun; Peter Caldwell; Steven G. McNulty; Asko Noormets; Jean-Christophe Domec; John King; Zhiqiang Zhang; Xudong Zhang; Guanghui Lin; Guangsheng Zhou; Jingfeng Xiao; Jiquan Chen

    2015-01-01

    Evapotranspiration (ET) is arguably the most uncertain ecohydrologic variable for quantifying watershed water budgets. Although numerous ET and hydrological models exist, accurately predicting the effects of global change on water use and availability remains challenging because of model deficiency and/or a lack of input parameters. The objective of this study was to...

  9. Effects of invasive insects and fire on energy exchange and evapotranspiration in the New Jersey pine lands

    Science.gov (United States)

    Kenneth L. Clark; Nicholas Skowronski; Michael Gallagher; Hedi Renninger; Karina. Schafer

    2012-01-01

    We used eddy covariance and meteorological measurements to quantify energy exchange and evapotranspiration (Et) in three representative upland forest stands in the New Jersey Pinelands that were either defoliated by gypsy moth (Lymantria dispar L.) or burned in prescribed fires during the study period. Latent (λE) and sensible heat (H)...

  10. Response of evapotranspiration to changes in land use and land cover and climate in China during 2001–2013

    Science.gov (United States)

    Gen Li; Fangmin Zhang; Yuanshu Jing; Yibo Liu; Ge Sun

    2017-01-01

    Land surface evapotranspiration (ET) is a central component of the Earth's global energy balance and water cycle. Understanding ET is important in quantifying the impacts of human influences on the hydrological cycle and thus helps improving water use efficiency and strengthening water use planning and watershed management. China has experienced tremendous land...

  11. Thermal and visible remote sensing for estimation of evapotranspiration of rainfed agrosystems and its impact on groundwater in SE Australia

    Science.gov (United States)

    Roohi, Rakhshan; Webb, John A.

    2016-05-01

    Rainfed agrosystems are important components of the world's food production system and account for 65-95% of total agriculture. In contrast to irrigated production systems, relatively little attention has been paid to understanding the hydrological interactions between the components of rainfed agrosystems and their impact on water resources, especially groundwater. A new model, the Surface Energy Balance Algorithm for Rainfed Agriculture (SEBARA), has been developed to estimate the spatial pattern of evapotranspiration in these agrosystems using satellite images (thermal, infrared and visible spectra). The model was calibrated for two competing land uses (Eucalyptus globules tree plantations and pastures) in adjacent catchments in western Victoria, southeastern Australia. Using measurements from a flux tower in the pasture catchment and adjusted sapflow measurements in the plantation catchment, an estimation accuracy of 95% was achieved. The tree plantations had higher available net radiation, lower soil heat flux and higher latent heat flux, resulting in 15-20% higher evapotranspirative demand than the pasture, depending upon the age and canopy of plantations. The evapotranspiration rate of plantations declines where groundwater depth is >12m or where shallow groundwater is saline. The shallow root system of the pasture means that it relies solely on soil moisture to meet its water requirements and thus has lower evapotranspiration, which varies according to the pasture species.

  12. Trend analysis and forecast of precipitation, reference evapotranspiration and rainfall deficit in the Blackland Prairie of eastern Mississippi

    Science.gov (United States)

    Trend analysis and estimation of monthly and annual precipitation, reference evapotranspiration (ETo) and rainfall deficit are essential for water resources management and cropping system design. Rainfall, ETo, and water deficit patterns and trends in eastern Mississippi USA for a 120-year period (1...

  13. Stimulation of methane oxidation potential and effects on vegetation growth by bottom ash addition in a landfill final evapotranspiration cover

    NARCIS (Netherlands)

    Kim, G.W.; Ho, A.; Kim, P.J.; Kim, Sang Yun

    2016-01-01

    The landfilling of municipal solid waste is a significant source of atmospheric methane (CH4), contributing up to 20% of total anthropogenic CH4 emissions. The evapotranspiration (ET) cover system, an alternative final cover system in waste landfills, has been considered to be a promising way to

  14. Evapotranspiration and land surface process responses to afforestation in western Taiwan: A comparison between dry and wet weather conditions

    Science.gov (United States)

    Yongqiang Liu; L.B. Zhang; L. Hao; Ge Sun; S.-C. Liu

    2016-01-01

    An afforestation project was initiated in the western plain of Taiwan to convert abandoned farming lands into forests to improve the ecological and environmental conditions. This study was conducted to understand the potential impacts of this land cover change on evapotranspiration (ET) and other land surface processes and the...

  15. Assessing actual evapotranspiration via surface energy balance aiming to optimize water and energy consumption in large scale pressurized irrigation systems

    Science.gov (United States)

    Awada, H.; Ciraolo, G.; Maltese, A.; Moreno Hidalgo, M. A.; Provenzano, G.; Còrcoles, J. I.

    2017-10-01

    Satellite imagery provides a dependable basis for computational models that aimed to determine actual evapotranspiration (ET) by surface energy balance. Satellite-based models enables quantifying ET over large areas for a wide range of applications, such as monitoring water distribution, managing irrigation and assessing irrigation systems' performance. With the aim to evaluate the energy and water consumption of a large scale on-turn pressurized irrigation system in the district of Aguas Nuevas, Albacete, Spain, the satellite-based image-processing model SEBAL was used for calculating actual ET. The model has been applied to quantify instantaneous, daily, and seasonal actual ET over high- resolution Landsat images for the peak water demand season (May to September) and for the years 2006 - 2008. The model provided a direct estimation of the distribution of main energy fluxes, at the instant when the satellite overpassed over each field of the district. The image acquisition day Evapotranspiration (ET24) was obtained from instantaneous values by assuming a constant evaporative fraction (Λ) for the entire day of acquisition; then, monthly and seasonal ET were estimated from the daily evapotranspiration (ETdaily) assuming that ET24 varies in proportion to reference ET (ETr) at the meteorological station, thus accounting for day to day variation in meteorological forcing. The comparison between the hydrants water consumption and the actual evapotranspiration, considering an irrigation efficiency of 85%, showed that a considerable amount of water and energy can be saved at district level.

  16. The Artificial Neural Network Estimation for Daily and Hourly Rice Evapotranspiration in the Region of Red Soil, South China

    Science.gov (United States)

    Jing, Yuanshu; Ruthaikarn, Buaphean; Jin, Xinyi; Pang, Bo

    The evapotranspiration estimation is a key item for irrigation program. It has the important practical significance for high stable yield and water-saving in the region of red soil, South China. Penman-Monteith equation, recommended by FAO, is verified to be the most effective calculation to actual evaporation in many regions of the world. The only default is it has to use complete meteorological factors. To solve this problem, we are trying to find out a artificial neural network model (ANN) which can easily get its information and easy to calculate as well as guaranteed accuracy. A Bowen ratio energy balance (BREB) system and automatic weather station were employed for simultaneous measurement of actual evapotranspiration above the rice field. The frequency of 20-min recording provided the possibility for the estimation of daily and hourly evapotranspiration. The determined coefficient from the artificial neural network model on daily scale R2 is 0.9642, while hourly scale R2 is 0.9880. The reason was that the hourly scale training samples was greater than the daily scale measures. In general, the model gives an effective and feasible way for the evaluation of paddy rice evapotranspiration by the conventional parameters.

  17. Spatially distributed evapotranspiration estimation using remote sensing and ground-based radiometers over cotton at Maricopa, Arizona

    Science.gov (United States)

    Spatially distributed estimates of evapotranspiration (ET) over agricultural lands could be valuable for water management in arid environments and for monitoring irrigated croplands. In recent year various ET estimation approaches have been developed that utilize remote sense data to provide the nee...

  18. Calibration of a large-scale hydrological model using satellite-based soil moisture and evapotranspiration products

    Science.gov (United States)

    López López, Patricia; Sutanudjaja, Edwin H.; Schellekens, Jaap; Sterk, Geert; Bierkens, Marc F. P.

    2017-06-01

    A considerable number of river basins around the world lack sufficient ground observations of hydro-meteorological data for effective water resources assessment and management. Several approaches can be developed to increase the quality and availability of data in these poorly gauged or ungauged river basins; among them, the use of Earth observations products has recently become promising. Earth observations of various environmental variables can be used potentially to increase knowledge about the hydrological processes in the basin and to improve streamflow model estimates, via assimilation or calibration. The present study aims to calibrate the large-scale hydrological model PCRaster GLOBal Water Balance (PCR-GLOBWB) using satellite-based products of evapotranspiration and soil moisture for the Moroccan Oum er Rbia River basin. Daily simulations at a spatial resolution of 5 × 5 arcmin are performed with varying parameters values for the 32-year period 1979-2010. Five different calibration scenarios are inter-compared: (i) reference scenario using the hydrological model with the standard parameterization, (ii) calibration using in situ-observed discharge time series, (iii) calibration using the Global Land Evaporation Amsterdam Model (GLEAM) actual evapotranspiration time series, (iv) calibration using ESA Climate Change Initiative (CCI) surface soil moisture time series and (v) step-wise calibration using GLEAM actual evapotranspiration and ESA CCI surface soil moisture time series. The impact on discharge estimates of precipitation in comparison with model parameters calibration is investigated using three global precipitation products, including ERA-Interim (EI), WATCH Forcing methodology applied to ERA-Interim reanalysis data (WFDEI) and Multi-Source Weighted-Ensemble Precipitation data by merging gauge, satellite and reanalysis data (MSWEP). Results show that GLEAM evapotranspiration and ESA CCI soil moisture may be used for model calibration resulting in

  19. Comparing Landsat-7 ETM+ and ASTER Imageries to Estimate Daily Evapotranspiration Within a Mediterranean Vineyard Watershed

    Science.gov (United States)

    Montes, Carlo; Jacob, Frederic

    2017-01-01

    We compared the capabilities of Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imageries for mapping daily evapotranspiration (ET) within a Mediterranean vineyard watershed. We used Landsat and ASTER data simultaneously collected on four dates in 2007 and 2008, along with the simplified surface energy balance index (S-SEBI) model. We used previously ground-validated good quality ASTER estimates as reference, and we analyzed the differences with Landsat retrievals in light of the instrumental factors and methodology. Although Landsat and ASTER retrievals of S-SEBI inputs were different, estimates of daily ET from the two imageries were similar. This is ascribed to the S-SEBI spatial differencing in temperature, and opens the path for using historical Landsat time series over vineyards.

  20. Vegetation Greening and Climate Change Promote Multidecadal Rises of Global Land Evapotranspiration.

    Science.gov (United States)

    Zhang, Ke; Kimball, John S; Nemani, Ramakrishna R; Running, Steven W; Hong, Yang; Gourley, Jonathan J; Yu, Zhongbo

    2015-10-30

    Recent studies showed that anomalous dry conditions and limited moisture supply roughly between 1998 and 2008, especially in the Southern Hemisphere, led to reduced vegetation productivity and ceased growth in land evapotranspiration (ET). However, natural variability of Earth's climate system can degrade capabilities for identifying climate trends. Here we produced a long-term (1982-2013) remote sensing based land ET record and investigated multidecadal changes in global ET and underlying causes. The ET record shows a significant upward global trend of 0.88 mm yr(-2) (P Continuation of these trends will likely exacerbate regional drought-induced disturbances, especially during regional dry climate phases associated with strong El Niño events.

  1. [Spatiotemporal characteristics of reference crop evapotranspiration in inland river basins of Hexi region].

    Science.gov (United States)

    Lü, Xiao-Dong; Wang, He-ling; Ma, Zhong-ming

    2010-12-01

    Based on the 1961-2008 daily observation data from 17 meteorological stations in the inland river basins in Hexi region, the daily reference crop evapotranspiration (ET0) in the basins was computed by Penman-Monteith equation, and the spatiotemporal characteristics of seasonal and annual ET0 were studied by GIS and IDW inverse-distance spatial interpolation. In 1961-2008, the mean annual ET0 (700-1330 mm) increased gradually from southeast to northwest across the basins. The high value of mean annual ET0 in Shule River basin and Heihe River basin declined significantly (P spring > autumn > winter. Wind speed and maximum temperature were the primary factors affecting the ET0 in the basins. Furthermore, wind speed was the predominant factor of downward trend of ET0 in Shule and Heihe basins, while maximum temperature and sunshine hours played an important role in the upward trend of ET0 in Shiyang basin.

  2. Direct measurement of evapotranspiration from a forest using a superconducting gravimeter

    Science.gov (United States)

    Van Camp, Michel; Viron, Olivier; Pajot-Métivier, Gwendoline; Casenave, Fabien; Watlet, Arnaud; Dassargues, Alain; Vanclooster, Marnik

    2016-10-01

    Evapotranspiration (ET) controls the flux between the land surface and the atmosphere. Assessing the ET ecosystems remains a key challenge in hydrology. We have found that the ET water mass loss can be directly inferred from continuous gravity measurements: as water evaporates and transpires from terrestrial ecosystems, the mass distribution of water decreases, changing the gravity field. Using continuous superconducting gravity measurements, we were able to identify daily gravity changes at the level of, or smaller than, 10-9 nm s-2 (or 10-10 g) per day. This corresponds to 1.7 mm of water over an area of 50 ha. The strength of this method is its ability to enable a direct, traceable and continuous monitoring of actual ET for years at the mesoscale with a high accuracy.

  3. Global Ecosystem Response Types Derived from the Standardized Precipitation Evapotranspiration Index and FPAR3g Series

    DEFF Research Database (Denmark)

    Ivits, Eva; Horion, Stéphanie Marie Anne F; Fensholt, Rasmus

    2014-01-01

    -temporal patterns in time-series of Standardized Precipitation Evapotranspiration Index (SPEI) and FPAR3g anomalies (1982–2011) by using an extended Principal Component Analysis. The ERTs represent region specific spatio-temporal patterns of ecosystems responding to drought or ecosystems with decreasing severity...... in drought events as well as ecosystems where drought was not a dominant factor in a 30-year period. Highest explanatory values in the SPEI12-FPAR3g anomalies and strongest SPEI12-FPAR3g correlations were seen in the ERTs of Australia and South America whereas lowest explanatory value and lowest correlations......Observing trends in global ecosystem dynamics is an important first step, but attributing these trends to climate variability represents a further step in understanding Earth system changes. In the present study, we classified global Ecosystem Response Types (ERTs) based on common spatio...

  4. Monitoring the variations of evapotranspiration due to land use/cover change in a semiarid shrubland

    Science.gov (United States)

    Gong, Tingting; Lei, Huimin; Yang, Dawen; Jiao, Yang; Yang, Hanbo

    2017-02-01

    Evapotranspiration (ET) is an important process in the hydrological cycle, and vegetation change is a primary factor that affects ET. In this study, we analyzed the annual and inter-annual characteristics of ET using continuous observation data from eddy covariance (EC) measurement over 4 years (1 July 2011 to 30 June 2015) in a semiarid shrubland of Mu Us Sandy Land, China. The Normalized Difference Vegetation Index (NDVI) was demonstrated as the predominant factor that influences the seasonal variations in ET. Additionally, during the land degradation and vegetation rehabilitation processes, ET and normalized ET both increased due to the integrated effects of the changes in vegetation type, topography, and soil surface characteristics. This study could improve our understanding of the effects of land use/cover change on ET in the fragile ecosystem of semiarid regions and provide a scientific reference for the sustainable management of regional land and water resources.

  5. Effects of Spatial Heterogeneity in Rainfall and Vegetation Type on Soil Moisture and Evapotranspiration

    CERN Document Server

    Puma, Michael J; Rodriguez-Iturbe, Ignacio; Nordbotten, Jan M; Guswa, Andrew J; Kavetski, Dmitri

    2016-01-01

    Nonlinear plant-scale interactions controlling the soil-water balance are generally not valid at larger spatial scales due to spatial heterogeneity in rainfall and vegetation type. The relationships between spatially averaged variables are hysteretic even when unique relationships are imposed at the plant scale. The characteristics of these hysteretic relationships depend on the size of the averaging area and the spatial properties of the soil, vegetation, and rainfall. We upscale the plant-scale relationships to the scale of a regional land-surface model based on simulation data obtained through explicit representation of spatial heterogeneity in rainfall and vegetation type. The proposed upscaled function improves predictions of spatially averaged soil moisture and evapotranspiration relative to the effective-parameter approach for a water-limited Texas shrubland. The degree of improvement is a function of the scales of heterogeneity and the size of the averaging area. We also find that single-valued functi...

  6. Modeling landscape evapotranspiration by integrating land surface phenology and a water balance algorithm

    Science.gov (United States)

    Senay, Gabriel B.

    2008-01-01

    The main objective of this study is to present an improved modeling technique called Vegetation ET (VegET) that integrates commonly used water balance algorithms with remotely sensed Land Surface Phenology (LSP) parameter to conduct operational vegetation water balance modeling of rainfed systems at the LSP’s spatial scale using readily available global data sets. Evaluation of the VegET model was conducted using Flux Tower data and two-year simulation for the conterminous US. The VegET model is capable of estimating actual evapotranspiration (ETa) of rainfed crops and other vegetation types at the spatial resolution of the LSP on a daily basis, replacing the need to estimate crop- and region-specific crop coefficients.

  7. Use of Willows in Evapotranspirative Systems for Onsite Wastewater Management – Theory and Experiences from Denmark

    DEFF Research Database (Denmark)

    Brix, Hans; Arias, Carlos Alberto

    2011-01-01

    of the nutrients can be recycled via the plant biomass, and the harvested biomass can serve as a source of bio-energy. In Denmark more than 500 ET systems planted with willows are in operation. The systems generally consist of a 1.5 m deep high-density polyethylene-lined basin filled with soil and planted...... dimensioning parameter. Settled sewage is dispersed underground into the bed under pressure. The stems of the willows are harvested on a regular basis to stimulate the growth of the willows and to remove some nutrients and heavy metals. In this paper, the theory behind the operation of willow based ET systems......Evapotranspiration (ET) is a method of onsite wastewater treatment and disposal that is an alternative to conventional soil absorption systems, particularly for sites where protecting surface water and ground water is essential or where soil infiltration is not possible. One of the most important...

  8. Use of willows in evapotranspirative systems for onsite wastewater management – theory and experiences from Denmark

    DEFF Research Database (Denmark)

    Brix, Hans; Arias, Carlos Alberto

    2011-01-01

    of the nutrients can be recycled via the plant biomass, and the harvested biomass can serve as a source of bio-energy. In Denmark more than 500 ET systems planted with willows are in operation. The systems generally consist of a 1.5 m deep high-density polyethylene-lined basin filled with soil and planted...... dimensioning parameter. Settled sewage is dispersed underground into the bed under pressure. The stems of the willows are harvested on a regular basis to stimulate the growth of the willows and to remove some nutrients and heavy metals. In this paper, the theory behind the operation of willow based ET systems......Evapotranspiration (ET) is a method of onsite wastewater treatment and disposal that is an alternative to conventional soil absorption systems, particularly for sites where protecting surface water and ground water is essential or where soil infiltration is not possible. One of the most important...

  9. Development OF A Multi-Scale Framework for Mapping Global Evapotranspiration

    Science.gov (United States)

    Hain, Christopher R.; Anderson, Martha C.; Schull, Mitchell; Neale, Christopher; Zhan, Xiwu

    2017-01-01

    As the worlds water resources come under increasing tension due to dual stressors of climate change and population growth, accurate knowledge of water consumption through evapotranspiration (ET) over a range in spatial scales will be critical in developing adaptation strategies. Remote sensing methods for monitoring consumptive water use (e.g, ET) are becoming increasingly important, especially in areas of significant water and food insecurity. One method to estimate ET from satellite-based methods, the Atmosphere Land Exchange Inverse (ALEXI) model uses the change in mid-morning land surface temperature to estimate the partitioning of sensible and latent heat fluxes which are then used to estimate daily ET. This presentation will outline several recent enhancements to the ALEXI modeling system, with a focus on global ET and drought monitoring.

  10. Use of Satellite-based Remote Sensing to inform Evapotranspiration parameters in Cropping System Models

    Science.gov (United States)

    Dhungel, S.; Barber, M. E.

    2016-12-01

    The objectives of this paper are to use an automated satellite-based remote sensing evapotranspiration (ET) model to assist in parameterization of a cropping system model (CropSyst) and to examine the variability of consumptive water use of various crops across the watershed. The remote sensing model is a modified version of the Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC™) energy balance model. We present the application of an automated python-based implementation of METRIC to estimate ET as consumptive water use for agricultural areas in three watersheds in Eastern Washington - Walla Walla, Lower Yakima and Okanogan. We used these ET maps with USDA crop data to identify the variability of crop growth and water use for the major crops in these three watersheds. Some crops, such as grapes and alfalfa, showed high variability in water use in the watershed while others, such as corn, had comparatively less variability. The results helped us to estimate the range and variability of various crop parameters that are used in CropSyst. The paper also presents a systematic approach to estimate parameters of CropSyst for a crop in a watershed using METRIC results. Our initial application of this approach was used to estimate irrigation application rate for CropSyst for a selected farm in Walla Walla and was validated by comparing crop growth (as Leaf Area Index - LAI) and consumptive water use (ET) from METRIC and CropSyst. This coupling of METRIC with CropSyst will allow for more robust parameters in CropSyst and will enable accurate predictions of changes in irrigation practices and crop rotation, which are a challenge in many cropping system models.

  11. Measured Evapotranspiration from Different Urban Green Spaces in New York City

    Science.gov (United States)

    DiGiovanni, K. A.; Montalto, F. A.

    2013-12-01

    For decades, researchers have recognized a need to better characterize evapotranspiration (ET) from heterogeneous landscapes, and especially urban spaces. At the microscale, ET can be directly measured using weighing lysimeters and also quantified using soil moisture depletion approaches. In the studies presented, ET rates was directly measured from four different urban green spaces using weighing lysimeters for periods ranging from one to three years. ET was also estimated using soil moisture depletion techniques for two additional sites for periods of one and two years respectively. The experimental sites are all in New York City and include a green roof, three bioretention areas with curb cuts allowing street runoff in, a bioretention area surrounded by a contiguous curb, and a section of old growth forest.. The ET measurements are statistically compared using non-parametric tests. The results, also visually presented using box and whisker plots, show statistically significant differences in data sets of ET rates between and within different green spaces, with differences due mostly to soil moisture availability. Soil moisture limits ET from the green roof during the summer, while ET from the bioretention area receiving street runoff exceeds that measured at the hydraulically isolated one. ET at topographic low points of bioretention areas are also estimated to be significantly greater than at topographic high points. However, shading in the urban forest site seems to be more important than moisture availability in curtailing ET. These findings are discussed in the context of goal setting and design decisions associated with urban green infrastructure programs. Box and whisker plot over seasonal periods of daily evapotranspiration rates measured by weighing lysimeter collected over two year period at bioretention areas with contiguous curb

  12. Integrating satellite actual evapotranspiration patterns into distributed model parametrization and evaluation for a mesoscale catchment

    Science.gov (United States)

    Demirel, M. C.; Mai, J.; Stisen, S.; Mendiguren González, G.; Koch, J.; Samaniego, L. E.

    2016-12-01

    Distributed hydrologic models are traditionally calibrated and evaluated against observations of streamflow. Spatially distributed remote sensing observations offer a great opportunity to enhance spatial model calibration schemes. For that it is important to identify the model parameters that can change spatial patterns before the satellite based hydrologic model calibration. Our study is based on two main pillars: first we use spatial sensitivity analysis to identify the key parameters controlling the spatial distribution of actual evapotranspiration (AET). Second, we investigate the potential benefits of incorporating spatial patterns from MODIS data to calibrate the mesoscale Hydrologic Model (mHM). This distributed model is selected as it allows for a change in the spatial distribution of key soil parameters through the calibration of pedo-transfer function parameters and includes options for using fully distributed daily Leaf Area Index (LAI) directly as input. In addition the simulated AET can be estimated at the spatial resolution suitable for comparison to the spatial patterns observed using MODIS data. We introduce a new dynamic scaling function employing remotely sensed vegetation to downscale coarse reference evapotranspiration. In total, 17 parameters of 47 mHM parameters are identified using both sequential screening and Latin hypercube one-at-a-time sampling methods. The spatial patterns are found to be sensitive to the vegetation parameters whereas streamflow dynamics are sensitive to the PTF parameters. The results of multi-objective model calibration show that calibration of mHM against observed streamflow does not reduce the spatial errors in AET while they improve only the streamflow simulations. We will further examine the results of model calibration using only multi spatial objective functions measuring the association between observed AET and simulated AET maps and another case including spatial and streamflow metrics together.

  13. Sensitivity of potential evapotranspiration to changes in climate variables for different Australian climatic zones

    Science.gov (United States)

    Guo, Danlu; Westra, Seth; Maier, Holger R.

    2017-04-01

    Assessing the factors that have an impact on potential evapotranspiration (PET) sensitivity to changes in different climate variables is critical to understanding the possible implications of climatic changes on the catchment water balance. Using a global sensitivity analysis, this study assessed the implications of baseline climate conditions on the sensitivity of PET to a large range of plausible changes in temperature (T), relative humidity (RH), solar radiation (Rs) and wind speed (uz). The analysis was conducted at 30 Australian locations representing different climatic zones, using the Penman-Monteith and Priestley-Taylor PET models. Results from both models suggest that the baseline climate can have a substantial impact on overall PET sensitivity. In particular, approximately 2-fold greater changes in PET were observed in cool-climate energy-limited locations compared to other locations in Australia, indicating the potential for elevated water loss as a result of increasing actual evapotranspiration (AET) in these locations. The two PET models consistently indicated temperature to be the most important variable for PET, but showed large differences in the relative importance of the remaining climate variables. In particular for the Penman-Monteith model, wind and relative humidity were the second-most important variables for dry and humid catchments, respectively, whereas for the Priestley-Taylor model solar radiation was the second-most important variable, with the greatest influence in warmer catchments. This information can be useful to inform the selection of suitable PET models to estimate future PET for different climate conditions, providing evidence on both the structural plausibility and input uncertainty for the alternative models.

  14. Watershed-scale Evapotranspiration Changed Little over 50 years of Agricultural Land Abandonment in Southern Michigan

    Science.gov (United States)

    Hamilton, S. K.; Hussain, M. Z.; Lowrie, C. J.

    2015-12-01

    The difference between precipitation and stream discharge over annual periods provides an indication of the total water loss to evaporation and evapotranspiration. The response of evaporative water loss to land cover change affects groundwater recharge, stream flow, and lake levels. This study examined the watershed water balance for Augusta Creek, which drains a 95-km2 glacial landscape in southwestern Michigan covered by cropland, grassland, forest, and wetlands. The climate is humid and temperate; between 1964-2014 the water-year precipitation averaged 948 mm and ranged from 695-1386 mm with no temporal trend. Over the study period the percentage of land in agriculture has decreased to about a third of its original extent, with abandoned lands gradually transitioning from old fields to woody vegetation. Comparison of precipitation on the upland watershed to baseflow discharge (USGS data; baseflow estimation by WHAT model) across the 50-year record shows that total evaporative water loss averaged 563 + 103 mm and ranged from 385-897 mm, with no apparent trend over the record. The evaporative water loss accounts for a mean + s.d. of 59 + 6% of precipitation (range, 48-70%). Evaporative water loss was positively related to total precipitation (r2 = 0.74. These results are interpreted using a Budyko plot framework to facilitate comparison with other settings. This water balance approach to infer evaporative water loss compares well with direct measurements in the same watershed since 2009 using eddy covariance (grasslands and crops) and soil moisture monitoring by time-domain reflectometry (grasslands, crops, and forest). Thus the evaporative water loss, which is predominantly by evapotranspiration, has been remarkably similar across a period of changing land cover, leaving a relatively consistent proportion for groundwater recharge and streamflow.

  15. A glimpse at short-term controls of evapotranspiration along the southern slopes of Kilimanjaro.

    Science.gov (United States)

    Detsch, Florian; Otte, Insa; Appelhans, Tim; Nauss, Thomas

    2017-08-23

    Future climate characteristics of the southern Kilimanjaro region, Tanzania, are mainly determined by local land-use and global climate change. Reinforcing increasing dryness throughout the twentieth century, ongoing land transformation processes emphasize the need for a proper understanding of the regional-scale water budget and possible implications on related ecosystem functioning and services. Here, we present an analysis of scintillometer-based evapotranspiration (ET) covering seven distinct habitat types across a massive climate gradient from the colline savanna woodlands to the upper-mountain Helichrysum zone (940 to 3960 m.a.s.l.). Random forest-based mean variable importance indicates an outstanding significance of net radiation (R net) on the observed ET across all elevation levels. Accordingly, topography and frequent cloud/fog events have a dampening effect at high elevations, whereas no such constraints affect the energy and moisture-rich submontane coffee/grassland level. By contrast, long-term moisture availability is likely to impose restrictions upon evapotranspirative net water loss in savanna, which particularly applies to the pronounced dry season. At plot scale, ET can thereby be approximated reasonably using R net, soil heat flux, and to a lesser degree, vapor pressure deficit and rainfall as predictor variables (R 2 0.59 to 1.00). While multivariate regression based on pooled meteorological data from all plots proves itself useful for predicting hourly ET rates across a broader range of ecosystems (R 2 = 0.71), additional gains in explained variance can be achieved when vegetation characteristics as seen from the NDVI are considered (R 2 = 0.87). To sum up, our results indicate that valuable insights into land cover-specific ET dynamics, including underlying drivers, may be derived even from explicitly short-term measurements in an ecologically highly diverse landscape.

  16. Application of artificial intelligence to estimate the reference evapotranspiration in sub-humid Doon valley

    Science.gov (United States)

    Nema, Manish K.; Khare, Deepak; Chandniha, Surendra K.

    2017-11-01

    Estimation of evapotranspiration (ET) is an essential component of the hydrologic cycle, which is also requisite for efficient irrigation water management planning and hydro-meteorological studies at both the basin and catchment scales. There are about twenty well-established methods available for ET estimation which depends upon various meteorological parameters and assumptions. Most of these methods are physically based and need a variety of input data. The FAO-56 Penman-Monteith method (PM) for estimating reference evapotranspiration (ET0) is recommend for irrigation scheduling worldwide, because PM generally yields the best results under various climatic conditions. This study investigates the abilities of artificial neural networks (ANN) to improve the accuracy of monthly evaporation estimation in sub-humid climatic region of Dehradun. In the first part of the study, different ANN models, comprising various combinations of training function and number of neutrons were developed to estimate the ET0 and it has been compared with the Penman-Monteith (PM) ET0 as the ideal (observed) ET0. Various statistical approaches were considered to estimate the model performance, i.e. Coefficient of Correlation ( r), Sum of Squared Errors, Root Mean Square Error, Nash-Sutcliffe Efficiency Index (NSE) and Mean Absolute Error. The ANN model with Levenberg-Marquardt training algorithm, single hidden layer and nine number of neutron schema was found the best predicting capabilities for the study station with Coefficient of Correlation ( r) and NSE value of 0.996 and 0.991 for calibration period and 0.990 and 0.980 for validation period, respectively. In the subsequent part of the study, the trend analysis of ET0 time series revealed a rising trend in the month of March, and a falling trend during June to November, except August, with more than 90% significance level and the annual declining rate was found to 1.49 mm per year.

  17. Mapping daily evapotranspiration at Landsat spatial scales during the BEAREX'08 field campaign

    Science.gov (United States)

    Anderson, Martha C.; Kustas, William P.; Alfieri, Joseph G.; Gao, Feng; Hain, Christopher; Prueger, John H.; Evett, Steven; Colaizzi, Paul; Howell, Terry; Chávez, José L.

    2012-12-01

    Robust spatial information about environmental water use at field scales and daily to seasonal timesteps will benefit many applications in agriculture and water resource management. This information is particularly critical in arid climates where freshwater resources are limited or expensive, and groundwater supplies are being depleted at unsustainable rates to support irrigated agriculture as well as municipal and industrial uses. Gridded evapotranspiration (ET) information at field scales can be obtained periodically using land-surface temperature-based surface energy balance algorithms applied to moderate resolution satellite data from systems like Landsat, which collects thermal-band imagery every 16 days at a resolution of approximately 100 m. The challenge is in finding methods for interpolating between ET snapshots developed at the time of a clear-sky Landsat overpass to provide complete daily time-series over a growing season. This study examines the efficacy of a simple gap-filling algorithm designed for applications in data-sparse regions, which does not require local ground measurements of weather or rainfall, or estimates of soil texture. The algorithm relies on general conservation of the ratio between actual ET and a reference ET, generated from satellite insolation data and standard meteorological fields from a mesoscale model. The algorithm was tested with ET retrievals from the Atmosphere-Land Exchange Inverse (ALEXI) surface energy balance model and associated DisALEXI flux disaggregation technique, which uses Landsat-scale thermal imagery to reduce regional ALEXI maps to a finer spatial resolution. Daily ET at the Landsat scale was compared with lysimeter and eddy covariance flux measurements collected during the Bushland Evapotranspiration and Agricultural Remote sensing EXperiment of 2008 (BEAREX08), conducted in an irrigated agricultural area in the Texas Panhandle under highly advective conditions. The simple gap-filling algorithm performed

  18. Sensitivity of the projected hydroclimatic environment of the Delaware River basin to formulation of potential evapotranspiration

    Science.gov (United States)

    Williamson, Tanja N.; Nystrom, Elizabeth A.; Milly, Paul C.D.

    2016-01-01

    The Delaware River Basin (DRB) encompasses approximately 0.4 % of the area of the United States (U.S.), but supplies water to 5 % of the population. We studied three forested tributaries to quantify the potential climate-driven change in hydrologic budget for two 25-year time periods centered on 2030 and 2060, focusing on sensitivity to the method of estimating potential evapotranspiration (PET) change. Hydrology was simulated using the Water Availability Tool for Environmental Resources (Williamson et al. 2015). Climate-change scenarios for four Coupled Model Intercomparison Project Phase 5 (CMIP5) global climate models (GCMs) and two Representative Concentration Pathways (RCPs) were used to derive monthly change factors for temperature (T), precipitation (PPT), and PET according to the energy-based method of Priestley and Taylor (1972). Hydrologic simulations indicate a general increase in annual (especially winter) streamflow (Q) as early as 2030 across the DRB, with a larger increase by 2060. This increase in Q is the result of (1) higher winter PPT, which outweighs an annual actual evapotranspiration (AET) increase and (2) (for winter) a major shift away from storage of PPT as snow pack. However, when PET change is evaluated instead using the simpler T-based method of Hamon (1963), the increases in Q are small or even negative. In fact, the change of Q depends as much on PET method as on time period or RCP. This large sensitivity and associated uncertainty underscore the importance of exercising caution in the selection of a PET method for use in climate-change analyses.

  19. Parameters influencing the regeneration of a green roof's retention capacity via evapotranspiration

    Science.gov (United States)

    Poë, Simon; Stovin, Virginia; Berretta, Christian

    2015-04-01

    The extent to which the finite hydrological capacity of a green roof is available for retention of a storm event largely determines the scale of its contribution as a Sustainable Drainage System (SuDS). Evapotranspiration (ET) regenerates the retention capacity at a rate that is variably influenced by climate, vegetation treatment, soil and residual moisture content. Experimental studies have been undertaken to monitor the drying cycle behaviour of 9 different extensive green roof configurations with 80 mm substrate depth. A climate-controlled chamber at the University of Sheffield replicated typical UK spring and summer diurnal cycles. The mass of each microcosm, initially at field capacity, was continuously recorded, with changes inferred to be moisture loss/gain (or ET/dew). The ranges of cumulative ET following a 28 day dry weather period (ADWP) were 0.6-1.0 mm/day in spring and 0.7-1.25 mm/day in summer. These ranges reflect the influence of configuration on ET. Cumulative ET was highest from substrates with the greatest storage capacity. Significant differences in ET existed between vegetated and non-vegetated configurations. Initially, seasonal mean ET was affected by climate. Losses were 2.0 mm/day in spring and 3.4 mm/day in summer. However, moisture availability constrained ET, which fell to 1.4 mm/day then 1.0 mm/day (with an ADWP of 7 and 14 days) in spring; compared to 1.0 mm/day and 0.5 mm/day in summer. A modelling approach, which factors Potential Evapotranspiration (PET) according to stored moisture content, predicts daily ET with very good accuracy (PBIAS = 2.0% [spring]; -0.8% [summer]).

  20. Impact of evapotranspiration process representation on runoff projections from conceptual rainfall-runoff models

    Science.gov (United States)

    Guo, Danlu; Westra, Seth; Maier, Holger R.

    2017-01-01

    Conceptual rainfall-runoff models are commonly used to estimate potential changes in runoff due to climate change. The development of these models has generally focused on reproducing runoff characteristics, with less scrutiny on other important processes such as the conversion from potential evapotranspiration (PET) to actual evapotranspiration (AET). This study uses three conceptual rainfall-runoff models (GR4J, AWBM, and IHACRES_CMD) and five catchments in climatologically different regions of Australia to explore the role of ET process representation on the sensitivity of runoff to plausible future changes in PET. The changes in PET were simulated using the Penman-Monteith model and by perturbing each of the driving variables (temperature, solar radiation, humidity, and wind) separately. Surprisingly, the results showed the potential of a more than sevenfold difference in runoff sensitivity per unit change in annual average PET, depending on both the rainfall-runoff model and the climate variable used to perturb PET. These differences were largely due to different ways used to convert PET to AET in the conceptual rainfall-runoff models, with particular dependencies on the daily wet/dry status, as well as the seasonal variations in store levels. By comparing the temporal patterns in simulated AET with eddy-covariance-based observations at two of the study locations, we highlighted some unrealistic behavior in the simulated AET from AWBM. Such process-based evaluations are useful for scrutinizing the representation of physical processes in alternative conceptual rainfall-runoff models, which can be particularly useful for selecting models for projecting runoff under a changing climate.

  1. Estimating Daily Reference Evapotranspiration in a Semi-Arid Region Using Remote Sensing Data

    Directory of Open Access Journals (Sweden)

    Peshawa M. Najmaddin

    2017-07-01

    Full Text Available Estimating daily evapotranspiration is challenging when ground observation data are not available or scarce. Remote sensing can be used to estimate the meteorological data necessary for calculating reference evapotranspiration ETₒ. Here, we assessed the accuracy of daily ETₒ estimates derived from remote sensing (ETₒ-RS compared with those derived from four ground-based stations (ETₒ-G in Kurdistan (Iraq over the period 2010–2014. Near surface air temperature, relative humidity and cloud cover fraction were derived from the Atmospheric Infrared Sounder/Advanced Microwave Sounding Unit (AIRS/AMSU, and wind speed at 10 m height from MERRA (Modern-Era Retrospective Analysis for Research and Application. Four methods were used to estimate ETₒ: Hargreaves–Samani (HS, Jensen–Haise (JH, McGuinness–Bordne (MB and the FAO Penman Monteith equation (PM. ETₒ-G (PM was adopted as the main benchmark. HS underestimated ETₒ by 2%–3% (R2 = 0.86 to 0.90; RMSE = 0.95 to 1.2 mm day−1 at different stations. JH and MB overestimated ETₒ by 8% to 40% (R2= 0.85 to 0.92; RMSE from 1.18 to 2.18 mm day−1. The annual average values of ETₒ estimated using RS data and ground-based data were similar to one another reflecting low bias in daily estimates. They ranged between 1153 and 1893 mm year−1 for ETₒ-G and between 1176 and 1859 mm year−1 for ETₒ-RS for the different stations. Our results suggest that ETₒ-RS (HS can yield accurate and unbiased ETₒ estimates for semi-arid regions which can be usefully employed in water resources management.

  2. Long-term evapotranspiration estimates in the Walnut River Watershed in Kansas.

    Energy Technology Data Exchange (ETDEWEB)

    Coulter, R. L.; Klazura, G. E.; Lesht, B. M.; Wesely, M. L.

    1999-08-04

    This project focuses on improving and testing a simple method for using reflectance data obtained from satellites to infer the effects on evapotranspiration of variations in soil moisture availability. The major advantage to the method, which is based on the parameterization of subgrid-scale surface fluxes (PASS) model (Gao 1995; Gao et al. 1998), is that it can be applied to areas having diverse surface characteristics where direct surface flux measurements either do not exist or are not feasible and where meteorological data are available from only a limited number of ground stations. The emphasis of the PASS model is on improving (1) methods for using high-resolution satellite remote sensing data to derive the essential parameters for individual types of surfaces overlarge areas, (2) algorithms for describing the interactions of near-surface atmospheric conditions with surface processes, and (3) algorithms for computing surface energy and water vapor flux at a scale close to the size of a satellite pixel. An operational modeling system is being developed. Testing of the system is accomplished by applying it to the Walnut River Wak-shed (WRW), instrumented watershed of moderate area (5,000 km{sup 2}) located just east of Wichita, Kansas. Data from field experiments such as the intensive field campaign in 1997 by the Cooperative Atmosphere-Surface Exchange Study (CASES) and from routine operation of the Atmospheric Boundary Layer Experiments (ABLE) in the WRW are used to evaluate the ability of the PASS model to estimate accumulated water loss over a growing season. The research goals of the project areas follow: (1) Improve the existing satellite-data interfacing modules, especially the parameterization of soil moisture availability and water vapor flux; (2) Apply and evaluate the methods by using measurements at ground stations distributed within the WRW; and (3) Develop an operational version of the modeling system, and apply it to derive long

  3. Estimating Impacts of Agricultural Subsurface Drainage on Evapotranspiration Using the Landsat Imagery-Based METRIC Model

    Directory of Open Access Journals (Sweden)

    Kul Khand

    2017-11-01

    Full Text Available Agricultural subsurface drainage changes the field hydrology and potentially the amount of water available to the crop by altering the flow path and the rate and timing of water removal. Evapotranspiration (ET is normally among the largest components of the field water budget, and the changes in ET from the introduction of subsurface drainage are likely to have a greater influence on the overall water yield (surface runoff plus subsurface drainage from subsurface drained (TD fields compared to fields without subsurface drainage (UD. To test this hypothesis, we examined the impact of subsurface drainage on ET at two sites located in the Upper Midwest (North Dakota-Site 1 and South Dakota-Site 2 using the Landsat imagery-based METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration model. Site 1 was planted with corn (Zea mays L. and soybean (Glycine max L. during the 2009 and 2010 growing seasons, respectively. Site 2 was planted with corn for the 2013 growing season. During the corn growing seasons (2009 and 2013, differences between the total ET from TD and UD fields were less than 5 mm. For the soybean year (2010, ET from the UD field was 10% (53 mm greater than that from the TD field. During the peak ET period from June to September for all study years, ET differences from TD and UD fields were within 15 mm (<3%. Overall, differences between daily ET from TD and UD fields were not statistically significant (p > 0.05 and showed no consistent relationship.

  4. [Evapotranspiration characteristics of artificial and natural forests in Liupan Mountains of Ningxia, China during growth season].

    Science.gov (United States)

    Cao, Gong-xiang; Wang, Xu-fang; Xiong, Wei; Wang, Yan-hui; Yu, Peng-tao; Wang, Yun-ni; Xu, Li-hong; Li, Zhen-hua

    2013-08-01

    In order to understand the effects of the structure of forest ecosystem on the hydrological processes, a comparative study by using thermal dissipation technique and hydrological methodology was made on the evapotranspiration (ET) and its components of Larix principis-rupprechtii plantation and Pinus armandi natural forest in two adjacent stands in a small catchment Xiangshuihe of Liupan Mountains during the growth season (May-October) in 2009. Throughout the growth season, the total ET from the plantation was 518.2 mm, which accounted for 104.6% of the precipitation and was much higher than that (420.5 mm) of the natural forest. The allocation of ET in the vertical layers performed similarly between the two stands, with the order of canopy layer > herb and soil layer > shrub layer, but the ratio of each component to total ET differed significantly. The plantation consumed 0.2 and 0.9 times more water for canopy interception (19.6 mm per month) and tree transpiration (25.2 mm per month) than the natural forest, respectively. However, the transpiration from the plantation was 4.4 mm per month, and took up 23.4% of the natural forest. In contrast, the sum of soil evaporation and herbage evapotranspiration consumed 37.1 mm water per month in the plantation, which was 0.8 times higher than that in the natural forest. The ET was calculated by Penman-Monteith equation to compare the results estimated by sap flow measurements, and the values estimated by the two methods were similar.

  5. Development of daily temperature scenarios and their impact on paddy crop evapotranspiration in Kangsabati command area

    Science.gov (United States)

    Dhage, P. M.; Raghuwanshi, N. S.; Singh, R.; Mishra, A.

    2017-05-01

    Production of the principal paddy crop in West Bengal state of India is vulnerable to climate change due to limited water resources and strong dependence on surface irrigation. Therefore, assessment of impact of temperature scenarios on crop evapotranspiration (ETc) is essential for irrigation management in Kangsabati command (West Bengal). In the present study, impact of the projected temperatures on ETc was studied under climate change scenarios. Further, the performance of the bias correction and spatial downscaling (BCSD) technique was compared with the two well-known downscaling techniques, namely, multiple linear regression (MLR) and Kernel regression (KR), for the projections of daily maximum and minimum air temperatures for four stations, namely, Purulia, Bankura, Jhargram, and Kharagpur. In National Centers for Environmental Prediction (NCEP) and General Circulation Model (GCM), 14 predictors were used in MLR and KR techniques, whereas maximum and minimum surface air temperature predictor of CanESM2 GCM was used in BCSD technique. The comparison results indicated that the performance of the BCSD technique was better than the MLR and KR techniques. Therefore, the BCSD technique was used to project the future temperatures of study locations with three Representative Concentration Pathway (RCP) scenarios for the period of 2006-2100. The warming tendencies of maximum and minimum temperatures over the Kangsabati command area were projected as 0.013 and 0.014 °C/year under RCP 2.6, 0.015 and 0.023 °C/year under RCP 4.5, and 0.056 and 0.061 °C/year under RCP 8.5 for 2011-2100 period, respectively. As a result, kharif (monsoon) crop evapotranspiration demand of Kangsabati reservoir command (project area) will increase by approximately 10, 8, and 18 % over historical demand under RCP 2.6, 4.5, and 8.5 scenarios, respectively.

  6. Climate and vegetation controls on the surface water balance: Synthesis of evapotranspiration measured across a global network of flux towers

    Science.gov (United States)

    Williams, Christopher A.; Reichstein, Markus; Buchmann, Nina; Baldocchi, Dennis; Beer, Christian; Schwalm, Christopher; Wohlfahrt, Georg; Hasler, Natalia; Bernhofer, Christian; Foken, Thomas; Papale, Dario; Schymanski, Stan; Schaefer, Kevin

    2012-06-01

    The Budyko framework elegantly reduces the complex spatial patterns of actual evapotranspiration and runoff to a general function of two variables: mean annual precipitation (MAP) and net radiation. While the methodology has first-order skill, departures from a globally averaged curve can be significant and may be usefully attributed to additional controls such as vegetation type. This paper explores the magnitude of such departures as detected from flux tower measurements of ecosystem-scale evapotranspiration, and investigates their attribution to site characteristics (biome, seasonal rainfall distribution, and frozen precipitation). The global synthesis (based on 167 sites with 764 tower-years) shows smooth transition from water-limited to energy-limited control, broadly consistent with catchment-scale relations and explaining 62% of the across site variation in evaporative index (the fraction of MAP consumed by evapotranspiration). Climate and vegetation types act as additional controls, combining to explain an additional 13% of the variation in evaporative index. Warm temperate winter wet sites (Mediterranean) exhibit a reduced evaporative index, 9% lower than the average value expected based on dryness index, implying elevated runoff. Seasonal hydrologic surplus explains a small but significant fraction of variance in departures of evaporative index from that expected for a given dryness index. Surprisingly, grasslands on average have a higher evaporative index than forested landscapes, with 9% more annual precipitation consumed by annual evapotranspiration compared to forests. In sum, the simple framework of supply- or demand-limited evapotranspiration is supported by global FLUXNET observations but climate type and vegetation type are seen to exert sizeable additional controls.

  7. Possible Scenarios of Impacts of Climatic Change on Potential Evapotranspiration in the Watershed of the Conchos River, Mexico

    Science.gov (United States)

    Raynal-Villasenor, J. A.; Rodriguez-Pineda, J. A.

    2007-12-01

    The watershed of the Conchos River is the main watershed of the state of Chihuahua, Mexico, and it is the main source of water of the watershed of the Grande river downstream El Paso, Texas. Such part of the watershed of the Grande River is also the border between Mexico and the United States of America, from El Paso-Ciudad Juarez up to Brownsville-Matamoros. It is very important for the state of Chihuahua and Mexico as a whole, to construct possible scenarios of the effects of the global climatic change in the potential evapotranspiration in such watershed and to construct likely scenarios which results will help to define an integrated watershed management to mitigate those global climate change impacts. The results of a recent study sponsored by the alliance between WWF-Fundacion Gonzalo Rio Arronte, are presented in the paper. The study was conducted to construct possible scenarios on the effects of the global climatic change on the potential evapotranspiration in the watershed of the Conchos River in Mexico. Three watershed characteristic meteorological stations were selected to conduct such study. The predictions of change of the surface air temperature and the change of the rainfall produced by the global climatic change, by the end of the XXI Century, were those published by the Hadley Center. The results show that air temperature increment of one degree centigrade increases evapotranspiration values between 3 and 3.5% with respect current values. As a consequence moisture deficiency increases from 9% to 40%. With an air temperature increment of three degrees centigrades, the potential evapotranspiration increases between 8.8% and 10% increasing moisture deficiency from 27.5% up to 116%. The expected rainfall increment values show a negligible contribution for the potential evapotranspiration reduction in the Rio Conchos watershed. These results conclude that immediate actions need to be taken to mitigate climate change impacts all along the watershed.

  8. Impact of tile drainage on evapotranspiration in South Dakota, USA, based on high spatiotemporal resolution evapotranspiration time series from a multi-satellite data fusion system

    Science.gov (United States)

    Yang, Yun; Anderson, Martha C.; Gao, Feng; Hain, Christopher; Kustas, William P.; Meyers, Tilden P.; Crow, Wade; Finocchiaro, Raymond G.; Otkin, Jason; Sun, Liang; Yang, Yang

    2017-01-01

    Soil drainage is a widely used agricultural practice in the midwest USA to remove excess soil water to potentially improve the crop yield. Research shows an increasing trend in baseflow and streamflow in the midwest over the last 60 years, which may be related to artificial drainage. Subsurface drainage (i.e., tile) in particular may have strongly contributed to the increase in these flows, because of its extensive use and recent gain in the popularity as a yield-enhancement practice. However, how evapotranspiration (ET) is impacted by tile drainage on a regional level is not well-documented. To explore spatial and temporal ET patterns and their relationship to tile drainage, we applied an energy balance-based multisensor data fusion method to estimate daily 30-m ET over an intensively tile-drained area in South Dakota, USA, from 2005 to 2013. Results suggest that tile drainage slightly decreases the annual cumulative ET, particularly during the early growing season. However, higher mid-season crop water use suppresses the extent of the decrease of the annual cumulative ET that might be anticipated from widespread drainage. The regional water balance analysis during the growing season demonstrates good closure, with the average residual from 2005 to 2012 as low as -3 mm. As an independent check of the simulated ET at the regional scale, the water balance analysis lends additional confidence to the study. The results of this study improve our understanding of the influence of agricultural drainage practices on regional ET, and can affect future decision making regarding tile drainage systems.

  9. Modeling impacts of climate change on evapotranspiration and soil moisture spatial patterns in an alpine catchment

    Science.gov (United States)

    Brenner, Johannes G.; Bertoldi, Giacomo; Della Chiesa, Stefano; Niedrist, Georg; Tappeiner, Ulrike; Bronstert, Axel

    2014-05-01

    A climate change impact study on spatial pattern of evaporation and soil moisture was performed in the Venosta/Vinschgau valley (South Tyrol, Italy). Locating hot spots of future changes for these main components of the water cycle is essential for the development of mitigation and adaptation strategies in this dry inner alpine valley, which is already affected by water scarcity issues. The GEOtop hydrological model was used for 1-dimensional simulations, resulting in soil water content, evapotranspiration and snow water equivalent for 300 locations within the valley. Simulation locations were chosen by means of a multidimensional sampling (K-means clustering) of the most important aspects of land surface heterogeneities of the complex, mountainous topography, and land use cover, based on 20m grid maps. This approach reduced considerably computational time with respect to a full 3-dimensional simulation. An ensemble of 7 regional climate models (RCM) was downscaled using the Δ-change approach, to drive the hydrological model for the scenario periods 2040-2059 (scen2060) and 2080-2099 (scen2100). A baseline simulation is covering the period 1990-2009. Calibration and validation studies were successfully carried out for three locations along an elevation transect (station B10: 1000m a.s.l., station B15: 1500m a.s.l., station B20: 2000m a.s.l.), where detailed observations of meteorological inputs, evapotranspiration, snow cover and soil moisture were available. The annual cycle of the Δ-change signal for temperature and precipitation reveals explicit differences between the 7 RCMs. Especially precipitation patterns exhibit high uncertainty, but, nevertheless, they show an average increase of 17%(±36%) in autumn and a decrease of 13%(±23%) in summer (scen2100). Temperature pattern are more homogenous, reaching a maximum increase in summer (4.2±0.9°C, scen2100). Decreasing temperatures are not projected. Simulations show a strong impact of increasing temperature

  10. Effects of spatial aggregation on the multi-scale estimation of evapotranspiration

    KAUST Repository

    Ershadi, Ali

    2013-04-01

    The influence of spatial resolution on the estimation of land surface heat fluxes from remote sensing is poorly understood. In this study, the effects of aggregation from fine (< 100 m) to medium (approx. 1. km) scales are investigated using high resolution Landsat 5 overpasses. A temporal sequence of satellite imagery and needed meteorological data were collected over an agricultural region, capturing distinct variations in crop stage and phenology. Here, we investigate both the impact of aggregating the input forcing and of aggregating the derived latent heat flux. In the input aggregation scenario, the resolution of the Landsat based radiance data was increased incrementally from 120. m to 960. m, with the land surface temperature calculated at each specific resolution. Reflectance based land surface parameters such as vegetation height and leaf area index were first calculated at the native 30. m Landsat resolution and then aggregated to multiple spatial scales. Using these data and associated meteorological forcing, surface heat fluxes were calculated at each distinct resolution using the Surface Energy Balance System (SEBS) model. Results indicate that aggregation of input forcing using a simple averaging method has limited effect on the land surface temperature and available energy, but can reduce evapotranspiration estimates at the image scale by up to 15%, and at the pixel scale by up to 50%. It was determined that the predominant reason for the latent heat flux reduction in SEBS was a decrease in the aerodynamic resistance at coarser resolutions, which originates from a change in the roughness length parameters of the land surface due to the aggregation. In addition, the magnitude of errors in surface heat flux estimation due to input aggregation was observed to be a function of the heterogeneity of the land surface and evaporative elements. In examining the response of flux aggregation, fine resolution (120. m) heat fluxes were aggregated to coarser

  11. STOMP Sparse Vegetation Evapotranspiration Model for the Water-Air-Energy Operational Mode

    Energy Technology Data Exchange (ETDEWEB)

    Ward, Anderson L.; White, Mark D.; Freeman, Eugene J.; Zhang, Z. F.

    2005-09-15

    The Water-Air-Energy (WAE) Operational Mode of the Subsurface Transport Over Multiple Phases (STOMP) numerical simulator solves the coupled conservation equations for water mass, air mass, and thermal energy in multiple dimensions. This addendum describes the theory, input file formatting, and application of a soil-vegetation-atmosphere transfer (SVAT) scheme for STOMP that is based on a sparse vegetation evapotranspiration model. The SVAT scheme is implemented as a boundary condition on the upper surface of the computational domain and has capabilities for simulating evaporation from bare surfaces as well as evapotranspiration from sparsely vegetated surfaces populated with single or multiple plant species in response to meteorological forcings. With this extension, the model calculates water mass, air mass and thermal energy across a boundary surface in addition to root-water transport between the subsurface and atmosphere. This mode represents the barrier extension of the WAE mode and is designated as STOMP-WAE-B. Input for STOMP-WAE-B is specified via three input cards and include: atmospheric conditions through the Atmospheric Conditions Card; time-invariant plant species data through the Plant Properties Card; and time varying plant species data through the Boundary Conditions Card. Two optional cards, the Observed Data and UCODE Control Cards allow use of STOMP-WAE with UCODE in an inverse mode to estimate model parameters. STOMP-WAE was validated by solving a number of test problems from the literature that included experimental observations as well as analytical or numerical solutions. Several of the UNSAT-H verification problems are included along with a benchmark simulation derived from a recently published intercode comparison for barrier design tools. Results show that STOMP is able to meet, and in most cases, exceed performance of other commonly used simulation codes without having to resort to may of their simplifying assumptions. Use of the fully

  12. Evapotranspiration Cover for the 92-Acre Area Retired Mixed Waste Pits:Interim CQA Report

    Energy Technology Data Exchange (ETDEWEB)

    The Delphi Groupe, Inc., and J. A. Cesare and Associates, Inc.

    2011-06-20

    This Interim Construction Quality Assurance (CQA) Report is for the 92-Acre Evapotranspiration Cover, Area 5 Waste Management Division (WMD) Retired Mixed Waste Pits, Nevada National Security Site, Nevada for the period of January 20, 2011 to May 12, 2011. This Interim Construction Quality Assurance (CQA) Report is for the 92-Acre Evapotranspiration Cover, Area 5 Waste Management Division (WMD) Retired Mixed Waste Pits, Nevada National Security Site, Nevada for the period of January 20, 2011 to May 12, 2011. Construction was approved by the Nevada Division of Environmental Protection (NDEP) under the Approval of Corrective Action Decision Document/Corrective Action Plan (CADD/CAP) for Corrective Action Unit (CAU) 111: Area 5 WMD Retired Mixed Waste Pits, Nevada National Security Site, Nevada, on January 6, 2011, pursuant to Subpart XII.8a of the Federal Facility Agreement and Consent Order. The project is located in Area 5 of the Radioactive Waste Management Complex (RWMC) at the Nevada National Security Site (NNSS), formerly known as the Nevada Test Site, located in southern Nevada, approximately 65 miles northwest of Las Vegas, Nevada, in Nye County. The project site, in Area 5, is located in a topographically closed basin approximately 14 additional miles north of Mercury Nevada, in the north-central part of Frenchman Flat. The Area 5 RWMS uses engineered shallow-land burial cells to dispose of packaged waste. The 92-Acre Area encompasses the southern portion of the Area 5 RWMS, which has been designated for the first final closure operations. This area contains 13 Greater Confinement Disposal (GCD) boreholes, 16 narrow trenches, and 9 broader pits. With the exception of two active pits (P03 and P06), all trenches and pits in the 92-Acre Area had operational covers approximately 2.4 meters thick, at a minimum, in most areas when this project began. The units within the 92-Acre Area are grouped into the following six informal categories based on physical location

  13. Assessing factors that influence deviations between measured and calculated reference evapotranspiration

    Science.gov (United States)

    Rodny, Marek; Nolz, Reinhard

    2017-04-01

    Evapotranspiration (ET) is a fundamental component of the hydrological cycle, but challenging to be quantified. Lysimeter facilities, for example, can be installed and operated to determine ET, but they are costly and represent only point measurements. Therefore, lysimeter data are traditionally used to develop, calibrate, and validate models that allow calculating reference evapotranspiration (ET0) based on meteorological data, which can be measured more easily. The standardized form of the well-known FAO Penman-Monteith equation (ASCE-EWRI) is recommended as a standard procedure for estimating ET0 and subsequently plant water requirements. Applied and validated under different climatic conditions, the Penman-Monteith equation is generally known to deliver proper results. On the other hand, several studies documented deviations between measured and calculated ET0 depending on environmental conditions. Potential reasons are, for example, differing or varying surface characteristics of the lysimeter and the location where the weather instruments are placed. Advection of sensible heat (transport of dry and hot air from surrounding areas) might be another reason for deviating ET-values. However, elaborating causal processes is complex and requires comprehensive data of high quality and specific analysis techniques. In order to assess influencing factors, we correlated differences between measured and calculated ET0 with pre-selected meteorological parameters and related system parameters. Basic data were hourly ET0-values from a weighing lysimeter (ET0_lys) with a surface area of 2.85 m2 (reference crop: frequently irrigated grass), weather data (air and soil temperature, relative humidity, air pressure, wind velocity, and solar radiation), and soil water content in different depths. ET0_ref was calculated in hourly time steps according to the standardized procedure after ASCE-EWRI (2005). Deviations between both datasets were calculated as ET0_lys-ET0_ref and

  14. The effect of warming on grassland evapotranspiration partitioning using laser-based isotope monitoring techniques

    KAUST Repository

    Wang, Lixin

    2013-06-01

    The proportion of transpiration (T) in total evapotranspiration (ET) is an important parameter that provides insight into the degree of biological influence on the hydrological cycles. Studies addressing the effects of climatic warming on the ecosystem total water balance are scarce, and measured warming effects on the T/ET ratio in field experiments have not been seen in the literature. In this study, we quantified T/ET ratios under ambient and warming treatments in a grassland ecosystem using a stable isotope approach. The measurements were made at a long-term grassland warming site in Oklahoma during the May-June peak growing season of 2011. Chamber-based methods were used to estimate the δ2H isotopic composition of evaporation (δE), transpiration (δT) and the aggregated evapotranspiration (δET). A modified commercial conifer leaf chamber was used for δT, a modified commercial soil chamber was used for δE and a custom built chamber was used for δET. The δE, δET and δT were quantified using both the Keeling plot approach and a mass balance method, with the Craig-Gordon model approach also used to calculate δE. Multiple methods demonstrated no significant difference between control and warming plots for both δET and δT. Though the chamber-based estimates and the Craig-Gordon results diverged by about 12‰, all methods showed that δE was more depleted in the warming plots. This decrease in δE indicates that the evaporation flux as a percentage of total water flux necessarily decreased for δET to remain constant, which was confirmed by field observations. The T/ET ratio in the control treatment was 0.65 or 0.77 and the ratio found in the warming treatment was 0.83 or 0.86, based on the chamber method and the Craig-Gordon approach. Sensitivity analysis of the Craig-Gordon model demonstrates that the warming-induced decrease in soil liquid water isotopic composition is the major factor responsible for the observed δE depletion and the temperature

  15. Remote sensing algorithm for surface evapotranspiration considering landscape and statistical effects on mixed pixels

    Directory of Open Access Journals (Sweden)

    Z. Q. Peng

    2016-11-01

    Full Text Available Evapotranspiration (ET plays an important role in surface–atmosphere interactions and can be monitored using remote sensing data. However, surface heterogeneity, including the inhomogeneity of landscapes and surface variables, significantly affects the accuracy of ET estimated from satellite data. The objective of this study is to assess and reduce the uncertainties resulting from surface heterogeneity in remotely sensed ET using Chinese HJ-1B satellite data, which is of 30 m spatial resolution in VIS/NIR bands and 300 m spatial resolution in the thermal-infrared (TIR band. A temperature-sharpening and flux aggregation scheme (TSFA was developed to obtain accurate heat fluxes from the HJ-1B satellite data. The IPUS (input parameter upscaling and TRFA (temperature resampling and flux aggregation methods were used to compare with the TSFA in this study. The three methods represent three typical schemes used to handle mixed pixels from the simplest to the most complex. IPUS handles all surface variables at coarse resolution of 300 m in this study, TSFA handles them at 30 m resolution, and TRFA handles them at 30 and 300 m resolution, which depends on the actual spatial resolution. Analyzing and comparing the three methods can help us to get a better understanding of spatial-scale errors in remote sensing of surface heat fluxes. In situ data collected during HiWATER-MUSOEXE (Multi-Scale Observation Experiment on Evapotranspiration over heterogeneous land surfaces of the Heihe Watershed Allied Telemetry Experimental Research were used to validate and analyze the methods. ET estimated by TSFA exhibited the best agreement with in situ observations, and the footprint validation results showed that the R2, MBE, and RMSE values of the sensible heat flux (H were 0.61, 0.90, and 50.99 W m−2, respectively, and those for the latent heat flux (LE were 0.82, −20.54, and 71.24 W m−2, respectively. IPUS yielded the largest errors

  16. Using Simplified Thermal Inertia to Determine the Theoretical Dry Line in Feature Space for Evapotranspiration Retrieval

    Directory of Open Access Journals (Sweden)

    Sujuan Mi

    2015-08-01

    Full Text Available With the development of quantitative remote sensing, regional evapotranspiration (ET modeling based on the feature space has made substantial progress. Among those feature space based evapotranspiration models, accurate determination of the dry/wet lines remains a challenging task. This paper reports the development of a new model, named DDTI (Determination of Dry line by Thermal Inertia, which determines the theoretical dry line based on the relationship between the thermal inertia and the soil moisture. The Simplified Thermal Inertia value estimated in the North China Plain is consistent with the value measured in the laboratory. Three evaluation methods, which are based on the comparison of the locations of the theoretical dry line determined by two models (DDTI model and the heat energy balance model, the comparison of ET results, and the comparison of the evaporative fraction between the estimates from the two models and the in situ measurements, were used to assess the performance of the new model DDTI. The location of the theoretical dry line determined by DDTI is more reasonable than that determined by the heat energy balance model. ET estimated from DDTI has an RMSE (Root Mean Square Error of 56.77 W/m2 and a bias of 27.17 W/m2; while the heat energy balance model estimated ET with an RMSE of 83.36 W/m2 and a bias of −38.42 W/m2. When comparing the coeffcient of determination for the two models with the observations from Yucheng, DDTI demonstrated ET with an R2 of 0.9065; while the heat energy balance model has an R2 of 0.7729. When compared with the in situ measurements of evaporative fraction (EF at Yucheng Experimental Station, the ET model based on DDTI reproduces the pixel scale EF with an RMSE of 0.149, much lower than that based on the heat energy balance model which has an RMSE of 0.220. Also, the EF bias between the DDTI model and the in situ measurements is 0.064, lower than the EF bias of the heat energy balance model

  17. The estimation of evapotranspiration from wetland sites - the impact of soil physical properties near saturation

    Science.gov (United States)

    Frahm, Enrico; Tiemeyer, Bärbel; Salzmann, Thomas; Miegel, Konrad

    2010-05-01

    The evapotranspiration (ET) is a significant process within the soil-plant-atmosphere continuum (SPAC). Especially on wetland sites ET is an important component of the water balance due to the high biomass and ET of wetland vegetation. Thus, comprehensive knowledge of all hydrological processes is the basis for a sustainable management of wetlands. Determining wetland ET still suffers from large uncertainties as it is notoriously difficult to measure directly due to its inherent complexities and small scale spatial and temporal variations. Consequently, there is a wide range of approaches to derive evapotranspiration losses indirectly from other parameters, but all have their significant assets and drawbacks. One of the commonly used methods is the interpretation of diurnal ground water fluctuations (DGF), which has been successfully applied to estimate the ET of phreatophytic vegetation (ETGW). The basic idea behind this method is the assumption of a directly coupled system of incoming solar radiation, vegetation ET, water transport within the plants and water uptake by the root system of the phreatophytic vegetation from both the vadose zone and the groundwater. Such a system is characterised by a strong diurnal cycle and significant DGFs. In the presented study, DGFs measured in a rewetted riverine fen in North-Eastern Germany were analysed to estimate ETGW. With maximum daily values of 5.9 mm for reed (Phragmites australis) and 7.9 mm for willow (Salix spp.), the method yields generally plausible results. However, a comparison of the time series of ETGW and ET according to the Penman-Monteith method (ETPM) shows considerable discrepancies. Despite continuous sufficient water supply the ETGW results fall up to 90 % below the results of ETPM. The aim of the presented study was to identify processes explaining these differences. As a first step, we could identify a clear connection between these errors and the hydrological conditions: The difference between ETGW

  18. Percentage of Hypothetical Well Pumpage Causing Depletions to Simulated Base Flow, Evapotranspiration, and Groundwater Storage in the Elkhorn and Loup River Basins, 2006 through 2055

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — This data release includes a polygon shapefile of grid cells attributed with values representing the simulated base-flow, evapotranspiration, and groundwater-storage...

  19. Effects of land cover change on evapotranspiration and streamflow of small catchments in the Upper Xingu River Basin, Central Brazil

    Directory of Open Access Journals (Sweden)

    Lívia Cristina Pinto Dias

    2015-09-01

    New hydrological insights for the region: Converting natural vegetation to agriculture substantially modifies evapotranspiration and streamflow in small catchments. Measured mean streamflow in soy catchments was about three times greater than that of forest catchments, while the mean annual amplitude of flow in soy catchments was more than twice that of forest catchments. Simulated mean annual evapotranspiration was 39% lower in agricultural ecosystems (pasture and soybean cropland than in natural ecosystems (tropical rainforest and cerrado. Observed and simulated mean annual streamflows in agricultural ecosystems were more than 100% higher than in natural ecosystems. The accuracy of the simulations was improved by using field-measured soil hydraulic properties. The inclusion of local measurements of key soil parameters is likely to improve hydrological simulations in other tropical regions.

  20. The effect of background hydrometeorological conditions on the sensitivity of evapotranspiration to model parameters: analysis with measurements from an Italian alpine catchment

    Directory of Open Access Journals (Sweden)

    N. Montaldo

    2003-01-01

    Full Text Available Recent developments have made land-surface models (LSMs more complex through the inclusion of more processes and controlling variables, increasing numbers of parameters and uncertainty in their estimates. To overcome these uncertainties, prior to applying a distributed LSM over the whole Toce basin (Italian Alps, a field campaign was carried out at an experimental plot within the basin before exploring the skill and parameter importance (sensitivity using the TOPLATS model, an existing LSM. In the summer and autumn of 1999, which included both wet (atmosphere controlled and dry (soil controlled periods, actual evapotranspiration estimates were performed using Bowen ratio and, for a short period, eddy correlation methods. Measurements performed with the two methods are in good agreement. The calibrated LSM predicts actual evapotranspiration quite well over the whole observation period. A sensitivity analysis of the evapotranspiration to model parameters was performed through the global multivariate technique during both wet and dry periods of the campaign. This approach studies the influence of each parameter without conditioning on certain values of the other variables. Hence, all parameters are varied simultaneously using, for instance, a uniform sampling strategy through a Monte Carlo simulation framework. The evapotranspiration is highly sensitive to the soil parameters, especially during wet periods. However, the evapotranspiration is also sensitive to some vegetation parameters and, during dry periods, wilting point is the most critical for evapotranspiration predictions. This result confirms the importance of correct representation of vegetation properties which, in water-limited conditions, control evapotranspiration. Keywords: evapotranspiration, sensitivity analysis, land surface model, eddy correlation, Alpine basin

  1. Evapotranspiration over spatially extensive plant communities in the Big Cypress National Preserve, southern Florida, 2007-2010

    Science.gov (United States)

    Shoemaker, W. Barclay; Lopez, Christian D.; Duever, Michael J.

    2011-01-01

    Evapotranspiration (ET) was quantified over plant communities within the Big Cypress National Preserve (BCNP) using the eddy covariance method for a period of 3 years from October 2007 to September 2010. Plant communities selected for study included Pine Upland, Wet Prairie, Marsh, Cypress Swamp, and Dwarf Cypress. These plant communities are spatially extensive in southern Florida, and thus, the ET measurements described herein can be applied to other humid subtropical locations such as the Everglades.

  2. Non-Lambertian Corrected Albedo and Vegetation Index for Estimating Land Evapotranspiration in a Heterogeneous Semi-Arid Landscape

    OpenAIRE

    Isabella Mariotto; Gutschick, Vincent P.

    2010-01-01

    The application of energy balance algorithms to remotely sensed imagery often fails to account for surface roughness variation with diverse land cover, resulting in poor resolution of evapotranspiration (ET) variations. Furthermore, the assumption of a horizontally homogeneous Lambertian surface reflecting energy equally in all directions affects the calculations of albedo and vegetation index. The primary objective of this study is to improve the accuracy of the estimation and discrimination...

  3. Regional estimation of daily to annual regional evapotranspiration with MODIS data in the Yellow River Delta wetland

    Directory of Open Access Journals (Sweden)

    L. Jia

    2009-10-01

    Full Text Available Evapotranspiration (ET from the wetland of the Yellow River Delta (YRD is one of the important components in the water cycle, which represents the water consumption by the plants and evaporation from the water and the non-vegetated surfaces. Reliable estimates of the total evapotranspiration from the wetland is useful information both for understanding the hydrological process and for water management to protect this natural environment. Due to the heterogeneity of the vegetation types and canopy density and of soil water content over the wetland (specifically over the natural reserve areas, it is difficult to estimate the regional evapotranspiration extrapolating measurements or calculations usually done locally for a specific land cover type. Remote sensing can provide observations of land surface conditions with high spatial and temporal resolution and coverage. In this study, a model based on the Energy Balance method was used to calculate daily evapotranspiration (ET using instantaneous observations of land surface reflectance and temperature from MODIS when the data were available on clouds-free days. A time series analysis algorithm was then applied to generate a time series of daily ET over a year period by filling the gaps in the observation series due to clouds. A detailed vegetation classification map was used to help identifying areas of various wetland vegetation types in the YRD wetland. Such information was also used to improve the parameterizations in the energy balance model to improve the accuracy of ET estimates.

    This study showed that spatial variation of ET was significant over the same vegetation class at a given time and over different vegetation types in different seasons in the YRD wetland.

  4. Secondary Forest as a counterbalance on the deforestation effects: its role on evapotranspiration and water use efficiency

    Science.gov (United States)

    Von Randow, Rita C. S.; Tomasella, Javier; Von Randow, Celso; Araujo, Alessandro C.; Manzi, Antonio O.

    2017-04-01

    Since the 70's, the Amazon basin is under constant pressure first because of agricultural expansion, and recently also because of resources extraction. The conversion of pristine forest to other types of land cover as pasture and agriculture, affects the local water balance diminishing the evapotranspiration and increasing the discharge. Those changes can buffer the climate change effects and vice-versa. On the other hand, secondary forest growth resulting from abandoned deforested areas presents higher evaporative fraction (Giambelluca, 2002), leading to higher evapotranspiration rates than pristine forests, what can compensate the effects of deforestation on energy and water balances. In this work we will show four years of eddy flux measurements of a pristine forest and of a secondary growth about 20 years old, located in Central Amazonia, comparing the evapotranspiration and water use efficiency of both sites. The innovative aspect of the present work is the measurement of fluxes above a secondary growth forest in a relatively advanced stage. The measurements of eddy covariance are in accordance with the increase of evaporative fraction with the age of secondary forest presented by Giambelluca (2002). The yearly evaporative fraction (ratio of energy used for evapotranspiration to net radiation) on the primary forest was 0.74-0.81, while in the secondary forest it was 0.85-0.87. On the other hand, secondary forest shows a water use efficiency of 1.9 g C kg-1 H2O, while the pristine forest gives 2.9 g C kg-1 H2O.

  5. Reference Evapotranspiration Estimation in Climate Change Scenarios for Rio Verde in the State of Goiás, Brazil

    Directory of Open Access Journals (Sweden)

    Lucas da Costa Santos

    2017-07-01

    Full Text Available Long-term changes in evapotranspiration can have extreme effects in hydrological processes as well as crop yields. The objective of this study was to quantify the expected changes in evapotranspiration in climate change scenarios using the Penman Monteith/FAO56 (PM standard method and empirical equations for estimating reference evapotranspiration (ET0, specifically for the conditions of Rio Verde, in the state of Goiás, Brazil. Data from the National Institute of Meteorology, and Meteorology and Hydrology System of the State of Goiás were used to estimate the ET0 by using the following methods: Modified Penman, Radiation, Blaney-Criddle, Hargreaves-Samani, and Priestley-Taylor and Turc, which were compared with the PM method on the daily scale. From the ET0 obtained in each of these methods, their performance was evaluated through statistical indices in four future climate scenarios. The projections originated from two emission scenarios based on the HadGEM2-ES global climate model with medium (2040-2069 and long (2070-2099 term scenarios. The results presented that the Radiation and Turc methods are currently—and can be under the predicted conditions of future climate scenarios—the best options for estimation of ET0 in Rio Verde, when meteorological data are not available to implement the PM method. The Modified Penman and the Hargreaves-Samani methods should not be considered for estimating ET0 in the location evaluated.

  6. Development of an Evapotranspiration Data Assimilation Technique for Streamflow Estimates: A Case Study in a Semi-Arid Region

    Directory of Open Access Journals (Sweden)

    Ying Zhang

    2017-09-01

    Full Text Available Streamflow estimates are substantially important as fresh water shortages increase in arid and semi-arid regions where evapotranspiration (ET is a significant contribution to the water balance. In this regard, evapotranspiration data can be assimilated into a distributed hydrological model (SWAT, Soil and Water Assessment Tool for improving streamflow estimates. The SWAT model has been widely used for streamflow estimations, but the applications combining SWAT and ET products were rare. Thus, this study aims to develop a SWAT-based evapotranspiration data assimilation system. In particular, SWAT is gridded at Hydrologic Response Unit (HRU level to incorporate gridded ET products acquired from the remote sensing-based ETMonitor model. In the modeling case, Gridded SWAT (GSWAT shows a good agreement of streamflow modeling with the original SWAT. Such a scant margin between them is due to the modeling domain mismatch caused by different HRU delineations. In the ET assimilation case, we carry out a synthetic data experiment to illustrate the state augmentation Direct Insertion (DI method and a real data experiment for the upper Heihe River Basin. The results demonstrate the benefits of the ET assimilation for improving hydrologic processes representations. In the future, more remotely sensed data can be assimilated into the data assimilation system to provide more reliable hydrological predictions.

  7. Evaluation and Recalibration of Empirical Constant for Estimation of Reference Crop Evapotranspiration against the Modified Penman Method

    Science.gov (United States)

    Sasireka, K.; Jagan Mohan Reddy, C.; Charan Reddy, C.; Ramakrishnan, K.

    2017-07-01

    The major demand in our country is irrigation demand. Looking to the low irrigation potential and small water resources, it is felt necessary to see that water must be used economically and efficiently. This may be achieved by using latest methods of determination of water requirements for crops and applying the proper water management practices. Evapotranspiration (ET) is a basic for calculation of water requirement for crops. The various popular empirical equations for reference crop evapotranspiration (ETr) belong to three categories namely, Temperature, Radiation based methods and Combined methods. The above methods are site specific; hence it is necessary to recalibrate the coefficients for applying them in India. In the present paper, the standard combined method namely FAO modified Penman method was used to recalibrate the constants in temperature based (TB) methods and it can also be used to determine the ETr for the selected station. Four TB evapotranspiration models namely Blaney-Criddle, Romanenko, Kharrufa, and, Thronthwaite methods are recalibrated and the constant in each method are redefined for the data from Lekkur station, Cuddalore district in India. The result shows that, large error existed when ETr has been calculated with original constants. Hence regression equations were developed to minimise these variations in magnitude. It was found that out of four methods the Blaney-Criddle method suits better for the selected region.

  8. Investigation of climate change impact on water resources for an Alpine basin in northern Italy: implications for evapotranspiration modeling complexity.

    Science.gov (United States)

    Ravazzani, Giovanni; Ghilardi, Matteo; Mendlik, Thomas; Gobiet, Andreas; Corbari, Chiara; Mancini, Marco

    2014-01-01

    Assessing the future effects of climate change on water availability requires an understanding of how precipitation and evapotranspiration rates will respond to changes in atmospheric forcing. Use of simplified hydrological models is required because of lack of meteorological forcings with the high space and time resolutions required to model hydrological processes in mountains river basins, and the necessity of reducing the computational costs. The main objective of this study was to quantify the differences between a simplified hydrological model, which uses only precipitation and temperature to compute the hydrological balance when simulating the impact of climate change, and an enhanced version of the model, which solves the energy balance to compute the actual evapotranspiration. For the meteorological forcing of future scenario, at-site bias-corrected time series based on two regional climate models were used. A quantile-based error-correction approach was used to downscale the regional climate model simulations to a point scale and to reduce its error characteristics. The study shows that a simple temperature-based approach for computing the evapotranspiration is sufficiently accurate for performing hydrological impact investigations of climate change for the Alpine river basin which was studied.

  9. A one-layer satellite surface energy balance for estimating evapotranspiration rates and crop water stress indexes.

    Science.gov (United States)

    Barbagallo, Salvatore; Consoli, Simona; Russo, Alfonso

    2009-01-01

    Daily evapotranspiration fluxes over the semi-arid Catania Plain area (Eastern Sicily, Italy) were evaluated using remotely sensed data from Landsat Thematic Mapper TM5 images. A one-source parameterization of the surface sensible heat flux exchange using satellite surface temperature has been used. The transfer of sensible and latent heat is described by aerodynamic resistance and surface resistance. Required model inputs are brightness, temperature, fractional vegetation cover or leaf area index, albedo, crop height, roughness lengths, net radiation, air temperature, air humidity and wind speed. The aerodynamic resistance (r(ah)) is formulated on the basis of the Monin-Obukhov surface layer similarity theory and the surface resistance (r(s)) is evaluated from the energy balance equation. The instantaneous surface flux values were converted into evaporative fraction (EF) over the heterogeneous land surface to derive daily evapotranspiration values. Remote sensing-based assessments of crop water stress (CWSI) were also made in order to identify local irrigation requirements. Evapotranspiration data and crop coefficient values obtained from the approach were compared with: (i) data from the semi-empirical approach "K(c) reflectance-based", which integrates satellite data in the visible and NIR regions of the electromagnetic spectrum with ground-based measurements and (ii) surface energy flux measurements collected from a micrometeorological tower located in the experiment area. The expected variability associated with ET flux measurements suggests that the approach-derived surface fluxes were in acceptable agreement with the observations.

  10. Flooding Regime Impacts on Radiation, Evapotranspiration, and Latent Energy Fluxes over Groundwater-Dependent Riparian Cottonwood and Saltcedar Forests

    Directory of Open Access Journals (Sweden)

    James Cleverly

    2015-01-01

    Full Text Available Radiation and energy balances are key drivers of ecosystem water and carbon cycling. This study reports on ten years of eddy covariance measurements over groundwater-dependent ecosystems (GDEs in New Mexico, USA, to compare the role of drought and flooding on radiation, water, and energy budgets of forests differing in species composition (native cottonwood versus nonnative saltcedar and flooding regime. After net radiation (700–800 W m−2, latent heat flux was the largest energy flux, with annual values of evapotranspiration exceeding annual precipitation by 250–600%. Evaporative cooling dominated the energy fluxes of both forest types, although cottonwood generated much lower daily values of sensible heat flux (<−5 MJ m−2 d−1. Drought caused a reduction in evaporative cooling, especially in the saltcedar sites where evapotranspiration was also reduced, but without a substantial decline in depth-to-groundwater. Our findings have broad implications on water security and the management of native and nonnative vegetation within semiarid southwestern North America. Specifically, consideration of the energy budgets of GDEs as they respond to fluctuations in climatic conditions can inform the management options for reducing evapotranspiration and maintaining in-stream flow, which is legally mandated as part of interstate and international water resources agreements.

  11. Calculating Soil Wetness, Evapotranspiration and Carbon Cycle Processes Over Large Grid Areas Using a New Scaling Technique

    Science.gov (United States)

    Sellers, Piers

    2012-01-01

    Soil wetness typically shows great spatial variability over the length scales of general circulation model (GCM) grid areas (approx 100 km ), and the functions relating evapotranspiration and photosynthetic rate to local-scale (approx 1 m) soil wetness are highly non-linear. Soil respiration is also highly dependent on very small-scale variations in soil wetness. We therefore expect significant inaccuracies whenever we insert a single grid area-average soil wetness value into a function to calculate any of these rates for the grid area. For the particular case of evapotranspiration., this method - use of a grid-averaged soil wetness value - can also provoke severe oscillations in the evapotranspiration rate and soil wetness under some conditions. A method is presented whereby the probability distribution timction(pdf) for soil wetness within a grid area is represented by binning. and numerical integration of the binned pdf is performed to provide a spatially-integrated wetness stress term for the whole grid area, which then permits calculation of grid area fluxes in a single operation. The method is very accurate when 10 or more bins are used, can deal realistically with spatially variable precipitation, conserves moisture exactly and allows for precise modification of the soil wetness pdf after every time step. The method could also be applied to other ecological problems where small-scale processes must be area-integrated, or upscaled, to estimate fluxes over large areas, for example in treatments of the terrestrial carbon budget or trace gas generation.

  12. Investigating the Relationship between Evapotranspiration and Soil Salinity Using a Surface Energy Balance Model (ReSET).

    Science.gov (United States)

    Garcia, L. A.; Elhaddad, A.

    2008-12-01

    Reliable estimates of evapotranspiration (ET) from vegetation are needed for many types of water-resource investigations. This presentation introduces an enhanced surface energy balance-based model, the Remote Sensing of Evapotranspiration or ReSET model, for estimating ET. ReSET is an ET estimation model that takes into consideration the spatial variability in weather parameters, which makes it particularly applicable for calculating regional scale ET. ReSET also has the capability of interpolating between the available weather stations in time and space. The model's accuracy at daily and seasonal time scales is evaluated in several case studies. A special application of the model to investigate the relationship between ET and soil salinity in agricultural areas is presented. The case study focuses on the impacts of salinity on ET in corn and alfalfa in the Lower Arkansas River Basin in Colorado during the period 1999 to 2007. Evapotranspiration values were regressed against the spatially corresponding soil salinity values to develop a relation between ET and soil salinity. The ET values correlate well with the soil salinity levels in the study region, with a correlation coefficient of up to 0.86.

  13. Reference evapotranspiration for Londrina, Paraná, Brazil: performance of different estimation methods

    Directory of Open Access Journals (Sweden)

    Rodrigo Dlugosz da Silva

    2017-08-01

    Full Text Available Aiming at assessing the performance of alternative methods to Penman-Monteith FAO56 for estimating the reference evapotranspiration (ETo for Londrina, Paraná, Brazil, the methods temperature radiation, Hicks-Hess, Hargreaves-Samani (1982, Turc, Priestley-Taylor, Tanner-Pelton, Jensen-Haise, Makkink, modified Hargreaves, Stephens-Stewart, Abtew, global radiation, Ivanov, Lungeon, Hargreaves-Samani (1985, Benavides-Lopez, original Penman, Linacre, Blaney-Morin, Romanenko, Hargreaves (1974, McCloud, Camargo, Hamon, Kharrufa, McGuiness-Bordne, and Blaney-Criddle were compared to that standard method recommended by FAO. The estimations were correlated by linear regression and assessed by using the Person’s correlation coefficient (r, concordance index (d, and performance index (c using a set of meteorological data of approximately 40 years. The methods modified Hargreaves, Stephens-Stewart, Abtew, global radiation, Ivanov, Lungeon, Hargreaves-Samani (1985, Benavides-Lopez, original Penman, and Linacre should be avoided, as they did not present excellent results. The methods McCloud, Camargo, Hamon, Kharrufa, McGuinness-Bordne, Blaney-Criddle, Hargreaves (1974, Romanenko, and Blaney-Morin were classified as very bad, not being recommended. In contrast, the methods temperature radiation, Hicks-Hess, Hargreaves-Samani (1982, Turc, Priestley-Taylor, Tenner-Pelton, Jensen-Haise, and Makkink presented excellent performance indices and can be applied in the study region.

  14. Agricultural Applications for Remotely Sensed Evapotranspiration Data in Monitoring Water Use, Water Quality, and Water Security

    Science.gov (United States)

    Anderson, M. C.; Hain, C.; Gao, F.; Yang, Y.; Sun, L.; Dulaney, W.; Sharifi, A.; Holmes, T. R.; Kustas, W. P.

    2016-12-01

    Across the U.S. and globally there are ever increasing and competing demands for freshwater resources in support of food production, ecosystems services and human/industrial consumption. Recent studies using the GRACE satellite have identified severely stressed aquifers globally, which are being unsustainably depleted due to over-extraction primarily in support of irrigated agriculture. In addition, historic droughts and ongoing political conflicts threaten food and water security in many parts of the world. To facilitate wise water management, and to develop sustainable agricultural systems that will feed the Earth's growing population into the future, there is a critical need for robust assessments of daily water use, or evapotranspiration (ET), over a wide range in spatial scales - from field to globe. While Earth Observing (EO) satellites can play a significant role in this endeavor, no single satellite provides the combined spatial, spectral and temporal characteristics required for actionable ET monitoring world-wide. In this presentation we discuss new methods for combining information from the current suite of EO satellites to address issues of water use, water quality and water security, particularly as they pertain to agricultural production. These methods fuse multi-scale diagnostic ET retrievals generated using shortwave, thermal infrared and microwave datasets from multiple EO platforms to generate ET datacubes with both high spatial and temporal resolution. We highlight several case studies where such ET datacubes are being mined to investigate changes in water use patterns over agricultural landscapes in response to changing land use, land management, and climate forcings.

  15. Applications for remotely sensed evapotranspiration data in monitoring water quality, water use, and water security

    Science.gov (United States)

    Anderson, Martha; Hain, Christopher; Feng, Gao; Yang, Yun; Sun, Liang; Yang, Yang; Dulaney, Wayne; Sharifi, Amir; Kustas, William; Holmes, Thomas

    2017-04-01

    Across the globe there are ever-increasing and competing demands for freshwater resources in support of food production, ecosystems services and human/industrial consumption. Recent studies using the GRACE satellite have identified severely stressed aquifers that are being unsustainably depleted due to over-extraction, primarily in support of irrigated agriculture. In addition, historic droughts and ongoing political conflicts threaten food and water security in many parts of the world. To facilitate wise water management, and to develop sustainable agricultural systems that will feed the Earth's growing population into the future, there is a critical need for robust assessments of daily water use, or evapotranspiration (ET), over a wide range in spatial scales - from field to globe. While Earth Observing (EO) satellites can play a significant role in this endeavor, no single satellite provides the combined spatial, spectral and temporal characteristics required for actionable ET monitoring world-wide. In this presentation we discuss new methods for combining information from the current suite of EO satellites to address issues of water quality, water use and water security, particularly as they pertain to agricultural production. These methods fuse multi-scale diagnostic ET retrievals generated using shortwave, thermal infrared and microwave datasets from multiple EO platforms to generate ET datacubes with both high spatial and temporal resolution. We highlight several case studies where such ET datacubes are being mined to investigate changes in water use patterns over agricultural landscapes in response to changing land use, land management, and climate forcings.

  16. Modeling the Effect of Plants and Peat on Evapotranspiration in Constructed Wetlands

    Directory of Open Access Journals (Sweden)

    Florent Chazarenc

    2010-01-01

    Full Text Available Evapotranspiration (ET in constructed wetlands (CWs represents a major factor affecting hydrodynamics and treatment performances. The presence of high ET was shown to improve global treatment performances, however ET is affected by a wide range of parameters including plant development and CWs age. Our study aimed at modelling the effect of plants and peat on ET in CWs; since we hypothesized peat could behave like the presence of accumulated organic matter in old CWs. Treatment performances, hydraulic behaviour, and ET rates were measured in eight 1 m2 CWs mesocosm (1 unplanted, 1 unplanted with peat, 2 planted with Phragmites australis, 2 planted with Typha latifolia and 2 planted with Phragmites australis with peat. Two models were built using first order kinetics to simulate COD and TKN removal with ET as an input. The effect of peat was positive on ET and was related to the better growth conditions it offered to macrophytes. Removal efficiency in pilot units with larger ET was higher for TKN. On average, results show for COD a k20 value of 0.88 d-1 and 0.36 d-1 for TKN. We hypothesized that the main effect of ET was to concentrate effluent, thus enhancing degradation rates.

  17. Estimating Daily Evapotranspiration From Remotely Sensed Instantaneous Observations With Simplified Derivations of a Theoretical Model

    Science.gov (United States)

    Tang, Ronglin; Li, Zhao-Liang

    2017-10-01

    Surface evapotranspiration (ET) is one of the key components in global hydrological cycle and energy budget on Earth. This paper designs a theoretical relationship between daily and instantaneous ETs with a multiplication of multiple fractions through a mathematical derivation of the physics-based Penman-Monteith equation and further develops five methods for converting remotely sensed instantaneous ET to daily values, one of which is equivalent to the conventional constant evaporative fraction (EF) method. The five methods are then evaluated and intercompared using long-term ground-based eddy covariance system-measured half-hourly latent heat flux (LE) and three groups of Moderate Resolution Imaging Spectroradiometer-based instantaneous LE data sets collected from April 2009 to late October 2011 at the Yucheng station. Overall, the constant decoupling factor (Ω) method, the constant surface resistance (Rc) method, and the constant ratio of surface resistance to aerodynamic resistance (Rc/Ra) method could produce daily LE estimates that are in reasonably good agreement with the ground-based eddy covariance measurements, whereas the constant EF method and the constant Priestley-Taylor parameter (α) method underestimate the daily LE with larger biases and root-mean-square errors. The former three methods are of more solid physical foundation and can effectively capture the effect of temporally variable meteorological factors on the diurnal pattern of surface ET. They provide good alternatives to the nowadays commonly applied methods for the conversion of remotely sensed instantaneous ET to daily values.

  18. Evaluating the generalizability of GEP models for estimating reference evapotranspiration in distant humid and arid locations

    Science.gov (United States)

    Kiafar, Hamed; Babazadeh, Hosssien; Marti, Pau; Kisi, Ozgur; Landeras, Gorka; Karimi, Sepideh; Shiri, Jalal

    2017-10-01

    Evapotranspiration estimation is of crucial importance in arid and hyper-arid regions, which suffer from water shortage, increasing dryness and heat. A modeling study is reported here to cross-station assessment between hyper-arid and humid conditions. The derived equations estimate ET0 values based on temperature-, radiation-, and mass transfer-based configurations. Using data from two meteorological stations in a hyper-arid region of Iran and two meteorological stations in a humid region of Spain, different local and cross-station approaches are applied for developing and validating the derived equations. The comparison of the gene expression programming (GEP)-based-derived equations with corresponding empirical-semi empirical ET0 estimation equations reveals the superiority of new formulas in comparison with the corresponding empirical equations. Therefore, the derived models can be successfully applied in these hyper-arid and humid regions as well as similar climatic contexts especially in data-lack situations. The results also show that when relying on proper input configurations, cross-station might be a promising alternative for locally trained models for the stations with data scarcity.

  19. Relative Contribution of the Topographic Influence on the Triangle Approach for Evapotranspiration Estimation over Mountainous Areas

    Directory of Open Access Journals (Sweden)

    Xiaosong Zhao

    2014-01-01

    Full Text Available Evapotranspiration (ET is an important component of the water budget. Estimation ET through remote sensing over a mountainous terrain is typically obstructed by topographic effects. In this paper, topographic corrections were applied to ET estimates using the surface-air temperature difference-Normalized Difference Vegetation Index ((Ts-Ta-NDVI triangle method with MODIS data for the Taihu Basin in China. The effect of topography on ET was evaluated over an area with a complex terrain. After applying the topographic correction, the results indicate that the ET decreased with elevation and slope. The slope had a stronger impact on ET than the elevation, which caused the corrected ET to decrease by 90% from 6.8 mm day−1 to 0.6 mm day−1 for slopes over 50°. On average, the corrected ET decreased by 10.4% and 32.1% for north- and south-facing slopes, respectively. The ET corrected using the triangle method strongly depended on the evaporative fraction correction, which can mainly be attributed to the surface temperature correction. We conclude that a topographic correction is necessary when the triangle method is applied to areas with a complex terrain.

  20. Estimation of actual evapotranspiration in the Nagqu river basin of the Tibetan Plateau

    Science.gov (United States)

    Zou, Mijun; Zhong, Lei; Ma, Yaoming; Hu, Yuanyuan; Feng, Lu

    2017-05-01

    As a critical component of the energy and water cycle, terrestrial actual evapotranspiration (ET) can be influenced by many factors. This study was mainly devoted to providing accurate and continuous estimations of actual ET for the Tibetan Plateau (TP) and analyzing the effects of its impact factors. In this study, summer observational data from the Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau (CAMP/Tibet) for 2003 to 2004 was selected to determine actual ET and investigate its relationship with energy, hydrological, and dynamical parameters. Multiple-layer air temperature, relative humidity, net radiation flux, wind speed, precipitation, and soil moisture were used to estimate actual ET. The regression model simulation results were validated with independent data retrieved using the combinatory method. The results suggested that significant correlations exist between actual ET and hydro-meteorological parameters in the surface layer of the Nagqu river basin, among which the most important factors are energy-related elements (net radiation flux and air temperature). The results also suggested that how ET is eventually affected by precipitation and two-layer wind speed difference depends on whether their positive or negative feedback processes have a more important role. The multivariate linear regression method provided reliable estimations of actual ET; thus, 6-parameter simplified schemes and 14-parameter regular schemes were established.

  1. Spatial-Temporal Patterns and Controls of Evapotranspiration across the Tibetan Plateau (2000–2012

    Directory of Open Access Journals (Sweden)

    Hao Zhang

    2017-01-01

    Full Text Available Evapotranspiration (ET is a key factor to further our understanding of climate change processes, especially on the Tibetan Plateau, which is sensitive to global change. Herein, the spatial patterns of ET are examined, and the effects of environmental factors on ET at different scales are explored from the years 2000 to 2012. The results indicated that a steady trend in ET was detected over the past decade. Meanwhile, the spatial distribution shows an increase of ET from the northwest to the southeast, and the rate of change in ET is lower in the middle part of the Tibetan Plateau. Besides, the positive effect of radiation on ET existed mainly in the southwest. Based on the environment gradient transects, the ET had positive correlations with temperature (R>0.85, p 0.89, p 0.75, p < 0.0001, but a negative correlation between ET and radiation (R = 0.76, p < 0.0001 was observed. We also found that the relationships between environmental factors and ET differed in the different grassland ecosystems, which indicated that vegetation type is one factor that can affect ET. Generally, the results indicate that ET can serve as a valuable ecological indicator.

  2. Daily and seasonal patterns of CO2 fluxes and evapotranspiration in maize-grass intercropping

    Directory of Open Access Journals (Sweden)

    Cássia B. Machado

    Full Text Available ABSTRACT Studies that investigate the relationships between CO2 fluxes and evapotranspiration (ET are important for predicting how agricultural ecosystems will respond to climate changes. However, none was made on the maize-grass intercropping system in Brazil. The aim of this study was to determine the ET and CO2 fluxes in a signal grass pasture intercropped with maize, in São João, Pernambuco, Brazil, in a drought year. Furthermore, the soil water storage (SWS and leaf area index (LAI were determined. The latent heat flux was the main consumer of the available energy and the daily and seasonal ET and CO2 variations were mainly controlled by rainfall, through the changes in soil water content and consequently in SWS. The agroecosystem acted as an atmospheric carbon source, during drier periods and lower LAI, and as an atmospheric carbon sink, during wetter periods and higher LAI values. In a dry year, the intercropping sequestered 2.9 t C ha-1, which was equivalent to 8.0 kg C ha-1 d-1. This study showed strong seasonal fluctuations in maize-grass intercropping CO2 fluxes, due to seasonality of rainfall, and that this agroecosystem is vulnerable to low SWS, with significant reduction in CO2 uptake during these periods.

  3. Direct Measurement of Daily Evapotranspiration From a Deciduous Forest Using a Superconducting Gravimeter

    Science.gov (United States)

    Van Camp, M. J.; de Viron, O.; Pajot-Métivier, G.; Cazenave, F.; Watlet, A.; Dassargues, A.; Vanclooster, M.

    2015-12-01

    The conversion of liquid water into water vapor strongly controls the energy transfer between the Earth and the atmosphere, and plays one of the most important roles in the hydrological cycle. This process, called evapotranspiration (ET), deeply constraints the amount of green water in the total global water balance. However, assessing the ET from terrestrial ecosystems remains a key challenge in hydrology. We show that the liquid water mass losses can be directly inferred from continuous gravity measurements: as water evaporates and transpires from terrestrial ecosystems, the mass distribution varies through the system, changing its gravity field. Using continuous superconducting gravity measurements, we were able to identify a daily changes in gravity at the level of, or smaller than 10-10 g per day. This corresponds to 2.0 mm of water over an area of 50 ha.The strength of this method is its ability to ensure a direct, traceable and continuous monitoring of actual ET for years at the mesoscale (~50 ha) with a precision of a few tenths of mm of water. This paves the way for the development of the method in different land-use, land-cover and geological contexts, using superconducting and coming quantum gravimeters.

  4. A calibrated, high-resolution goes satellite solar insolation product for a climatology of Florida evapotranspiration

    Science.gov (United States)

    Paech, S.J.; Mecikalski, J.R.; Sumner, D.M.; Pathak, C.S.; Wu, Q.; Islam, S.; Sangoyomi, T.

    2009-01-01

    Estimates of incoming solar radiation (insolation) from Geostationary Operational Environmental Satellite observations have been produced for the state of Florida over a 10-year period (1995-2004). These insolation estimates were developed into well-calibrated half-hourly and daily integrated solar insolation fields over the state at 2 km resolution, in addition to a 2-week running minimum surface albedo product. Model results of the daily integrated insolation were compared with ground-based pyranometers, and as a result, the entire dataset was calibrated. This calibration was accomplished through a three-step process: (1) comparison with ground-based pyranometer measurements on clear (noncloudy) reference days, (2) correcting for a bias related to cloudiness, and (3) deriving a monthly bias correction factor. Precalibration results indicated good model performance, with a station-averaged model error of 2.2 MJ m-2/day (13%). Calibration reduced errors to 1.7 MJ m -2/day (10%), and also removed temporal-related, seasonal-related, and satellite sensor-related biases. The calibrated insolation dataset will subsequently be used by state of Florida Water Management Districts to produce statewide, 2-km resolution maps of estimated daily reference and potential evapotranspiration for water management-related activities. ?? 2009 American Water Resources Association.

  5. Modeling contribution of shallow groundwater to evapotranspiration and yield of maize in an arid area

    Science.gov (United States)

    Gao, Xiaoyu; Huo, Zailin; Qu, Zhongyi; Xu, Xu; Huang, Guanhua; Steenhuis, Tammo S.

    2017-01-01

    Capillary rise from shallow groundwater can decrease the need for irrigation water. However, simple techniques do not exist to quantify the contribution of capillary flux to crop water use. In this study we develop the Agricultural Water Productivity Model for Shallow Groundwater (AWPM-SG) for calculating capillary fluxes from shallow groundwater using readily available data. The model combines an analytical solution of upward flux from groundwater with the EPIC crop growth model. AWPM-SG was calibrated and validated with 2-year lysimetric experiment with maize. Predicted soil moisture, groundwater depth and leaf area index agreed with the observations. To investigate the response of model, various scenarios were run in which the irrigation amount and groundwater depth were varied. Simulations shows that at groundwater depth of 1 m capillary upward supplied 41% of the evapotranspiration. This reduced to 6% at groundwater depth of 2 m. The yield per unit water consumed (water productivity) was nearly constant for 2.3 kg/m3. The yield per unit water applied (irrigation water productivity) increased with decreasing irrigation water because capillary rise made up in part for the lack of irrigation water. Consequently, using AWPM-SG in irrigation scheduling will be beneficial to save more water in areas with shallow groundwater. PMID:28220874

  6. [An operational remote sensing algorithm of land surface evapotranspiration based on NOAA PAL dataset].

    Science.gov (United States)

    Hou, Ying-Yu; He, Yan-Bo; Wang, Jian-Lin; Tian, Guo-Liang

    2009-10-01

    Based on the time series 10-day composite NOAA Pathfinder AVHRR Land (PAL) dataset (8 km x 8 km), and by using land surface energy balance equation and "VI-Ts" (vegetation index-land surface temperature) method, a new algorithm of land surface evapotranspiration (ET) was constructed. This new algorithm did not need the support from meteorological observation data, and all of its parameters and variables were directly inversed or derived from remote sensing data. A widely accepted ET model of remote sensing, i. e., SEBS model, was chosen to validate the new algorithm. The validation test showed that both the ET and its seasonal variation trend estimated by SEBS model and our new algorithm accorded well, suggesting that the ET estimated from the new algorithm was reliable, being able to reflect the actual land surface ET. The new ET algorithm of remote sensing was practical and operational, which offered a new approach to study the spatiotemporal variation of ET in continental scale and global scale based on the long-term time series satellite remote sensing images.

  7. Estimating Evapotranspiration from an Improved Two-Source Energy Balance Model Using ASTER Satellite Imagery

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    Qifeng Zhuang

    2015-11-01

    Full Text Available Reliably estimating the turbulent fluxes of latent and sensible heat at the Earth’s surface by remote sensing is important for research on the terrestrial hydrological cycle. This paper presents a practical approach for mapping surface energy fluxes using Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER images from an improved two-source energy balance (TSEB model. The original TSEB approach may overestimate latent heat flux under vegetative stress conditions, as has also been reported in recent research. We replaced the Priestley-Taylor equation used in the original TSEB model with one that uses plant moisture and temperature constraints based on the PT-JPL model to obtain a more accurate canopy latent heat flux for model solving. The collected ASTER data and field observations employed in this study are over corn fields in arid regions of the Heihe Watershed Allied Telemetry Experimental Research (HiWATER area, China. The results were validated by measurements from eddy covariance (EC systems, and the surface energy flux estimates of the improved TSEB model are similar to the ground truth. A comparison of the results from the original and improved TSEB models indicates that the improved method more accurately estimates the sensible and latent heat fluxes, generating more precise daily evapotranspiration (ET estimate under vegetative stress conditions.

  8. SMAP Soil Moisture Data To Improve Remotely Sensed Global Estimates of Evapotranspiration

    Science.gov (United States)

    Purdy, A. J.; Fisher, J.; Goulden, M.; Famiglietti, J. S.

    2016-12-01

    Surface water availability limits plant productivity and the ability to transport water from the soil to the atmosphere in over 1/3rd of earth's vegetated land. Quantifying evapotranspiration (ET) across large areas requires the integration of satellite-observed land surface variables into physical or empirical equations that govern the transfer of mass and energy from land to the atmosphere. Many satellite ET algorithms have been developed to compute ET globally, but the current methods of two widely-used ET algorithms rely on implicit representation of soil moisture, limiting their capacity to impose proper physical constraints on ET under water limiting conditions. The successful launch of the Soil Moisture Active Passive (SMAP) satellite provides the first space-based soil moisture observations with the fidelity and the necessary spatio-temporal resolution to integrate directly into remote sensing ET algorithms and compare to in situ observations. Here we incorporate SMAP soil moisture observations into two widely used ET algorithms, the Priestley Taylor Jet Propulsion Laboratory (PT-JPL) ET model and the Penman Monteith MOD16. We present new soil moisture stress formulation and parameterization for each algorithm and evaluate model performance before and after soil moisture integration across a suite of in situ observations spanning a range of plant functional types and climates.

  9. Implementation of evapotranspiration data assimilation with catchment scale distributed hydrological model via an ensemble Kalman Filter

    Science.gov (United States)

    Zou, Lei; Zhan, Chesheng; Xia, Jun; Wang, Tiejun; Gippel, Christopher J.

    2017-06-01

    Terrestrial actual evapotranspiration (ETa) is a crucial component of terrestrial water cycles. The most common methods of estimating catchment-scale ETa are remote sensing and hydrological models. These methods have limitations when applied at the catchment scale due to coarse resolutions of data and uncertainties in model predictions. Data assimilation techniques that combine complementary information from hydrological models and observed data can overcome some of the limitations. These techniques have been used in many hydrological modeling studies, but few have applied data assimilation to ETa within a distributed precipitation-runoff catchment modeling framework. This paper proposes a catchment scale ETa data assimilation technique (termed ET-DA) that assimilates remotely sensed ETa data into a distributed time-variant gain hydrological model (DTVGM-ET) for improving hydrological model simulations. The DTVGM-ET improved the ETa computation on the basis of a nonlinear soil water availability function to establish an explicit time response relationship between ETa and soil moisture for implementing the ETa assimilation. The proposed ET-DA system was tested in the Upper Huai River Basin (UHRB), China using data from 2000 to 2012. Through synthetic simulation experiments, the capability of ET-DA for obtaining accurate, continuous time series of ETa estimates and achieving assimilation feedback on soil moisture and streamflow was examined. The results demonstrated that ET-DA provided improved regional ETa monitoring capability, and assimilation of ETa into the hydrological model led to improved model predictions of soil moisture and streamflow.

  10. Evapotranspiration estimation using Landsat-8 data with a two-layer framework

    Science.gov (United States)

    Yin, Jian; Wang, Hailong; Zhan, Chesheng; Lu, Yang

    2017-01-01

    Evapotranspiration (ET) plays an important role in hydrological cycle by linking land surface and atmosphere through water and energy transfers. Based on the data from the Landsat-8 satellite for typical days with clear sky condition from 2013 to 2016, a two-layer daily ET remote sensing framework was built, which includes four compartments: surface feature parameter estimation, evaporative fraction estimation, daily net radiation estimation, and daily ET extension. Based on the model, evaporation, transpiration, and daily ET in Shahe River Basin were estimated. The estimated daily ET showed a mean absolute percentage error of 8.7% in the plain areas, and 12.1% in the mountainous areas, compared to observations using large aperture scintillometer and eddy covariance system. The method gave higher accuracy than other remote sensing models applied in the same area previously, including the surface energy balance system and the ETWatch. By analyzing the relationship between land use types and surface water/heat fluxes, it was found that the surface energy balance components in the basin have prominent spatial-temporal features, and the soil component's features are more obvious. It indicated that the proposed two-layer approach is superior to others in terms of simulation accuracy, and applicable to daily scale ET estimations on complex terrains.

  11. Global Ecosystem Response Types Derived from the Standardized Precipitation Evapotranspiration Index and FPAR3g Series

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    Eva Ivits

    2014-05-01

    Full Text Available Observing trends in global ecosystem dynamics is an important first step, but attributing these trends to climate variability represents a further step in understanding Earth system changes. In the present study, we classified global Ecosystem Response Types (ERTs based on common spatio-temporal patterns in time-series of Standardized Precipitation Evapotranspiration Index (SPEI and FPAR3g anomalies (1982–2011 by using an extended Principal Component Analysis. The ERTs represent region specific spatio-temporal patterns of ecosystems responding to drought or ecosystems with decreasing severity in drought events as well as ecosystems where drought was not a dominant factor in a 30-year period. Highest explanatory values in the SPEI12-FPAR3g anomalies and strongest SPEI12-FPAR3g correlations were seen in the ERTs of Australia and South America whereas lowest explanatory value and lowest correlations were observed in Asia and North America. These ERTs complement traditional pixel based methods by enabling the combined assessment of the location, timing, duration, frequency and severity of climatic and vegetation anomalies with the joint assessment of wetting and drying climatic conditions. The ERTs produced here thus have potential in supporting global change studies by mapping reference conditions of long term ecosystem changes.

  12. On the correlation of water vapor and CO2: Application to flux partitioning of evapotranspiration

    Science.gov (United States)

    Wang, Wen; Smith, James A.; Ramamurthy, Prathap; Baeck, Mary Lynn; Bou-Zeid, Elie; Scanlon, Todd M.

    2016-12-01

    The partitioning of evapotranspiration (ET) between plant transpiration (Et) and direct evaporation (Ed) presents one of the most important and challenging problems for characterizing ecohydrological processes. The exchange of water vapor (q) and CO2 (c) are closely coupled in ecosystem processes and knowledge of their controls can be gained through joint investigation of q and c. In this study we examine the correlation of water vapor and CO2 (Rqc) through analyses of high-frequency time series derived from eddy covariance measurements collected over a suburban grass field in Princeton, NJ during a 2 year period (2011-2013). Rqc at the study site exhibits pronounced seasonal and diurnal cycles, with maximum anticorrelation in June and maximum decorrelation in January. The diurnal cycle of Rqc varies seasonally and is characterized by a near-symmetric shape with peak anticorrelation around local noon. Wavelet and spectral analyses suggest that q and c are jointly transported for most eddy scales (1-200 m), which is important for ET partitioning methods based on flux variance similarity. The diurnal cycle of the transpiration fraction (ratio of Et to total ET) exhibits an asymmetric diurnal cycle, especially during the warm season, with peak values occurring in the afternoon. These ET partitioning results give similar diurnal and seasonal patterns compared with numerical simulations from the Noah Land Surface Model using the Jarvis canopy resistance formulation.

  13. Microwave based implementation of a two-source energy balance model to estimate evapotranspiration

    Science.gov (United States)

    Holmes, Thomas; Hain, Christopher; Anderson, Martha; Kustas, Bill; Crow, Wade

    2017-04-01

    There is a need for observation-based methodologies to estimate evapotranspiration (ET) at diverse spatial domains. The ALEXI methodology (Atmosphere Land Exchange Inverse) is a time difference implementation of the two-source energy balance method and provides diagnostic estimates of actual ET. ALEXI has been implemented with thermal infrared (TIR) observations at diverse spatial scales to estimate crop water use, as an indicator of agricultural drought, and for the study hydrological impacts of climate variations and land-use change. While TIR is the most direct measurement of physical land surface temperature (LST), sole reliance on TIR limits the sampling to clear skies. It also impacts the accuracy if the cloud masking fails. Passive microwave (MW) methods to estimate LST could help to overcome this limitation and provide a more cloud tolerant alternative to TIR. As a first test of the functioning of a MW-based LST within the ALEXI framework we ran two parallel implementations of ALEXI, one with TIR-LST (MODIS), and one with MW-LST (without any calibrations to accommodate MW-LST). This paper presents an analysis of the clear sky ET estimates for the years 2003-2013 and explores the level of agreement between the MW- and TIR-based ET and derived stress indices.

  14. Partitioning Evapotranspiration into Green and Blue Water Sources in the Conterminous United States.

    Science.gov (United States)

    Velpuri, Naga Manohar; Senay, Gabriel B

    2017-07-21

    In this study, we combined two 1 km actual evapotranspiration datasets (ET), one obtained from a root zone water balance model and another from an energy balance model, to partition annual ET into green (rainfall-based) and blue (surface water/groundwater) sources. Time series maps of green water ET (GWET) and blue water ET (BWET) are produced for the conterminous United States (CONUS) over 2001-2015. Our results indicate that average green and blue water for all land cover types in CONUS accounts for nearly 70% and 30% of the total ET, respectively. The ET in the eastern US arises mostly from GWET, and in the western US, it is mostly BWET. Analysis of the BWET in the 16 irrigated areas in CONUS revealed interesting results. While the magnitude of the BWET gradually showed a decline from west to east, the increase in coefficient of variation from west to east confirmed greater use of supplemental irrigation in the central and eastern US. We also established relationships between different hydro-climatology zones and their blue water requirements. This study provides insights on the relative contributions and the spatiotemporal dynamics of GWET and BWET, which could lead to improved water resources management.

  15. Impacts of Deforestation and Climate Variability on Terrestrial Evapotranspiration in Subarctic China

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    Yunjun Yao

    2014-10-01

    Full Text Available Although deforestation affects hydrological and climatic variables over tropical regions, its actual contributions to changes in evapotranspiration (ET over subarctic China remain unknown. To establish a quantitative relationship between deforestation and terrestrial ET variations, we estimated ET using a semi-empirical Penman (SEMI-PM algorithm driven by meteorological and satellite data at both local and regional scales. The results indicate that the estimated ET can be used to analyse the observed inter-annual variations. There is a statistically significant positive relationship between local-scale forest cover changes (∆F and annual ET variations (∆ET of the following form: ∆ET = 0.0377∆F – 2.11 (R2 = 0.43, p < 0.05. This relationship may be due to deforestation-induced increases in surface albedo and a reduction in the fractional vegetation cover (FVC. However, the El Niño/Southern Oscillation (ENSO, rather than deforestation, dominates the multi-decadal ET variability due to regional-scale wind speed changes, but the exact effects of deforestation and ENSO on ET are challenging to quantify.

  16. Towards an unbiased filter routine to determine precipitation and evapotranspiration from high precision lysimeter measurements

    Science.gov (United States)

    Peters, Andre; Groh, Jannis; Schrader, Frederik; Durner, Wolfgang; Vereecken, Harry; Pütz, Thomas

    2017-06-01

    Weighing lysimeters are considered to be the best means for a precise measurement of water fluxes at the interface between the soil-plant system and the atmosphere. Any decrease of the net mass of the lysimeter can be interpreted as evapotranspiration (ET), any increase as precipitation (P). However, the measured raw data need to be filtered to separate real mass changes from noise. Such filter routines typically apply two steps: (i) a low pass filter, like moving average, which smooths noisy data, and (ii) a threshold filter that separates significant from insignificant mass changes. Recent developments of these filters have identified and solved some problems regarding bias in the data processing. A remaining problem is that each change in flow direction is accompanied with a systematic flow underestimation due to the threshold scheme. In this contribution, we analyze this systematic effect and show that the absolute underestimation is independent of the magnitude of a flux event. Thus, for small events, like dew or rime formation, the relative error is high and can reach the same magnitude as the flux itself. We develop a heuristic solution to the problem by introducing a so-called "snap routine". The routine is calibrated and tested with synthetic flux data and applied to real measurements obtained with a precision lysimeter for a 10-month period. The heuristic snap routine effectively overcomes these problems and yields an almost unbiased representation of the real signal.

  17. Regionalization of the Hargreaves coefficient to estimate long-term reference evapotranspiration series in SE Spain

    Directory of Open Access Journals (Sweden)

    J. F. Maestre-Valero

    2013-10-01

    Full Text Available This study employs a methodological approach for estimating long-term series of monthly reference evapotranspiration (ETo from historical data. To carry it out a regionally calibrated version of the Hargreaves equation was applied at old ordinary weather stations which only provide data of air temperature and precipitation. The proposed approach was based on the analysis of: (1 the Hargreaves coefficient obtained by local calibration from data of 66 modern automatic weather stations; (2 the regional characterization of the spatial variability of that coefficient by means of a “regional function”; and (3 the final application of this function to the old ordinary weather stations. This approach was assessed under the semiarid conditions of the Segura River Basin (south-eastern Spain by comparing ETo estimates against those obtained with the Penman-Monteith method, which was used as reference. Spatial variability of the Hargreaves coefficient was well correlated with the annual and monthly means of daily temperature range, so they were selected as explanatory variables for the regionalization of the Hargreaves coefficient following two approaches: a global regional function and monthly regional functions. The regionally calibrated version of the Hargreaves equation by monthly functions clearly improved the performance of its original parameterization (average relative error decreased from 19.8% to 10.1% although, as expected, estimates were not as good as those obtained with the local calibration (average relative error=7.7%.

  18. A Thermal-based Two-Source Energy Balance Model for Estimating Evapotranspiration over Complex Canopies

    Science.gov (United States)

    Kustas, William; Anderson, Martha; Nieto, Hector; Andreu, Ana; Yang, Yun; Cammalleri, Carmelo; Alfieri, Joseph; Gao, Feng; Hain, Christopher; Torres-Rua, Alfonso

    2017-04-01

    Land surface temperature (LST) provides valuable information for quantifying root-zone water availability, evapotranspiration (ET) and crop condition as well as providing useful information for constraining prognostic land surface models. This presentation describes a robust but relatively simple LST-based land surface model called the Two-Source Energy Balance (TSEB) model. The TSEB algorithms solve for the soil/substrate and canopy temperatures that achieves a balance in the radiation and turbulent heat flux exchange for the soil/substrate and vegetation elements coupled to the lower atmosphere. As a result, the TSEB modeling framework is applicable to a wide range of environmental and canopy cover conditions, which has been a limitation in many other LST-based energy balance approaches. This is particularly relevant in applying surface energy balance models using LST over heterogeneous landscapes with complex vegetation distribution and architecture/structure. An overview of applications of the TSEB modeling framework to a variety of landscapes will be presented. In addition, a modeling system will be described called the Atmosphere-Land Exchange Inverse (ALEXI) that couples the TSEB scheme with an atmospheric boundary layer model in time-differencing mode to routinely map continental-scale daily ET at 5 to 10-km resolution using geostationary satellites. A related algorithm (DisALEXI) spatially disaggregates ALEXI output down to finer spatial resolutions using polar orbiting satellites such as Landsat, which provides pixel resolutions at the scale of human management activities affecting land use⪉nd cover.

  19. Evapotranspiration Measurement and Crop Coefficient Estimation over a Spring Wheat Farmland Ecosystem in the Loess Plateau

    Science.gov (United States)

    Yang, Fulin; Zhang, Qiang; Wang, Runyuan; Zhou, Jing

    2014-01-01

    Evapotranspiration (ET) is an important component of the surface energy balance and hydrological cycle. In this study, the eddy covariance technique was used to measure ET of the semi-arid farmland ecosystem in the Loess Plateau during 2010 growing season (April to September). The characteristics and environmental regulations of ET and crop coefficient (Kc) were investigated. The results showed that the diurnal variation of latent heat flux (LE) was similar to single-peak shape for each month, with the largest peak value of LE occurring in August (151.4 W m−2). The daily ET rate of the semi-arid farmland in the Loess Plateau also showed clear seasonal variation, with the maximum daily ET rate of 4.69 mm day−1. Cumulative ET during 2010 growing season was 252.4 mm, and lower than precipitation. Radiation was the main driver of farmland ET in the Loess Plateau, which explained 88% of the variances in daily ET (psemi-arid farmland in the Loess Plateau, driven by Ws, RH, SWC and VPD, was developed, showing a good consistency between the simulated and the measured Kc values. PMID:24941017

  20. Influence of green-house cover on potential evapotranspiration and cucumber water requirements

    Directory of Open Access Journals (Sweden)

    F.A. Hashem

    2011-06-01

    Full Text Available Pollen grain morphology and seed coat characters of 11 cultivars belonging to two species. The experiment was conducted through two successive seasons of 2008 and 2009 at El-Bosaily farm, El-Behira governorate at the North Coastal of the Nile Delta, in Egypt. This work aimed to study the effect of three green-house covers (polyethylene sheet, white and black net and three irrigation levels [80%, 100% and 120% of the potential evapotranspiration estimated according to class A pan equation (ETo], applied by drip irrigation system, on plant growth and crop yield of Cucumber (Cucumis sativus L. cv. Reda F1. The experimental design was split–plot with three replicates. The results showed that white net green-house cover optimized growth and yield of cucumber plant. White net cover treatment recorded the highest vegetative growth (plant height, number of leaves, total leaves area, total fresh and dry weights, and significantly increased total yield. The highest vegetative growth was obtained by 100% ETo compared to 80% and 120% ETo treatments. The interaction among water treatment and green-house cover indicated the highest vegetative growth and crop yield was obtained under white net cover with 100% ETo.

  1. Use of eddy-covariance methods to "calibrate" simple estimators of evapotranspiration

    Science.gov (United States)

    Sumner, David M.; Geurink, Jeffrey S.; Swancar, Amy

    2017-01-01

    Direct measurement of actual evapotranspiration (ET) provides quantification of this large component of the hydrologic budget, but typically requires long periods of record and large instrumentation and labor costs. Simple surrogate methods of estimating ET, if “calibrated” to direct measurements of ET, provide a reliable means to quantify ET. Eddy-covariance measurements of ET were made for 12 years (2004-2015) at an unimproved bahiagrass (Paspalum notatum) pasture in Florida. These measurements were compared to annual rainfall derived from rain gage data and monthly potential ET (PET) obtained from a long-term (since 1995) U.S. Geological Survey (USGS) statewide, 2-kilometer, daily PET product. The annual proportion of ET to rainfall indicates a strong correlation (r2=0.86) to annual rainfall; the ratio increases linearly with decreasing rainfall. Monthly ET rates correlated closely (r2=0.84) to the USGS PET product. The results indicate that simple surrogate methods of estimating actual ET show positive potential in the humid Florida climate given the ready availability of historical rainfall and PET.

  2. Time Series Forecasting of Daily Reference Evapotranspiration by Neural Network Ensemble Learning for Irrigation System

    Science.gov (United States)

    Manikumari, N.; Murugappan, A.; Vinodhini, G.

    2017-07-01

    Time series forecasting has gained remarkable interest of researchers in the last few decades. Neural networks based time series forecasting have been employed in various application areas. Reference Evapotranspiration (ETO) is one of the most important components of the hydrologic cycle and its precise assessment is vital in water balance and crop yield estimation, water resources system design and management. This work aimed at achieving accurate time series forecast of ETO using a combination of neural network approaches. This work was carried out using data collected in the command area of VEERANAM Tank during the period 2004 – 2014 in India. In this work, the Neural Network (NN) models were combined by ensemble learning in order to improve the accuracy for forecasting Daily ETO (for the year 2015). Bagged Neural Network (Bagged-NN) and Boosted Neural Network (Boosted-NN) ensemble learning were employed. It has been proved that Bagged-NN and Boosted-NN ensemble models are better than individual NN models in terms of accuracy. Among the ensemble models, Boosted-NN reduces the forecasting errors compared to Bagged-NN and individual NNs. Regression co-efficient, Mean Absolute Deviation, Mean Absolute Percentage error and Root Mean Square Error also ascertain that Boosted-NN lead to improved ETO forecasting performance.

  3. Effects of horizontal grid resolution on evapotranspiration partitioning using TerrSysMP

    Science.gov (United States)

    Shrestha, P.; Sulis, M.; Simmer, C.; Kollet, S.

    2018-02-01

    Biotic leaf transpiration (T) and abiotic evaporation (E) are the two major pathways by which water is transferred from land surfaces to the atmosphere. Earth system models simulating the terrestrial water, carbon and energy cycle are required to reliably embed the role of soil and vegetation processes in order to realistically reproduce both fluxes including their relative contributions to total evapotranspiration (ET). Earth system models are also being used with increasing spatial resolutions to better simulate the effects of surface heterogeneity on the regional water and energy cycle and to realistically include effects of subsurface lateral flow paths, which are expected to feed back on the exchange fluxes and their partitioning in the model. Using the hydrological component of the Terrestrial Systems Modeling Platform (TerrSysMP), we examine the uncertainty in the estimates of T/ET ratio due to horizontal model grid resolution for a dry and wet year in the Inde catchment (western Germany). The aggregation of topography results in smoothing of slope magnitudes and the filtering of small-scale convergence and divergence zones, which directly impacts the surface-subsurface flow. Coarsening of the grid resolution from 120 m to 960 m increased the available soil moisture for ground evaporation, and decreased T/ET ratio by about 5% and 8% for dry and wet year respectively. The change in T/ET ratio was more pronounced for agricultural crops compared to forested areas, indicating a strong local control of vegetation on the ground evaporation, affecting the domain average statistics.

  4. Lake Fluctuation Effectively Regulates Wetland Evapotranspiration: A Case Study of the Largest Freshwater Lake in China

    Directory of Open Access Journals (Sweden)

    Xiaosong Zhao

    2014-08-01

    Full Text Available Lakes and wetlands provide valuable water resources. Wetland evapotranspiration (ET is a key hydrologic component; however, the effects of lake fluctuation on wetland ET remain unclear. The Poyang Lake is the largest freshwater lake in China and experiences a dramatic fluctuation in water level and inundated area. This study used remote sensing data to estimate the wetland ET for Poyang Lake and to illustrate the distribution of wetland ET and its response to lake fluctuations. Our results showed that wetland ET was related to lake fluctuation both spatially and temporally. Within the same year, the difference between annual water evaporation (Ewater and wetland ET (ETwetland was primarily attributed to lake fluctuation through its effects on inundated area and exposure days. A 1% increase in inundated area would result in a 7.87 ± 1.13 mm a−1 reduction in annual Ewater-to-ETwetland differences, and a 10-day elongation of exposure could lead to an 11.1 ± 1.6 mm a−1 increase in annual Ewater-to-ETwetland differences, on average. Inter-annually, the Ewater-to-ETwetland differences were attributed to the combined effects of atmospheric and environmental variables and lake fluctuation. The lake fluctuation contributed 73% to the inter-annual ET difference, followed by relative humidity (19%, net radiation (5%, and wind speed (4%. Overall, lake fluctuation effectively regulates wetland ET, and its effect should receive careful consideration in hydrological and water resources studies under the current changing climate.

  5. Operational evapotranspiration mapping using remote sensing and weather datasets: a new parameterization for the SSEB approach

    Science.gov (United States)

    Senay, Gabriel B.; Bohms, Stefanie; Singh, Ramesh K.; Gowda, Prasanna H.; Velpuri, Naga Manohar; Alemu, Henok; Verdin, James P.

    2013-01-01

    The increasing availability of multi-scale remotely sensed data and global weather datasets is allowing the estimation of evapotranspiration (ET) at multiple scales. We present a simple but robust method that uses remotely sensed thermal data and model-assimilated weather fields to produce ET for the contiguous United States (CONUS) at monthly and seasonal time scales. The method is based on the Simplified Surface Energy Balance (SSEB) model, which is now parameterized for operational applications, renamed as SSEBop. The innovative aspect of the SSEBop is that it uses predefined boundary conditions that are unique to each pixel for the "hot" and "cold" reference conditions. The SSEBop model was used for computing ET for 12 years (2000-2011) using the MODIS and Global Data Assimilation System (GDAS) data streams. SSEBop ET results compared reasonably well with monthly eddy covariance ET data explaining 64% of the observed variability across diverse ecosystems in the CONUS during 2005. Twelve annual ET anomalies (2000-2011) depicted the spatial extent and severity of the commonly known drought years in the CONUS. More research is required to improve the representation of the predefined boundary conditions in complex terrain at small spatial scales. SSEBop model was found to be a promising approach to conduct water use studies in the CONUS, with a similar opportunity in other parts of the world. The approach can also be applied with other thermal sensors such as Landsat.

  6. Evapotranspiration and crop coefficient of poplar and willow short-rotation coppice used as vegetation filter.

    Science.gov (United States)

    Guidi, Werther; Piccioni, Emiliano; Bonari, Enrico

    2008-07-01

    Ten-day evapotranspiration (ETc) and crop coefficient (k(c)) of willow and poplar SRC used as vegetation filter and grown under fertilised (F) and unfertilised (NF) conditions, were determined for two successive growing seasons using volumetric lysimeters. During the first growing season, total ETc observed was, respectively, 620 (NF)-1190 (F)mm in willow and 590 (NF)-725 (F) in poplar. During the second growing season, ETc showed a general increase, mainly in fertilised lysimeters where it ranged between 890 (NF)-1790 mm (F) in willow and 710 (NF)-1100 mm (NF) in poplar. kc reached in both years its maximum between the end of August and the beginning of September. In 2004 maximum kc ranged from 1.25-2.84 in willow and 1.06-1.90 in poplar, whereas in 2005 it ranged from 1.97-5.30 in willow and 1.71-4.28 in poplar. ETc seemed to be strongly correlated to plant development and mainly dependent on its nutritional status rather than on the differences between the species.

  7. Evapotranspiration partition at sub-daily scale using laser and chamber techniques

    Science.gov (United States)

    Wang, L.; Parkes, S. D.; McCabe, M. F.; Azcurra, C.; Wang, J.

    2012-12-01

    Evapotranspiration (ET) partitioning is important for quantifying the water budget and understanding vegetation control on water cycles in various ecosystems. With the development of spectroscopy-based techniques for in-situ isotope measurements, the use of stable isotope based ET partition is rising rapidly. The sub-daily scale ET partition, however, is still rarely seen in the literature. In this study, we conducted an intensive field campaign measuring ET partition using laser-based isotope and chamber techniques in a pasture system between May and June 2012 in eastern Australia. Six soil collars were used, three of which had natural vegetation and the other three were bare soil collars where vegetation was artificially removed. The vegetated and bare soil collars were used to determine the isotopic composition of ET and evaporation, respectively. The isotopic composition of the transpiration flux was determined using a Licor leaf chamber for grasses inside the vegetated collars. The diurnal patterns in isotopic compositions were observed. In the morning, the isotopic compositions were depleted. The isotopic composition of ET became more enriched and leveled off during midday. Similar patterns were found for the isotopic composition of evaporation. Overall the total ET flux over the campaign was dominated by evaporation, though transpiration contributions were high between 10am and 12pm. This study demonstrated the use of chamber-based measurements for direct partitioning of ET at sub-daily scale and showed a rarely observed diurnal pattern of ET partition.

  8. Comparison of specific-yield estimates for calculating evapotranspiration from diurnal groundwater-level fluctuations

    Science.gov (United States)

    Gribovszki, Zoltán

    2017-11-01

    Methods that use diurnal groundwater-level fluctuations are commonly used for shallow water-table environments to estimate evapotranspiration (ET) and recharge. The key element needed to obtain reliable estimates is the specific yield (Sy), a soil-water storage parameter that depends on unsaturated soil-moisture and water-table fluxes, among others. Soil-moisture profile measurement down to the water table, along with water-table-depth measurements, can provide a good opportunity to calculate Sy values even on a sub-daily scale. These values were compared with Sy estimates derived by traditional techniques, and it was found that slug-test-based Sy values gave the most similar results in a sandy soil environment. Therefore, slug-test methods, which are relatively cheap and require little time, were most suited to estimate Sy using diurnal fluctuations. The reason for this is that the timeframe of the slug-test measurement is very similar to the dynamic of the diurnal signal. The dynamic characteristic of Sy was also analyzed on a sub-daily scale (depending mostly on the speed of drainage from the soil profile) and a remarkable difference was found in Sy with respect to the rate of change of the water table. When comparing constant and sub-daily (dynamic) Sy values for ET estimation, the sub-daily Sy application yielded higher correlation, but only a slightly smaller deviation from the control ET method, compared with the usage of constant Sy.

  9. Satellite-based drought monitoring in the Sahel: Evaluation of two global physically-based evapotranspiration algorithms

    Science.gov (United States)

    Garcia, Monica; Mu, Qiaozhen; Ceccato, Pietro; Ardö, Jonas; Mougin, Eric; Kergoat, Laurent; Timouk, Franck; Sandholt, Inge; Fisher, Joshua

    2013-04-01

    Regional estimates of daily evapotranspiration and surface fluxes in water-scarce and climatic vulnerable regions are critical for improving agricultural and hydrological information as well as our understanding of land surface-atmosphere interactions. The final aim of this study is to evaluate two global operational evapotranspiration algorithms in the Sahelian grasslands of Africa, where in-situ data are scarce, relying on satellite products at 1 km spatial resolution with no field calibration or in-situ variables. Two process-based models were applied to estimate surface fluxes including evapotranspiration (ET): the global MODIS evapotranspiration algorithm (MOD16), based on a three source Penman-Monteith approach; and a version of the PT-JPL model, based on a three source Priestley-Taylor model with an apparent thermal inertia module to estimate soil moisture. Both models were forced using climatic reanalyses data from two sources: MERRA GMAO (NASA reanalysis GEOS-5) and NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research). Additionally, to assess if errors were due to algorithm assumptions or with the quality of input data in-situ climatic tower data were used to compare with results from reanalyses. All model results were compared with eddy covariance data from two field sites in Mali and Sudan spanning a total period of 5 years. Preliminary results showed a better performance of both algorithms using in-situ climatic data, with a superior performance of the PT-JPL model despite a low bias relative to the measured ET. Climatic forcing with MERRA provided better results than using NCEP data. Aggregation of results from daily to 8-day time scale decreased errors significantly. The PT-JPL model version with a thermal inertia approach to estimate soil moisture offers great potential for regionalization in regions where the main limitation to evapotranspiration is soil moisture, such as the Sahel as no field

  10. High spatial resolution WorldView-2 imagery for mapping NDVI and its relationship to temporal urban landscape evapotranspiration factors

    Science.gov (United States)

    Nouri, Hamideh; Beecham, Simon; Anderson, Sharolyn; Nagler, Pamela

    2014-01-01

    Evapotranspiration estimation has benefitted from recent advances in remote sensing and GIS techniques particularly in agricultural applications rather than urban environments. This paper explores the relationship between urban vegetation evapotranspiration (ET) and vegetation indices derived from newly-developed high spatial resolution WorldView-2 imagery. The study site was Veale Gardens in Adelaide, Australia. Image processing was applied on five images captured from February 2012 to February 2013 using ERDAS Imagine. From 64 possible two band combinations of WorldView-2, the most reliable one (with the maximum median differences) was selected. Normalized Difference Vegetation Index (NDVI) values were derived for each category of landscape cover, namely trees, shrubs, turf grasses, impervious pavements, and water bodies. Urban landscape evapotranspiration rates for Veale Gardens were estimated through field monitoring using observational-based landscape coefficients. The relationships between remotely sensed NDVIs for the entire Veale Gardens and for individual NDVIs of different vegetation covers were compared with field measured urban landscape evapotranspiration rates. The water stress conditions experienced in January 2013 decreased the correlation between ET and NDVI with the highest relationship of ET-Landscape NDVI (Landscape Normalized Difference Vegetation Index) for shrubs (r2 = 0.66) and trees (r2 = 0.63). However, when the January data was excluded, there was a significant correlation between ET and NDVI. The highest correlation for ET-Landscape NDVI was found for the entire Veale Gardens regardless of vegetation type (r2 = 0.95, p > 0.05) and the lowest one was for turf (r2 = 0.88, p > 0.05). In support of the feasibility of ET estimation by WV2 over a longer period, an algorithm recently developed that estimates evapotranspiration rates based on the Enhanced Vegetation Index (EVI) from MODIS was employed. The results revealed a significant positive

  11. Application of ANFIS and SVM Systems in Order to Estimate Monthly Reference Crop Evapotranspiration in the Northwest of Iran

    Directory of Open Access Journals (Sweden)

    F. Ahmadi

    2016-10-01

    Full Text Available Introduction Crop evapotranspiration modeling process mainly performs with empirical methods, aerodynamic and energy balance. In these methods, the evapotranspiration is calculated based on the average values of meteorological parameters at different time steps. The linear models didn’t have a good performance in this field due to high variability of evapotranspiration and the researchers have turned to the use of nonlinear and intelligent models. For accurate estimation of this hydrologic variable, it should be spending much time and money to measure many data (19. Materials and Methods Recently the new hybrid methods have been developed by combining some of methods such as artificial neural networks, fuzzy logic and evolutionary computation, that called Soft Computing and Intelligent Systems. These soft techniques are used in various fields of engineering. A fuzzy neurosis is a hybrid system that incorporates the decision ability of fuzzy logic with the computational ability of neural network, which provides a high capability for modeling and estimating. Basically, the Fuzzy part is used to classify the input data set and determines the degree of membership (that each number can be laying between 0 and 1 and decisions for the next activity made based on a set of rules and move to the next stage. Adaptive Neuro-Fuzzy Inference Systems (ANFIS includes some parts of a typical fuzzy expert system which the calculations at each step is performed by the hidden layer neurons and the learning ability of the neural network has been created to increase the system information (9. SVM is a one of supervised learning methods which used for classification and regression affairs. This method was developed by Vapink (15 based on statistical learning theory. The SVM is a method for binary classification in an arbitrary characteristic space, so it is suitable for prediction problems (12. The SVM is originally a two-class Classifier that separates the classes

  12. Evapotranspiration (ET) data at Dead River forested wetland site, Hillsborough County, Florida, December 2009 - February 2016

    Science.gov (United States)

    Swancar, Amy

    2016-01-01

    The data set consists of evapotranspiration measurements made at the USGS Dead River forested wetland climate station beginning November 21, 2009 and ending February 29, 2016. Annual ET rates corrected to a near-surface energy-budget varied from 1448 mm (2012) to 1614 mm (2010). The eddy-covariance method was used, with high-frequency sensors installed above the forest canopy to measure sensible and latent heat fluxes. Ancillary meteorological data are also included in the data set: net radiation, soil temperature and moisture, air temperature, relative humidity, wind speed and direction, rainfall, and ground-water levels. Data were collected at 30-minute resolution, with evapotranspiration corrected to the near-surface energy-budget at a daily timescale. The study was conducted at an undeveloped mixed hardwood swamp within Dead River Wilderness Park, located at the end of Dead River Rd., west of U.S. Highway 301, 27 km northeast of Tampa in Hillsborough County, Florida (latitude 28 07’ 43” N  longitude 82 15’ 44” W, Section 13, Township 27S, Range 20E). Study instruments were installed in November 2009. The 46-m instrument tower was located about 90 m northeast of the final pullout before the parking area, which is 2.6 km from the park entrance gate on Dead River Rd.  The station is within the Hillsborough River floodplain, and is inundated at high river stages (Lewelling, 2004).  The site is classified as a freshwater palustrine forested broad-leaf deciduous wetland that is seasonally flooded (U.S. Fish and Wildlife Service, 2010).  Dominant tree species are cabbage palm (Sabal palmetto), red maple (Acer rubrum), sweet-gum (Liquidambar styraciflua), live oak (Quercus virginiana), elm (Ulmus americana), with occasional slash pine, magnolia, and hickory.  Canopy height is 20-24 m.  The site is located near the middle of the floodplain at least 1 km away from different land cover types in all directions.  The floodplain extends farther to the

  13. Analysis of Evapotranspiration Model Sensitivity to Climate and Vegetation Parameters With Dependence

    Science.gov (United States)

    Levy, M. C.

    2013-12-01

    Evapotranspiration (ET) is a dominant component of the global water balance and in the study of hydroclimatic effects of climate change. However, its computation remains challenging due to the multiple environmental factors that influence the magnitude of ET flux. Therefore, understanding the sensitivity of ET models to changes in climate and vegetation inputs remains a major concern for hydrologists, biometeorologists, and climatologists. To date, sensitivity analyses (SAs) of evapotranspiration (ET) models are incomplete on two counts: 1) contemporary, data-driven SAs do not account for the effects of both climate and vegetation input variables on model output (ET estimates); and 2) SAs do not account for the effects of input variable correlation on model output. This is problematic because of the potentially dominant role of vegetation in controlling ET, and the non-trivial interactions between climate variables, and climate and vegetation variables. Ignoring the role of interactions between variables limits the value of SAs for reducing model dimensionality and guiding model calibration, and may lead to incorrect assessments of environmental system response to climate change, where the synchronies between climate variables change over time and space. The problems addressed by this study are the issues identified above: the lack of accounting for both climate and vegetation inputs, and correlated inputs, on ET model SAs. This study: 1) performs a SA of the standardized American Society of Civil Engineers (ASCE) Penman-Monteith (PM) equation for reference ET to both climate and vegetation variables using a mixed empirical and simulation based global Sobol' SA; and 2) performs a SA of ASCE PM reference ET to both climate and vegetation variables through a simulation-based analysis using a new Sobol' SA analogue developed for models with correlated input variables. At the time of completion, this study constitutes the first use of a Sobol' SA (Sobol', 2001

  14. Evapotranspiration data at Starkey pasture site, Pasco County, Florida, January 2010 - April 2016

    Science.gov (United States)

    Swancar, Amy

    2017-01-01

    This U.S. Geological Survey (USGS) data release consists of evapotranspiration measurements made at the USGS Starkey pasture climate station beginning January 1, 2010 and ending April 30, 2016. Annual ET rates corrected to a near-surface energy-budget for the 12 calendar years of record at this site (2004-2015) varied from 718 mm (2007) to 903 mm (2010). The eddy-covariance method was used, with high-frequency sensors installed above the pasture to measure sensible and latent heat fluxes. Ancillary meteorological data are also included in the data set: net radiation, soil temperature and moisture, air temperature, relative humidity, wind speed and direction, rainfall, and ground-water levels. Data were collected at 30-minute resolution, with evapotranspiration corrected to the near-surface energy-budget at that timescale. Related data sets are presented at 30-minute, daily, and monthly time intervals. The study was conducted at a nearly flat, non-irrigated site (latitude 28 13 31 N and longitude 82 33 33 W, (in degrees minutes and seconds, NAD 1927), Section 13, Township 26S, Range 17E) within the Anclote River Ranch property owned by the Southwest Florida Water Management District in Pasco County, Florida. Instrumentation was installed in April 2003. The dominant (about 80 percent of surface coverage) plant cover at the study site is bahiagrass (Paspalum notatum) that varies from a lush green during the summer to a drab brown during the winter. The bahiagrass is ungrazed and grass height can reach 0.5 meter (m). During the study, the pasture was mowed periodically to 0.2 m. Vegetation tables provided with each data release list when mowing occurred. Maximum grass rooting depth at the site is about 0.5 m. Other plants at the study site, intermixed with the bahiagrass and occurring as distinct patches, include bushy broom grass (Andropogon glomeratus), rush (Juncus spp.), dog fennel (Eupatorium capillifolium), flat-topped goldenrod (Euthamia minor), and groundsel

  15. Improved predictability of droughts over southern Africa using the standardized precipitation evapotranspiration index and ENSO

    Science.gov (United States)

    Manatsa, Desmond; Mushore, Terrence; Lenouo, Andre

    2017-01-01

    The provision of timely and reliable climate information on which to base management decisions remains a critical component in drought planning for southern Africa. In this observational study, we have not only proposed a forecasting scheme which caters for timeliness and reliability but improved relevance of the climate information by using a novel drought index called the standardised precipitation evapotranspiration index (SPEI), instead of the traditional precipitation only based index, the standardised precipitation index (SPI). The SPEI which includes temperature and other climatic factors in its construction has a more robust connection to ENSO than the SPI. Consequently, the developed ENSO-SPEI prediction scheme can provide quantitative information about the spatial extent and severity of predicted drought conditions in a way that reflects more closely the level of risk in the global warming context of the sub region. However, it is established that the ENSO significant regional impact is restricted only to the period December-March, implying a revisit to the traditional ENSO-based forecast scheme which essentially divides the rainfall season into the two periods, October to December and January to March. Although the prediction of ENSO events has increased with the refinement of numerical models, this work has demonstrated that the prediction of drought impacts related to ENSO is also a reality based only on observations. A large temporal lag is observed between the development of ENSO phenomena (typically in May of the previous year) and the identification of regional SPEI defined drought conditions. It has been shown that using the Southern Africa Regional Climate Outlook Forum's (SARCOF) traditional 3-month averaged Nino 3.4 SST index (June to August) as a predictor does not have an added advantage over using only the May SST index values. In this regard, the extended lead time and improved skill demonstrated in this study could immensely benefit

  16. Effects of climate and terrestrial storage on temporal variability of actual evapotranspiration

    Science.gov (United States)

    Wu, Chuanhao; Hu, Bill X.; Huang, Guoru; Zhang, Hang

    2017-06-01

    Knowledge of the temporal variability in actual evapotranspiration (E) is essential for a better understanding of the interaction and feedback between atmospheric and land surface hydrologic processes under various natural and anthropogenic conditions. Recently, Zeng and Cai (2015) proposed a decomposition framework of the E variance, based on water balance and the Budyko hypothesis. On the basis of a long-term (1960-2008) land surface dataset, this study applies the theoretical framework to assess the effects of climate and terrestrial storage factors on the interannual and intra-annual variance in E across China. An error decomposition framework is developed to quantify the key factors in the error of the predicted E variance. The results show that the prediction of the E variance is more accurate in arid climates than in humid climates, and the corresponding error is primarily controlled by the variability of precipitation (P) and runoff (R). Climate is the primary source for the E variance, and the dominant sources shift from potential evaporation (PET) in humid climates to P in arid climates. The interactions between P and PET tend to dampen the E interannual variance and enhance the E intra-annual variance, and this effect is especially significant in humid climates. Terrestrial storage change is more capable of accommodating climatic fluctuations at the intra-annual scale than at the interannual scale, and for some arid regions it is the dominant factor influencing the E variance. The response of terrestrial storage to P is more significant than its response to PET, especially for regions with strong human impact. Neglecting the effects of terrestrial storage would possibly underestimate or overestimate the E variance in both humid and arid climates, due to the interactions between climate and the change in the terrestrial storage.

  17. Assessing reference evapotranspiration at regional scale based on remote sensing, weather forecast and GIS tools

    Science.gov (United States)

    Ramírez-Cuesta, J. M.; Cruz-Blanco, M.; Santos, C.; Lorite, I. J.

    2017-03-01

    Reference evapotranspiration (ETo) is a key component in efficient water management, especially in arid and semi-arid environments. However, accurate ETo assessment at the regional scale is complicated by the limited number of weather stations and the strict requirements in terms of their location and surrounding physical conditions for the collection of valid weather data. In an attempt to overcome this limitation, new approaches based on the use of remote sensing techniques and weather forecast tools have been proposed. Use of the Land Surface Analysis Satellite Application Facility (LSA SAF) tool and Geographic Information Systems (GIS) have allowed the design and development of innovative approaches for ETo assessment, which are especially useful for areas lacking available weather data from weather stations. Thus, by identifying the best-performing interpolation approaches (such as the Thin Plate Splines, TPS) and by developing new approaches (such as the use of data from the most similar weather station, TS, or spatially distributed correction factors, CITS), errors as low as 1.1% were achieved for ETo assessment. Spatial and temporal analyses reveal that the generated errors were smaller during spring and summer as well as in homogenous topographic areas. The proposed approaches not only enabled accurate calculations of seasonal and daily ETo values, but also contributed to the development of a useful methodology for evaluating the optimum number of weather stations to be integrated into a weather station network and the appropriateness of their locations. In addition to ETo, other variables included in weather forecast datasets (such as temperature or rainfall) could be evaluated using the same innovative methodology proposed in this study.

  18. Water deficit and water surplus maps for Brazil, based on FAO Penman-Monteith potential evapotranspiration

    Directory of Open Access Journals (Sweden)

    Ronalton Evandro Machado

    2008-12-01

    Full Text Available The climatological water balance (CWB proposed by Thornthwaite and Mather (1957 is a useful tool for agricultural planning. This method requires the soil water holding capacity (SWHC, rainfall (R and potential evapotranspiration (PET data as input. Among the methods used to estimate PET, the one proposed by Thornthwaite (1948 is the simplest and the most used in Brazil, however it presents limitations of use, which is caused by its empirical relationships. When Thornthwaite PET method is used into the CWB, the errors associated to PET are transferred to the output variables, mainly water deficit (WD and water surplus (WS. As all maps of WD and WS for Brazil are based on Thornthwaite PET, the objective of this study was to produce new maps of these variables considering Penman-Monteith PET. For this purpose, monthly normal climate data base (1961-1990 from Brazilian Meteorological Service (INMET, with 219 locations in all country, was used. PET data were estimated by Thornthwaite (TH and FAO Penman-Monteith (PM methods. PET, from both methods, and R data were used to estimate the CWB for a SWHC of 100 mm, having as results actual ET (AET, WD and WS. Results obtained with PET from the two methods were compared by regression analysis. The results showed that TH method underestimated annual PM PET by 13% in 84% of the places. Such underestimation also led to AET and WD underestimations of 7% (in 69% of places and 40% (in 83% of places, respectively. For WS, the use of TH PET data in the CWB resulted in overestimations of about 80% in 78% of places. The differences observed in the CWB variables resulted in changes in the maps of WD and WS for Brazil. These new maps, based on PM PET, provide more accurate information, mainly for agricultural and hydrological planning and irrigation and drainage projects purposes.

  19. Performance of five surface energy balance models for estimating daily evapotranspiration in high biomass sorghum

    Science.gov (United States)

    Wagle, Pradeep; Bhattarai, Nishan; Gowda, Prasanna H.; Kakani, Vijaya G.

    2017-06-01

    Robust evapotranspiration (ET) models are required to predict water usage in a variety of terrestrial ecosystems under different geographical and agrometeorological conditions. As a result, several remote sensing-based surface energy balance (SEB) models have been developed to estimate ET over large regions. However, comparison of the performance of several SEB models at the same site is limited. In addition, none of the SEB models have been evaluated for their ability to predict ET in rain-fed high biomass sorghum grown for biofuel production. In this paper, we evaluated the performance of five widely used single-source SEB models, namely Surface Energy Balance Algorithm for Land (SEBAL), Mapping ET with Internalized Calibration (METRIC), Surface Energy Balance System (SEBS), Simplified Surface Energy Balance Index (S-SEBI), and operational Simplified Surface Energy Balance (SSEBop), for estimating ET over a high biomass sorghum field during the 2012 and 2013 growing seasons. The predicted ET values were compared against eddy covariance (EC) measured ET (ETEC) for 19 cloud-free Landsat image. In general, S-SEBI, SEBAL, and SEBS performed reasonably well for the study period, while METRIC and SSEBop performed poorly. All SEB models substantially overestimated ET under extremely dry conditions as they underestimated sensible heat (H) and overestimated latent heat (LE) fluxes under dry conditions during the partitioning of available energy. METRIC, SEBAL, and SEBS overestimated LE regardless of wet or dry periods. Consequently, predicted seasonal cumulative ET by METRIC, SEBAL, and SEBS were higher than seasonal cumulative ETEC in both seasons. In contrast, S-SEBI and SSEBop substantially underestimated ET under too wet conditions, and predicted seasonal cumulative ET by S-SEBI and SSEBop were lower than seasonal cumulative ETEC in the relatively wetter 2013 growing season. Our results indicate the necessity of inclusion of soil moisture or plant water stress

  20. Spatial pattern of reference evapotranspiration change and its temporal evolution over Southwest China

    Science.gov (United States)

    Sun, Shanlei; Wang, Guojie; Huang, Jin; Mu, Mengyuan; Yan, Guixia; Liu, Chunwei; Gao, Chujie; Li, Xing; Yin, Yixing; Zhang, Fangmin; Zhu, Siguang; Hua, Wenjian

    2017-11-01

    Due to the close relationship of climate change with reference evapotranspiration (ETo), detecting changes in ETo spatial distribution and its temporal evolution at local and regional levels is favorable to comprehensively understand climate change-induced impacts on hydrology and agriculture. In this study, the objective is to identify whether climate change has caused variation of ETo spatial distribution in different analysis periods [i.e., long- (20-year), medium- (10-year), and short-term (5-year)] and to investigate its temporal evolution (namely, when these changes happened) at annual and monthly scales in Southwest China (SWC). First, we estimated ETo values using the United Nations Food and Agriculture Organization (FAO) Penman-Monteith equation, based on historical climate data measured at 269 weather sites during 1973-2012. The analysis of variance (ANOVA) results indicated that the spatial pattern of annual ETo had significantly changed during the past 40 years, particularly in west SWC for the long-term analysis period, and west and southeast SWC in both medium- and short-term periods, which corresponded to the percent area of significant differences which were 21.9, 58.0, and 48.2 %, respectively. For investigating temporal evolution of spatial patterns of annual ETo, Duncan's multiple range test was used, and we found that the most significant changes appeared during 1988-2002 with the significant area of higher than 25.0 %. In addition, for long-, medium-, and short-term analysis periods, the spatial distribution has significantly changed during March, September, November, and December, especially in the corresponding periods of 1988-1997, 1983-1992, 1973-1977, and 1988-2002. All in all, climate change has resulted in significant ETo changes in SWC since the 1970s. Knowledge of climate change-induced spatial distribution of ETo and its temporal evolution would aid in formulating strategies for water resources and agricultural managements.

  1. Evapotranspiration in a cottonwood (Populus fremontii) restoration plantation estimated by sap flow and remote sensing methods

    Science.gov (United States)

    Nagler, P.; Jetton, A.; Fleming, J.; Didan, K.; Glenn, E.; Erker, J.; Morino, K.; Milliken, J.; Gloss, S.

    2007-01-01

    Native tree plantations have been proposed for the restoration of wildlife habitat in human-altered riparian corridors of western U.S. rivers. Evapotranspiration (ET) by riparian vegetation is an important, but poorly quantified, term in river water budgets. Native tree restoration plots will potentially increase ET. We used sap flow sensors and satellite imagery to estimate ET in a 8 ha, cottonwood (Populus fremontii) restoration plot on the Lower Colorado River. Biometric methods were used to scale leaf area to whole trees and stands of trees. This technique was used to validate our estimates of ET obtained by scaling from branch level to stand (or plot) level measurements of ET. Cottonwood trees used 6-10 mm day-1 of water during the peak of the growing season as determined by sap flow sensors, and annual rates scaled by time-series MODIS satellite imagery were approximately 1.2 m year-1. Although irrigation was not quantified, the field had been flood irrigated at 2 week intervals during the 3 years prior to the study, receiving approximately 2 m year-1 of water. A frequency-domain electromagnetic induction survey of soil moisture content showed that the field was saturated (26-28% gravimetric water content) at the 90-150 cm soil depth under the field. Trees were apparently rooted into the saturated soil, and considerable saving of water could potentially be achieved by modifying the irrigation regime to take into account that cottonwoods are phreatophytes. The study showed that cottonwood ET can be monitored by remote sensing methods calibrated with ground measurements with an accuracy or uncertainty of 20-30% in western riparian corridors. ?? 2007 Elsevier B.V. All rights reserved.

  2. Trend analysis of evapotranspiration over India: Observed from long-term satellite measurements

    Science.gov (United States)

    Goroshi, Sheshakumar; Pradhan, Rohit; Singh, Raghavendra P.; Singh, K. K.; Parihar, Jai Singh

    2017-12-01

    Owing to the lack of consistent spatial time series data on actual evapotranspiration ( ET), very few studies have been conducted on the long-term trend and variability in ET at a national scale over the Indian subcontinent. The present study uses biome specific ET data derived from NOAA satellite's advanced very high resolution radiometer to investigate the trends and variability in ET over India from 1983 to 2006. Trend analysis using the non-parametric Mann-Kendall test showed that the domain average ET decreased during the period at a rate of 0.22 mm year^{-1}. A strong decreasing trend (m = -1.75 mm year^{-1}, F = 17.41, P 0.01) was observed in forest regions. Seasonal analyses indicated a decreasing trend during southwest summer monsoon (m= -0.320 mm season^{-1} year^{-1}) and post-monsoon period (m= -0.188 mm season^{-1 } year^{-1}). In contrast, an increasing trend was observed during northeast winter monsoon (m = 0.156 mm season^{-1 } year^{-1}) and pre-monsoon (m = 0.068 mm season^{-1 } year^{-1}) periods. Despite an overall net decline in the country, a considerable increase ( 4 mm year^{-1}) was observed over arid and semi-arid regions. Grid level correlation with various climatic parameters exhibited a strong positive correlation (r >0.5) of ET with soil moisture and precipitation over semi-arid and arid regions, whereas a negative correlation (r -0.5) occurred with temperature and insolation in dry regions of western India. The results of this analysis are useful for understanding regional ET dynamics and its relationship with various climatic parameters over India. Future studies on the effects of ET changes on the hydrological cycle, carbon cycle, and energy partitioning are needed to account for the feedbacks to the climate.

  3. Causative impact of air pollution on evapotranspiration in the North China Plain.

    Science.gov (United States)

    Yao, Ling

    2017-10-01

    Atmospheric dispersion conditions strongly impact air pollution under identical surface emissions. The degree of air pollution in the Jing-Jin-Ji region is so severe that it may impose feedback on local climate. Reference evapotranspiration (ET 0 ) plays a significant role in the estimation of crop water requirements, as well as in studies on climate variation and change. Since the traditional correlation analysis cannot capture the causality, we apply the convergent cross mapping method (CCM) in this study to observationally investigate whether the air pollution impacts ET 0 . The results indicate that southwest regions of Jing-Jin-Ji always suffer higher PM 2.5 concentration than north regions through the whole year, and correlation analysis suggests that PM 2.5 concentration has a significant negative effect on ET 0 in most cities. The causality detection with CCM quantitatively demonstrates the significantly causative influence of PM 2.5 concentration on ET 0 , higher PM 2.5 concentration decreasing ET 0 . However, CCM analysis suggests that PM 2.5 concentration has a relatively weak causal influence on ET 0 while the correlation analysis gives the near zero correlation coefficient in Zhangjiakou city, indicating that the causative influence of PM 2.5 concentration on ET 0 is better revealed with CCM method than the correlation analysis. Considering that ET 0 is strongly associated with crop water requirement, the amount of water for agricultural irrigation could be reduced at high PM 2.5 concentrations. These findings can be utilized to improve the efficiency of water resources utilization, and reduce the exploiting amount of groundwater in the Jing-Jin-Ji region, although PM 2.5 is detrimental to human health. Copyright © 2017 Elsevier Inc. All rights reserved.

  4. Soil moisture and evapotranspiration of different land cover types in the Loess Plateau, China

    Science.gov (United States)

    Wang, S.; Fu, B. J.; Gao, G. Y.; Yao, X. L.; Zhou, J.

    2012-08-01

    We studied the impacts of re-vegetation on soil moisture dynamics and evapotranspiration (ET) of five land cover types in the Loess Plateau in northern China. Soil moisture and temperature variations under grass (Andropogon), subshrub (Artemisia scoparia), shrub (Spiraea pubescens), plantation forest (Robinia pseudoacacia), and crop (Zea mays) vegetation were continuously monitored during the growing season of 2011. There were more than 10 soil moisture pulses during the period of data collection. Surface soil moisture of all of the land cover types showed an increasing trend in the rainy season. Soil moisture under the corn crop was consistently higher than the other surfaces. Grass and subshrubs showed an intermediate moisture level. Grass had slightly higher readings than those of subshrub most of the time. Shrubs and plantation forests were characterized by lower soil moisture readings, with the shrub levels consistently being slightly higher than those of the forests. Despite the greater post-rainfall loss of moisture under subshrub and grass vegetation than forests and shrubs, subshrub and grass sites exhibit a higher soil moisture content due to their greater soil retention capacity in the dry period. The daily ET trends of the forests and shrub sites were similar and were more stable than those of the other types. Soils under subshrubs acquired and retained soil moisture resources more efficiently than the other cover types, with a competitive advantage in the long term, representing an adaptive vegetation type in the study watershed. The interactions between vegetation and soil moisture dynamics contribute to structure and function of the ecosystems studied.

  5. Sensitivity analysis of monthly reference crop evapotranspiration trends in Iran: a qualitative approach

    Science.gov (United States)

    Mosaedi, Abolfazl; Ghabaei Sough, Mohammad; Sadeghi, Sayed-Hossein; Mooshakhian, Yousof; Bannayan, Mohammad

    2017-05-01

    The main objective of this study was to analyze the sensitivity of the monthly reference crop evapotranspiration (ETo) trends to key climatic factors (minimum and maximum air temperature ( T max and T min), relative humidity (RH), sunshine hours ( t sun), and wind speed ( U 2)) in Iran by applying a qualitative detrended method, rather than the historical mathematical approach. Meteorological data for the period of 1963-2007 from five synoptic stations with different climatic characteristics, including Mashhad (mountains), Tabriz (mountains), Tehran (semi-desert), Anzali (coastal wet), and Shiraz (semi-mountains) were used to address this objective. The Mann-Kendall test was employed to assess the trends of ETo and the climatic variables. The results indicated a significant increasing trend of the monthly ETo for Mashhad and Tabriz for most part of the year while the opposite conclusion was drawn for Tehran, Anzali, and Shiraz. Based on the detrended method, RH and U 2 were the two main variables enhancing the negative ETo trends in Tehran and Anzali stations whereas U 2 and temperature were responsible for this observation in Shiraz. On the other hand, the main meteorological variables affecting the significant positive trend of ETo were RH and t sun in Tabriz and T min, RH, and U 2 in Mashhad. Although a relative agreement was observed in terms of identifying one of the first two key climatic variables affecting the ETo trend, the qualitative and the quantitative sensitivity analysis solutions did never coincide. Further research is needed to evaluate this interesting finding for other geographic locations, and also to search for the major causes of this discrepancy.

  6. Combining remote sensing and water-balance evapotranspiration estimates for the conterminous United States

    Science.gov (United States)

    Reitz, Meredith; Senay, Gabriel; Sanford, Ward E.

    2017-01-01

    Evapotranspiration (ET) is a key component of the hydrologic cycle, accounting for ~70% of precipitation in the conterminous U.S. (CONUS), but it has been a challenge to predict accurately across different spatio-temporal scales. The increasing availability of remotely sensed data has led to significant advances in the frequency and spatial resolution of ET estimates, derived from energy balance principles with variables such as temperature used to estimate surface latent heat flux. Although remote sensing methods excel at depicting spatial and temporal variability, estimation of ET independently of other water budget components can lead to inconsistency with other budget terms. Methods that rely on ground-based data better constrain long-term ET, but are unable to provide the same temporal resolution. Here we combine long-term ET estimates from a water-balance approach with the SSEBop (operational Simplified Surface Energy Balance) remote sensing-based ET product for 2000–2015. We test the new combined method, the original SSEBop product, and another remote sensing ET product (MOD16) against monthly measurements from 119 flux towers. The new product showed advantages especially in non-irrigated areas where the new method showed a coefficient of determination R2 of 0.44, compared to 0.41 for SSEBop or 0.35 for MOD16. The resulting monthly data set will be a useful, unique contribution to ET estimation, due to its combination of remote sensing-based variability and ground-based long-term water balance constraints.

  7. Dynamic hyporheic exchange at intermediate timescales: Testing the relative importance of evapotranspiration and flood pulses

    Science.gov (United States)

    Larsen, Laurel G.; Harvey, Judson W.; Maglio, Morgan M.

    2014-01-01

    Hyporheic fluxes influence ecological processes across a continuum of timescales. However, few studies have been able to characterize hyporheic fluxes and residence time distributions (RTDs) over timescales of days to years, during which evapotranspiration (ET) and seasonal flood pulses create unsteady forcing. Here we present a data-driven, particle-tracking piston model that characterizes hyporheic fluxes and RTDs based on measured vertical head differences. We used the model to test the relative influence of ET and seasonal flood pulses in the Everglades (FL, USA), in a manner applicable to other low-energy floodplains or broad, shallow streams. We found that over the multiyear timescale, flood pulses that drive relatively deep (˜1 m) flow paths had the dominant influence on hyporheic fluxes and residence times but that ET effects were discernible at shorter timescales (weeks to months) as a break in RTDs. Cumulative RTDs on either side of the break were generally well represented by lognormal functions, except for when ET was strong and none of the standard distributions applied to the shorter timescale. At the monthly timescale, ET increased hyporheic fluxes by 1-2 orders of magnitude; it also decreased 6 year mean residence times by 53-87%. Long, slow flow paths driven by flood pulses increased 6 year hyporheic fluxes by another 1-2 orders of magnitude, to a level comparable to that induced over the short term by shear flow in streams. Results suggest that models of intermediate-timescale processes should include at least two-storage zones with different RTDs, and that supporting field data collection occur over 3-4 years.

  8. Stand-level variation in evapotranspiration in non-water-limited eucalypt forests

    Science.gov (United States)

    Benyon, Richard G.; Nolan, Rachael H.; Hawthorn, Sandra N. D.; Lane, Patrick N. J.

    2017-08-01

    To better understand water and energy cycles in forests over years to decades, measurements of spatial and long-term temporal variability in evapotranspiration (Ea) are needed. In mountainous terrain, plot-level measurements are important to achieving this. Forest inventory data including tree density and size measurements, often collected repeatedly over decades, sample the variability occurring within the geographic and topographic range of specific forest types. Using simple allometric relationships, tree stocking and size data can be used to estimate variables including sapwood area index (SAI), which may be strongly correlated with annual Ea. This study analysed plot-level variability in SAI and its relationship with overstorey and understorey transpiration, interception and evaporation over a 670 m elevation gradient, in non-water-limited, even-aged stands of Eucalyptus regnans F. Muell. to determine how well spatial variation in annual Ea from forests can be mapped using SAI. Over the 3 year study, mean sap velocity in five E. regnans stands was uncorrelated with overstorey sapwood area index (SAI) or elevation: annual transpiration was predicted well by SAI (R2 0.98). Overstorey and total annual interception were positively correlated with SAI (R2 0.90 and 0.75). Ea from the understorey was strongly correlated with vapour pressure deficit (VPD) and net radiation (Rn) measured just above the understorey, but relationships between understorey Ea and VPD and Rn differed between understorey types and understorey annual Ea was not correlated with SAI. Annual total Ea was also strongly correlated with SAI: the relationship being similar to two previous studies in the same region, despite differences in stand age and species. Thus, spatial variation in annual Ea can be reliably mapped using measurements of SAI.

  9. Long-term change analysis of satellite-based evapotranspiration over Indian vegetated surface

    Science.gov (United States)

    Gupta, Shweta; Bhattacharya, Bimal K.; Krishna, Akhouri P.

    2016-05-01

    In the present study, trend of satellite based annual evapotranspiration (ET) and natural forcing factors responsible for this were analyzed. Thirty years (1981-2010) of ET data at 0.08° grid resolution, generated over Indian region from opticalthermal observations from NOAA PAL and MODIS AQUA satellites, were used. Long-term data on gridded (0.5° x 0.5°) annual rainfall (RF), annual mean surface soil moisture (SSM) ERS scatterometer at 25 km resolution and annual mean incoming shortwave radiation from MERRA-2D reanalysis were also analyzed. Mann-Kendall tests were performed with time series data for trend analysis. Mean annual ET loss from Indian ago-ecosystem was found to be almost double (1100 Cubic Km) than Indian forest ecosystem (550 Cubic Km). Rainfed vegetation systems such as forest, rainfed cropland, grassland showed declining ET trend @ - 4.8, -0.6 &-0.4 Cubic Kmyr-1, respectively during 30 years. Irrigated cropland initially showed ET decline upto 1995 @ -0.8 cubic Kmyr-1 which could possibly be due to solar dimming followed by increasing ET @ 0.9 cubic Kmyr-1 after 1995. A cross-over point was detected between forest ET decline and ET increase in irrigated cropland during 2008. During 2001-2010, the four agriculturally important Indian states eastern, central, western and southern showed significantly increasing ET trend with S-score of 15-25 and Z-score of 1.09-2.9. Increasing ET in western and southern states was found to be coupled with increase in annual rainfall and SSM. But in eastern and central states no significant trend in rainfall was observed though significant increase in ET was noticed. The study recommended to investigate the influence of anthropogenic factors such as increase in area under irrigation, increased use of water for irrigation through ground water pumping, change in cropping pattern and cultivars on increasing ET.

  10. Rice evapotranspiration at the field and canopy scales under water-saving irrigation

    Science.gov (United States)

    Liu, Xiaoyin; Xu, Junzeng; Yang, Shihong; Zhang, Jiangang

    2017-02-01

    Evapotranspiration (ET) is an important process of land surface water and thermal cycling, with large temporal and spatial variability. To reveal the effect of water-saving irrigation (WSI) on rice ET at different spatial scales and understand the cross spatial scale difference, rice ET under WSI condition at canopy (ETCML) and field scale (ETEC) were measured simultaneously by mini-lysimeter and eddy covariance (EC) in the rice season of 2014. To overcome the shortage of energy balance deficit by EC system, and evaluate the influence of energy balance closure degree on ETEC, ETEC was corrected as ET_{EC}^{*} by energy balance closure correction according to the evaporative fraction. Seasonal average daily ETEC, ET_{EC}^{*} and ETCML of rice under WSI practice were estimated as 3.12, 4.03 and 4.35 mm day-1, smaller than the values reported in flooded paddy fields. Daily ETEC, ET_{EC}^{*} and ETCML varied in a similar trends and reached the maximum in late tillering, then decreased along with the crop growth in late season. The value of ETEC was much lower than ETCML, and was frequently 1-2 h lagged behind ETCML. It indicated that the energy balance deficit resulted in underestimation of crop ET by EC system. The corrected value of ET_{EC}^{*} matched ETCML much better than ETEC, with a smaller RMSE (0.086 mm h-1) and higher R 2 (0.843) and IOA (0.961). The time lapse between ET_{EC}^{*} and ETCML was mostly shortened to less than 0.5 h. The multiple stepwise regression analysis indicated that net radiation (R n) is the dominant factor for rice ET, and soil moisture (θ) is another significant factor (p rice fields. The difference between ETCML and ET_{EC}^{*} (ET_{CML} - ET_{EC^{*} ) were significantly (p rice ET in WSI fields, and for its cross scale conversion.

  11. Evapotranspiration Within the Groundwater Model Domain of the Tuba City, Arizona, Disposal Site Interim Report

    Energy Technology Data Exchange (ETDEWEB)

    None, None

    2015-03-01

    The revised groundwater model includes estimates of evapotranspiration (ET). The types of vegetation and the influences of ET on groundwater hydrology vary within the model domain. Some plant species within the model domain, classified as phreatophytes, survive by extracting groundwater. ET within these plant communities can result in a net discharge of groundwater if ET exceeds precipitation. Other upland desert plants within the model domain survive on meteoric water, potentially limiting groundwater recharge if ET is equivalent to precipitation. For all plant communities within the model domain, excessive livestock grazing or other disturbances can tip the balance to a net groundwater recharge. This task characterized and mapped vegetation within the groundwater model domain at the Tuba City, Arizona, Site, and then applied a remote sensing algorithm to estimate ET for each vegetation type. The task was designed to address five objectives: 1. Characterize and delineate different vegetation or ET zones within the groundwater model domain, focusing on the separation of plant communities with phreatophytes that survive by tapping groundwater and upland plant communities that are dependent on precipitation. 2. Refine a remote sensing method, developed to estimate ET at the Monument Valley site, for application at the Tuba City site. 3. Estimate recent seasonal and annual ET for all vegetation zones, separating phreatophytic and upland plant communities within the Tuba City groundwater model domain. 4. For selected vegetation zones, estimate ET that might be achieved given a scenario of limited livestock grazing. 5. Analyze uncertainty of ET estimates for each vegetation zone and for the entire groundwater model domain.

  12. Evapotranspiration Dynamics and Effects on Groundwater Recharge and Discharge at the Tuba City, Arizona, Disposal Site

    Energy Technology Data Exchange (ETDEWEB)

    None, None

    2016-02-01

    The U.S. Department of Energy Office of Legacy Management is evaluating groundwater flow and contaminant transport at a former uranium mill site near Tuba City, Arizona. We estimated effects of temporal and spatial variability in evapotranspiration (ET) on recharge and discharge within a groundwater model domain (GMD) as part of this evaluation. We used remote sensing algorithms and precipitation (PPT) data to estimate ET and the ET/PPT ratios within the 3531 hectare GMD. For the period from 2000 to 2012, ET and PPT were nearly balanced (129 millimeters per year [mm yr-1] and 130 mm yr-1, respectively; ET/PPT = 0.99). However, seasonal and annual variability in ET and PPT were out of phase, and spatial variability in vegetation differentiated discharge and recharge areas within the GMD. Half of ET occurred during spring and early summer when PPT was low, and about 70% of PPT arriving in fall and winter was discharged as plant transpiration in the spring and summer period. Vegetation type and health had a significant effect on the site water balance. Plant cover and ET were significantly higher (1) during years of lighter compared to years of heavier grazing pressure, and (2) on rangeland protected from grazing compared to rangeland grazed by livestock. Heavy grazing increased groundwater recharge (PPT > ET over the 13-year period). Groundwater discharge (ET > PPT over the 13-year period) was highest in riparian phreatophyte communities but insignificant in desert phreatophyte communities impacted by heavy grazing. Grazing management in desert upland and phreatophyte communities may result in reduced groundwater recharge, increased groundwater discharge, and could be used to influence local groundwater flow.

  13. Combining land surface models and remote sensing data to estimate evapotranspiration for drought monitoring in Europe

    Science.gov (United States)

    Cammalleri, C.; Sepulcre-Cantó, G.; Vogt, J.

    2014-10-01

    The main hydrologic feedback from the land-surface to the atmosphere is the evapotranspiration, ET, which embraces the response of both the soil and vegetated surface to the atmospheric forcing (e.g., precipitation and temperature), as well as influences locally atmospheric humidity, cloud formation and precipitation, the main driver for drought. Actual ET is regulated by several factors, including biological quantities (e.g., rooting depth, leaf area, fraction of absorbed photosynthetically active radiation) and soil water status. The ET temporal dynamic is strongly affected by rainfall deficits, and in turn it represents a robust proxy of the effects of water shortage on plants. These characteristics make ET a promising quantity for monitoring environmental drought, defined as a shortage of water availability that reduces the ecosystem productivity. In the last few decades, the capability to accurately model ET over large areas in a spatial-distributed fashion has increased notably. Most of the improvements in this field are related to the increasing availability of remote sensing data, and the achievements in modelling of ET-related quantities. Several land-surface models exploit the richness of newly available datasets, including the Community Land Model (CLM) and the Meteosat Second Generation (MSG) ET outputs. Here, the potentiality of ET maps obtained by combining land-surface models and remote sensing data through these two schemes is explored, with a special focus on the reliability of ET (and derived standardized variables) as drought indicator. Tests were performed over Europe at moderate spatial resolution (3-5 km), with the final goal to improve the estimation of soil water status as a contribution to the European Drought Observatory (EDO, http://edo.jrc.ec.europa.eu).

  14. Evapotranspiration of urban landscapes in Los Angeles, California at the municipal scale

    Science.gov (United States)

    Litvak, E.; Manago, K. F.; Hogue, T. S.; Pataki, D. E.

    2017-05-01

    Evapotranspiration (ET), an essential process in biosphere-atmosphere interactions, is highly uncertain in cities that maintain cultivated and irrigated landscapes. We estimated ET of irrigated landscapes in Los Angeles by combining empirical models of turfgrass ET and tree transpiration derived from in situ measurements with previously developed remotely sensed estimates of vegetation cover and ground-based vegetation surveys. We modeled irrigated landscapes as a two-component system comprised of trees and turfgrass to assess annual and spatial patterns of ET. Annual ET from vegetated landscapes (ETveg) was 1110 ± 53 mm/yr and ET from the whole city (vegetated and nonvegetated areas, ETland) was three times smaller, reflecting the fractional vegetation cover. With the exception of May and June, monthly ETland was significantly higher than predicted by the North American Land Data Assimilation System. ETveg was close to potential ET, indicating abundant irrigation inputs. Monthly averaged ETveg varied from 1.5 ± 0.1 mm/d (December) to 4.3 ± 0.2 mm/d (June). Turfgrass was responsible for ˜70% of ETveg. For trees, angiosperm species (71% of all trees) contributed over 90% to total tree transpiration, while coniferous and palm species made very small contributions. ETland was linearly correlated with median household income across the city, confirming the importance of social factors in determining spatial distribution of urban vegetation. These estimates have important implications for constraining the municipal water budget of Los Angeles and improving regional-scale hydrologic models, as well as for developing water-saving practices. The methodology used in this study is also transferable to other semiarid regions for quantification of urban landscape ET.

  15. Mapping daily evapotranspiration at field to continental scales using geostationary and polar orbiting satellite imagery

    Directory of Open Access Journals (Sweden)

    M. C. Anderson

    2011-01-01

    Full Text Available Thermal infrared (TIR remote sensing of land-surface temperature (LST provides valuable information about the sub-surface moisture status required for estimating evapotranspiration (ET and detecting the onset and severity of drought. While empirical indices measuring anomalies in LST and vegetation amount (e.g., as quantified by the Normalized Difference Vegetation Index; NDVI have demonstrated utility in monitoring ET and drought conditions over large areas, they may provide ambiguous results when other factors (e.g., air temperature, advection are affecting plant functioning. A more physically based interpretation of LST and NDVI and their relationship to sub-surface moisture conditions can be obtained with a surface energy balance model driven by TIR remote sensing. The Atmosphere-Land Exchange Inverse (ALEXI model is a multi-sensor TIR approach to ET mapping, coupling a two-source (soil + canopy land-surface model with an atmospheric boundary layer model in time-differencing mode to routinely and robustly map daily fluxes at continental scales and 5 to 10-km resolution using thermal band imagery and insolation estimates from geostationary satellites. A related algorithm (DisALEXI spatially disaggregates ALEXI fluxes down to finer spatial scales using moderate resolution TIR imagery from polar orbiting satellites. An overview of this modeling approach is presented, along with strategies for fusing information from multiple satellite platforms and wavebands to map daily ET down to resolutions on the order of 10 m. The ALEXI/DisALEXI model has potential for global applications by integrating data from multiple geostationary meteorological satellite systems, such as the US Geostationary Operational Environmental Satellites, the European Meteosat satellites, the Chinese Fen-yung 2B series, and the Japanese Geostationary Meteorological Satellites. Work is underway to further evaluate multi-scale ALEXI implementations over the US, Europe, Africa

  16. Soil moisture and evapotranspiration of different land cover types in the Loess Plateau, China

    Directory of Open Access Journals (Sweden)

    S. Wang

    2012-08-01

    Full Text Available We studied the impacts of re-vegetation on soil moisture dynamics and evapotranspiration (ET of five land cover types in the Loess Plateau in northern China. Soil moisture and temperature variations under grass (Andropogon, subshrub (Artemisia scoparia, shrub (Spiraea pubescens, plantation forest (Robinia pseudoacacia, and crop (Zea mays vegetation were continuously monitored during the growing season of 2011. There were more than 10 soil moisture pulses during the period of data collection. Surface soil moisture of all of the land cover types showed an increasing trend in the rainy season. Soil moisture under the corn crop was consistently higher than the other surfaces. Grass and subshrubs showed an intermediate moisture level. Grass had slightly higher readings than those of subshrub most of the time. Shrubs and plantation forests were characterized by lower soil moisture readings, with the shrub levels consistently being slightly higher than those of the forests. Despite the greater post-rainfall loss of moisture under subshrub and grass vegetation than forests and shrubs, subshrub and grass sites exhibit a higher soil moisture content due to their greater soil retention capacity in the dry period. The daily ET trends of the forests and shrub sites were similar and were more stable than those of the other types. Soils under subshrubs acquired and retained soil moisture resources more efficiently than the other cover types, with a competitive advantage in the long term, representing an adaptive vegetation type in the study watershed. The interactions between vegetation and soil moisture dynamics contribute to structure and function of the ecosystems studied.

  17. Estimating Evapotranspiration of an Apple Orchard Using a Remote Sensing-Based Soil Water Balance

    Directory of Open Access Journals (Sweden)

    Magali Odi-Lara

    2016-03-01

    Full Text Available The main goal of this research was to estimate the actual evapotranspiration (ETc of a drip-irrigated apple orchard located in the semi-arid region of Talca Valley (Chile using a remote sensing-based soil water balance model. The methodology to estimate ETc is a modified version of the Food and Agriculture Organization of the United Nations (FAO dual crop coefficient approach, in which the basal crop coefficient (Kcb was derived from the soil adjusted vegetation index (SAVI calculated from satellite images and incorporated into a daily soil water balance in the root zone. A linear relationship between the Kcb and SAVI was developed for the apple orchard Kcb = 1.82·SAVI − 0.07 (R2 = 0.95. The methodology was applied during two growing seasons (2010–2011 and 2012–2013, and ETc was evaluated using latent heat fluxes (LE from an eddy covariance system. The results indicate that the remote sensing-based soil water balance estimated ETc reasonably well over two growing seasons. The root mean square error (RMSE between the measured and simulated ETc values during 2010–2011 and 2012–2013 were, respectively, 0.78 and 0.74 mm·day−1, which mean a relative error of 25%. The index of agreement (d values were, respectively, 0.73 and 0.90. In addition, the weekly ETc showed better agreement. The proposed methodology could be considered as a useful tool for scheduling irrigation and driving the estimation of water requirements over large areas for apple orchards.

  18. Dynamic hyporheic exchange at intermediate timescales: testing the relative importance of evapotranspiration and flood pulses

    Science.gov (United States)

    Larsen, Laurel G.; Harvey, Judson W.; Maglio, Morgan M.

    2014-01-01

    Hyporheic fluxes influence ecological processes across a continuum of timescales. However, few studies have been able to characterize hyporheic fluxes and residence time distributions (RTDs) over timescales of days to years, during which evapotranspiration (ET) and seasonal flood pulses create unsteady forcing. Here we present a data-driven, particle-tracking piston model that characterizes hyporheic fluxes and RTDs based on measured vertical head differences. We used the model to test the relative influence of ET and seasonal flood pulses in the Everglades (FL, USA), in a manner applicable to other low-energy floodplains or broad, shallow streams. We found that over the multiyear timescale, flood pulses that drive relatively deep (∼1 m) flow paths had the dominant influence on hyporheic fluxes and residence times but that ET effects were discernible at shorter timescales (weeks to months) as a break in RTDs. Cumulative RTDs on either side of the break were generally well represented by lognormal functions, except for when ET was strong and none of the standard distributions applied to the shorter timescale. At the monthly timescale, ET increased hyporheic fluxes by 1–2 orders of magnitude; it also decreased 6 year mean residence times by 53–87%. Long, slow flow paths driven by flood pulses increased 6 year hyporheic fluxes by another 1–2 orders of magnitude, to a level comparable to that induced over the short term by shear flow in streams. Results suggest that models of intermediate-timescale processes should include at least two-storage zones with different RTDs, and that supporting field data collection occur over 3–4 years.

  19. Clarify the role of evapotranspiration in improving the predictability of summer droughts over US Great Plains

    Science.gov (United States)

    Fu, R.; Chakraborty, S.; Fernando, N.; Sun, Y.; Pu, B.; Zhuang, Y.; Tang, W.

    2016-12-01

    Although the importance of land-surface feedbacks to summer drought predictability has been recognized for decades, it is still not clear whether such feedbacks could improve drought predictability on the seasonal scale. We explore the roles of soil moisture/vegetation in determining persistent drought memory over the US Great Plains (GP) using a suite of satellite datasets (SMAP/SMOS, GOME2/OCO-2, GRACE), the North America Land Data Assimilation Systems (NLDAS) and the North America Reanalysis (NARR) products. Our results suggest that a combined knowledge about soil moisture, vegetation photosynthesis, and evapotranspiration (ET) is important for drought monitoring and early warning. Over warmer and less densely vegetated areas, such as the southern GP (SGP), ET reducion appears to be a result of the soil moisture deficit caused by a rainfall deficit. Soil moisture anomalies, as measured by SMAP/SMOS, can be an effective indictor for drought monitoring. Over colder and denser vegetated area, such as over the northern GP (NGP), an increase of vegetation photosynthesis and ET responding to warmer spring temperature can exacerbate the depletion of soil moisture in summer. Thus, a combination of the observations of vegetation photosynthesis and subsurface soil moisture are important for drought monitoring and early warning. The persistent spring-to-summer drought memory is a result of multi-scale coupling between ET, the atmospheric boundary layer, clouds, rainfall and large-scale drought circulation. To explore the importance of ET to the improvement of drought predictability on seasonal scale, we use a process-based statistical model to hindcast and predict summer rainfall and soil moisture anomalies using combined soil moisture/photosynthesis/terrestrial water storage index, lower tropospheric instability and large-scale mid-tropospheric circulation anomalies observed in spring. The higher seasonal prediction skills achieved by the statistical model than the

  20. Estimating Field Scale Crop Evapotranspiration using Landsat and MODIS Satellite Observations

    Science.gov (United States)

    Wong, A.; Jin, Y.; Snyder, R. L.; Daniele, Z.; Gao, F.

    2016-12-01

    Irrigation accounts for 80% of human freshwater consumption, and most of it return to the atmosphere through Evapotranspiration (ET). Given the challenges of already-stressed water resources and ground water regulation in California, a cost-effective, timely, and consistent spatial estimate of crop ET, from the farm to watershed level, is becoming increasingly important. The Priestley-Taylor (PT) approach, calibrated with field data and driven by satellite observations, shows great promise for accurate ET estimates across diverse ecosystems. We here aim to improve the robustness of the PT approach in agricultural lands, to enable growers and farm managers to tailor irrigation management based on in-field spatial variability and in-season variation. We optimized the PT coefficients for each crop type with available ET measurements from eddy covariance towers and/or surface renewal stations at six crop fields (Alfalfa, Almond, Citrus, Corn, Pistachio and Rice) in California. Good agreement was found between satellite-based estimates and field measurements of net radiation, with a RMSE of less than 36 W m-2. The crop type specific optimization performed well, with a RMSE of 30 W m-2 and a correlation of 0.81 for predicted daily latent heat flux. The calibrated algorithm was used to estimate ET at 30 m resolution over the Sacramento-San Joaquin Delta region for 2015 water year. It captures well the seasonal dynamics and spatial distribution of ET in Sacramento-San Joaquin Delta. A continuous monitoring of the dynamics and spatial heterogeneity of canopy and consumptive water use at a field scale, will help the growers to be well prepared and informed to adaptively manage water, canopy, and grove density to maximize the yield with the least amount of water.

  1. Identifying the interferences of irrigation on evapotranspiration variability over the Northern High Plains

    Science.gov (United States)

    Zeng, R.; Cai, X.

    2016-12-01

    Irrigation has considerably interfered with hydrological processes in arid and semi-arid areas with heavy irrigated agriculture. With the increasing demand for food production and evaporative demand due to climate change, irrigation water consumption is expected to increase, which would aggravate the interferences to hydrologic processes. Current studies focus on the impact of irrigation on the mean value of evapotranspiration (ET) at either local or regional scale, however, how irrigation changes the variability of ET has not been well understood. This study analyzes the impact of extensive irrigation on ET variability in the Northern High Plains. We apply an ET variance decomposition framework developed from our previous work to quantify the effects of both climate and irrigation on ET variance in the Northern High Plains watersheds. Based on climate and water table observations, we assess the monthly ET variance and its components for two periods: 1930s-1960s with less irrigation development 970s-2010s with more development. It is found that irrigation not only caused the well-recognized groundwater drawdown and stream depletion problems in the region, but also buffered ET variance from climatic fluctuations. In addition to increasing food productivity, irrigation also stabilizes crop yield by mitigating the impact of hydroclimatic variability. With complementary water supply from irrigation, ET often approaches to the potential ET, and thus the observed ET variance is more attributed to climatic variables especially temperature; meanwhile irrigation causes significant seasonal fluctuations to groundwater storage. For sustainable water resources management in the Northern High Plains, we argue that both the mean value and the variance of ET should be considered together for the regulation of irrigation in this region.

  2. Evapotranspiration across plant types and geomorphological units in polygonal Arctic tundra

    Science.gov (United States)

    Raz-Yaseef, Naama; Young-Robertson, Jessica; Rahn, Thom; Sloan, Victoria; Newman, Brent; Wilson, Cathy; Wullschleger, Stan D.; Torn, Margaret S.

    2017-10-01

    Coastal tundra ecosystems are relatively flat, and yet display large spatial variability in ecosystem traits. The microtopographical differences in polygonal geomorphology produce heterogeneity in permafrost depth, soil temperature, soil moisture, soil geochemistry, and plant distribution. Few measurements have been made, however, of how water fluxes vary across polygonal tundra plant types, limiting our ability to understand and model these ecosystems. Our objective was to investigate how plant distribution and geomorphological location affect actual evapotranspiration (ET). These effects are especially critical in light of the rapid change polygonal tundra systems are experiencing with Arctic warming. At a field site near Barrow, Alaska, USA, we investigated the relationships between ET and plant cover in 2014 and 2015. ET was measured at a range of spatial and temporal scales using: (1) An eddy covariance flux tower for continuous landscape-scale monitoring; (2) An automated clear surface chamber over dry vegetation in a fixed location for continuous plot-scale monitoring; and (3) Manual measurements with a clear portable chamber in approximately 60 locations across the landscape. We found that variation in environmental conditions and plant community composition, driven by microtopographical features, has significant influence on ET. Among plant types, ET from moss-covered and inundated areas was more than twice that from other plant types. ET from troughs and low polygonal centers was significantly higher than from high polygonal centers. ET varied seasonally, with peak fluxes of 0.14 mm h-1 in July. Despite 24 hours of daylight in summer, diurnal fluctuations in incoming solar radiation and plant processes produced a diurnal cycle in ET. Combining the patterns we observed with projections for the impact of permafrost degradation on polygonal structure suggests that microtopographic changes associated with permafrost thaw have the potential to alter tundra

  3. Quantifying Climatic Impact on Reference Evapotranspiration Trends in the Huai River Basin of Eastern China

    Directory of Open Access Journals (Sweden)

    Meng Li

    2018-02-01

    Full Text Available Reference evapotranspiration (ETref is an important study object for hydrological cycle processes in the context of drought-flood risks of the Huai River Basin (HRB. In this study, the FAO-56 Penman–Monteith (PM model was employed to calculate seasonal and annual ETref based on 137 meteorological station data points in HRB from 1961 to 2014. The Mann–Kendall (MK trend analysis was adopted together with Theil–Sen’s estimator to detect tendencies of ETref and climate factors. Furthermore, a developed differential equation method based on the FAO-56 PM model was applied to quantify the sensitivities of ETref to meteorological factors and their contributions to ETref trends. The results showed that the ETref demonstrated a strong spatially heterogeneity in the whole HRB at each time scale. ETref showed a significant decreasing trend in the upper-middle HRB and Yi-Shu-Si River Basin, especially at the annual time scale, in growing season and summer, while a generally increasing trend in ETref was detected in the lower HRB, and the significance only showed in spring. These phenomena could be reasonably explained by a significantly increasing mean temperature (TA, a significantly decreasing wind speed (WS, solar radiation (SR, and a slightly decreasing relative humidity (RH. The most sensitive factor to ETref was RH in most sub-regions and most time scales, except in the growing season and summer. Based on the developed differential equation method, the dominant factor of the decreasing ETref was WS in the annual time scale, spring, autumn, and winter in most sub-regions, except the lower HRB, which then shifted to SR in the growing season and summer. However, in the lower HRB, the significantly decreasing RH was the most dominant factor, especially in the annual time scale, growing season, and spring, which might be responsible for the slightly increasing ETref there.

  4. Estimating Agricultural Water Use using the Operational Simplified Surface Energy Balance Evapotranspiration Estimation Method

    Science.gov (United States)

    Forbes, B. T.

    2015-12-01

    Due to the predominantly arid climate in Arizona, access to adequate water supply is vital to the economic development and livelihood of the State. Water supply has become increasingly important during periods of prolonged drought, which has strained reservoir water levels in the Desert Southwest over past years. Arizona's water use is dominated by agriculture, consuming about seventy-five percent of the total annual water demand. Tracking current agricultural water use is important for managers and policy makers so that current water demand can be assessed and current information can be used to forecast future demands. However, many croplands in Arizona are irrigated outside of areas where water use reporting is mandatory. To estimate irrigation withdrawals on these lands, we use a combination of field verification, evapotranspiration (ET) estimation, and irrigation system qualification. ET is typically estimated in Arizona using the Modified Blaney-Criddle method which uses meteorological data to estimate annual crop water requirements. The Modified Blaney-Criddle method assumes crops are irrigated to their full potential over the entire growing season, which may or may not be realistic. We now use the Operational Simplified Surface Energy Balance (SSEBop) ET data in a remote-sensing and energy-balance framework to estimate cropland ET. SSEBop data are of sufficient resolution (30m by 30m) for estimation of field-scale cropland water use. We evaluate our SSEBop-based estimates using ground-truth information and irrigation system qualification obtained in the field. Our approach gives the end user an estimate of crop consumptive use as well as inefficiencies in irrigation system performance—both of which are needed by water managers for tracking irrigated water use in Arizona.

  5. Ecosystem Evapotranspiration as a Response to Climate and Vegetation Coverage Changes in Northwest Yunnan, China.

    Directory of Open Access Journals (Sweden)

    Hao Yang

    Full Text Available Climate and human-driven changes play an important role in regional droughts. Northwest Yunnan Province is a key region for biodiversity conservation in China, and it has experienced severe droughts since the beginning of this century; however, the extent of the contributions from climate and human-driven changes remains unclear. We calculated the ecosystem evapotranspiration (ET and water yield (WY of northwest Yunnan Province, China from 2001 to 2013 using meteorological and remote sensing observation data and a Surface Energy Balance System (SEBS model. Multivariate regression analyses were used to differentiate the contribution of climate and vegetation coverage to ET. The results showed that the annual average vegetation coverage significantly increased over time with a mean of 0.69 in spite of the precipitation fluctuation. Afforestation/reforestation and other management efforts attributed to vegetation coverage increase in NW Yunnan. Both ET and WY considerably fluctuated with the climate factors, which ranged from 623.29 mm to 893.8 mm and -51.88 mm to 384.40 mm over the time period. Spatially, ET in the southeast of NW Yunnan (mainly in Lijiang increased significantly, which was in line with the spatial trend of vegetation coverage. Multivariate linear regression analysis indicated that climatic factors accounted for 85.18% of the ET variation, while vegetation coverage explained 14.82%. On the other hand, precipitation accounted for 67.5% of the WY. We conclude that the continuous droughts in northwest Yunnan were primarily climatically driven; however, man-made land cover and vegetation changes also increased the vulnerability of local populations to drought. Because of the high proportion of the water yield consumed for subsistence and poor infrastructure for water management, local populations have been highly vulnerable to climate drought conditions. We suggest that conservation of native vegetation and development of water

  6. Ecosystem Evapotranspiration as a Response to Climate and Vegetation Coverage Changes in Northwest Yunnan, China.

    Science.gov (United States)

    Yang, Hao; Luo, Peng; Wang, Jun; Mou, Chengxiang; Mo, Li; Wang, Zhiyuan; Fu, Yao; Lin, Honghui; Yang, Yongping; Bhatta, Laxmi Dutt

    2015-01-01

    Climate and human-driven changes play an important role in regional droughts. Northwest Yunnan Province is a key region for biodiversity conservation in China, and it has experienced severe droughts since the beginning of this century; however, the extent of the contributions from climate and human-driven changes remains unclear. We calculated the ecosystem evapotranspiration (ET) and water yield (WY) of northwest Yunnan Province, China from 2001 to 2013 using meteorological and remote sensing observation data and a Surface Energy Balance System (SEBS) model. Multivariate regression analyses were used to differentiate the contribution of climate and vegetation coverage to ET. The results showed that the annual average vegetation coverage significantly increased over time with a mean of 0.69 in spite of the precipitation fluctuation. Afforestation/reforestation and other management efforts attributed to vegetation coverage increase in NW Yunnan. Both ET and WY considerably fluctuated with the climate factors, which ranged from 623.29 mm to 893.8 mm and -51.88 mm to 384.40 mm over the time period. Spatially, ET in the southeast of NW Yunnan (mainly in Lijiang) increased significantly, which was in line with the spatial trend of vegetation coverage. Multivariate linear regression analysis indicated that climatic factors accounted for 85.18% of the ET variation, while vegetation coverage explained 14.82%. On the other hand, precipitation accounted for 67.5% of the WY. We conclude that the continuous droughts in northwest Yunnan were primarily climatically driven; however, man-made land cover and vegetation changes also increased the vulnerability of local populations to drought. Because of the high proportion of the water yield consumed for subsistence and poor infrastructure for water management, local populations have been highly vulnerable to climate drought conditions. We suggest that conservation of native vegetation and development of water

  7. Evapotranspiration measurement and crop coefficient estimation over a spring wheat Farmland ecosystem in the Loess Plateau.

    Science.gov (United States)

    Yang, Fulin; Zhang, Qiang; Wang, Runyuan; Zhou, Jing

    2014-01-01

    Evapotranspiration (ET) is an important component of the surface energy balance and hydrological cycle. In this study, the eddy covariance technique was used to measure ET of the semi-arid farmland ecosystem in the Loess Plateau during 2010 growing season (April to September). The characteristics and environmental regulations of ET and crop coefficient (Kc) were investigated. The results showed that the diurnal variation of latent heat flux (LE) was similar to single-peak shape for each month, with the largest peak value of LE occurring in August (151.4 W m(-2)). The daily ET rate of the semi-arid farmland in the Loess Plateau also showed clear seasonal variation, with the maximum daily ET rate of 4.69 mm day(-1). Cumulative ET during 2010 growing season was 252.4 mm, and lower than precipitation. Radiation was the main driver of farmland ET in the Loess Plateau, which explained 88% of the variances in daily ET (pdaily Kc and its major environmental factors indicated that wind speed (Ws), relative humidity (RH), soil water content (SWC), and atmospheric vapor pressure deficit (VPD) were the major environmental regulations of daily Kc. The regression analysis results showed that Kc exponentially decreased with Ws increase, an exponentially increased with RH, SWC increase, and a linearly decreased with VPD increase. An experiential Kc model for the semi-arid farmland in the Loess Plateau, driven by Ws, RH, SWC and VPD, was developed, showing a good consistency between the simulated and the measured Kc values.

  8. The application of unmanned aerial vehicle to precision agriculture: Chlorophyll, nitrogen, and evapotranspiration estimation

    Science.gov (United States)

    Elarab, Manal

    Precision agriculture (PA) is an integration of a set of technologies aiming to improve productivity and profitability while sustaining the quality of the surrounding environment. It is a process that vastly relies on high-resolution information to enable greater precision in the management of inputs to production. This dissertation explored the usage of multispectral high resolution aerial imagery acquired by an unmanned aerial systems (UAS) platform to serve precision agriculture application. The UAS acquired imagery in the visual, near infrared and thermal infrared spectra with a resolution of less than a meter (15--60 cm). This research focused on developing two models to estimate cm-scale chlorophyll content and leaf nitrogen. To achieve the estimations a well-established machine learning algorithm (relevance vector machine) was used. The two models were trained on a dataset of in situ collected leaf chlorophyll and leaf nitrogen measurements, and the machine learning algorithm intelligently selected the most appropriate bands and indices for building regressions with the highest prediction accuracy. In addition, this research explored the usage of the high resolution imagery to estimate crop evapotranspiration (ET) at 15 cm resolution. A comparison was also made between the high resolution ET and Landsat derived ET over two different crop cover (field crops and vineyards) to assess the advantages of UAS based high resolution ET. This research aimed to bridge the information embedded in the high resolution imagery with ground crop parameters to provide site specific information to assist farmers adopting precision agriculture. The framework of this dissertation consisted of three components that provide tools to support precision agriculture operational decisions. In general, the results for each of the methods developed were satisfactory, relevant, and encouraging.

  9. A zero discharge green roof system and species selection to optimize evapotranspiration and water retention

    Energy Technology Data Exchange (ETDEWEB)

    Compton, J.S.; Whitlow, T.H. [Cornell, Univ., Urban Horticulture Inst., Ithaca, NY (United States). Dept. of Horticulture

    2006-07-01

    Economic benefits must outweigh costs, with or without governmental subsidies or enforcement in order for green roofs to become commonplace in American cities. Municipal advantages to green roofs include stormwater management, environmental quality and an expansion of the native plant palette. These benefits are difficult to quantify monetarily for the owner of the roof, yet greater water evaporation from storm water attenuation has the ability to increase cooling of the building, an economic benefit to the owner. Current green roof design and testing methods fail to explore systems that maximize stormwater retention and evaporative cooling benefits that are often associated with green roofs. This paper presented the results of a study that investigated an alternate approach that optimizes water loss through evapotranspiration using a zero discharge target and plants that tolerate both medium drought and saturation. Species selection emphasizes native species and salt tolerance, which allows the possibility of grey water irrigation. Species studied include spartina alternafiora and solidago canadensis. Plants were studied over a growing season to examine the rates of ET as they relate to weather conditions, growing media composition and saturation levels, and plant species. The study was conducted on top of a four storey school building located in the South Bronx, New York City. In June 2005, a 3,500 square foot extensive green roof was installed. The conference described the site and study in detail followed by a discussion of the results. This includes a discussion of the planting containers, planting mediums, plant materials, data collection, and irrigation trials. It was concluded that further research is needed to test this concept, and to examine the possibility of supplemental irrigation via off-season rainwater catchment or grey water irrigation. 17 refs., 4 figs.

  10. Evapotranspiration of the urban forest at the municipal scale in Los Angeles, CA

    Science.gov (United States)

    Litvak, E.; Pataki, D. E.

    2015-12-01

    The severest drought on record in southern California and predictions of continued water shortages make it essential to understand urban water use. However, urban evapotranspiration (ET), which is an important part of municipal water budgets, remains a major uncertainty. Urban ET is difficult to measure and model, particularly in cities with diverse plant composition. The city of Los Angeles contains more than 6 million trees, most of which are non-natives that originate from multiple geographic regions, which further complicates predictions of urban forest transpiration. Previously, we made extensive in situ measurements of tree transpiration and turfgrass ET in greater Los Angeles area. Here, we utilize these data to systematize transpiration of different tree species based on physiological mechanisms underlying plant water relations. The resulting empirical model estimates Los Angeles urban forest ET from easy-to-collect plant characteristics and freely available environmental parameters. Plant characteristics are tree diameter, wood type (e.g. coniferous), phenological type (e.g. evergreen) and plant composition. Environmental parameters are vapor pressure deficit of the air, incoming solar radiation and reference ET (all available at http://cimis.water.ca.gov). By combining this model with existing surveys of urban trees in Los Angeles, we estimated that citywide ET of irrigated landscapes varies from 1.2 ± 0.5 mm/d in winter to 2.8 ± 1.1 mm/d in summer. On average, trees and turfgrass contributed 27% and 73% to total tree+turfgrass ET, correspondingly. To our knowledge, this model provides the first citywide estimates of Los Angeles ET differentiated by wood types and plant composition. These results will inform decision makers about species-specific water use by urban trees and assist with determining landscape designs that are beneficial for water conservation. This model may also be incorporated into a regional hydrologic model to provide spatially

  11. Evaluating relationships between urban land cover composition and evapotranspiration in semi-arid regions

    Science.gov (United States)

    Manago, K. F.; Hogue, T. S.; Litvak, E.; Pataki, D. E.

    2016-12-01

    California experienced its most severe drought on record in 2013 and 2014, forcing the governor to call for the first statewide reductions in urban water use. This led to numerous water conservation efforts including turf removal and restrictions on outdoor irrigation. The decrease in irrigation across the city of Los Angeles has had major effects on regional hydrologic fluxes. Previous studies have found that conservation efforts have decreased streamflow but little work has been done on the impact of reduced irrigation on Evapotranspiration (ET). ET is one of the most difficult variables to measure as a result of its heterogeneity both spatially and temporally; yet, it is imperative in characterizing energy and hydrologic processes and in aiding water management decisions. Estimating ET is further complicated in urban regions where land cover composition is extremely variable, even at small scales. Irrigated landscape and impervious surfaces are two of the most common land cover types associated with urbanization, but they have opposite effects on ET. While numerous studies have evaluated changes in ET caused by urbanization, they have all produced varying results. This is expected as changes to ET are highly dependent on land cover composition. In this study, we modeled the relationship between ET and urban land cover change in Los Angeles. We utilized empirical equations derived from in situ measurements to calculate tree and irrigated turfgrass ET and compared the results to estimates based on remote-sensing and California Irrigation Management Information System (CIMIS) network of weather stations. We found that unshaded turfgrass largely increased ET compared to impervious surfaces, which reveals lavish irrigation practices. Trees also increased ET, but they provided shade that decreased ET from turf grass. With much of the western United States facing drought and water supply uncertainty due to climate change, understanding and predicting how land cover

  12. Spatiotemporal downscaling approaches for monitoring 8-day 30 m actual evapotranspiration

    Science.gov (United States)

    Ke, Yinghai; Im, Jungho; Park, Seonyoung; Gong, Huili

    2017-04-01

    Continuous monitoring of actual evapotranspiration (ET) is critical for water resources management at both regional and local scales. Although the MODIS ET product (MOD16A2) provides viable sources for ET monitoring at 8-day intervals, the spatial resolution (1 km) is too coarse for local scale applications. In this study, we propose a machine learning and spatial temporal fusion (STF)-integrated approach in order to generate 8-day 30 m ET based on both MOD16A2 and Landsat 8 data with three schemes. Random forest machine learning was used to downscale MODIS 1 km ET to 30 m resolution based on nine Landsat-derived indicators including vegetation indices (VIs) and land surface temperature (LST). STF-based models including Spatial and Temporal Adaptive Reflectance Fusion Model and Spatio-Temporal Image Fusion Model were used to derive synthetic Landsat surface reflectance (scheme 1)/VIs (scheme 2)/ET (scheme 3) on Landsat-unavailable dates. The approach was tested over two study sites in the United States. The results showed that fusion of Landsat VIs produced the best accuracy of predicted ET (R2 = 0.52-0.97, RMSE = 0.47-3.0 mm/8 days and rRMSE = 6.4-37%). High density of cloud-clear Landsat image acquisitions and low spatial heterogeneity of Landsat VIs benefit the ET prediction. The downscaled 30 m ET had good agreement with MODIS ET (RMSE = 0.42-3.4 mm/8 days, rRMSE = 3.2-26%). Comparison with the in situ ET measurements showed that the downscaled ET had higher accuracy than MODIS ET.

  13. Continuous evapotranspiration monitoring and water stress at watershed scale in a Mediterranean oak savanna

    Science.gov (United States)

    Carpintero, E.; González Dugo, M. P.; Hain, C.; Nieto, H.; Gao, F.; Andreu, A.; Kustas, W. P.; Anderson, M. C.

    2016-10-01

    The regular monitoring of the evapotranspiration rates and their links with vegetation conditions and soil moisture may support management and hydrological planning leading to reduce the economic and environmental vulnerability of complex water-controlled Mediterranean ecosystems. In this work, the monitoring of water use over a basin with a predominant oak savanna (known in Spain as dehesa) was conducted for two years, 2013 and 2014, monitoring ET at both fine spatial and temporal resolution in different seasons. A global 5 km daily ET product, developed with the ALEXI model and MODIS day-night temperature difference, was used as starting point. Flux estimations with higher spatial resolutions were obtained with the associated flux disaggregation scheme, DisALEXI, using surface temperature data from the polar orbiting satellites MODIS (1 Km, daily) and Landsat 7/8 (60-120m and sharpened to 30m, 16 days) and the previously estimated coarse resolution fluxes. The results achieved supported the ability of this scheme to accurately estimate daytime-integrated energy fluxes over this system, using input data with different spatio-temporal resolution and without the need for ground observations. Daily ET series at 30 m spatial resolution, generated using STARFM fusion technique, has provided a significant improvement in spatial heterogeneity assessment of the ET series, with RMSE values of 0.56 and 0.68 mm/day for each year, representing an enhancement with respect to interpolated Landsat series. In summary, this approach was demostrated to be robust and operative to map ET at watershed scale with a suitable spatial and temporal resolution for applications over the dehesa ecosystem.

  14. Estimation of Actual Evapotranspiration in Mahidasht using SEBS Algorithm and LANDSAT Images

    Directory of Open Access Journals (Sweden)

    Bahman Farhadi Bansouleh

    2017-02-01

    Full Text Available Introduction: Evapotranspiration (ET is one of the key parameters in water resource planning and design of irrigation systems. ET could have spatial variations in a plain due to the diversity of plant species and spatial variability of meteorological parameters. Common methods of ET measurement are mostly point based and generalization of their results to the regional level are costly, time consuming and difficult. During the last three decades, several algorithms have been developed to estimate regional ET based on remote sensing techniques. Verstraeten et al. (2008 classified remote sensing-based methods for ET estimation into four categories i methods based on the surface energy balance, ii Penman-Monteith equation, iii water balance and iv the relationship between surface temperature and vegetation indices. SEBS (Surface Energy Balance System, SEBAL, METRIC and SEBI are examples of the algorithms which is developed based on the surface energy balance approach. SEBS is developed by Su (2002 and has been evaluated by several researchers. However this algorithm has been examined in the several studies in the world,it has been used rarely in Iran. The aim of the current study was to assess the results of SEBS algorithm in Mahidasht, Kermanshah, Iran. The study area is located at the latitude of 34º 5' – 34º 32' N and longitude of 46º 31' - 47º 06' E. Materials and Methods: A brief description of the SEBS algorithm (in Persian as well as its procedure to calculate ET based on Landsat images were presented in this paper. All equations of the algorithm were coded in the ERDAS Imagine package software using model maker tools. Actual ET over the study area was estimated using SEBS algorithm during the growth period of grain maize in the year 2010. For this purpose, available LANDSAT TM satellite images during the growing season of maize in 2010 (25 June, 11 July, 27 July and 12 August were downloaded free of charge from the http

  15. Development of a Disaggregation Framework toward the Estimation of Subdaily Reference Evapotranspiration: 2- Estimation of Subdaily Reference Evapotranspiration Using Disaggregated Weather Data

    Directory of Open Access Journals (Sweden)

    F. Parchami Araghi

    2016-09-01

    Full Text Available Introduction: Subdaily estimates of reference evapotranspiration (ET o are needed in many applications such as dynamic agro-hydrological modeling. However, in many regions, the lack of subdaily weather data availability has hampered the efforts to quantify the subdaily ET o. In the first presented paper, a physically based framework was developed to desegregate daily weather data needed for estimation of subdaily reference ET o, including air temperature, wind speed, dew point, actual vapour pressure, relative humidity, and solar radiation. The main purpose of this study was to estimate the subdaily ETo using disaggregated daily data derived from developed disaggregation framework in the first presented paper. Materials and Methods: Subdaily ET o estimates were made, using ASCE and FAO-56 Penman–Monteith models (ASCE-PM and FAO56-PM, respectively and subdaily weather data derived from the developed daily-to-subdaily weather data disaggregation framework. To this end, long-term daily weather data got from Abadan (59 years and Ahvaz (50 years synoptic weather stations were collected. Sensitivity analysis of Penman–Monteith model to the different meteorological variables (including, daily air temperature, wind speed at 2 m height, actual vapor pressure, and solar radiation was carried out, using partial derivatives of Penman–Monteith equation. The capability of the two models for retrieving the daily ETo was evaluated, using root mean square error RMSE (mm, the mean error ME (mm, the mean absolute error ME (mm, Pearson correlation coefficient r (-, and Nash–Sutcliffe model efficiency coefficient EF (-. Different contributions to the overall error were decomposed using a regression-based method. Results and Discussion: The results of the sensitivity analysis showed that the daily air temperature and the actual vapor pressure are the most significant meteorological variables, which affect the ETo estimates. In contrast, low sensitivity

  16. Evapotranspiration Rate Measurements of Vegetation Typical of Ground-Water Discharge Areas in the Basin and Range Carbonate-Rock Aquifer System, White Pine County, Nevada, and Adjacent Areas in Nevada and Utah, September 2005-August 2006

    Science.gov (United States)

    Moreo, Michael T.; Laczniak, Randell J.; Stannard, David I.

    2007-01-01

    Evapotranspiration was measured at six eddy-correlation sites for a 1-year period between September 1, 2005, and August 31, 2006. Five sites were in phreatophytic shrubland dominated by greasewood, and one site was in a grassland meadow. The measured annual evapotranspiration ranged from 10.02 to 12.77 inches at the shrubland sites and 26.94 inches at the grassland site. Evapotranspiration rates correlated to measured vegetation densities and to satellite-derived vegetation indexes. Evapotranspiration rates were greater at sites with denser vegetation. The primary water source supporting evapotranspiration was water derived from local precipitation at the shrubland sites, and ground water at the grassland site. Measured precipitation, ranging from 6.21 to 11.41 inches, was within 20 percent of the computed long-term annual mean. The amount of ground water consumed by phreatophytes depends primarily on local precipitation and vegetation density. The ground-water contribution to local evapotranspiration ranged from 6 to 38 percent of total evapotranspiration at the shrubland sites, and 70 percent of total evapotranspiration at the grassland site. Average depth to water ranged from 7.2 to 32.4 feet below land surface at the shrubland sites, and 3.9 feet at the grassland site. Water levels declined throughout the growing season and recovered during the non-growing season. Diurnal water-level fluctuations associated with evapotranspiration were evident at some sites but not at others.

  17. Accuracy comparison of remotely sensed evapotranspiration products and their associated water stress footprints under different land cover types in Korean peninsula

    KAUST Repository

    Liaqat, Umar Waqas

    2016-09-09

    Robust spatial information of evapotranspiration from multiple land cover types is deemed critical for several applications in agriculture and water balance studies. Energy balance models, used in association with satellite observations, are beneficial to map spatial variability of evapotranspiration which is mainly governed by different vegetation practices and local environmental conditions. This study utilize the Surface Energy Balance System model to estimate actual evapotranspiration and water scarcity footprints under complex landscape of Korean peninsula using Moderate-Resolution Imaging Spectroradiometer satellite data for a complete hydrological year of 2012. The modeled evapotranspiration was compared with flux tower measurements obtained from a subhumid cropland and temperate forest sites for the accuracy assessment. This accuracy comparison at daily scale had good agreement yielding reasonable coefficient of determination (0.72, 0.51), bias (0.41 mm day−1, 1.01 mm day−1) and root mean squared error (0.92 mm day−1, 1.53 mm day−1) at two observation (cropland, forest) sites, respectively. Furthermore, the monthly aggregated evapotranspiration from Surface Energy Balance System showed promising results than those of obtained from Moderate-Resolution Imaging Spectroradiometer based readymade global evapotranspiration product, i.e., MOD16, when both products were compared with unclosed and closed flux tower measurements. However, the variations in monthly evapotranspiration obtained from both products were significantly controlled by several climate factors and vegetation characteristics. Water stress mapping at regional and monthly scale also revealed strong contrast between the products of two approaches. Highest mean water stress (0.74) was observed for land use areas associated with evergreen forest and under sparsely vegetation condition by using estimated evapotranspiration from Surface Energy Balance System while an extreme mean water stress

  18. Investigation on the Reference Evapotranspiration Distribution at Regional Scale By Alternative Methods to Compute the FAO Penman-Monteith Equation

    Science.gov (United States)

    Snyder, R. L.; Mancosu, N.; Spano, D.

    2014-12-01

    This study derived the summer (June-August) reference evapotranspiration distribution map for Sardinia (Italy) based on weather station data and use of the geographic information system (GIS). A modified daily Penman-Monteith equation from the Food and Agriculture Organization of the United Nations (UN-FAO) and the American Society of Civil Engineers Environmental and Water Resources Institute (ASCE-EWRI) was used to calculate the Standardized Reference Evapotranspiration (ETos) for all weather stations having a "full" set of required data for the calculations. For stations having only temperature data (partial stations), the Hargreaves-Samani equation was used to estimate the reference evapotranspiration for a grass surface (ETo). The ETos and ETo results were different depending on the local climate, so two methods to estimate ETos from the ETo were tested. Substitution of missing solar radiation, wind speed, and humidity data from a nearby station within a similar microclimate was found to give better results than using a calibration factor that related ETos and ETo. Therefore, the substitution method was used to estimate ETos at "partial" stations having only temperature data. The combination of 63 full and partial stations was sufficient to use GIS to map ETos for Sardinia. Three interpolation methods were studied, and the ordinary kriging model fitted the observed data better than a radial basis function or the inverse distance weighting method. Using station data points to create a regional map simplified the zonation of ETos when large scale computations were needed. Making a distinction based on ETos classes allows the simulation of crop water requirements for large areas and it can potentially lead to improved irrigation management and water savings. It also provides a baseline to investigate possible impact of climate change.

  19. Interaction effects of water salinity and hydroponic growth medium on eggplant yield, water-use efficiency, and evapotranspiration

    Directory of Open Access Journals (Sweden)

    Farnoosh Mahjoor

    2016-06-01

    Full Text Available Eggplant (Solanum melongena L. is a plant native to tropical regions of Southeast Asia. The water crisis and drought on the one hand and eggplant greenhouse crop development as one of the most popular fruit vegetables for people on the other hand, led to the need for more research on the use of saline water and water stress to optimize salinity level and their impact on eggplant evapotranspiration and encounter better yield and crop quality. The objective of the present study was to investigate the interactions of water salinity and hydroponic growth medium on qualitative and quantitative properties of eggplant and its water-use efficiency. The study used the factorial experiment based on completely randomized design with three replications of four levels of water salinity (electrical conductivity of 0.8 (control, 2.5, 5, and 7 dS m−1 and three growth media (cocopeat, perlite, and a 50–50 mixture of the two by volume. Total yield, yield components, evapotranspiration, and water-use efficiency were determined during two growing periods, one each in 2012 and 2013. All of these indices decreased significantly as water salinity increased. Water with of 0.8 dS m−1 produced an average eggplant yield of 2510 g per plant in 2012 and 2600 g in 2013. The highest yield was observed in cocopeat. Water with 7 dS m−1 reduced yield to 906 g per plant in 2012 and to 960 g in 2013. Lowest yield was observed in perlite. The highest evapotranspiration values occurred in cocopeat at the lowest salinity in both years. Cocopeat and the cocopeat–perlite mixture were equally good substrates. The mixture significantly improved the quantitative and qualitative properties of eggplant yield.

  20. Variations in evapotranspiration fluxes across geomorphological units and plant functional types in a polygonal-structure Tundra in Barrow, Alaska

    Science.gov (United States)

    Raz Yaseef, N.; Young, J. M.; Rahn, T. A.; Newman, B. D.; Torn, M. S.

    2014-12-01

    Although the landscape in tundra ecosystems is relatively flat, and the vegetation is typically shorter than 10 cm, micro-topographical changes within the polygonal structure produce spatial heterogeneity in the form of permafrost depth, soil temperature, soil moisture, and wind speed. Plants react to these conditions and form linkages with the landscape. For example, mosses occupy the wet troughs and lichens are more abundant in the drier high-centred polygons. We conducted measurements in a polygonal-structure tundra site at Barrow, Alaska, to investigate the interconnections between evapotranspiration fluxes, geomorphology and plant cover, during two consecutive years. Fluxes were measured at three spatial and temporal scales: (1) Eddy covariance flux tower, (2) Continuous, fixed, surface clear chamber, and (3) Discontinuous measurements with mobile chambers in approximately 60 locations across the landscape. Our results indicate that different environmental conditions (soil moisture, soil temperature, wind speed, and thaw depth) and plant community composition, driven by microtopographical features, have significant influences on soil greenhouse gas and energy fluxes. Among plant types, evapotranspiration fluxes from moss-covered and inundated areas were more than twice those from other plant types. Continuous chamber measurements were similar in trend and values to eddy-covariance measurements, implying on the high contribution of surface fluxes to atmospheric concentrations. However, wind direction influenced the upscaling of fluxes from chamber to tower, because maritime winds had different moisture content and temperature than terrestrial winds. Microclimate was also affected by microtopography, and wind speed was higher on polygon ridges, and lower in the more protected trough areas, affecting evapotranspiration fluxes. In addition, we observed a strong seasonal trend in fluxes. During peak summer, although 24-hour daylight occurs, our results indicated

  1. Spatial and temporal evolution of climatic factors and its impacts on potential evapotranspiration in Loess Plateau of Northern Shaanxi, China.

    Science.gov (United States)

    Li, C; Wu, P T; Li, X L; Zhou, T W; Sun, S K; Wang, Y B; Luan, X B; Yu, X

    2017-07-01

    Agriculture is very sensitive to climate change, and correct forecasting of climate change is a great help to accurate allocation of irrigation water. The use of irrigation water is influenced by crop water demand and precipitation. Potential evapotranspiration (ET0) is a measure of the ability of the atmosphere to remove water from the surface through the processes of evaporation and transpiration, assuming no control on water supply. It plays an important role in assessing crop water requirements, regional dry-wet conditions, and other factors of water resource management. This study analyzed the spatial and temporal evolution processes and characteristics of major meteorological parameters at 10 stations in the Loess Plateau of northern Shaanxi (LPNS). By using the Mann-Kendall trend test with trend-free pre-whitening and the ArcGIS platform, the potential evapotranspiration of each station was quantified by using the Penman-Monteith equation, and the effects of climatic factors on potential evapotranspiration were assessed by analyzing the contribution rate and sensitivity of the climatic factors. The results showed that the climate in LPNS has become warmer and drier. In terms of the sensitivity of ET0 to the variation of each climatic factor in LPNS, relative humidity (0.65) had the highest sensitivity, followed by daily maximum temperature, wind speed, sunshine hours, and daily minimum temperature (-0.05). In terms of the contribution rate of each factor to ET0, daily maximum temperature (5.16%) had the highest value, followed by daily minimum temperature, sunshine hours, relative humidity, and wind speed (1.14%). This study provides a reference for the management of agricultural water resources and for countermeasures to climate change. According to the climate change and the characteristics of the study area, farmers in the region should increase irrigation to guarantee crop water demand. Copyright © 2017. Published by Elsevier B.V.

  2. Simulation of soil moisture and evapotranspiration in a soil profile during the 1999 MAP-Riviera Campaign

    Directory of Open Access Journals (Sweden)

    M. Zappa

    2003-01-01

    Full Text Available Detailed plot-scale observations of basic hydrometeorological variables represent valuable data for assessing the quality of the soil moisture module and evapotranspiration scheme in hydrological models. This study presents the validation of soil moisture and evapotranspiration (ET simulation during the special observing period (R-SOP of the Riviera Project (July–November 1999, a sub-project of the Mesoscale Alpine Programme (MAP. The location investigated was a sandy soil plot at the edge of a corn field. The hydrological model PREVAH was driven using three meteorological data sets: hourly data from an experimental tower in the Riviera Valley (southern Switzerland, hourly data interpolated for the Riviera site during the R-SOP period from permanent automatic stations (MeteoSwiss network and interpolated daily data (1980–2000. The quality of the interpolated meteorological data was evaluated with respect to data collected at an experimental tower. The interpolated data proved fairly representative for the location under investigation. The hydrological simulations were compared with recorded observations of soil moisture and latent heat flux (LE. The simulation of soil moisture was accurate in case of all three meteorological data sets. The results of ET simulations with three simple parameterisations showed high correlation to LE derived using the Bowen ratio and measured through eddy correlation. The quantitative agreement between observed and simulated LE was poorer because of the presence of a fully developed wind valley system during periods of good weather. This wind system claims part of the available energy and therefore reduces the amount of energy available for LE. The 21-year simulation at daily time step shows that the R-SOP period in 1999 was warm and wet compared to the last 21 years. Keywords: MAP-Riviera Project, soil moisture, evapotranspiration, hydrological modelling, model evaluation

  3. Tracing the allocation of water in rainfed rice ecosystem by partitioning evapotranspiration of rainfed rice (Oryza Sativa L.)

    Science.gov (United States)

    Nay-Htoon, Bhone; Dubbert, Maren; Wei, Xue; Cuntz, Matthias; Ko, Jonghan; Tenhunen, John; Werner, Christiane

    2015-04-01

    To understand productive and unproductive water use of crop production, partitioning evapotranspiration (ET ) into evaporation (E) and transpiration (T ) is important. Water movements within the eco-hydrologic cycle of agroecosystems can be traced by stable oxygen isotopes of water (δ18O) and plant transpiration and soil evaporation can also be estimated by tracing the δ18O. We quantified the contribution of transpiration to total ecosystem evapotranspiration of rainfed rice field by a stable oxygen isotope approach and FAO 56 dual crop modelling approach. Our study aims to provide quantification of ecosystem water cycle of rainfed rice by partitioning productive and unproductive water use since productivity and water use of rice which is a highly water demanding agroecosystem, is under intense research. Crop season total evapotranspiration fluxes from rainfed rice was mainly dominated by transpiration (T to ET contribution (T /ET ) = 65%) and domination of transpiration over evaporation fluxes was noted since early vegetative stage (Leaf Area Index = 0.8 m2 m-2) until harvesting. T /ET of rainfed rice fluctuated with changes in soil water content (SWC) and the highest T /ET was found at SWC of 0.34 m3 m-3, during seedling stage. Our results demonstrate that partitioning ET by FAO 56 dual crop model is in a good agreement with δ18O isotope based ET partitioning results. Using monthly mean values of leaf resistance and vegetation index derived crop coefficients instead of original fixed parameters of the FAO 56 dual crop model resulted better agreement with δ18O isotope based ET partitioning.

  4. Study on Microclimate Characteristics and Vertical Variation of Potential Evapotranspiration of the Robinia pseudoacacia Forest in the Loess Plateau of China

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    Jianjun Zhang

    2013-01-01

    Full Text Available With the water and soil conservation forests of Robinia pseudoacacia in the Malian beach of Hongqi farm, Ji County, Shanxi province, as the research object, this study estimated the potential evapotranspiration in the open space outside the forest and at the heights of 3 m, 6 m, and 10 m in the forests with the climate data during 2011-2012 and the upgraded Penman-Monteith formula; then, this study explored the microclimate characteristics inside and outside the Robinia pseudoacacia forest and thereafter revealed the vertical variation rules of potential evapotranspiration of Robinia pseudoacacia. The results indicate that the air temperature, relative humidity, wind speed, and potential evapotranspiration at different heights above the ground surface showed similar changing trends, but with some variation during different periods. In addition, the weather also had impacts on the potential evapotranspiration. In April, July, and October, the change of potential evapotranspiration of the Robinia pseudoacacia forests showed a bimodal curve in the sunny days and rainy days, while it showed a single-peak curve with quite small fluctuation in the rainy days. However, it showed a single-peak pattern even in the sunny days in January, and it showed no fluctuation in the snowy days in January.

  5. Comparison of two simple tools (TSEB and FAO-56) to retrieve evapotranspiration of irrigated agriculture in semi-arid areas.

    Science.gov (United States)

    Diarra, Alhousseine; Jarlan, Lionel; Er-Raki, Salah; Le Page, Michel; Khabba, Said; Boulet, Gilles

    2016-04-01

    In a context of climate change and an increasing water demand, the semi-arid climate region face heightened pressure on the availability of water resources. About 85% of available water is used for irrigation in these regions. There is thus a crucial need to develop tools for a better management of irrigation through accurate estimates of crop water requirement. The objective of this study was to adapt and evaluate two parsimonious modeling approaches feeded by remote sensing observations, which have potential for the operational monitoring of evapotranspiration (ET): the two-source surface energy balance (TSEB) model developed by Norman et al. (1995) and the FAO-56 dual crop coefficient method (Allen et al., 1998), through the SAMIR tool (Simonneaux et al., 2009). At the field scale, both models were evaluated on four sites located in the Haouz plain (Marrakech, Morocco) during two agricultural seasons: wheat and sugar beet in 2012 and two other wheat crops in 2013; all belonging to an irrigated perimeter of 2800 ha. A time series of 12 high spatial resolution images acquired by SPOT-5 and ASTER images was collected during the growing seasons of wheat and sugar beet. The simulation results showed that both models offer fair performances of ET compared to measured one by eddy covariance with an average root mean square error (RMSE) lower than 1 mm/day for the sugar beet where the simulation are lower by the FAO-56 approach due to water inputs are uncertain. By contrast, the TSEB model, which not needs the water supply as input, offers smoother performances in all cases. At the scale of the perimeter, both approaches show similar spatial patterns because of homogeneous water conditions at the date of remote sensing image acquisitions. The partition of evapotranspiration between soil evaporation and transpiration from vegetation is estimated indirectly by confrontation between simulated soil evaporation and surface (0-5 cm) soil moisture acquired spatially with Theta

  6. Determination of the isotopic composition of evapotranspiration in a mature oil palm plantation in Jambi province, Indonesia.

    Science.gov (United States)

    Bonazza, Mattia; Meijide, Ana; Knohl, Alexander

    2017-04-01

    Evapotranspiration (ET) is defined as the sum of the water vapor fluxes from evaporation (E) and transpiration (T). The relative proportion between these two quantities depends on the species, on their age and on the structure of the stand and canopy. Evaporation represents the fraction of water that doesn't contribute to plants growth hence it often considered as "unused" water by the plants root system. For this reason, in a fast changing environment like Indonesia where, since almost 30 years, tropical rainforests are gradually converted into extensive oil palm plantation, it is important to quantify the amount of evaporated water to improve agricultural practices and water quality. As powerful tracers of the hydrological cycle, water stable isotopes represent an important tool to estimate the isotopic composition of the evapotranspiration flux and they can be used as a starting point for the determination of the T/ET ratio, which can be considered as a plant water uptake efficiency indicator. The isotopic composition (δDvand δ18Ov) and the mixing ratio (qv) of water vapor measured in a stand is the result of the isotopic mixing between two members; ecosystem evapotranspiration (δET) and background air (δa). With the implementation of laser-based isotopic analysers we are now able to improve the measurement frequency of δDvand δ18Ov that leads us to an improved estimation of δET. Here we present the results of a measurement campaign, performed with a Picarro L-2120i and conducted in a mature oil palm plantation in the province of Jambi, Indonesia. We measured the atmospheric water vapor mixing ratio and isotopic composition at 5 sampling heights (21 m, 16 m, 9 m, 3.5 and 0.3 m) along a flux tower throughout the oil palm canopy (average height 10 m). The range of the water vapor isotopic composition was between -19 and -11 and -134 and -82 ‰ for δ18Ov and δDvrespectively. A fairly open canopy structure resulted in small mixing ratio gradients along the

  7. Estimation of actual evapotranspiration of Mediterranean perennial crops by means of remote-sensing based surface energy balance models

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    G. Rallo

    2009-07-01

    Full Text Available Actual evapotranspiration from typical Mediterranean crops has been assessed in a Sicilian study area by using surface energy balance (SEB and soil-water balance models. Both modelling approaches use remotely sensed data to estimate evapotranspiration fluxes in a spatially distributed way. The first approach exploits visible (VIS, near-infrared (NIR and thermal (TIR observations to solve the surface energy balance equation whereas the soil-water balance model uses only VIS-NIR data to detect the spatial variability of crop parameters. Considering that the study area is characterized by typical spatially sparse Mediterranean vegetation, i.e. olive, citrus and vineyards, alternating bare soil and canopy, we focused the attention on the main conceptual differences between one-source and two-sources energy balance models. Two different models have been tested: the widely used one-source SEBAL model, where soil and vegetation are considered as the sole source (mostly appropriate in the case of uniform vegetation coverage and the two-sources TSEB model, where soil and vegetation components of the surface energy balance are treated separately. Actual evapotranspiration estimates by means of the two surface energy balance models have been compared vs. the outputs of the agro-hydrological SWAP model, which was applied in a spatially distributed way to simulate one-dimensional water flow in the soil-plant-atmosphere continuum. Remote sensing data in the VIS and NIR spectral ranges have been used to infer spatially distributed vegetation parameters needed to set up the upper boundary condition of SWAP. Actual evapotranspiration values obtained from the application of the soil water balance model SWAP have been considered as the reference to be used for energy balance models accuracy assessment.

    Airborne hyperspectral data acquired during a NERC (Natural Environment Research Council, UK campaign in 2005 have been used. The results of this

  8. Non-Lambertian Corrected Albedo and Vegetation Index for Estimating Land Evapotranspiration in a Heterogeneous Semi-Arid Landscape

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    Isabella Mariotto

    2010-03-01

    Full Text Available The application of energy balance algorithms to remotely sensed imagery often fails to account for surface roughness variation with diverse land cover, resulting in poor resolution of evapotranspiration (ET variations. Furthermore, the assumption of a horizontally homogeneous Lambertian surface reflecting energy equally in all directions affects the calculations of albedo and vegetation index. The primary objective of this study is to improve the accuracy of the estimation and discrimination of ET among different land cover types in Southern New Mexico from ASTER datasets, by formulating the spatial variation of non-Lambertian reflectance using a wavelength-dependent Minnaert function.

  9. A method for simultaneous estimation of groundwater evapotranspiration and inflow rates in the discharge area using seasonal water table fluctuations

    Science.gov (United States)

    Jiang, Xiao-Wei; Sun, Zhi-Chao; Zhao, Ke-Yu; Shi, Fu-Sheng; Wan, Li; Wang, Xu-Sheng; Shi, Zhe-Ming

    2017-05-01

    As an indispensable component of groundwater circulation, groundwater evapotranspiration rate (ETG) estimation using water table fluctuations is a hot research topic in the past decades. However, most existing methods for estimating ETG using either diurnal or seasonal water table fluctuations are based on the assumptions that groundwater recharge equals 0 in the whole period and ETG equals 0 in a specific duration of time. The aim of the current study is to develop a method to estimate ETG when both assumptions do not apply. In the discharge area of a semi-arid catchment in the Ordos Plateau, NW China, it is found out that the water table fluctuations are influenced greatly by recharge, ETG and the vertical inflow rate (qin) in the seasonal scale but are controlled by atmospheric pressure instead of evapotranspiration in the diurnal scale, which implies that the existing methods are not applicable. Therefore, we propose a method to estimate ETG and qin using the seasonal water table fluctuations based on the assumptions that qin is stable throughout the year and ETG has a linear relationship to the reference evapotranspiration (ET0). It is found out that qin is around 1.12 mm/d, and the ratio of ETG to ET0 is around 0.4. ETG in April through July with the highest ET0 of the year is found to be around 3 mm/d, which is much larger than qin, thus leads to significant decline in water table. ETG in November with the lowest ET0 of the unfrozen period is found to be 1.0 mm/d, which is slightly smaller than qin, thus results in a weak increase in water table. The vertical component of regional groundwater inflow is found to exceed precipitation recharge, indicating that regional groundwater inflow plays the major role on maintaining the shallow water table in the discharge area. Groundwater evapotranspiration is also found to exceed precipitation recharge in most time of the unfrozen period, indicating a specified-flux upper boundary with water loss in the discharge area

  10. Evapotranspiration flux partitioning using an Iso-SPAC model in a temperate grassland ecosystem

    Science.gov (United States)

    Wang, P.

    2014-12-01

    To partition evapotranspiration (ET) into soil evaporation and vegetation transpiration (T), a new numerical Iso-SPAC (coupled heat, water with isotopic tracer in Soil-Plant-Atmosphere-Continuum) model was developed and applied to a temperate-grassland ecosystem in central Japan. Several models of varying complexity have been tested with the aim of obtaining the close to true value for the isotope composition of leaf water and transpiration flux. The agreement between the model predictions and observations demonstrates that the Iso-SPAC model with a steady-state assumption for transpiration flux can reproduce seasonal variations of all the surface energy balance components,leaf and ground surface temperature as well as isotope data (canopy foliage and ET flux). This good performance was confirmed not only at diurnal timescale but also at seasonal timescale. Thus, although the non-steady-state behavior of isotope budget in a leaf and isotopic diffusion between leaf and stem or root is exactly important, the steady-state assumption is practically acceptable for seasonal timescale as a first order approximation. Sensitivity analysis both in physical flux part and isotope part suggested that T/ET is relatively insensitive to uncertainties/errors in assigned model parameters and measured input variables, which illustrated the partitioning validity. Estimated transpiration fractions using isotope composition in ET flux by Iso-SPAC model and Keeling plot are generally in good agreement, further proving validity of the both approaches. However, Keeling plot approach tended to overestimate the fraction during an early stage of glowing season and a period just after clear cutting. This overestimation is probably due to insufficient fetch and influence of transpiration from upwind forest. Consequently, Iso-SPAC model is more reliable than Keeling plot approach in most cases.The T/ET increased with grass growth, and the sharp reduction caused by clear cutting was well

  11. Reference Evapotranspiration Retrievals from a Mesoscale Model Based Weather Variables for Soil Moisture Deficit Estimation

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    Prashant K. Srivastava

    2017-10-01

    Full Text Available Reference Evapotranspiration (ETo and soil moisture deficit (SMD are vital for understanding the hydrological processes, particularly in the context of sustainable water use efficiency in the globe. Precise estimation of ETo and SMD are required for developing appropriate forecasting systems, in hydrological modeling and also in precision agriculture. In this study, the surface temperature downscaled from Weather Research and Forecasting (WRF model is used to estimate ETo using the boundary conditions that are provided by the European Center for Medium Range Weather Forecast (ECMWF. In order to understand the performance, the Hamon’s method is employed to estimate the ETo using the temperature from meteorological station and WRF derived variables. After estimating the ETo, a range of linear and non-linear models is utilized to retrieve SMD. The performance statistics such as RMSE, %Bias, and Nash Sutcliffe Efficiency (NSE indicates that the exponential model (RMSE = 0.226; %Bias = −0.077; NSE = 0.616 is efficient for SMD estimation by using the Observed ETo in comparison to the other linear and non-linear models (RMSE range = 0.019–0.667; %Bias range = 2.821–6.894; NSE = 0.013–0.419 used in this study. On the other hand, in the scenario where SMD is estimated using WRF downscaled meteorological variables based ETo, the linear model is found promising (RMSE = 0.017; %Bias = 5.280; NSE = 0.448 as compared to the non-linear models (RMSE range = 0.022–0.707; %Bias range = −0.207–−6.088; NSE range = 0.013–0.149. Our findings also suggest that all the models are performing better during the growing season (RMSE range = 0.024–0.025; %Bias range = −4.982–−3.431; r = 0.245–0.281 than the non−growing season (RMSE range = 0.011–0.12; %Bias range = 33.073–32.701; r = 0.161–0.244 for SMD estimation.

  12. Global estimates of evapotranspiration and gross primary production based on MODIS and global meteorology data

    Science.gov (United States)

    Yuan, W.; Liu, S.; Yu, G.; Bonnefond, J.-M.; Chen, J.; Davis, K.; Desai, A.R.; Goldstein, Allen H.; Gianelle, D.; Rossi, F.; Suyker, A.E.; Verma, S.B.

    2010-01-01

    The simulation of gross primary production (GPP) at various spatial and temporal scales remains a major challenge for quantifying the global carbon cycle. We developed a light use efficiency model, called EC-LUE, driven by only four variables: normalized difference vegetation index (NDVI), photosynthetically active radiation (PAR), air temperature, and the Bowen ratio of sensible to latent heat flux. The EC-LUE model may have the most potential to adequately address the spatial and temporal dynamics of GPP because its parameters (i.e., the potential light use efficiency and optimal plant growth temperature) are invariant across the various land cover types. However, the application of the previous EC-LUE model was hampered by poor prediction of Bowen ratio at the large spatial scale. In this study, we substituted the Bowen ratio with the ratio of evapotranspiration (ET) to net radiation, and revised the RS-PM (Remote Sensing-Penman Monteith) model for quantifying ET. Fifty-four eddy covariance towers, including various ecosystem types, were selected to calibrate and validate the revised RS-PM and EC-LUE models. The revised RS-PM model explained 82% and 68% of the observed variations of ET for all the calibration and validation sites, respectively. Using estimated ET as input, the EC-LUE model performed well in calibration and validation sites, explaining 75% and 61% of the observed GPP variation for calibration and validation sites respectively.Global patterns of ET and GPP at a spatial resolution of 0.5° latitude by 0.6° longitude during the years 2000–2003 were determined using the global MERRA dataset (Modern Era Retrospective-Analysis for Research and Applications) and MODIS (Moderate Resolution Imaging Spectroradiometer). The global estimates of ET and GPP agreed well with the other global models from the literature, with the highest ET and GPP over tropical forests and the lowest values in dry and high latitude areas. However, comparisons with observed

  13. Benchmark products for land evapotranspiration: LandFlux-EVAL multi-data set synthesis

    KAUST Repository

    Mueller, B.

    2013-10-01

    Land evapotranspiration (ET) estimates are available from several global data sets.Here, Monthly Global Land et Synthesis Products, Merged from These Individual Data Sets over the Time Periods 1989-1995 (7 Yr) and 1989-2005 (17 Yr), Are Presented. the Merged Synthesis Products over the Shorter Period Are Based on A Total of 40 Distinct Data Sets while Those over the Longer Period Are Based on A Total of 14 Data Sets. in the Individual Data Sets, et Is Derived from Satellite And/or in Situ Observations (Diagnostic Data Sets) or Calculated Via Land-surface Models (LSMs) Driven with Observations-based Forcing or Output from Atmospheric Reanalyses. Statistics for Four Merged Synthesis Products Are Provided, One Including All Data Sets and Three Including only Data Sets from One Category Each (Diagnostic, LSMs, and Reanalyses). the Multi-annual Variations of et in the Merged Synthesis Products Display Realistic Responses. They Are Also Consistent with Previous Findings of A Global Increase in et between 1989 and 1997 (0.13 Mm yr-2 in Our Merged Product) Followed by A Significant Decrease in This Trend (-0.18 Mm yr-2), although These Trends Are Relatively Small Compared to the Uncertainty of Absolute et Values. the Global Mean et from the Merged Synthesis Products (Based on All Data Sets) Is 493 Mm yr-1 (1.35 Mm d-1) for Both the 1989-1995 and 1989-2005 Products, Which Is Relatively Low Compared to Previously Published Estimates. We Estimate Global Runoff (Precipitation Minus ET) to 263 Mm yr -1 (34 406 km3 yr-1) for A Total Land Area of 130 922 000 km2. Precipitation, Being An Important Driving Factor and Input to Most Simulated et Data Sets, Presents Uncertainties between Single Data Sets As Large As Those in the et Estimates. in Order to Reduce Uncertainties in Current et Products, Improving the Accuracy of the Input Variables, Especially Precipitation, As Well As the Parameterizations of ET, Are Crucial. 2013 Author(s).

  14. Estimation of evapotranspiration from MODIS TOA radiances in the Poyang Lake basin, China

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    J. Peng

    2013-04-01

    Full Text Available Routine and rapid estimation of ET (evapotranspiration at regional scale is of great significance for agricultural, hydrological and climatic studies. A simplified single-source energy balance parameterization scheme, known as the LST/NDVI (land surface temperature/normalized difference vegetation index triangle method, has been applied successfully to estimate regional clear sky ET in many studies. Based on the triangle method, we proposed a new method in this study to estimate daily ET directly using the TOA (top of atmosphere radiances without performing atmospheric correction and other complicated processes. Firstly, the EF (evaporative fraction, defined as the ratio of latent heat flux to surface available energy was estimated by interpolation in the LST/NDVI triangular-shaped scatter space, which was constructed using the MODIS (Moderate Resolution Imaging Spectroradiometer TOA radiances over a heterogeneous area of the Poyang Lake basin in China. Then the net radiation over the same study area was derived based entirely on MODIS TOA radiances as well. Finally, daily ET maps were estimated from these EF maps and net radiation maps by using a sinusoidal temporal interpolation model. The estimated EF, net radiation and ET have been validated against field observations collected for the period October 2007–July 2008. The results indicate comparable accuracy to results of other current widely used satellite-based methods. In addition, intercomparisons between the proposed method-based estimates and MODIS products-based estimates were also carried out over the validation site. The results suggest that the proposed method could reach similar level of accuracy as the MODIS products-based triangle method. Overall, the proposed algorithm requires fewer assumptions and can avoid complex atmospheric corrections associated with the satellite derived products. It should facilitate direct use of satellite data for determining ET and relevant

  15. Evapotranspiration models for a maize agro-ecosystem in irrigated and rainfed conditions

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    Arianna Facchi

    2013-09-01

    Full Text Available A high level of accuracy in the estimation of crop evapotranspiration (ET may lead to significant savings of economic and water resources in irrigated agriculture. Although ET is a fundamental process in many applications, it cannot be directly measured but it has to be estimated by monitoring the exchange of energy/water above the vegetated surface (micrometeorological methods, or as a residual term of the hydrological balance (lysimeters, soil water budget. The techniques to be adopted are often complex, costly and require specific equipment. Thus, since the ‘50s, many researchers have devoted their activity to the development of models for its estimation. The available approaches can be classified in “direct” methods, based on the original Penman-Monteith (PM equation, in which the canopy resistance rc is modelled, and “indirect” methods, based on the preliminary calculation of ET for a well-watered reference grass (ET0 with a constant rc, which is then multiplied by a crop coefficient Kc and, in case, by a stress coefficient Ks to obtain ET. Even if the latter approaches are more widely adopted for their practical simplicity, many authors show that the former often provide better ET estimates in absence of calibration of crop parameters. In this study the performances of different direct and indirect methods were evaluated in the case of a surface irrigated and of a rainfed maize grown in the Padana Plain (Northern Italy. The following models were considered: the “one-layer” original PM equation with three different models for rc (Monteith, Jarvis, Katerji-Perrier, the “two-layers” PM model proposed by Shuttleworth and Wallace, the “single” and “double” crop coefficient models illustrated in the Paper FAO-56. Latent heat fluxes measured in 2006 and 2011 in an experimental maize field by eddy-covariance were used to evaluate the models accuracy. Crop, soil and meteo data monitored contextually were used for the

  16. CO2 exchange and evapotranspiration across dryland ecosystems of southwestern North America.

    Science.gov (United States)

    Biederman, Joel A; Scott, Russell L; Bell, Tom W; Bowling, David R; Dore, Sabina; Garatuza-Payan, Jaime; Kolb, Thomas E; Krishnan, Praveena; Krofcheck, Dan J; Litvak, Marcy E; Maurer, Gregory E; Meyers, Tilden P; Oechel, Walter C; Papuga, Shirley A; Ponce-Campos, Guillermo E; Rodriguez, Julio C; Smith, William K; Vargas, Rodrigo; Watts, Christopher J; Yepez, Enrico A; Goulden, Michael L

    2017-10-01

    Global-scale studies suggest that dryland ecosystems dominate an increasing trend in the magnitude and interannual variability of the land CO2 sink. However, such analyses are poorly constrained by measured CO2 exchange in drylands. Here we address this observation gap with eddy covariance data from 25 sites in the water-limited Southwest region of North America with observed ranges in annual precipitation of 100-1000 mm, annual temperatures of 2-25°C, and records of 3-10 years (150 site-years in total). Annual fluxes were integrated using site-specific ecohydrologic years to group precipitation with resulting ecosystem exchanges. We found a wide range of carbon sink/source function, with mean annual net ecosystem production (NEP) varying from -350 to +330 gCm(-2) across sites with diverse vegetation types, contrasting with the more constant sink typically measured in mesic ecosystems. In this region, only forest-dominated sites were consistent carbon sinks. Interannual variability of NEP, gross ecosystem production (GEP), and ecosystem respiration (Reco ) was larger than for mesic regions, and half the sites switched between functioning as C sinks/C sources in wet/dry years. The sites demonstrated coherent responses of GEP and NEP to anomalies in annual evapotranspiration (ET), used here as a proxy for annually available water after hydrologic losses. Notably, GEP and Reco were negatively related to temperature, both interannually within site and spatially across sites, in contrast to positive temperature effects commonly reported for mesic ecosystems. Models based on MODIS satellite observations matched the cross-site spatial pattern in mean annual GEP but consistently underestimated mean annual ET by ~50%. Importantly, the MODIS-based models captured only 20-30% of interannual variation magnitude. These results suggest the contribution of this dryland region to variability of regional to global CO2 exchange may be up to 3-5 times larger than current estimates

  17. Deriving Daily Time Series Evapotranspiration, Evaporation and Transpiration Maps With Landsat Data

    Science.gov (United States)

    Paul, G.; Gowda, P. H.; Marek, T.; Xiao, X.; Basara, J. B.

    2014-12-01

    Mapping high resolution evapotranspiration (ET) over large region at daily time step is complex and computationally intensive. Utility of high resolution daily ET maps are large ranging from crop water management to watershed management. The aim of this work is to generate daily time series (10 years) ET and its components vegetation transpiration (T) and soil water evaporation (E) maps using Landsat 5 satellite data for Southern Great Plains forage-rangeland-winter wheat production system in Oklahoma (OK). Framework for generating these products included the two source energy balance (TSEB) algorithm and other important features were: (a) atmospheric correction algorithm; (b) spatially interpolated weather inputs; (c) functions for varying Priestley-Taylor coefficient; and (d) ET, E and T extrapolating algorithm utilizing reference ET. An extensive network of 140 weather stations managed by Oklahoma Mesonet was utilized to generate spatially interpolated inputs of air temperature, relative humidity, wind speed, solar radiation, pressure, and reference ET. Validation of the ET maps were done against eddy covariance data from two grassland sites at El Reno, OK suggested good performance (Table 1). Figure 1 illustrates a daily ET map for a very small subset of 18thJuly 2006 ET map, where difference in ET among different land uses such as the irrigated cropland, vegetation along drainage, and grassland is very distinct. Results indicated that the proposed ET mapping framework is suitable for deriving high resolution time series daily ET maps at regional scale with Landsat Thematic Mapper data. . Table 1: Daily actual ET performance statistics for two grassland locations at El Reno OK for year 2005 . Management Type Mean (obs) (mm d-1) Mean (est) (mm d-1) MBE (mm d-1) % MBE (%) RMSE (mm d-1) RMSE (%) MAE (mm d-1) MAPD (%) NSE R2 Control 2.2 1.8 -0.43 -19.4 0.87 38.9 0.65 29.5 0.71 0.79 Burnt 2.0 1.8 -0.15 -7.7 0.80 39.8 0.62 30.7 0.73 0.77

  18. Comparison of Satellite-based Basal and Adjusted Evapotranspiration for Several California Crops

    Science.gov (United States)

    Johnson, L.; Lund, C.; Melton, F. S.

    2013-12-01

    There is a continuing need to develop new sources of information on agricultural crop water consumption in the arid Western U.S. Pursuant to the California Water Conservation Act of 2009, for instance, the stakeholder community has developed a set of quantitative indicators involving measurement of evapotranspiration (ET) or crop consumptive use (Calif. Dept. Water Resources, 2012). Fraction of reference ET (or, crop coefficients) can be estimated from a biophysical description of the crop canopy involving green fractional cover (Fc) and height as per the FAO-56 practice standard of Allen et al. (1998). The current study involved 19 fields in California's San Joaquin Valley and Central Coast during 2011-12, growing a variety of specialty and commodity crops: lettuce, raisin, tomato, almond, melon, winegrape, garlic, peach, orange, cotton, corn and wheat. Most crops were on surface or subsurface drip, though micro-jet, sprinkler and flood were represented as well. Fc was retrospectively estimated every 8-16 days by optical satellite data and interpolated to a daily timestep. Crop height was derived as a capped linear function of Fc using published guideline maxima. These variables were used to generate daily basal crop coefficients (Kcb) per field through most or all of each respective growth cycle by the density coefficient approach of Allen & Pereira (2009). A soil water balance model for both topsoil and root zone, based on FAO-56 and using on-site measurements of applied irrigation and precipitation, was used to develop daily soil evaporation and crop water stress coefficients (Ke, Ks). Key meteorological variables (wind speed, relative humidity) were extracted from the California Irrigation Management Information System (CIMIS) for climate correction. Basal crop ET (ETcb) was then derived from Kcb using CIMIS reference ET. Adjusted crop ET (ETc_adj) was estimated by the dual coefficient approach involving Kcb, Ke, and incorporating Ks. Cumulative ETc

  19. Spatio-temporal Characteristics of Actual Evapotranspiration Trends in sub-Saharan Africa

    Science.gov (United States)

    Marshall, M. T.; Funk, C. C.; Michaelsen, J.

    2010-12-01

    Actual evapotranspiration (AET) is an important moisture flux linking the Earth’s surface to the atmospheric hydrologic cycle. Global warming is expected to intensify this cycle, leading to moisture deficits over the sub-tropics, which will influence climate at higher latitudes. The spatio-temporal characterization of tropical AET is critical to understanding regional and global climate. To date, many studies on the temporal characteristics of AET across sub-Saharan Africa have employed vegetation-based indices derived from satellite imagery. Although these studies implicitly reflect trends in AET, they quantify the magnitude of change. In this study, we used the latest developments in remote sensing and land-surface modeling to characterize the magnitude and timing of AET in sub-Saharan Africa. We considered several models were evaluated from 1981-2000 using monthly discharge and precipitation from ten sub-basins representative of hydrology in sub-Saharan Africa. Discharge data was provided by the Global Runoff Data Centre, while precipitation data was comprised of ECMWF, NCAR, NOAA/GDAS, and CMAP reanalysis fields synthesized in the Global Land Data Assimilation System (GLDAS). The AET models included the Community Land Model, Variable Infiltration Capacity (VIC) model, Noah, and two hybrids that we developed driven by a dynamic vegetation component defined in Fisher et al. 2008. The dynamic canopy components in our hybrid models were driven by the LTDR AVHRR daily corrected reflectance data over the evaluation period. The evaluation revealed that VIC was superior to the other models in capturing the magnitude and variability of runoff in the sub-basins. A trend analysis was then performed on VIC AET from 1979-2009 using standard parametric and non-parametric techniques. Linear and median trend analysis was performed on seasonal and annual AET totals to measure the magnitude of change. The analysis revealed several alarming patterns, including large and

  20. A worldwide evaluation of basin-scale evapotranspiration estimates against the water balance method

    Science.gov (United States)

    Liu, Wenbin; Wang, Lei; Zhou, Jing; Li, Yanzhong; Sun, Fubao; Fu, Guobin; Li, Xiuping; Sang, Yan-Fang

    2016-07-01

    Evapotranspiration (ET) plays a critical role in linking the water and energy cycles but is difficult to estimate at regional and basin scales. In this study, we present a worldwide evaluation of nine ET products (three diagnostic products, three land surface model (LSM) simulations and three reanalysis-based products) against reference ET (ETwb) calculated using the water balance method corrected for the water storage change at an annual time scale over the period 1983-2006 for 35 global river basins. The results indicated that there was no significant intra-category discrepancy in the annual ET estimates for the 35 basins calculated using the different products in 35 basins, but some products performed better than others, such as the Global Land surface Evaporation estimated using the Amsterdam Methodology (GLEAM_E) in the diagnostic products, ET obtained from the Global Land Data Assimilation System version 1 (GLDAS 1) with the Community Land Model scheme (GCLM_E) in LSM simulations, and ET from the National Aeronautics and Space Administration (NASA) Modern Era Retrospective-analysis for Research and Applications reanalysis dataset (MERRA_E) in the reanalysis-based products. Almost all ET products (except MERRA_E) reasonably estimated the annual means (especially in the dry basins) but systematically underestimated the inter-annual variability (except for MERRA_E, GCLM_E and ET simulation from the GLDAS 1 with the MOSAIC scheme - GMOS_E) and could not adequately estimate the trends (e.g. GCLM_E and MERRA_E) of ETwb (especially in the energy-limited wet basins). The uncertainties in nine ET products may be primarily attributed to the discrepancies in the forcing datasets and model structural limitations. The enhancements of global forcing data (meteorological data, solar radiation, soil moisture stress and water storage changes) and model physics (reasonable consideration of the water and energy balance and vegetation processes such as canopy interception loss

  1. Estimation of real evapotranspiration and its variation in Mediterranean landscapes of central-southern Chile

    Science.gov (United States)

    Olivera-Guerra, L.; Mattar, C.; Galleguillos, M.

    2014-05-01

    Evapotranspiration (ETd) is a key controller in the ecohydrological processes of semi-arid landscapes. This is the case of the dry land in Chile's central-southern zone, where forestry, farming and livestock activities must adapt to precipitation with considerable year-on-year variations. In this study, the spatial distribution of ETd was estimated in relation to the land use map and physical parameters of the soil. The ETd was estimated through the Simplified Surface Energy Balance Index (S-SEBI) using data from weather stations and remote data provided by the ASTER and MODIS sensors for November 2004 and 2006, respectively. The spatial variability of ETd was compared among different plant types, soil textural classes and depths using non-parametric statistical tests. In this comparison, the highest rates of ETd were obtained in the forest covers with values of 7.3 ± 0.8 and 8.4 ± 0.8 mm d-1 for 2004 and 2006, respectively. The lowest values were estimated for pastures and shrublands with values of 3.5 ± 1.2 mm d-1 and for crops with rates of 4.4 ± 1.6 mm d-1. Comparison of the ETd of the native forest covers and plantations of exotic species showed statistically significant differences; however, no great variation was noted, at least in the study months. Additionally, the highest rates of ETd were found in the clay loam textures (6.0 ± 1.8 and 6.4 ± 2.0 mm d-1) and the lowest rates in the sandy loam soils (3.7 ± 1.6 and 3.9 ± 1.6 mm d-1) for 2004 and 2006, respectively. The results enable analysis of the spatial patterns of the landscape in terms of the relation between water consumption, ET and the biophysical characteristics of a Mediterranean ecosystem. These results form part of the creation of tools useful in the optimization of decision-making for the management and planning of water resources and soil use in territories with few measuring instruments.

  2. Forest Surface Energy Balance and Evapotranspiration Estimated From Four Eddy Covariance Towers

    Science.gov (United States)

    Rabbani, G. A.; Adam, J. C.; Elliot, W. J.; Liu, H.

    2016-12-01

    Evapotranspiration (ET), which refers to the combined effect of surface water evaporation and plant transpiration, is one of the vital elements of the global water balance. It is also an important process for plants, providing water, nutrient, and cooling needs, and helping to regulate carbon dioxide entry through open/closure of the plant's stomata. Quantifying ET in forested environments is an ongoing research area. Complex physiological responses with climatic variation, combined with difficulty in making wide-spread measurements, makes ET one of the least understood components of a forest water balance. The objective of this study is to estimate ET and energy balance closure by using flux net data from eddy covariance towers. ET is estimated for different forest types with multiple age classes during the years of 2011, 2012 and 2013. We studied two coniferous forests (F1, F2), one deciduous forest (F3) and one mixed forest (F4) in Washington, Wyoming, Wisconsin and New Jersey, respectively. Label 2 (Data checked and formatted by Carbon Dioxide Information Analysis Center) gap filled flux data were collected from the AmeriFlux database (ameriflux.ornl.gov). Discrepancies between turbulent fluxes and available energy are investigated. Among the studied forests, the highest and lowest average monthly ET are exhibited by the mixed forest (F4) and coniferous forest (F1) in 2012 which are 2,692 and 633 mm/month, respectively. Difference in average monthly ET can be an implication of substantial age difference between these two types of forest. The regression analysis showed significant correlation between turbulent fluxes and available energy (R2=0.91) for mixed forest where the discrepancy varied from 5-11%. Conversely, for coniferous and deciduous forests, the discrepancy varied from 46-49% and 28%, respectively, with almost similar correlation between the fluxes (0.86 and 0.84, respectively). This study will facilitate an improved understanding of how forest type

  3. Actual evapotranspiration modeling using the operational Simplified Surface Energy Balance (SSEBop) approach

    Science.gov (United States)

    Savoca, Mark E.; Senay, Gabriel B.; Maupin, Molly A.; Kenny, Joan F.; Perry, Charles A.

    2013-01-01

    Remote-sensing technology and surface-energy-balance methods can provide accurate and repeatable estimates of actual evapotranspiration (ETa) when used in combination with local weather datasets over irrigated lands. Estimates of ETa may be used to provide a consistent, accurate, and efficient approach for estimating regional water withdrawals for irrigation and associated consumptive use (CU), especially in arid cropland areas that require supplemental water due to insufficient natural supplies from rainfall, soil moisture, or groundwater. ETa in these areas is considered equivalent to CU, and represents the part of applied irrigation water that is evaporated and/or transpired, and is not available for immediate reuse. A recent U.S. Geological Survey study demonstrated the application of the remote-sensing-based Simplified Surface Energy Balance (SSEB) model to estimate 10-year average ETa at 1-kilometer resolution on national and regional scales, and compared those ETa values to the U.S. Geological Survey’s National Water-Use Information Program’s 1995 county estimates of CU. The operational version of the operational SSEB (SSEBop) method is now used to construct monthly, county-level ETa maps of the conterminous United States for the years 2000, 2005, and 2010. The performance of the SSEBop was evaluated using eddy covariance flux tower datasets compiled from 2005 datasets, and the results showed a strong linear relationship in different land cover types across diverse ecosystems in the conterminous United States (correlation coefficient [r] ranging from 0.75 to 0.95). For example, r for woody savannas (0.75), grassland (0.75), forest (0.82), cropland (0.84), shrub land (0.89), and urban (0.95). A comparison of the remote-sensing SSEBop method for estimating ETa and the Hamon temperature method for estimating potential ET (ETp) also was conducted, using regressions of all available county averages of ETa for 2005 and 2010, and yielded correlations of r = 0

  4. Quantifying the impact of groundwater depth on evapotranspiration in a semi-arid grassland region

    Directory of Open Access Journals (Sweden)

    M. E. Soylu

    2011-03-01

    Full Text Available Interactions between shallow groundwater and land surface processes play an important role in the ecohydrology of riparian zones. Some recent land surface models (LSMs incorporate groundwater-land surface interactions using parameterizations at varying levels of detail. In this paper, we examine the sensitivity of land surface evapotranspiration (ET to water table depth, soil texture, and two commonly used soil hydraulic parameter datasets using four models with varying levels of complexity. The selected models are Hydrus-1D, which solves the pressure-based Richards equation, the Integrated Biosphere Simulator (IBIS, which simulates interactions among multiple soil layers using a (water-content variant of the Richards equation, and two forms of a steady-state capillary flux model coupled with a single-bucket soil moisture model. These models are first evaluated using field observations of climate, soil moisture, and groundwater levels at a semi-arid site in south-central Nebraska, USA. All four models are found to compare reasonably well with observations, particularly when the effects of groundwater are included. We then examine the sensitivity of modelled ET to water table depth for various model formulations, node spacings, and soil textures (using soil hydraulic parameter values from two different sources, namely Rawls and Clapp-Hornberger. The results indicate a strong influence of soil texture and water table depth on groundwater contributions to ET. Furthermore, differences in texture-specific, class-averaged soil parameters obtained from the two literature sources lead to large differences in the simulated depth and thickness of the "critical zone" (i.e., the zone within which variations in water table depth strongly impact surface ET. Depending on the depth-to-groundwater, this can also lead to large discrepancies in simulated ET (in some cases by more than a factor of two. When the Clapp-Hornberger soil parameter dataset is used, the

  5. Evapotranspiration and water balance of an anthropogenic coastal desert wetland: responses to fire, inflows and salinities

    Science.gov (United States)

    Glenn, Edward P.; Mexicano, Lourdes; Garcia-Hernandez, Jaqueline; Nagler, Pamela L.; Gomez-Sapiens, Martha M.; Tang, Dawei; Lomeli, Marcelo A.; Ramírez-Hernández, Jorge; Zamora-Arroyo, Francisco

    2013-01-01

    Evapotranspiration (ET) and other water balance components were estimated for Cienega de Santa Clara, an anthropogenic brackish wetland in the delta of the Colorado River in Mexico. The marsh is in the Biosphere Reserve of the Upper Gulf of California and Delta of the Colorado River, and supports a high abundance and diversity of wildlife. Over 95% of its water supply originates as agricultural drain water from the USA, sent for disposal in Mexico. This study was conducted from 2009 to 2011, before, during and after a trial run of the Yuma Desalting Plant in the USA, which will divert water from the wetland and replace it with brine from the desalting operation. The goal was to estimate the main components in the water budget to be used in creating management scenarios for this marsh. We used a remote sensing algorithm to estimate ET from meteorological data and Enhanced Vegetation Index values from the Moderate Resolution Imaging Spectrometer (MODIS) sensors on the Terra satellite. ET estimates from the MODIS method were then compared to results from a mass balance of water and salt inflows and outflows over the study period. By both methods, mean annual ET estimates ranged from 2.6 to 3.0 mm d−1, or 50 to 60% of reference ET (ETo). Water entered at a mean salinity of 2.6 g L−1 TDS and mean salinity in the wetland was 3.73 g L−1 TDS over the 33 month study period. Over an annual cycle, 54% of inflows supported ET while the rest exited the marsh as outflows; however, in winter when ET was low, up to 90% of the inflows exited the marsh. An analysis of ET estimates over the years 2000–2011 showed that annual ET was proportional to the volume of inflows, but was also markedly stimulated by fires. Spring fires in 2006 and 2011 burned off accumulated thatch, resulting in vigorous growth of new leaves and a 30% increase in peak summer ET compared to non-fire years. Following fires, peak summer ET estimates were equal to ETo, while in non-fire years peak ET was

  6. Performance of shrub willows (Salix spp.) as an evapotranspiration cover on Solvay wastebeds

    Science.gov (United States)

    Mirck, Jaconette

    2009-12-01

    Soda ash (Na2CO3) production in the Syracuse New York area created 607 ha of wastebeds over the course of about 100 years. Today the primary concern of the Solvay wastebeds is high chloride concentrations in the leachate and storm water that may end up in the groundwater and nearby Onondaga Lake. The potential of shrub willow evapotranspiration (ET) covers to minimize leaching and to manage storm water was assessed in two studies. A sap flow sensor field study to estimate transpiration rates of four shrub willow varieties over an entire growing season. A greenhouse study focused on recycling saline Solvay storm water onto shrub willows. Annual sap flow and crop coefficients (Kc) were similar among four shrub willows, but differences were present over the course of the growing season. Peak K c values did not coincide with peak leaf area index (LAI), as might be expected if LAI were the main driver of transpiration. Rather than solely being driven by LAI, coupling with the atmosphere was an important factor in stand level sap flow. Estimates of ET were measured during both experiments, the ET/sap flow rankings of the shrub willow varieties were similar; Salix miyabeana (SX64)water that contained 1,625 mg Cl - L-1 (close to the average storm water concentration) did not significantly decrease ET values or growth for any of the willow varieties. Mass balances of sodium and chloride were carried out to assess the potentials of recycling saline Solvay storm water back onto a shrub willow ET cover during the growing season. During a ten-week study the combination of a shallow depth soil (33 cm) and a high irrigation regime (170% of average precipitation in the Syracuse NY area) resulted in the accumulation of at least 62% of both sodium and chloride in the plant/soil system for all five Solvay storm water treatments. Both studies indicated that shrub willows have the characteristics to be part of a sustainable ET cover on the Solvay wastebeds, which will decrease leaching

  7. Downscaling of MODIS One Kilometer Evapotranspiration Using Landsat-8 Data and Machine Learning Approaches

    Directory of Open Access Journals (Sweden)

    Yinghai Ke

    2016-03-01

    Full Text Available This study presented a MODIS 8-day 1 km evapotranspiration (ET downscaling method based on Landsat 8 data (30 m and machine learning approaches. Eleven indicators including albedo, land surface temperature (LST, and vegetation indices (VIs derived from Landsat 8 data were first upscaled to 1 km resolution. Machine learning algorithms including Support Vector Regression (SVR, Cubist, and Random Forest (RF were used to model the relationship between the Landsat indicators and MODIS 8-day 1 km ET. The models were then used to predict 30 m ET based on Landsat 8 indicators. A total of thirty-two pairs of Landsat 8 images/MODIS ET data were evaluated at four study sites including two in United States and two in South Korea. Among the three models, RF produced the lowest error, with relative Root Mean Square Error (rRMSE less than 20%. Vegetation greenness related indicators such as Normalized Difference Vegetation Index (NDVI, Enhanced Vegetation Index (EVI, Soil Adjusted Vegetation Index (SAVI, and vegetation moisture related indicators such as Normalized Difference Infrared Index—Landsat 8 OLI band 7 (NDIIb7 and Normalized Difference Water Index (NDWI were the five most important features used in RF model. Temperature-based indicators were less important than vegetation greenness and moisture-related indicators because LST could have considerable variation during each 8-day period. The predicted Landsat downscaled ET had good overall agreement with MODIS ET (average rRMSE = 22% and showed a similar temporal trend as MODIS ET. Compared to the MODIS ET product, the downscaled product demonstrated more spatial details, and had better agreement with in situ ET observations (R2 = 0.56. However, we found that the accuracy of MODIS ET was the main control factor of the accuracy of the downscaled product. Improved coarse-resolution ET estimation would result in better finer-resolution estimation. This study proved the potential of using machine learning

  8. Separating precipitation and evapotranspiration from noise - a new filter routine for high resolution lysimeter data

    Science.gov (United States)

    Peters, A.; Nehls, T.; Schonsky, H.; Wessolek, G.

    2013-12-01

    Weighing lysimeters yield the most precise and realistic measures for evapotranspiration (ET) and precipitation (P), which are of great importance for many questions regarding soil and atmospheric sciences. An increase or a decrease of the system mass (lysimeter plus seepage) indicate P or ET. These real mass changes of the lysimeter system have to be separated from measurement noise (e.g. caused by wind). The typical way to filter noisy lysimeter data is (i) to introduce a smoothing routine, like a moving average with a certain averaging window w, and then (ii) to apply a certain threshold value δ, accounting for measurement accuracy, separating significant from insignificant weight changes. Thus, two filter parameters are used, namely w and δ. Especially the time variable noise due to wind and strong signals due to heavy precipitation pose challenges for such noise reduction algorithms. If w is too small, data noise might be interpreted as real system changes. If w is too wide, small weight changes in short time intervals might be disregarded. The same applies to too small or too large values for δ. Application of constant w and δ lead either to unnecessary losses of accuracy or to faulty data due to noise. The aim of this paper is to solve that problem with a new filter routine, which is appropriate for any event, ranging from smooth evaporation to strong wind and heavy precipitation. Therefore, the new routine uses adaptive w and δ in dependence on signal strength and noise (AWAT - Adaptive Window and Adaptive Threshold filter). The AWAT filter, a moving average filter and the Savitzky-Golay filter with constant w and δ were applied to real lysimeter data comprising the above mentioned events. The AWAT filter was the only filter which could handle the data of all events very well. A sensitivity study shows that the magnitude of the maximum threshold value has practically no influence on the results, so that only the maximum window width must be predefined

  9. A new filter routine to estimate evapotranspiration and precipitation from lysimeter data

    Science.gov (United States)

    Peters, Andre; Nehls, Thomas; Schonsky, Horst; Wessolek, Gerd

    2014-05-01

    Weighing lysimeters yield the most precise and realistic measures for evapotranspiration (ET) and precipitation (P), which are of great importance for many questions regarding soil and atmospheric sciences. An increase or a decrease of the system mass (lysimeter plus seepage) indicate P or ET. These real mass changes of the lysimeter system have to be separated from measurement noise (e.g. caused by wind). A promising way to filter noisy lysimeter data is (i) to introduce a smoothing routine, like a moving average with a certain averaging window w, and then (ii) to apply a certain threshold value d, accounting for measurement accuracy, separating significant from insignificant weight changes. Thus, two filter parameters are used, namely w and d. Especially the time variable noise due to wind and strong signals due to heavy precipitation pose challenges for such noise reduction algorithms. If w is too small, data noise might be interpreted as real system changes. If w is too wide, small weight changes in short time intervals might be disregarded. The same applies to too small or too large values for d. Application of constant w and d lead either to unnecessary losses of accuracy or to faulty data due to noise. The aim of this contribution is to solve that problem with a new filter routine, which is appropriate for any event, ranging from smooth evaporation to strong wind and heavy precipitation. Therefore, the new routine uses adaptive w and d in dependence on signal strength and noise (AWAT - Adaptive Window and Adaptive Threshold filter). The minimum threshold value and minimum window width are set to the scale resolution and temporal resolution of the measurement. The maximum values for both have to be defined by the user. For comparison a moving average filter and the Savitzky-Golay filter with constant w and d were used, where w and d have to be defined by the user. All three filters were applied to real lysimeter data comprising the above mentioned events. The

  10. Separating precipitation and evapotranspiration from noise - a new filter routine for high-resolution lysimeter data

    Science.gov (United States)

    Peters, A.; Nehls, T.; Schonsky, H.; Wessolek, G.

    2014-03-01

    Weighing lysimeters yield the most precise and realistic measures for evapotranspiration (ET) and precipitation (P), which are of great importance for many questions regarding soil and atmospheric sciences. An increase or a decrease of the system mass (lysimeter plus seepage) indicates P or ET. These real mass changes of the lysimeter system have to be separated from measurement noise (e.g., caused by wind). A promising approach to filter noisy lysimeter data is (i) to introduce a smoothing routine, like a moving average with a certain averaging window, w, and then (ii) to apply a certain threshold value, δ, accounting for measurement accuracy, separating significant from insignificant weight changes. Thus, two filter parameters are used, namely w and δ. In particular, the time-variable noise due to wind as well as strong signals due to heavy precipitation pose challenges for such noise-reduction algorithms. If w is too small, data noise might be interpreted as real system changes. If w is too wide, small weight changes in short time intervals might be disregarded. The same applies to too small or too large values for δ. Application of constant w and δ leads either to unnecessary losses of accuracy or to faulty data due to noise. The aim of this paper is to solve this problem with a new filter routine that is appropriate for any event, ranging from smooth evaporation to strong wind and heavy precipitation. Therefore, the new routine uses adaptive w and δ in dependence on signal strength and noise (AWAT - adaptive window and adaptive threshold filter). The AWAT filter, a moving-average filter and the Savitzky-Golay filter with constant w and δ were applied to real lysimeter data comprising the above-mentioned events. The AWAT filter was the only filter that could handle the data of all events very well. A sensitivity study shows that the magnitude of the maximum threshold value has practically no influence on the results; thus only the maximum window width

  11. Estimation of actual evapotranspiration by numerical modeling of water flow in the unsaturated zone: a case study in Buenos Aires, Argentina

    Science.gov (United States)

    Cesanelli, Andrés; Guarracino, Luis

    2009-03-01

    A method is presented to estimate actual evapotranspiration (ETA) from potential evapotranspiration (ETP) by numerical modeling of water flow in the unsaturated zone. Water flow is described by the Richards equation with a sink term representing the root water uptake. Evaporation is included in the model as a Neumann boundary condition at the soil surface. The Richards equation is solved in a one-dimensional domain using a mixed finite element method. The values of ETA are obtained by applying a water stress factor to ETP to account for soil moisture changes during the simulation period. The proposed numerical model is used to estimate ETA in an experimental plot located in a flatland area in Buenos Aires (Argentina). Numerical results show that the proposed model is a useful tool for evaluating evapotranspiration under different scenarios.

  12. A Comparison of ASCE and FAO56 Reference Evapotranspiration at Different Subdaily Timescales: a Numerical Study

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    Farzin Parchami-Araghi

    2017-01-01

    Full Text Available Introduction: Subdaily estimates of reference evapotranspiration (ETo are needed in many applications such as dynamic agro-hydrological modeling. The ASCE and FAO56 Penman–Monteith models (ASCE-PM and FAO56-PM, respectively has received favorable acceptance and application over much of the world, including the United States, for establishing a reference evapotranspiration (ETo index as a function of weather parameters. In the past several years various studies have evaluated ASCE-PM and FAO56-PM models for calculating the commonest hourly or 15-min ETo either by comparing them with lysimetric measurements or by comparison with one another (2, 3, 5, 9, 10, 11, 16, 17, 19. In this study, sub-daily ET o estimates made by the ASCE-PM and FAO56-PM models at different timescales (1-360 min were compared through conduction of a computational experiment, using a daily to sub-daily disaggregation framework developed by Parchami-Araghi et al. (14. Materials and Methods: Daily and sub-daily weather data at different timescales (1-360 min were generated via a daily-to-sub-daily weather data disaggregation framework developed by Parchami-Araghi et al. (14, using long-term (59 years daily weather data obtained from Abadan synoptic weather station. Daily/sub-daily net long wave radiation (Rnl was estimated through 6 different approaches, including using two different criteria for identifying the daytime/nighttime periods : 1 the standard criteria implemented in both ASCE-PM and FAO56-PM models and 2 criterion of actual time of sunset and sunrise in combination with 1 estimation of clear-sky radiation (Rso based on the standard approach implemented in both ASCE-PM and FAO56-PM models (1st and 2nd Rnl estimation approaches, respectively, 2 integral of the Rso estimates derived via a physically based solar radiation model developed by Yang et al. (25, YNG model, for one-second time-steps (3rd and 4th Rnl estimation approaches, respectively, and 3 integral of

  13. Validating HYLARSMET: a Hydrologically Consistent Land Surface Model for Soil Moisture and Evapotranspiration Modelling over Southern Africa using Remote Sensing and Meteorological Data

    Science.gov (United States)

    Sinclair, Scott; Pegram, Geoff; Mengitsu, Michael; Everson, Colin

    2015-04-01

    Timeous knowledge of the spatial distribution of soil moisture and evapotranspiration over a large region in fine detail has great value for coping with two weather extremes: flash floods and droughts, since the state of the wetness of the land surface has a major impact on runoff response. Also, the ability to monitor the wetness of the soil and the actual evapotranspiration over large regions, without having to laboriously take expensive samples, is a bonus for agricultural managers who need to predict crop yields. We present samples of the daily national Soil Moisture and Evapotranspiration estimates on a grid of 7300 locations centred in 12 km squares, then move on to the results of a validation study for soil moisture and evapotranspiration estimated using the PyTOPKAPI hydrological model in Land Surface Modelling mode, a system called HYLARSMET. The HYLARSMET estimates are compared with detailed evapotranspiration and soil moisture measurements made at the Baynesfield experimental farm in the KwaZulu-Natal province of South Africa, run by the University of KZN. The HYLARSMET evapotranspiration estimates compared very well with the measured estimates for the two chosen crop types, in spite of the fact that the HYLARSMET estimates were not designed to explicitly account for the crop types at each site. The same seasonality effects were evident in all 3 estimates, and there was a stronger ET relationship between HYLARSMET and the Soybean site (Pearson r = 0.81) than for Maize, (r = 0.59). The soil moisture relationship was stronger between the two in situ measured estimates (r = 0.98 at 0.5 m depth) than it was between HYLARSMET and the field estimates (r about 0.52 in both cases). Overall there was a reasonably good relationship between HYLARSMET and the in situ measurements of ET and SM at each site, indicating the value of the modelling procedure.

  14. Evaluation of Landsat-Based METRIC Modeling to Provide High-Spatial Resolution Evapotranspiration Estimates for Amazonian Forests

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    Izaya Numata

    2017-01-01

    Full Text Available While forest evapotranspiration (ET dynamics in the Amazon have been studied both as point estimates using flux towers, as well as spatially coarse surfaces using satellite data, higher resolution (e.g., 30 m resolution ET estimates are necessary to address finer spatial variability associated with forest biophysical characteristics and their changes by natural and human impacts. The objective of this study is to evaluate the potential of the Landsat-based METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration model to estimate high-resolution (30 m forest ET by comparing to flux tower ET (FT ET data collected over seasonally dry tropical forests in Rondônia, the southwestern region of the Amazon. Analyses were conducted at daily, monthly and seasonal scales for the dry seasons (June–September for Rondônia of 2000–2002. Overall daily ET comparison between FT ET and METRIC ET across the study site showed r2 = 0.67 with RMSE = 0.81 mm. For seasonal ET comparison, METRIC-derived ET estimates showed an agreement with FT ET measurements during the dry season of r2 >0.70 and %MAE <15%. We also discuss some challenges and potential applications of METRIC for Amazonian forests.

  15. Estimating groundwater evapotranspiration by a subtropical pine plantation using diurnal water table fluctuations: Implications from night-time water use

    Science.gov (United States)

    Fan, Junliang; Ostergaard, Kasper T.; Guyot, Adrien; Fujiwara, Stephen; Lockington, David A.

    2016-11-01

    Exotic pine plantations have replaced large areas of the native forests for timber production in the subtropical coastal Australia. To evaluate potential impacts of changes in vegetation on local groundwater discharge, we estimated groundwater evapotranspiration (ETg) by the pine plantation using diurnal water table fluctuations for the dry season of 2012 from August 1st to December 31st. The modified White method was used to estimate the ETg, considering the night-time water use by pine trees (Tn). Depth-dependent specific yields were also determined both experimentally and numerically for estimation of ETg. Night-time water use by pine trees was comprehensively investigated using a combination of groundwater level, sap flow, tree growth, specific yield, soil matric potential and climatic variables measurements. Results reveal a constant average transpiration flux of 0.02 mm h-1 at the plot scale from 23:00 to 05:00 during the study period, which verified the presence of night-time water use. The total ETg for the period investigated was 259.0 mm with an accumulated Tn of 64.5 mm, resulting in an error of 25% on accumulated evapotranspiration from the groundwater if night-time water use was neglected. The results indicate that the development of commercial pine plantations may result in groundwater losses in these areas. It is also recommended that any future application of diurnal water table fluctuation based methods investigate the validity of the zero night-time water use assumption prior to use.

  16. Hydrodynamic changes of the soil-cactus interface, effective actual evapotranspiration and its water efficiency under irrigation

    Directory of Open Access Journals (Sweden)

    José E. F. de Morais

    Full Text Available ABSTRACT The knowledge on soil water dynamics is the basis of crop water management. The soil water balance (SWB method is used for this purpose. However, its application in cactus may lead to misinterpretation in water efficiency analysis, since it does not consider the amount of water retained in the plant (WRP. This study aimed to evaluate SWB applicability, hydrodynamic changes and water efficiency of forage cactus clones under irrigation. The clones ‘Orelha de Elefante Mexicana’ (OEM, ‘IPA Sertânia’ (IPA and ‘Miúda’ (MIU were submitted to irrigation depths (2.5, 5.0 and 7.5 mm and frequencies (7, 14 and 28 days, in Serra Talhada, PE, Brazil, between March 2012 and August 2013. The SWB was applied, by adding the WRP in the estimate of the effective actual evapotranspiration (ETrEF. The water efficiency indicators were calculated. The actual evapotranspiration on SWB (ETrSWB overestimated ETrEF and, like other SWB components, it was affected by the factors irrigation depth, frequency and clone. The clone OEM is the most efficient, due to the use of the WRP, while MIU leads to highest gross economic returns for sale of cladodes as seed. As conclusion, the application of the soil water balance method in areas cultivated with cactus species must be accompanied by WRP.

  17. New alternatives for reference evapotranspiration estimation in West Africa using limited weather data and ancillary data supply strategies.

    Science.gov (United States)

    Landeras, Gorka; Bekoe, Emmanuel; Ampofo, Joseph; Logah, Frederick; Diop, Mbaye; Cisse, Madiama; Shiri, Jalal

    2017-04-01

    Accurate estimation of reference evapotranspiration (ET 0 ) is essential for the computation of crop water requirements, irrigation scheduling, and water resources management. In this context, having a battery of alternative local calibrated ET 0 estimation methods is of great interest for any irrigation advisory service. The development of irrigation advisory services will be a major breakthrough for West African agriculture. In the case of many West African countries, the high number of meteorological inputs required by the Penman-Monteith equation has been indicated as constraining. The present paper investigates for the first time in Ghana, the estimation ability of artificial intelligence-based models (Artificial Neural Networks (ANNs) and Gene Expression Programing (GEPs)), and ancillary/external approaches for modeling reference evapotranspiration (ET 0 ) using limited weather data. According to the results of this study, GEPs have emerged as a very interesting alternative for ET 0 estimation at all the locations of Ghana which have been evaluated in this study under different scenarios of meteorological data availability. The adoption of ancillary/external approaches has been also successful, moreover in the southern locations. The interesting results obtained in this study using GEPs and some ancillary approaches could be a reference for future studies about ET 0 estimation in West Africa.

  18. Analysis of evapotranspiration and biomass in pastures with degradation indicatives in the Upper Tocantins River Basin, in Brazilian Savanna

    Directory of Open Access Journals (Sweden)

    Ricardo Guimarães Andrade

    Full Text Available ABSTRACT The objective of this study was to apply the Simple Algorithm For Evapotranspiration Retrieving (SAFER with MODIS images together with meteorological data to analyze evapotranspiration (ET and biomass production (BIO according to indicative classes of pasture degradation in Upper Tocantins River Basin. Indicative classes of degraded pastures were obtained from the NDVI time-series (2002-2012. To estimate ET and BIO in each class, MODIS images and data from meteorological stations of the year 2012 were used. The results show that compared to not-degraded pastures, ET and BIO were different in pastures with moderate to strong degradation, mainly during water stress period. Therefore, changes in energy balance partition may occur according to the degradation levels, considering that those indicatives of degradation processes were identified in 24% of the planted pasture areas. In this context, ET and BIO estimates using remote sensing techniques can be a reliable indicator of forage availability, and large-scale aspects related to the degradation of pastures. It is expected that this knowledge may contribute to initiatives of public policies aimed at controlling the loss of production potential of pasture areas in the Upper Tocantins River Basin in the state of Goiás, Brazil.

  19. Remote sensing-based soil water balance to estimate Mediterranean holm oak savanna (dehesa) evapotranspiration under water stress conditions

    Science.gov (United States)

    Campos, Isidro; Villodre, Julio; Carrara, Arnaud; Calera, Alfonso

    2013-06-01

    This paper aims to present the use of a remote sensing-based soil water balance to estimate holm oak woodland evapotranspiration (ET). The model is based on the assimilation of MODIS reflectance-based vegetation indices in the dual crop coefficient methodology. A daily water balance was performed on the root zone soil to estimate plant water stress. The methodology was evaluated with respect to the actual ET measured by eddy covariance in Mediterranean holm oak savanna (dehesa) for five consecutive years (2004-2008). The model adequately reproduced the absolute values and tendencies measured at daily and weekly periods. Root mean square error (RMSE) was 0.50 mm/day for daily values and 2.70 mm/week for weekly accumulated values. The analysis demonstrated the presence of a long period of water stress during the summer and at the beginning of fall. Measured ET dropped during these periods, and the model replicated this tendency accurately, reaching a stress coefficient value close to 0.2. To be operative, the proposed method required low ground data (reference evapotranspiration and precipitation) and the results indicated a simple, robust method that can be used to map ET and water stress in the dehesa ecosystem.

  20. Using MOD16 products for analyzing evapotranspiration and evaporation on the surface of lakes. Case studies in Romania

    Science.gov (United States)

    Stan, Florentina; Madelin, Malika; Zaharia, Liliana

    2017-04-01

    Evapotranspiration and evaporation are some of the most complex atmospheric processes and major components of the water balance. The knowledge of these processes at several spatial and temporal scales has great practical importance in the field of water resources management and agriculture. However, the direct measurement of these parameters is generally a problem, because it requires accuracy and instruments (lysimeters and pans) difficult to install; therefore many equations based on physical processes or vegetation stages have been proposed by different scientists (Thornthwaite, Penman, etc.). The use of remote sensing is a good alternative to estimate the evapotranspiration, by taking advantage of the new generation of Earth Observation Satellites. In recent years, a remote sensing product from the MODerate Resolution Imaging Spectrometer - MOD16 has been developed. The MOD16 algorithm (Mu et al. 2007) combines on the one hand remote sensing data on land cover, albedo, leaf area index and in the other hand radiation, air temperature and vapor pressure deficit data, in order to estimate real evapotranspiration (ET) and potential evapotranspiration (PET), at 1 km2 resolution. Until now the MOD16 products were not used in the Romanian studies, so the product accuracy is unknown. The main objective of this study is to correlate the MOD16 ET and PET products with the evaporation (E) data measured at the surface of some lakes (Căldăruşani, Soleşti, Cinciş), located in different climate and landform conditions in Romania, in order to establish the relationships between those parameters, that could allow estimate indirectly the evaporation, based on the MODIS products. We correlated the daily recorded pan evaporation data with the MOD16 products, by taking into account R2 coefficients. Eight-day cumulative evaporation data from the considered pans was calculated to coincide with the eight-day MOD16 products over 2010 - 2012. A secondary purpose of the paper is to

  1. SRB/GEWEX evapotranspiration (Penman-Monteith) L4 3 hour 0.5 degree x 0.5 degree V1 (WC_PM_ET_050) at GES DISC

    Data.gov (United States)

    National Aeronautics and Space Administration — SRB/GEWEX evapotranspiration (Penman-Monteith) L4 3 hour 0.5 degree x 0.5 degree V1 is a global, 24-year (1984-2007), satellite-derived evapotranspiration over land...

  2. Analysis of evapotranspiration uncertainty due to uncertain forcing data in the Northern Eurasia

    Science.gov (United States)

    Liu, Y.; Zhuang, Q.; Tchebakova, N. M.; Kicklighter, D. W.; Melillo, J. M.

    2013-12-01

    Northern Eurasian ecosystems play an important role in the global water cycle and the climate system as a whole; evapotranspiration (ET) is a critical variable to understand this role, but ET over Northern Eurasia has not yet been well studied. Using an improved version of the Terrestrial Ecosystem Model (TEM), our work examines the uncertainties in the estimation of ET caused by different climate forcing data. The focus is on the period 1979-2008. Five widely-used forcing datasets are examined, including the Climate Research Unit (CRU) TS3.1, European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim), Global Modeling and Assimilation Office (GMAO) meteorological data, National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis, and Global Meteorological Forcing Dataset for land surface modeling by Princeton University (PU). Results show that the TEM ET from these different climate forcing data ranges from 263.5-369.3 mm yr-1, and that a variety of satellite observation-based ET products (e.g. GLEAM, LandFlux-EVAL multi-dataset synthesis, MODIS ET) fall in this range of estimates. TEM ET uncertainties might be explained by the differences in magnitude and spatial patterns of climate variables like precipitation (P), air temperature (T), global radiation (R) and vapor pressure deficit (VPD). The TEM ET driven by ERA-Interim is the highest (338.4-369.3 mm yr-1) which is consistent with the highest T and VPD. CRU estimates are the lowest (263.5-290.2 mm yr-1), agreeing with the lowest T, R and P. NCEP/NCAR P and R are the highest in the majority of the spatial domain, and GMAO shows the largest T in the Eastern part of the domain. Pearson's correlation coefficients (r) between TEM ET and each climate forcing indicate that TEM ET driven by CRU and ERA-Interim are most correlated to VPD, while those driven by NCEP/NCAR and PU are most correlated to T, and TEM ET driven by GMAO is most

  3. Evapotranspiration and water yield over China's landmass from 2000 to 2010

    Science.gov (United States)

    Liu, Y.; Zhou, Y.; Ju, W.; Chen, J.; Wang, S.; He, H.; Wang, H.; Guan, D.; Zhao, F.; Li, Y.; Hao, Y.

    2013-12-01

    Terrestrial carbon and water cycles are interactively linked at various spatial and temporal scales. Evapotranspiration (ET) plays a key role in the terrestrial water cycle, altering carbon sequestration of terrestrial ecosystems. The study of ET and its response to climate and vegetation changes is critical in China because water availability is a limiting factor for the functioning of terrestrial ecosystems in vast arid and semiarid regions. To constrain uncertainties in ET estimation, the process-based Boreal Ecosystem Productivity Simulator (BEPS) model was employed in conjunction with a newly developed leaf area index (LAI) data set, MODIS land cover, meteorological, and soil data to simulate daily ET and water yield at a spatial resolution of 500 m over China for the period from 2000 to 2010. The spatial and temporal variations of ET and water yield were analyzed. The influences of climatic factors (temperature and precipitation) and vegetation (land cover types and LAI) on these variations were assessed. Validations against ET measured at five ChinaFLUX sites showed that the BEPS model was able to simulate daily and annual ET well at site scales. Simulated annual ET exhibited a distinguishable southeast to northwest decreasing gradient, corresponding to climate conditions and vegetation types. It increased with the increase of LAI in 74% of China's landmass and was positively correlated with temperature in most areas of southwest, south, east, and central China. The correlation between annual ET and precipitation was positive in the arid and semiarid areas of northwest and north China, but negative in the Tibetan Plateau and humid southeast China. The national annual ET varied from 345.5 mm in 2001 to 387.8 mm in 2005, with an average of 369.8 mm during the study period. The overall rate of increase, 1.7 mm yr-1 (R2 = 0.18, p = 0.19), was mainly driven by the increase of total ET in forests. During 2006-2009, precipitation and LAI decreased widely and

  4. Evapotranspiration from Upper Klamath Lake: Reducing Uncertainty in the Water Balance

    Science.gov (United States)

    Stannard, D. I.; Gannett, M. W.; Polette, D.; Cameron, J. M.; Spears, J. M.

    2009-12-01

    The Klamath River basin is a large (~40,600 km2) watershed that straddles the border between southern Oregon and northern California, USA, and drains into the Pacific Ocean. A wide variety of interests has led to intense competition over water allocation in the upper, semi-arid parts of the basin in recent decades. Myriad water impoundments and diversions, wetland drainage, and recent wetland restoration, have complicated the development of resource-management and restoration strategies. An overarching question is how to provide enough water for irrigated agriculture and still preserve adequate stream-flow and wetland habitat for threatened (e.g. coho salmon) and endangered (e.g. Lost River and shortnose suckers) species. In the Upper Klamath Lake region, this hotly debated topic has raised questions about evaporative losses from Upper Klamath Lake, and its wetland marshes. Currently, surface-water outflow from the lake is gauged, but not all of the surface-water inflows are gauged, and net ground-water inflow is estimated. Lake-level management is based on a simplified water budget: NETin - SWout = ΔS, where NETin = SWin + GWnet - ET (called “net inflow”), SWout is measured surface-water outflow, ΔS is measured change in lake storage, SWin is surface-water inflow, GWnet is net ground-water inflow, and ET is evapotranspiration from the lake. Partitioning of NETin is not done routinely, so little is known about magnitudes of the un-gauged inflows, or ET (GWnet is a small term). To help partition NETin into its components, ET has been measured at three locations in Upper Klamath Lake since April, 2008. Two eddy covariance (EC) sites are located in Upper Klamath National Wildlife Refuge, an extensive wetland marsh in the northwest corner of the lake, and one Bowen-ratio energy-balance site is in open water. One EC station is situated in bulrush and the other is in a mixed bulrush, wocus, cattail community. Wetland marsh area is about 1/3 that of open water. The

  5. Evaluating Landsat 8 evapotranspiration for water use mapping in the Colorado River Basin

    Science.gov (United States)

    Senay, Gabriel; Friedrichs, MacKenzie O.; Singh, Ramesh K.; Velpuri, Naga Manohar

    2016-01-01

    Evapotranspiration (ET) mapping at the Landsat spatial resolution (100 m) is essential to fully understand water use and water availability at the field scale. Water use estimates in the Colorado River Basin (CRB), which has diverse ecosystems and complex hydro-climatic regions, will be helpful to water planners and managers. Availability of Landsat 8 images, starting in 2013, provides the opportunity to map ET in the CRB to assess spatial distribution and patterns of water use. The Operational Simplified Surface Energy Balance (SSEBop) model was used with 528 Landsat 8 images to create seamless monthly and annual ET estimates at the inherent 100 m thermal band resolution. Annual ET values were summarized by land use/land cover classes. Croplands were the largest consumer of “blue” water while shrublands consumed the most “green” water. Validation using eddy covariance (EC) flux towers and water balance approaches showed good accuracy levels with R2 ranging from 0.74 to 0.95 and the Nash–Sutcliffe model efficiency coefficient ranging from 0.66 to 0.91. The root mean square error (and percent bias) ranged from 0.48 mm (13%) to 0.60 mm (22%) for daily (days of satellite overpass) ET and from 7.75 mm (2%) to 13.04 mm (35%) for monthly ET. The spatial and temporal distribution of ET indicates the utility of Landsat 8 for providing important information about ET dynamics across the landscape. Annual crop water use was estimated for five selected irrigation districts in the Lower CRB where annual ET per district ranged between 681 mm to 772 mm. Annual ET by crop type over the Maricopa Stanfield irrigation district ranged from a low of 384 mm for durum wheat to a high of 990 mm for alfalfa fields. A rainfall analysis over the five districts suggested that, on average, 69% of the annual ET was met by irrigation. Although the enhanced cloud-masking capability of Landsat 8 based on the cirrus band and utilization of the Fmask algorithm improved the

  6. Recovery dynamics of evapotranspiration, flow, sediment and nutrients following severe wildfire in eucalypt forests

    Science.gov (United States)

    Lane, P. N.; Sheridan, G. J.; Nyman, P.; Nolan, R.; Nokse, P. J.

    2013-12-01

    Wildfire is a particularly significant disturbance event in forested landscapes. Around 40,000 km2 of largely forested land has been burnt in south eastern Australia in the past decade. Fire effects on erosion and water quality have been widely reported and studied in many environments, but nutrient dynamics and evapotranspiration (ET) and streamflow are also of significant concern or interest. However the hydrologic response and recovery trajectories of the majority of eucalypt forests has been poorly known. Likewise, the coupling of ET response with sediment and nutrient dynamics has not been explored widely. Our research over the past decade into sediment, nutrients and ET/flow dynamics in differing forest types has led to new insights into this resilience/recovery question in eucalypt forests. This research has encompassed scales from the point to large catchment, identified the driving processes, and led to models that deal with discrete events and risk/probability frameworks. Broadly, we suggest there are two distinct 'sets' of responses and recovery trajectories depending on forest type. (1) wet eucalypt stands of E. regnans and E. delegatensis and associated 'ash' stands; and (2) the drier 'mixed-species' forests. The hydrologic responses of (1) may be summarized as: (i) Widespread mortality of trees exposed to moderate-hot fire, leading to dense single-age regeneration. ET is suppressed for 1-3 years, then increases to exceed that of a stands > 30 years old, with a concomitant inverse effect on flow. This recovery trajectory may play out until forests reach maturity (~100 years) or are re-burnt (ii) Sediment and nutrients (P and N principally) exports can increase by 1-2 orders of magnitude, but export rates recover with 2 years of the fire. Erosion processes are largely non-rill. Water quality issues (per event) are relatively short term (days) For case (2): (i) These stands are fire-resistant and show low (~10 %) rates of mortality. Leaf are recovery

  7. Net ecosystem CO2 exchange and evapotranspiration of a sphagnum mire: field measurements and model simulations

    Science.gov (United States)

    Olchev, Alexander; Volkova, Elena; Karataeva, Tatiana; Zatsarinnaya, Dina; Novenko, Elena

    2014-05-01

    The spatial and temporal variability of net ecosystem exchange of CO2 (NEE) and evapotranspiration (ET) of a karst-hole sphagnum peat mire situated at the boundary between broad-leaved and forest-steppe zones in the central part of European Russia (54.06N, 37.59E, 260 m a.s.l.) was described using results of field measurements and simulations with Mixfor-3D model. The area of the mire is about 1.2 ha and it is surrounded by a broadleaved forest stand. It is a typical peat mire according to water and mineral supply as well as to vegetation composition. The vegetation of the peripheral parts of the mire is typical eutrophic whereas the vegetation in its central part is represented by meso-oligothrophic plant communities. To describe the spatial variability of NEE and ET within the mire a portable measuring system consisting of a transparent ventilated chamber combined with an infrared CO2 and H2O analyzer LI-840A (Li-Cor, USA) was used. The measurements were provided along a transect from the southern peripheral part of the mire to its center under sunny clear-sky weather conditions in the period from May to September of 2012 and from May 2013 to October 2013. The chamber method was used for measurements of NEE and ET fluxes because of small size of the mire, a very uniform surrounding forest stand and the mosaic mire vegetation. All these factors promote very heterogeneous exchange conditions within the mire and make it difficult to apply, for example, an eddy covariance method that is widely used for flux measurements in the field. The results of the field measurements showed a significant spatial and temporal variability of NEE and ET that was mainly influenced by incoming solar radiation, air temperature and ground water level. During the entire growing season the central part of the mire was a sink of CO2 for the atmosphere (up to 6.8±4.2 µmol m-2 s-1 in June) whereas its peripheral part, due to strong shading by the surrounding forest, was mainly a source of

  8. Large Scale Evapotranspiration Estimates: An Important Component in Regional Water Balances to Assess Water Availability

    Science.gov (United States)

    Garatuza-Payan, J.; Yepez, E. A.; Watts, C.; Rodriguez, J. C.; Valdez-Torres, L. C.; Robles-Morua, A.

    2013-05-01

    Water security, can be defined as the reliable supply in quantity and quality of water to help sustain future populations and maintaining ecosystem health and productivity. Water security is rapidly declining in many parts of the world due to population growth, drought, climate change, salinity, pollution, land use change, over-allocation and over-utilization, among other issues. Governmental offices (such as the Comision Nacional del Agua in Mexico, CONAGUA) require and conduct studies to estimate reliable water balances at regional or continental scales in order to provide reasonable assessments of the amount of water that can be provided (from surface or ground water sources) to supply all the human needs while maintaining natural vegetation, on an operational basis and, more important, under disturbances, such as droughts. Large scale estimates of evapotranspiration (ET), a critical component of the water cycle, are needed for a better comprehension of the hydrological cycle at large scales, which, in most water balances is left as the residual. For operational purposes, such water balance estimates can not rely on ET measurements since they do not exist, should be simple and require the least ground information possible, information that is often scarce or does not exist at all. Given this limitation, the use of remotely sensed data to estimate ET could supplement the lack of ground information, particularly in remote regions In this study, a simple method, based on the Makkink equation is used to estimate ET for large areas at high spatial resolutions (1 km). The Makkink model used here is forced using three remotely sensed datasets. First, the model uses solar radiation estimates obtained from the Geostationary Operational Environmental Satellite (GOES); Second, the model uses an Enhanced Vegetation Index (EVI) obtained from the Moderate-resolution Imaging Spectroradiometer (MODIS) normalized to get an estimate for vegetation amount and land use which was

  9. Estimation of crops biomass and evapotranspiration from high spatial and temporal resolutions remote sensing data

    Science.gov (United States)

    Claverie, Martin; Demarez, Valérie; Duchemin, Benoît.; Ceschia, Eric; Hagolle, Olivier; Ducrot, Danielle; Keravec, Pascal; Beziat, Pierre; Dedieu, Pierre

    2010-05-01

    Carbon and water cycles are closely related to agricultural activities. Agriculture has been indeed identified by IPCC 2007 report as one of the options to sequester carbon in soil. Concerning the water resources, their consumptions by irrigated crops are called into question in view of demographic pressure. In the prospect of an assessment of carbon production and water consumption, the use of crop models at a regional scale is a challenging issue. The recent availability of high spatial resolution (10 m) optical sensors associated to high temporal resolution (1 day) such as FORMOSAT-2 and, in the future, Venµs and SENTINEL-2 will offer new perspectives for agricultural monitoring. In this context, the objective of this work is to show how multi-temporal satellite observations acquired at high spatial resolution are useful for a regional monitoring of following crops biophysical variables: leaf area index (LAI), aboveground biomass (AGB) and evapotranspiration (ET). This study focuses on three summer crops dominant in South-West of France: maize, sunflower and soybean. A unique images data set (82 FORMOSAT-2 images over four consecutive years, 2006-2009) was acquired for this project. The experimental data set includes LAI and AGB measurements over eight agricultural fields. Two fields were intensively monitored where ET flux were measured with a 30 minutes time step using eddy correlation methods. The modelisation approach is based on FAO-56 method coupled with a vegetation functioning model based on Monteith theory: the SAFY model [5]. The model operates at a daily time step model to provide estimates of plant characteristics (LAI, AGB), soil conditions (soil water content) and water use (ET). As a key linking variable, LAI is deduced from FORMOSAT-2 reflectances images, and then introduced into the SAFY model to provide spatial and temporal estimates of these biophysical variables. Most of the SAFY parameters are crop related and have been fixed according to

  10. Modelling and monitoring vegetation and evapotranspiration on an anthropogenic grassland succession in the Andes of Ecuador

    Science.gov (United States)

    Silva, B.; Bendix, J.

    2012-04-01

    productivity and Setaria pasture showed to be as competitive as bracken. A productivity of 3.2 kg/m2/year was calculated for Setaria pasture against 2.7 kg/m2/year for bracken fern, while a slightly higher evapotranspiration 968 mm/year was calculated for Setaria canopy in comparison with that of bracken with 849 mm/year. In addition, model runs using future climate change scenarios point to higher competitiveness of Setaria pasture. Explanations are given by comparing independent data and different observations within the study area and discussions emphasize data acquisition issues and the on-going modeling approach. Aknowledgments. The current study was conducted within the framework of the DFG Research Group FOR 816 "Biodiversity and sustainable management of a megadiverse mountain rain forest in south Ecuador" funded by the German Research Foundation DFG (BE 473/38-1 and 2; SCHE 217/14-2). B. Silva would like to thank the Brazilian Council of Technological and Scientific Development (CNPq) for research grants (GDE 290033/2007-1).

  11. Upscaling instantaneous to daily evapotranspiration using modelled daily shortwave radiation for remote sensing applications: an artificial neural network approach

    Science.gov (United States)

    Wandera, Loise; Mallick, Kaniska; Kiely, Gerard; Roupsard, Olivier; Peichl, Mathias; Magliulo, Vincenzo

    2017-04-01

    Upscaling instantaneous evapotranspiration retrieved at any specific time-of-day (ETi) to daily evapotranspiration (ETd) is a key challenge in mapping regional ET using polar orbiting sensors. Various studies have unanimously cited the shortwave incoming radiation (RS) to be the most robust reference variable explaining the ratio between ETd and ETi . This study aims to contribute in ETi upscaling for global studies using the ratio between daily and instantaneous incoming shortwave radiation (RSd / RSi) as a factor for converting ETi to ETd. This paper proposes an artificial neural network (ANN) machine-learning algorithm first to predict RSd from RSi followed by using the RSd / RSi ratio to convert ETi to ETd across different terrestrial ecosystems. Using RSi and RSd observations from multiple sub-networks of the FLUXNET database spread across different climates and biomes (to represent inputs that would typically be obtainable from remote sensors during the overpass time) in conjunction with some astronomical variables (e.g. solar zenith angle, day length, exoatmospheric shortwave radiation), we developed the ANN model for reproducing RSd and further used it to upscale ETi to ETd. The efficiency of the ANN is evaluated for different morning and afternoon times of day, under varying sky conditions, and also at different geographic locations. RS-based upscaled ETd produced a significant linear relation (R 2 = 0.65 to 0.69), low bias (-0.31 to -0.56 MJ m-2 d -1 ; approx. 4 %), and good agreement (RMSE 1.55 to 1.86 MJ m-2 d -1 ; approx. 10 %) with the observed ETd, although a systematic overestimation of ETd was also noted under persistent cloudy sky conditions. Inclusion of soil moisture and rainfall information in ANN training reduced the systematic overestimation tendency in predominantly overcast days. An intercomparison with existing upscaling method at daily, 8-day, monthly, and yearly temporal resolution revealed a robust performance of the ANNdriven RS

  12. Combining remote sensing and GIS climate modelling to estimate daily forest evapotranspiration in a Mediterranean mountain area

    Directory of Open Access Journals (Sweden)

    J. Cristóbal

    2011-05-01

    Full Text Available Evapotranspiration monitoring allows us to assess the environmental stress on forest and agricultural ecosystems. Nowadays, Remote Sensing and Geographical Information Systems (GIS are the main techniques used for calculating evapotranspiration at catchment and regional scales. In this study we present a methodology, based on the energy balance equation (B-method, that combines remote sensing imagery with GIS-based climate modelling to estimate daily evapotranspiration (ETd for several dates between 2003 and 2005. The three main variables needed to compute ETd were obtained as follows: (i Land surface temperature by means of the Landsat-5 TM and Landsat-7 ETM+ thermal band, (ii air temperature by means of multiple regression analysis and spatial interpolation from meteorological ground stations data at satellite pass, and (iii net radiation by means of the radiative balance. We calculated ETd using remote sensing data at different spatial and temporal scales (Landsat-7 ETM+, Landsat-5 TM and TERRA/AQUA MODIS, with a spatial resolution of 60, 120 and 1000 m, respectively and combining three different approaches to calculate the B parameter, which represents an average bulk conductance for the daily-integrated sensible heat flux. We then compared these estimates with sap flow measurements from a Scots pine (Pinus sylvestris L. stand in a Mediterranean mountain area. This procedure allowed us to better understand the limitations of ETd modelling and how it needs to be improved, especially in heterogeneous forest areas. The method using Landsat data resulted in a good agreement, R2 test of 0.89, with a mean RMSE value of about 0.6 mm day−1 and an estimation error of ±30 %. The poor agreement obtained using TERRA/AQUA MODIS, with a mean RMSE value of 1.8 and 2.4 mm day−1 and an estimation error of about ±57 and 50 %, respectively. This

  13. Assessment of daily reference evapotranspiration in Sicily by means of POWER-NASA agro-climatology archive

    Science.gov (United States)

    Negm, Amro; Jabro, Jay; Provenzano, Giuseppe

    2016-04-01

    The importance of evapotranspiration, ET, processes has long been recognized in many disciplines, including hydrologic and drainage studies as well as for irrigation system design and management. A wide number of equations have been proposed to estimate crop reference evapotranspiration, ET0, based on the variables affecting the process. When a full data set of climate variables is available, the Food and Agriculture Organization (FAO) of the United Nations recommended to use the physically based FAO-56 Penman-Monteith equation. The lack of climate variables and particularly of solar radiation has led several researchers to propose simplified ET0 estimation equations using a limited number of climate variables. These equations, however, need site-specific validation prior to their use and cannot be generalized. Recently, the American National Aeronautics and Space Administration (NASA), created an efficient and open access agro-climatology archive in the frame of the Prediction Of Worldwide Energy Resource (POWER) project containing, on global scale, a long-series of meteorological variables and surface solar energy fluxes. The main objective of the research was to assess the suitability of POWER-NASA open access archive to estimate daily reference evapotranspiration, ET0, in Sicily, for the period 2006-2014. Daily ET0 were evaluated according to FAO-56 PM equation, by considering the POWER-NASA database characterized by a grid resolution of 1° latitude × 1° longitude, as well as the climate data measured on the ground, by a network of 36 meteorological stations installed in Sicily and belonging to the Agro-meteorological Information Service (SIAS). After comparing the climate data available in both databases (minimum, maximum and average air temperature and relative air humidity, wind speed, solar radiation and air pressure), a statistical comparison was also carried out on ET0 values estimated with the FAO-56 PM equation. The analysis showed a good correlation

  14. Contrasting patterns of groundwater evapotranspiration in grass and tree dominated riparian zones of a temperate agricultural catchment

    Science.gov (United States)

    Satchithanantham, Sanjayan; Wilson, Henry F.; Glenn, Aaron J.

    2017-06-01

    Consumptive use of shallow groundwater by phreatophytic vegetation is a significant part of the water budget in many regions, particularly in riparian areas. The influence of vegetation type on groundwater level fluctuations and evapotranspiration has rarely been quantified for contrasting plant communities concurrently although it has implications for downstream water yield and quality. Hourly groundwater evapotranspiration (ETG) rates were estimated for grass and tree riparian vegetation in southwestern Manitoba, Canada using two modified White methods. Groundwater table depth was monitored in four 21 m transects of five 3 m deep monitoring wells in the riparian zone of a stream reach including tree (Acer negundo; boxelder) and grass (Bromus inermis; smooth brome) dominated segments. The average depths to the groundwater table from the surface were 1.4 m and 1 m for the tree and grass segments, respectively, over the two-year study. During rain free periods of the growing season ETG was estimated for a total of 70 days in 2014 and 79 days in 2015 when diurnal fluctuations were present in groundwater level. Diurnal groundwater level fluctuations were observed during dry periods under both segments, however, ETG was significantly higher (p < 0.001) under trees compared to grass cover in 2014 (a wet year with 72% higher than normal growing season precipitation) and 2015 (a drier year with 15% higher than normal growing season precipitation). The two methods used to estimate ETG produced similar daily and seasonal values for the two segments. In 2014, total ETG was approximately 50% (148 mm) and 100% (282-285 mm) of reference evapotranspiration (ETref, 281 mm) for the grass and tree segments, respectively. In 2015, total ETG was approximately 40% (106-127 mm) and 120% (369-374 mm) of ETref (307 mm) for the grass and tree segments, respectively. Results from the study show the tree dominated portions of the stream reach consumed approximately 2.4 ML ha-1 yr-1 more

  15. Evaluation of Surface Energy Balance models for mapping evapotranspiration using very high resolution airborne remote sensing data

    Science.gov (United States)

    Paul, George

    Agriculture is the largest (90%) consumer of all fresh water in the world. The consumptive use of water by vegetation represented by the process evapotranspiration (ET) has a vital role in the dynamics of water, carbon and energy fluxes of the biosphere. Consequently, mapping ET is essential for making water a sustainable resource and also for monitoring ecosystem response to water stress and changing climate. Over the past three decades, numerous thermal remote sensing based ET mapping algorithms were developed and these have brought a significant theoretical and technical advancement in the spatial modeling of ET. Though these algorithms provided a robust, economical, and efficient tool for ET estimations at field and regional scales, yet the uncertainties in flux estimations were large, making evaluation a difficult task. The main objective of this study was to evaluate and improve the performance of widely used remote sensing based energy balance models, namely: the Surface Energy Balance Algorithm for Land (SEBAL), Mapping Evapotranspiration at high Resolution and with Internalized Calibration (METRIC), and Surface Energy Balance System (SEBS). Data used in this study was collected as part of a multi-disciplinary and multi-institutional field campaign BEAREX (Bushland Evapotranspiration and Agricultural Remote Sensing Experiment) that was conducted during 2007 and 2008 summer cropping seasons at the USDA-ARS Conservation and Production Research Laboratory (CPRL) in Bushland, Texas. Seventeen high resolution remote sensing images taken from multispectral sensors onboard aircraft and field measurements of the agro-meteorological variables from the campaign were used for model evaluation and improvement. Overall relative error measured in terms of mean absolute percent difference (MAPD) for instantaneous ET (mm h -1) were 22.7%, 23.2%, and 12.6% for SEBAL, METRIC, and SEBS, respectively. SEBAL and METRIC performances for irrigated fields representing higher ET

  16. Comparison of three different approaches to estimate evapotranspiration over large areas: remotely sensed method, complementary approach and SVAT model.

    Science.gov (United States)

    Tanguy, Maliko; Baille, Alain; Taylor, Christopher; Harris, Phil

    2010-05-01

    Methods able to accurately estimate ET over large areas are important for many applications. Spatial mapping of evapotranspiration (ET) is a prerequisite to a wide range of studies in hydrology, forestry, land and crop management, irrigation, water resources planning, etc. In this study, three different approaches to estimate ET over large areas are compared and evaluated. (1) The first one is a variant of the so-called "triangle" method (Jiang et al., 2004), which uses almost exclusively remote sensing data. Vegetation Fraction (Fv) - from the Normalised Difference Vegetation Index (NDVI) - and surface temperature (Ts) were obtained from MODIS products at satellite overpass. The graphical analysis of the Ts-Fv space allows estimating the evaporative fraction (EF), which is then used to derive ET. (2) The second method is the Advection-Aridity (AA) model (Brusaert et al., 1979). This simple approach, which only requires routinely available meteorological data, assumes that a complementary relationship exists between Potential Evapotranspiration (ETpot) and Actual Evapotranspiration (ETa). Although questioned for the lack of scientific basis of the complementary assumption, the AA model is currently used in hydrological applications requiring spatial mapping of ET. (3) The third method relies on the use of a land surface scheme ("JULES" - the Joint UK Land Environment Simulator) which is integrated within the UK Met Office climate model. This approach, based on equations that take into account the different biophysical processes involved in land surface environment, is likely to be the most reliable in theory but in practice it may be limited by the availability of parameters describing the soil and vegetation in a particular area, required to solve the set of equations describing land-atmosphere interactions. The three methods were applied to ET mapping of the Segura River Basin, a semi-arid region of South-Eastern Spain. Results from the case-study are presented

  17. Evapotranspiration of a Mid-Rotation Loblolly Pine Plantation and a Recently Harvested Stands on the Coastal Plain of North Carolina, U.S.A.

    Science.gov (United States)

    W. Cao; Ge Sun; Steve G. McNulty; J. Chen; A. Noormets; R. W. Skaggs; Devendra M. Amatya

    2006-01-01

    Evapotranspiration (ET) is the primary component of the forest hydrologic cycle, which includes plant transpiration, canopy rainfall interception, and soil evaporation. Quantifying ET processes and potential biophysical regulations is needed for assessing forest water management options. Loblolly pines are widely planted in the coastal plain of the Southeastern US, but...

  18. Daily Landsat-scale evapotranspiration estimation over a managed pine plantation in North Carolina, USA using multi-satellite data fusion

    Science.gov (United States)

    As a primary flux in the global water cycle, evapotranspiration (ET) connects hydrologic and biological processes and is directly affected by water and land management, land use change and climate variability. The Two Source Energy Balance (TSEB) model has been widely applied to quantify field- to g...

  19. Evapotranspiration and assimilation flux measurements in a corn-soybean rotation system and a reconstructed prairie using a portable canopy chamber

    Science.gov (United States)

    Measurement of Evapotranspiration (ET) and carbon dioxide assimilation flux (AF) is valuable for agricultural management, where ET indicates plant water use, and AF relates to photosynthesis and plant production. Portable canopy chambers were developed for directly measuring of ET and AF fluxes in v...

  20. Evapotranspiration and soil water relationships in a range of disturbed and undisturbed ecosystems in the semi-arid Inner Mongolia, China

    Science.gov (United States)

    Nan Lu; Shiping Chen; Burkhard Wilske; Ge Sun; Jiquan Chen

    2011-01-01

    Aims: Evapotranspiration (ET) is a key component of water balance and is closely linked to ecosystem productivity. In arid regions, large proportion of precipitation (PPT) is returned to the atmosphere through ET, with only a small amount available to plants. Our objective was to examine the variability in ET–soil water relationship based on a set of ecosystems that...

  1. Reference crop evapotranspiration derived from geo-stationary satellite imagery: a case study for the Fogera flood plain, NW-Ethiopia and the Jordan Valley, Jordan

    NARCIS (Netherlands)

    Bruin, de H.A.R.; Trigo, I.F.; Jitan, M.A.; Enku, N.T.; Tol, van der C.; Gieske, A.S.M.

    2010-01-01

    First results are shown of a project aiming to estimate daily values of reference crop evapotranspiration ET0 from geo-stationary satellite imagery. In particular, for Woreta, a site in the Ethiopian highland at an elevation of about 1800 m, we tested a radiation-temperature based approximate

  2. Evapotranspiration partitioning and variation of sap flow in female and male parents of maize for hybrid seed production in arid region

    Science.gov (United States)

    Understanding the variation of sap flow in female and male parents of maize for hybrid seed production and evapotranspiration (ET) partitioning is useful in accurately determining water use of the female and male parents and improving irrigation management of maize for hybrid seed production. Sap fl...

  3. Temporal and spatial evolution of the standardized precipitation evapotranspiration index (SPEI) in the Loess Plateau under climate change from 2001 to 2050.

    Science.gov (United States)

    Gao, Xuerui; Zhao, Qi; Zhao, Xining; Wu, Pute; Pan, Wenxiang; Gao, Xiaodong; Sun, Miao

    2017-10-01

    Loess Plateau has great uncertainty on drought occurrence due to climate change. This paper analyzes the evolution of precipitation, potential evapotranspiration and standardized precipitation evapotranspiration index (SPEI) based on the Coupled Model Inter-comparison Project Phase 5 (CMIP5) data and regional downscaling model (RegCM4.0). Results indicate that, under RCP2.6 Scenario, the precipitation will increase significantly (5% confidence level) at the rate of 16.40mm/10a. However, the potential evapotranspiration is showing non-significant decreasing trend at the rate of 2.16mm/10a. Moreover, the SPEI will decrease in the south and northernmost area and increase in the central northern area of Loess Plateau. Under RCP8.5 Scenario, the precipitation will increase significantly (5% confidence level) at the rate of 19.12mm/10a. The potential evapotranspiration will non-significantly decrease at the rate of 2.16mm/10a and the SPEI is showing increasing trend almost in the whole Loess Plateau. Generally, Loess Plateau is becoming wetter in the central part under RCP2.6 Scenario and the wet area will be enlarged to almost the whole plateau under RCP8.5 Scenario. Based on the results, the water resources will increase under global warming, which may alleviate the water scarcity issue in the Loess Plateau. Copyright © 2017. Published by Elsevier B.V.

  4. Estimation of Evapotranspiration ETc and Crop Coefficient Kc of Wheat, in south Nile Delta of Egypt Using integrated FAO-56 approach and remote sensing data

    Directory of Open Access Journals (Sweden)

    E. Farg

    2012-06-01

    Full Text Available Crop water requirements are represented by the actual crop evapotranspiration. Estimation of crop evapotranspiration (ETc and crop coefficient using remote-sensing data is essential for planning the irrigation water use in arid and semiarid regions. This study focuses on estimating the crop coefficient (Kc and crop evapotranspiration (ETc using SPOT-4 satellite data integrated with the meteorological data and FAO-56 approach. Reference evapotranspiration (ETo were estimated using FAO Penman-Monteith and tabled single crop coefficient values were adjusted to real values. SPOT-4 images geometrically and radio metrically corrected were used to drive the vegetation indices (NDVI and SAVI. Multi linear regression analysis was applied to develop the crop coefficient (Kc prediction equations for the different growth stages from vegetation indices. The results showed R2 were 0.82, 0.90 and 0.97 as well as adjusted R2 were 0.80, 0.86 and 0.96 for developing, mid-season and late-season growth stage respectively.

  5. Effect of nitrogen and water availability of three soil types on yield, radiation use efficiency and evapotranspiration in field-grown quinoa

    DEFF Research Database (Denmark)

    Razzaghi, Fatemeh; Plauborg, Finn; Jacobsen, Sven-Erik

    2012-01-01

    . This lead to higher interception of photosynthetic active radiation and higher seed yield on sandy clay loam (3.3 Mg ha−1) and sandy loam (3.0 Mg ha−1) than on sand (2.3 Mg ha−1). The soil with higher clay content had also the highest transpiration, crop evapotranspiration and yield due to the higher uptake...

  6. Reference evapotranspiration models using different time scales in the Jaboticabal region of São Paulo, Brazil

    Directory of Open Access Journals (Sweden)

    Natália Buzinaro Caporusso

    2014-11-01

    Full Text Available The aim of this paper is to compare 18 reference evapotranspiration models to the standard Penman-Monteith model in the Jaboticabal, São Paulo, region for the following time scales: daily, 5-day, 15-day and seasonal. A total of 5 years of daily meteorological data was used for the following analyses: accuracy (mean absolute percentage error, Mape, precision (R2 and tendency (bias (systematic error, SE. The results were also compared at the 95% probability level with Tukey’s test. The Priestley-Taylor (1972 method was the most accurate for all time scales, the Tanner-Pelton (1960 method was the most accurate in the winter, and the Thornthwaite (1948 method was the most accurate of the methods that only used temperature data in the equations.

  7. The Future of Evapotranspiration: Global requirements for ecosystem functioning, carbon and climate feedbacks, agricultural management, and water resources

    KAUST Repository

    Fisher, Joshua B.

    2017-03-11

    The fate of the terrestrial biosphere is highly uncertain given recent and projected changes in climate. This is especially acute for impacts associated with changes in drought frequency and intensity on the distribution and timing of water availability. The development of effective adaptation strategies for these emerging threats to food and water security are compromised by limitations in our understanding of how natural and managed ecosystems are responding to changing hydrological and climatological regimes. This information gap is exacerbated by insufficient monitoring capabilities from local to global scales. Here, we describe how evapotranspiration (ET) represents the key variable in linking ecosystem functioning, carbon and climate feedbacks, agricultural management, and water resources, and highlight both the outstanding science and applications questions and the actions, especially from a space-based perspective, necessary to advance them. This article is protected by copyright. All rights reserved.