Comparison of lysimeter based and calculated ASCE reference evapotranspiration in a subhumid climate

Science.gov (United States)

Nolz, Reinhard; Cepuder, Peter; Eitzinger, Josef

2016-04-01

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 (ET ref) and subsequently plant water requirements. 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 environmental and weather conditions. Therefore, it seems generally advisable to evaluate the model under local environmental conditions. In this study, reference evapotranspiration was determined at a subhumid site in northeastern Austria from 2005 to 2010 using a large weighing lysimeter (ET lys). The measured data were compared with ET ref calculations. Daily values differed slightly during a year, at which ET ref was generally overestimated at small values, whereas it was rather underestimated when ET was large, which is supported also by other studies. In our case, advection of sensible heat proved to have an impact, but it could not explain the differences exclusively. Obviously, there were also other influences, such as seasonal varying surface resistance or albedo. Generally, the ASCE-EWRI equation for daily time steps performed best at average weather conditions. The outcomes should help to correctly interpret ET ref data in the region and in similar environments and improve knowledge on the dynamics of influencing factors causing deviations.

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...

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.

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 ...

shoot water content and reference evapotranspiration

African Journals Online (AJOL)

ACSS

measurement affects irrigation amount, while in the atmospheric-based methods, the soil water content affects evapotranspiration. Most ... stem water potential, leaf water potential, and .... cells. No tillage plots were weeded by hand pulling of weeds; whereas hoes were used in ..... based on soil electrical conductivity and.

shoot water content and reference evapotranspiration

African Journals Online (AJOL)

ACSS

Based on a work ... Determination of water requirement for crops in resource limited areas is challenging, yet ... study was to indirectly determine crop evapotranspiration of soybean .... monitored, have been commended as the best option (Fernández, 2014) as they measure the ..... and climate change/ : Impacts on Kenyan.

Spatiotemporal Variations of Reference Crop Evapotranspiration in Northern Xinjiang, China

Directory of Open Access Journals (Sweden)

Jian Wang

2014-01-01

Full Text Available To set up a reasonable crop irrigation system in the context of global climate change in Northern Xinjiang, China, reference crop evapotranspiration (ET0 was analyzed by means of spatiotemporal variations. The ET0 values from 1962 to 2010 were calculated by Penman-Monteith formula, based on meteorological data of 22 meteorological observation stations in the study area. The spatiotemporal variations of ET0 were analyzed by Mann-Kendall test, Morlet wavelet analysis, and ArcGIS spatial analysis. The results showed that regional average ET0 had a decreasing trend and there was an abrupt change around 1983. The trend of regional average ET0 had a primary period about 28 years, in which there were five alternating stages (high-low-high-low-high. From the standpoint of spatial scale, ET0 gradually increased from the northeast and southwest toward the middle; the southeast and west had slightly greater variation, with significant regional differences. From April to October, the ET0 distribution significantly influenced the distribution characteristic of annual ET0. Among them sunshine hours and wind speed were two of principal climate factors affecting ET0.

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...

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...

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.

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.

Decadal changes of reference crop evapotranspiration attribution: Spatial and temporal variability over China 1960-2011

Science.gov (United States)

Fan, Ze-Xin; Thomas, Axel

2018-05-01

Atmospheric evaporative demand can be used as a measure of the hydrological cycle and the global energy balance. Its long-term variation and the role of driving climatic factors have received increasingly attention in climate change studies. FAO-Penman-Monteith reference crop evapotranspiration rates were estimated for 644 meteorological stations over China for the period 1960-2011 to analyze spatial and temporal attribution variability. Attribution of climatic variables to reference crop evapotranspiration rates was not stable over the study period. While for all of China the contribution of sunshine duration remained relatively stable, the importance of relative humidity increased considerably during the last two decades, particularly in winter. Spatially distributed attribution analysis shows that the position of the center of maximum contribution of sunshine duration has shifted from Southeast to Northeast China while in West China the contribution of wind speed has decreased dramatically. In contrast relative humidity has become an important factor in most parts of China. Changes in the Asian Monsoon circulation may be responsible for altered patterns of cloudiness and a general decrease of wind speeds over China. The continuously low importance of temperature confirms that global warming does not necessarily lead to rising atmospheric evaporative demand.

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

Directory of Open Access Journals (Sweden)

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.

Reference evapotranspiration estimation from class A pan in the northwest of Uruguay

International Nuclear Information System (INIS)

Otero, A.; Goni, C.; Castano, J.

2012-01-01

Efficient water management in agriculture requires accurate estimation of the evapotranspiration. The difficulty in obtaining records of all the variables needed to estimate reference evapotranspiration (E To) by the model proposed by Penman-Manhattan-FAO56 (Allen et al., 1998), leads to the use of alternative methods, such as pan evaporation class A (E o), which requires regional calibrations for successful implementation. This paper compares four methods for estimating the adjustment coefficient (Kp) of E o over ETo: i) the procedure proposed by Snyder (1992); i i) by Allen et al. (1998); III) by Pu ppo and Gar cia Petillo (2009); and i v) the Kp-combined obtained through the regression coefficient of E o to ETo for the region under study. The regression coefficient values of E o over ETo change slightly according to the average interval used, being 0.77, 0.75 and 0.73 for the monthly interval, de-iced (10 days) and weekly. The estimation error decreases as we average at longer intervals. The procedure i) significantly overestimated ETo, while i i) underestimated both, with a mean absolute error of 0.49 and 0.86 mm respectively, while in III) is 0.32 and the i v ) is 0.37 mm. Procedures III) and i v) with constant values of Kp had the best performance for the northwestern region of Uruguay

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

by a linear boundary. In this method, the nearest samples to the decision boundary called support vectors. These vectors define the equation of the decision boundary. The classic intelligent simulation algorithms such as artificial neural network usually minimize the absolute error or sum of square errors of the training data, but the SVM models, used the structural error minimization principle (5. Results Discussion Based on the results of performance evaluations, and RMSE and R criteria, both of the SVM and ANFIS models had a high accuracy in predicting the reference evapotranspiration of North West of Iran. From the results of Tables 6 and 8, it can be concluded that both of the models had similar performance and they can present high accuracy in modeling with different inputs. As the ANFIS model for achieving the maximum accuracy used the maximum, minimum and average temperature, sunshine (M8 and wind speed. But the SVM model in Urmia and Sanandaj stations with M8 pattern and in other stations with M9 pattern achieves the maximum performance. In all of the stations (apart from Sanandaj station the SVM model had a high accuracy and less error than the ANFIS model but, this difference is not remarkable and the SVM model used more input parameters (than the ANFIS model for predicting the evapotranspiration. Conclusion In this research, in order to predict monthly reference evapotranspiration two ANFIS and SVM models employed using collected data at the six synoptic stations in the period of 38 years (1973-2010 located in the north-west of Iran. At first monthly evapotranspiration of a reference crop estimated by FAO-Penman- Monteith method for selected stations as the output of SVM and ANFIS models. Then a regression equation between effective meteorological parameters on evapotranspiration fitted and different input patterns for model determined. Results showed Relative humidity as the less effective parameter deleted from an input of the model. Also in this paper

Utility of Penman-Monteith, Priestley-Taylor, reference evapotranspiration, and pan evaporation methods to estimate pasture evapotranspiration

Science.gov (United States)

Sumner, D.M.; Jacobs, J.M.

2005-01-01

Actual evapotranspiration (ETa) was measured at 30-min resolution over a 19-month period (September 28, 2000-April 23, 2002) from a nonirrigated pasture site in Florida, USA, using eddy correlation methods. The relative magnitude of measured ETa (about 66% of long-term annual precipitation at the study site) indicates the importance of accurate ET a estimates for water resources planning. The time and cost associated with direct measurements of ETa and the rarity of historical measurements of ETa make the use of methods relying on more easily obtainable data desirable. Several such methods (Penman-Monteith (PM), modified Priestley-Taylor (PT), reference evapotranspiration (ET 0), and pan evaporation (Ep)) were related to measured ETa using regression methods to estimate PM bulk surface conductance, PT ??, ET0 vegetation coefficient, and Ep pan coefficient. The PT method, where the PT ?? is a function of green-leaf area index (LAI) and solar radiation, provided the best relation with ET a (standard error (SE) for daily ETa of 0.11 mm). The PM method, in which the bulk surface conductance was a function of net radiation and vapor-pressure deficit, was slightly less effective (SE=0.15 mm) than the PT method. Vegetation coefficients for the ET0 method (SE=0.29 mm) were found to be a simple function of LAI. Pan coefficients for the Ep method (SE=0.40 mm) were found to be a function of LAI and Ep. Historical or future meteorological, LAI, and pan evaporation data from the study site could be used, along with the relations developed within this study, to provide estimates of ETa in the absence of direct measurements of ETa. Additionally, relations among PM, PT, and ET0 methods and ETa can provide estimates of ETa in other, environmentally similar, pasture settings for which meteorological and LAI data can be obtained or estimated. ?? 2004 Elsevier B.V. All rights reserved.

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

2018-05-01

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.

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.

Temporal variations of reference evapotranspiration and its sensitivity to meteorological factors in Heihe River Basin, China

OpenAIRE

Zhao, Jie; Xu, Zong-xue; Zuo, De-peng; Wang, Xu-ming

2015-01-01

On the basis of daily meteorological data from 15 meteorological stations in the Heihe River Basin (HRB) during the period from 1959 to 2012, long-term trends of reference evapotranspiration (ET0) and key meteorological factors that affect ET0 were analyzed using the Mann-Kendall test. The evaporation paradox was also investigated at 15 meteorological stations. In order to explore the contribution of key meteorological factors to the temporal variation of ET0, a sensitivity coefficient method...

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.

Drought in West Africa: How CHIRPS and Reference Evapotranspiration can be used for Index Insurance in a Non-Stationary Setting

Science.gov (United States)

Blakeley, S. L.; Husak, G. J.; Harrison, L.; Funk, C. C.; Osgood, D. E.; Peterson, P.

2017-12-01

Index insurance is increasingly used as a safety net and productivity tool in order to improve the resilience of small-holder farmers in developing countries. In West Africa, there are already index insurance projects in many countries, and various non-governmental organizations are eager to expand implementation of this risk management tool. Often, index insurance payouts rely on rainfall to determine drought years, but designation of years based on precipitation variations is particularly complex in places like West Africa where precipitation is subject to much natural variability across timescales [Giannini 2003, among others]. Furthermore, farmers must also rely on other weather factors for good crop yields, such as the availability of moisture for their plants to absorb and maximum daily temperatures staying within an acceptable range for the crops. In this presentation, the payouts of an index based on rainfall (as measured by the Climate Hazards Group Infrared Precipitation with Stations {CHIRPS} dataset) is compared to the payouts of an index using reference evapotranspiration data (using the ASCE's Penmen-Monteith formula and MERRA-2 drivers). The West African rainfall index exhibits a fair amount of long-term variability, reflective of the Atlantic Multidecadal Oscillation, but the reference evapotranspiration index shows different variability, through changes in radiative forcing and temperatures. Therefore, the use of rainfall for an index is appropriate for capturing rainfall deficits, but reference evapotranspiration may also be an appropriate addition to an index or as a stand-alone index for capturing crop stress. In summary, the results point to farmer input as an invaluable source of knowledge in determining the most appropriate dataset as an index for crop insurance. Alessandra Giannini, R Saravanan, and P Chang. Oceanic forcing of Sahel rainfall on interannual to interdecadal time scales. Science, 302(5647):1027-1030, 2003.

Crop maize evapotranspiration; 2: ratios between the evapotranspiration to class A pan evaporation, to the reference evapotranspiration and to global solar radiation, at three sowing dates

International Nuclear Information System (INIS)

Matzenauer, R.; Bergamashi, H.; Berlato, M.A.

1998-01-01

Water availability is the most limiting factor for growth and grain yield of maize in the State of Rio Grande do Sul, Brazil, reducing frequently this production. Therefore, studies involving the determination of the water requirements are important for irrigation management to minimize the water availability problem. The main objective of this study was to calculate ratios between the maize crop evapotranspiration (ETm) to the class A pan evaporation (Eo), to the reference evapotranspiration (ETo) and to global solar radiation (Rs), in order to obtain ralations between ETm/Eo, ETm/ETo and ETm/Rs, at different crop stages for three different sowing dates. Field experiments were carried out at the Experimental Station of Taquari/RS, 29°48’ of south latitude, 51°49’of west longitude, and 76m of altitude, from 1976/77 to 1988/89. ETm was measured using drainage lysimeters (Thornthwaite-Mather type). The average ratio between ETm and Eo for whole crop cycle (from sowing to physiological maturity) was 0.66, 0.72, and 0.68, respectively, in crops sown on September, October, and November. The average ratio between ETm and ETo for whole crop cycle was 0.74, 0.81, and 0.8, in crops sown on September, October, and November, while the average ratio between ETm and Rs was 0.45, 0.51, and 0.49 for the same sowing dates. The higher average values of crop coefficients occured from tasseling to the milk grain stage, when ETm/Eo was 0.81, 0.92, and 0.81; ETm/ETo was 0.97, 1.05, and 0.96, whereas ETm/Rs was 0.6, 0.68, and 0.6 for crops sown on September, October, and November, respectively [pt

Evaluation of reference evapotranspiration methods for the northeastern region of India

Directory of Open Access Journals (Sweden)

Pankaj K. Pandey

2016-03-01

Full Text Available The study planed to identify a suitable alternative to the FAO-56 Penman-Monteith (FAO56PM equation for calculating reference evapotranspiration (ET0 from chosen temperature and radiation based models utilizing monthly meteorological data from 30 destinations in diverse agro-ecological regions of the Northeast (NE India i.e., Assam Bengal Plain (ABP, eastern Himalaya (EH, and the northeastern hilly (NEH region. Radiation-based IRMAK3 most appropriate in the ABP (weighted root mean square deviation, WRMSD=0.17 mm d−1, r2=0.98, for Nagrakata, and TURC model being in the first three rank of most of the sites, with the lowest error and highest correlation in NEH (WRMSD=0.10 mm d−1, r2=0.92, for Shillong, and EH (WRMSD=0.23 mm d−1, r2=0.95, for Gangtok. Findings reveal that IRMAK3 and TURC models performed equally well and were observed to be the best among selected models for the majority of stations followed by FAO24 Blaney-Criddle (FAO24BC, and 1957MAKK. Pair-wise regression equations were developed for preferred FAO56PM ET0 estimates to ET0 estimates by alternative methods. Cross-correlation of eighteen chose methods demonstrated that the five equations (i.e. four radiation- and one temperature-based performed exceptionally well when contrasted with the FAO56PM model, thus being advised for assessing ET0 under limiting data conditions as have yielded a better estimate of ET0 with a small error.

Data error effects on net radiation and evapotranspiration estimation

International Nuclear Information System (INIS)

Llasat, M.C.; Snyder, R.L.

1998-01-01

The objective of this paper is to evaluate the potential error in estimating the net radiation and reference evapotranspiration resulting from errors in the measurement or estimation of weather parameters. A methodology for estimating the net radiation using hourly weather variables measured at a typical agrometeorological station (e.g., solar radiation, temperature and relative humidity) is presented. Then the error propagation analysis is made for net radiation and for reference evapotranspiration. Data from the Raimat weather station, which is located in the Catalonia region of Spain, are used to illustrate the error relationships. The results show that temperature, relative humidity and cloud cover errors have little effect on the net radiation or reference evapotranspiration. A 5°C error in estimating surface temperature leads to errors as big as 30 W m −2 at high temperature. A 4% solar radiation (R s ) error can cause a net radiation error as big as 26 W m −2 when R s ≈ 1000 W m −2 . However, the error is less when cloud cover is calculated as a function of the solar radiation. The absolute error in reference evapotranspiration (ET o ) equals the product of the net radiation error and the radiation term weighting factor [W = Δ(Δ1+γ)] in the ET o equation. Therefore, the ET o error varies between 65 and 85% of the R n error as air temperature increases from about 20° to 40°C. (author)

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

Analysis and prediction of reference evapotranspiration with climate change in Xiangjiang River Basin, China

Directory of Open Access Journals (Sweden)

Xin-e Tao

2015-10-01

Full Text Available Reference evapotranspiration (ET0 is often used to estimate actual evapotranspiration in water balance studies. In this study, the present and future spatial distributions and temporal trends of ET0 in the Xiangjiang River Basin (XJRB in China were analyzed. ET0 during the period from 1961 to 2010 was calculated with historical meteorological data using the FAO Penman-Monteith (FAO P-M method, while ET0 during the period from 2011 to 2100 was downscaled from the Coupled Model Intercomparison Project Phase 5 (CMIP5 outputs under two emission scenarios, representative concentration pathway 4.5 and representative concentration pathway 8.5 (RCP45 and RCP85, using the statistical downscaling model (SDSM. The spatial distribution and temporal trend of ET0 were interpreted with the inverse distance weighted (IDW method and Mann-Kendall test method, respectively. Results show that: (1 the mean annual ET0 of the XJRB is 1 006.3 mm during the period from 1961 to 2010, and the lowest and highest values are found in the northeast and northwest parts due to the high latitude and spatial distribution of climatic factors, respectively; (2 the SDSM performs well in simulating the present ET0 and can be used to predict the future ET0 in the XJRB; and (3 CMIP5 predicts upward trends in annual ET0 under the RCP45 and RCP85 scenarios during the period from 2011 to 2100. Compared with the reference period (1961–1990, ET0 increases by 9.8%, 12.6%, and 15.6% under the RCP45 scenario and 10.2%, 19.1%, and 27.3% under the RCP85 scenario during the periods from 2011 to 2040, from 2041 to 2070, and from 2071 to 2100, respectively. The predicted increasing ET0 under the RCP85 scenario is greater than that under the RCP45 scenario during the period from 2011 to 2100.

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.

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.

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.

Satellite-based monitoring of cotton evapotranspiration

Science.gov (United States)

Dalezios, Nicolas; Dercas, Nicholas; Tarquis, Ana Maria

2016-04-01

Water for agricultural use represents the largest share among all water uses. Vulnerability in agriculture is influenced, among others, by extended periods of water shortage in regions exposed to droughts. Advanced technological approaches and methodologies, including remote sensing, are increasingly incorporated for the assessment of irrigation water requirements. In this paper, remote sensing techniques are integrated for the estimation and monitoring of crop evapotranspiration ETc. The study area is Thessaly central Greece, which is a drought-prone agricultural region. Cotton fields in a small agricultural sub-catchment in Thessaly are used as an experimental site. Daily meteorological data and weekly field data are recorded throughout seven (2004-2010) growing seasons for the computation of reference evapotranspiration ETo, crop coefficient Kc and cotton crop ETc based on conventional data. Satellite data (Landsat TM) for the corresponding period are processed to estimate cotton crop coefficient Kc and cotton crop ETc and delineate its spatiotemporal variability. The methodology is applied for monitoring Kc and ETc during the growing season in the selected sub-catchment. Several error statistics are used showing very good agreement with ground-truth observations.

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.

Operational Retrievals of Evapotranspiration: Are we there yet?

Science.gov (United States)

Neale, C. M. U.; Anderson, M. C.; Hain, C.; Schull, M.; Isidro, C., Sr.; Goncalves, I. Z.

2017-12-01

Remote sensing based retrievals of evapotranspiration (ET) have progressed significantly over the last two decades with the improvement of methods and algorithms and the availability of multiple satellite sensors with shortwave and thermal infrared bands on polar orbiting platforms. The modeling approaches include simpler vegetation index (VI) based methods such as the reflectance-based crop coefficient approach coupled with surface reference evapotranspiration estimates to derive actual evapotranspiration of crops or, direct inputs to the Penman-Monteith equation through VI relationships with certain input variables. Methods that are more complex include one-layer or two-layer energy balance approaches that make use of both shortwave and longwave spectral band information to estimate different inputs to the energy balance equation. These models mostly differ in the estimation of sensible heat fluxes. For continental and global scale applications, other satellite-based products such as solar radiation, vegetation leaf area and cover are used as inputs, along with gridded re-analysis weather information. This presentation will review the state-of-the-art in satellite-based evapotranspiration estimation, giving examples of existing efforts to obtain operational ET retrievals over continental and global scales and discussing difficulties and challenges.

Time series analysis of reference crop evapotranspiration using soft computing techniques for Ganjam District, Odisha, India

Science.gov (United States)

Patra, S. R.

2017-12-01

Evapotranspiration (ET0) influences water resources and it is considered as a vital process in aridic hydrologic frameworks. It is one of the most important measure in finding the drought condition. Therefore, time series forecasting of evapotranspiration is very important in order to help the decision makers and water system mangers build up proper systems to sustain and manage water resources. Time series considers that -history repeats itself, hence by analysing the past values, better choices, or forecasts, can be carried out for the future. Ten years of ET0 data was used as a part of this study to make sure a satisfactory forecast of monthly values. In this study, three models: (ARIMA) mathematical model, artificial neural network model, support vector machine model are presented. These three models are used for forecasting monthly reference crop evapotranspiration based on ten years of past historical records (1991-2001) of measured evaporation at Ganjam region, Odisha, India without considering the climate data. The developed models will allow water resource managers to predict up to 12 months, making these predictions very useful to optimize the resources needed for effective water resources management. In this study multistep-ahead prediction is performed which is more complex and troublesome than onestep ahead. Our investigation proposed that nonlinear relationships may exist among the monthly indices, so that the ARIMA model might not be able to effectively extract the full relationship hidden in the historical data. Support vector machines are potentially helpful time series forecasting strategies on account of their strong nonlinear mapping capability and resistance to complexity in forecasting data. SVMs have great learning capability in time series modelling compared to ANN. For instance, the SVMs execute the structural risk minimization principle, which allows in better generalization as compared to neural networks that use the empirical risk

Reference evapotranspiration forecasting based on local meteorological and global climate information screened by partial mutual information

Science.gov (United States)

Fang, Wei; Huang, Shengzhi; Huang, Qiang; Huang, Guohe; Meng, Erhao; Luan, Jinkai

2018-06-01

In this study, reference evapotranspiration (ET0) forecasting models are developed for the least economically developed regions subject to meteorological data scarcity. Firstly, the partial mutual information (PMI) capable of capturing the linear and nonlinear dependence is investigated regarding its utility to identify relevant predictors and exclude those that are redundant through the comparison with partial linear correlation. An efficient input selection technique is crucial for decreasing model data requirements. Then, the interconnection between global climate indices and regional ET0 is identified. Relevant climatic indices are introduced as additional predictors to comprise information regarding ET0, which ought to be provided by meteorological data unavailable. The case study in the Jing River and Beiluo River basins, China, reveals that PMI outperforms the partial linear correlation in excluding the redundant information, favouring the yield of smaller predictor sets. The teleconnection analysis identifies the correlation between Nino 1 + 2 and regional ET0, indicating influences of ENSO events on the evapotranspiration process in the study area. Furthermore, introducing Nino 1 + 2 as predictors helps to yield more accurate ET0 forecasts. A model performance comparison also shows that non-linear stochastic models (SVR or RF with input selection through PMI) do not always outperform linear models (MLR with inputs screen by linear correlation). However, the former can offer quite comparable performance depending on smaller predictor sets. Therefore, efforts such as screening model inputs through PMI and incorporating global climatic indices interconnected with ET0 can benefit the development of ET0 forecasting models suitable for data-scarce regions.

Análise de sensibilidade dos métodos de estimativa da evapotranspiração de referência e razão de Bowen em cultura da cana-de-açúcar Sensitivity analysis of methods for estimating reference evapotranspiration and sugarcane evapotranspiration

Directory of Open Access Journals (Sweden)

Bruce K. N Silva

2011-10-01

Full Text Available A técnica de análise de sensibilidade de modelos foi aplicada nos dados obtidos em experimento de campo conduzido no ano de 2009, na Destilaria Miriri, localizada no município de Capim, PB, e aos dados de evapotranspiração de referência (ETo, obtidos pela equação de Penman-Monteith (FAO/56, e da evapotranspiração da cultura da cana-de-açúcar (ETc, obtidos pelo balanço de energia com base na razão de Bowen. As análises de sensibilidade e de erros foram aplicadas ao método da razão de Bowen para os intervalos de medição de 15, 30, 60 e 120 minutos enquanto o método de Penman-Monteith foi aplicado para a escala diária durante o ano de 2009. Os resultados evidenciam que o saldo de radiação é a variável mais sensitiva no cálculo do balanço de energia, enquanto o fluxo de calor no solo oferece a menor contribuição; já os erros relativos de todas as variáveis envolvidas do cálculo balanço de energia baseado na razão de Bowen aumentaram significativamente com o aumento do intervalo de amostragem. A variável mais sensível na determinação da ETo pelo método de Penman-Monteith é o saldo de radiação seguida da umidade relativa, velocidade do vento a 2m de altura e a temperatura média do ar.The sensitivity analysis technique of models was applied to the data obtained from field experiment carried out during 2009 at Distillery Miriri, Capim, PB. This technique was applied to the reference evapotranspiration (ETo by Penman-Monteith (FAO/56 and the sugarcane evapotranspiration (ETc by energy balance equation based on Bowen ratio. The sensitivity analysis and errors were applied to the Bowen ratio method in measurement intervals of 15, 30, 60 and 120 min; however Penman-Monteith approach was applied on daily basis throughout the 2009 year. Results showed that the net radiation is the most sensitive variable in the energy equation balance and soil heat flux offers the lowest contribution. On the other hand, the relative

Temporal variations in reference evapotranspiration in Hubei Province, China, from 1960 to 2014

Science.gov (United States)

Wu, Hao; Wang, Xiugui; Wang, Yan; Xu, Yaxin; Han, Xudong

2018-01-01

Reference evapotranspiration (ET0) plays a critical role in irrigation planning and is also important for hydrological cycle, environmental, and other studies. Thus, this research examined the trends in ET0 on seasonal and annual timescales in Hubei Province, China. ET0 was estimated using the Penman Monteith method (P-M) at 16 meteorological stations located in different areas of Hubei Province during the period 1960-2014. The trends in seasonal and annual ET0 were investigated using the Mann-Kendall test and Sen's slope estimator. The periodicities of ET0 in different regions were investigated using wavelet analysis. The major meteorological factors affecting ET0 were investigated using partial correlation analysis and the contribution rate method. The results showed, on a seasonal timescale, that in spring, ET0 increased in all geographic zones. In summer, ET0 decreased in all geographic zones. In autumn and winter, ET0 displayed no significant changes in any of the geographic zones. On an annual timescale, ET0 decreased in all geographic zones, and the magnitudes of the negative trend in annual ET0 were 2.58-10.04 mm 10a-1. In the five geographic zones, the periodic characteristics of ET0 were identical; the significant wavelet power spectra of ET0 had 3-7, 13-17, and 24-32-year modulations in variation. Among the meteorological factors, sunshine hours were the major climate element that influenced the variability in ET0. The results will provide important references for scientific planning for agriculture, water resource allocation, and water-saving irrigation.

Realization of daily evapotranspiration in arid ecosystems based on remote sensing techniques

Science.gov (United States)

Elhag, Mohamed; Bahrawi, Jarbou A.

2017-03-01

Daily evapotranspiration is a major component of water resources management plans. In arid ecosystems, the quest for an efficient water budget is always hard to achieve due to insufficient irrigational water and high evapotranspiration rates. Therefore, monitoring of daily evapotranspiration is a key practice for sustainable water resources management, especially in arid environments. Remote sensing techniques offered a great help to estimate the daily evapotranspiration on a regional scale. Existing open-source algorithms proved to estimate daily evapotranspiration comprehensively in arid environments. The only deficiency of these algorithms is the course scale of the used remote sensing data. Consequently, the adequate downscaling algorithm is a compulsory step to rationalize an effective water resources management plan. Daily evapotranspiration was estimated fairly well using an Advance Along-Track Scanner Radiometer (AATSR) in conjunction with (MEdium Resolution Imaging Spectrometer) MERIS data acquired in July 2013 with 1 km spatial resolution and 3 days of temporal resolution under a surface energy balance system (SEBS) model. Results were validated against reference evapotranspiration ground truth values using standardized Penman-Monteith method with R2 of 0.879. The findings of the current research successfully monitor turbulent heat fluxes values estimated from AATSR and MERIS data with a temporal resolution of 3 days only in conjunction with reliable meteorological data. Research verdicts are necessary inputs for a well-informed decision-making processes regarding sustainable water resource management.

Catchments' hedging strategy on evapotranspiration for climatic variability

Science.gov (United States)

Ding, W.; Zhang, C.; Li, Y.; Tang, Y.; Wang, D.; Xu, B.

2017-12-01

Hydrologic responses to climate variability and change are important for human society. Here we test the hypothesis that natural catchments utilize hedging strategies for evapotranspiration and water storage carryover with uncertain future precipitation. The hedging strategy for evapotranspiration in catchments under different levels of water availability is analytically derived from the economic perspective. It is found that there exists hedging between evapotranspiration for current and future only with a portion of water availability. Observation data sets of 160 catchments in the United States covering the period from 1983 to 2003 demonstrate the existence of hedging in catchment hydrology and validate the proposed hedging strategies. We also find that more water is allocated to carryover storage for hedging against the future evapotranspiration risk in the catchments with larger aridity indexes or with larger uncertainty in future precipitation, i.e., long-term climate and precipitation variability control the degree of hedging.

Performance of different methods for reference evapotranspiration estimation in Jaíba, Brazil

Directory of Open Access Journals (Sweden)

Gustavo H. da Silva

Full Text Available ABSTRACT FAO Penman-Monteith (FO-PM is considered the standard method for the estimation of reference evapotranspiration (ET0 but requires various meteorological data, which are often not available. The objective of this work was to evaluate the performance of the FAO-PM method with limited meteorological data and other methods as alternatives to estimate ET0 in Jaíba-MG. The study used daily meteorological data from 2007 to 2016 of the National Institute of Meteorology’s station. Daily ET0 values were randomized, and 70% of these were used to determine the calibration parameters of the ET0 for the equations of each method under study. The remaining data were used to test the calibration against the standard method. Performance evaluation was based on Willmott’s index of agreement, confidence coefficient and root-mean-square error. When one meteorological variable was missing, either solar radiation, relative air humidity or wind speed, or in the simultaneous absence of wind speed and relative air humidity, the FAO-PM method showed the best performances and, therefore, was recommended for Jaíba. The FAO-PM method with two missing variables, one of them being solar radiation, showed intermediate performance. Methods that used only air temperature data are not recommended for the region.

Recent decline in the global land evapotranspiration trend due to limited moisture supply.

Science.gov (United States)

Jung, Martin; Reichstein, Markus; Ciais, Philippe; Seneviratne, Sonia I; Sheffield, Justin; Goulden, Michael L; Bonan, Gordon; Cescatti, Alessandro; Chen, Jiquan; de Jeu, Richard; Dolman, A Johannes; Eugster, Werner; Gerten, Dieter; Gianelle, Damiano; Gobron, Nadine; Heinke, Jens; Kimball, John; Law, Beverly E; Montagnani, Leonardo; Mu, Qiaozhen; Mueller, Brigitte; Oleson, Keith; Papale, Dario; Richardson, Andrew D; Roupsard, Olivier; Running, Steve; Tomelleri, Enrico; Viovy, Nicolas; Weber, Ulrich; Williams, Christopher; Wood, Eric; Zaehle, Sönke; Zhang, Ke

2010-10-21

More than half of the solar energy absorbed by land surfaces is currently used to evaporate water. Climate change is expected to intensify the hydrological cycle and to alter evapotranspiration, with implications for ecosystem services and feedback to regional and global climate. Evapotranspiration changes may already be under way, but direct observational constraints are lacking at the global scale. Until such evidence is available, changes in the water cycle on land−a key diagnostic criterion of the effects of climate change and variability−remain uncertain. Here we provide a data-driven estimate of global land evapotranspiration from 1982 to 2008, compiled using a global monitoring network, meteorological and remote-sensing observations, and a machine-learning algorithm. In addition, we have assessed evapotranspiration variations over the same time period using an ensemble of process-based land-surface models. Our results suggest that global annual evapotranspiration increased on average by 7.1 ± 1.0 millimetres per year per decade from 1982 to 1997. After that, coincident with the last major El Niño event in 1998, the global evapotranspiration increase seems to have ceased until 2008. This change was driven primarily by moisture limitation in the Southern Hemisphere, particularly Africa and Australia. In these regions, microwave satellite observations indicate that soil moisture decreased from 1998 to 2008. Hence, increasing soil-moisture limitations on evapotranspiration largely explain the recent decline of the global land-evapotranspiration trend. Whether the changing behaviour of evapotranspiration is representative of natural climate variability or reflects a more permanent reorganization of the land water cycle is a key question for earth system science.

High-resolution global grids of revised Priestley-Taylor and Hargreaves-Samani coefficients for assessing ASCE-standardized reference crop evapotranspiration and solar radiation

Science.gov (United States)

Aschonitis, Vassilis G.; Papamichail, Dimitris; Demertzi, Kleoniki; Colombani, Nicolo; Mastrocicco, Micol; Ghirardini, Andrea; Castaldelli, Giuseppe; Fano, Elisa-Anna

2017-08-01

The objective of the study is to provide global grids (0.5°) of revised annual coefficients for the Priestley-Taylor (P-T) and Hargreaves-Samani (H-S) evapotranspiration methods after calibration based on the ASCE (American Society of Civil Engineers)-standardized Penman-Monteith method (the ASCE method includes two reference crops: short-clipped grass and tall alfalfa). The analysis also includes the development of a global grid of revised annual coefficients for solar radiation (Rs) estimations using the respective Rs formula of H-S. The analysis was based on global gridded climatic data of the period 1950-2000. The method for deriving annual coefficients of the P-T and H-S methods was based on partial weighted averages (PWAs) of their mean monthly values. This method estimates the annual values considering the amplitude of the parameter under investigation (ETo and Rs) giving more weight to the monthly coefficients of the months with higher ETo values (or Rs values for the case of the H-S radiation formula). The method also eliminates the effect of unreasonably high or low monthly coefficients that may occur during periods where ETo and Rs fall below a specific threshold. The new coefficients were validated based on data from 140 stations located in various climatic zones of the USA and Australia with expanded observations up to 2016. The validation procedure for ETo estimations of the short reference crop showed that the P-T and H-S methods with the new revised coefficients outperformed the standard methods reducing the estimated root mean square error (RMSE) in ETo values by 40 and 25 %, respectively. The estimations of Rs using the H-S formula with revised coefficients reduced the RMSE by 28 % in comparison to the standard H-S formula. Finally, a raster database was built consisting of (a) global maps for the mean monthly ETo values estimated by ASCE-standardized method for both reference crops, (b) global maps for the revised annual coefficients of the P

Control of dry season evapotranspiration over the Amazonian forest as inferred from observations at a southern Amazon forest site

NARCIS (Netherlands)

Negrón Juárez, R.I.; Hodnett, M.G.; Fu, R.; Goulden, M.L.; Randow, von C.

2007-01-01

The extent to which soil water storage can support an average dry season evapotranspiration (ET) is investigated using observations from the Rebio Jarú site for the period of 2000 to 2002. During the dry season, when total rainfall is less than 100 mm, the soil moisture storage available to root

Propagation of soil moisture memory to runoff and evapotranspiration

Science.gov (United States)

Orth, R.; Seneviratne, S. I.

2012-10-01

As a key variable of the land-climate system soil moisture is a main driver of runoff and evapotranspiration under certain conditions. Soil moisture furthermore exhibits outstanding memory (persistence) characteristics. Also for runoff many studies report distinct low frequency variations that represent a 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 runoff and evapotranspiration on different time scales. For this purpose we use a simple water balance model in which dependencies of runoff (normalized by precipitation) and evapotranspiration (normalized by radiation) on soil moisture are fitted using runoff observations. The model therefore allows to compute memory of soil moisture, runoff and evapotranspiration on catchment scale. We find considerable memory in soil moisture and runoff in many parts of the continent, and evapotranspiration also displays some memory on a monthly time scale in some catchments. We show that the memory of runoff and evapotranspiration jointly depend on soil moisture memory and on the strength of the coupling of runoff and evapotranspiration to soil moisture. Furthermore we find that the coupling strengths of runoff 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.

Evapotranspiration from selected fallowed agricultural fields on the Tule Lake National Wildlife Refuge, California, during May to October 2000

Science.gov (United States)

Bidlake, W.R.

2002-01-01

An investigation of evapotranspiration, vegetation quantity and composition, and depth to the water table below the land surface was made at three sites in two fallowed agricultural lots on the 15,800-hectare Tule Lake National Wildlife Refuge in northern California during the 2000 growing season. All three sites had been farmed during 1999, but were not irrigated since the 1999 growing season. Vegetation at the lot C1B and lot 6 stubble sites included weedy species and small grain plants. The lot 6 cover crop site supported a crop of cereal rye that had been planted during the previous winter. Percentage of coverage by live vegetation ranged from 0 to 43.2 percent at the lot C1B site, from approximately 0 to 63.2 percent at the lot 6 stubble site, and it was estimated to range from 0 to greater than 90 percent at the lot 6 cover crop site. Evapotranspiration was measured using the Bowen ratio energy balance technique and it was estimated using a model that was based on the Priestley-Taylor equation and a model that was based on reference evapotranspiration with grass as the reference crop. Total evapotranspiration during May to October varied little among the three evapotranspiration measurement sites, although the timing of evapotranspiration losses did vary among the sites. Total evapotranspiration from the lot C1B site was 426 millimeters, total evapotranspiration from the lot 6 stubble site was 444 millimeters, and total evapotranspiration from the lot 6 cover crop site was 435 millimeters. The months of May to July accounted for approximately 78 percent of the total evapotranspiration from the lot C1B site, approximately 63 percent of the evapotranspiration from the lot 6 stubble site, and approximately 86 percent of the total evapotranspiration from the lot 6 cover crop site. Estimated growing season precipitation accounted for 16 percent of the growing-season evapotranspiration at the lot C1B site and for 17 percent of the growing-season evapotranspiration

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.

Estimation of daily reference evapotranspiration (ETo) using artificial intelligence methods: Offering a new approach for lagged ETo data-based modeling

Science.gov (United States)

Mehdizadeh, Saeid

2018-04-01

Evapotranspiration (ET) is considered as a key factor in hydrological and climatological studies, agricultural water management, irrigation scheduling, etc. It can be directly measured using lysimeters. Moreover, other methods such as empirical equations and artificial intelligence methods can be used to model ET. In the recent years, artificial intelligence methods have been widely utilized to estimate reference evapotranspiration (ETo). In the present study, local and external performances of multivariate adaptive regression splines (MARS) and gene expression programming (GEP) were assessed for estimating daily ETo. For this aim, daily weather data of six stations with different climates in Iran, namely Urmia and Tabriz (semi-arid), Isfahan and Shiraz (arid), Yazd and Zahedan (hyper-arid) were employed during 2000-2014. Two types of input patterns consisting of weather data-based and lagged ETo data-based scenarios were considered to develop the models. Four statistical indicators including root mean square error (RMSE), mean absolute error (MAE), coefficient of determination (R2), and mean absolute percentage error (MAPE) were used to check the accuracy of models. The local performance of models revealed that the MARS and GEP approaches have the capability to estimate daily ETo using the meteorological parameters and the lagged ETo data as inputs. Nevertheless, the MARS had the best performance in the weather data-based scenarios. On the other hand, considerable differences were not observed in the models' accuracy for the lagged ETo data-based scenarios. In the innovation of this study, novel hybrid models were proposed in the lagged ETo data-based scenarios through combination of MARS and GEP models with autoregressive conditional heteroscedasticity (ARCH) time series model. It was concluded that the proposed novel models named MARS-ARCH and GEP-ARCH improved the performance of ETo modeling compared to the single MARS and GEP. In addition, the external

Linking precipitation, evapotranspiration and soil moisture content for the improvement of predictability over land

Science.gov (United States)

Catalano, Franco; Alessandri, Andrea; De Felice, Matteo

2013-04-01

Climate change scenarios are expected to show an intensification of the hydrological cycle together with modifications of evapotranspiration and soil moisture content. Evapotranspiration changes have been already evidenced for the end of the 20th century. The variance of evapotranspiration has been shown to be strongly related to the variance of precipitation over land. Nevertheless, the feedbacks between evapotranspiration, soil moisture and precipitation have not yet been completely understood at present-day. Furthermore, soil moisture reservoirs are associated to a memory and thus their proper initialization may have a strong influence on predictability. In particular, the linkage between precipitation and soil moisture is modulated by the effects on evapotranspiration. Therefore, the investigation of the coupling between these variables appear to be of primary importance for the improvement of predictability over the continents. The coupled manifold (CM) technique (Navarra and Tribbia 2005) is a method designed to separate the effects of the variability of two variables which are connected. This method has proved to be successful for the analysis of different climate fields, like precipitation, vegetation and sea surface temperature. In particular, the coupled variables reveal patterns that may be connected with specific phenomena, thus providing hints regarding potential predictability. In this study we applied the CM to recent observational datasets of precipitation (from CRU), evapotranspiration (from GIMMS and MODIS satellite-based estimates) and soil moisture content (from ESA) spanning a time period of 23 years (1984-2006) with a monthly frequency. Different data stratification (monthly, seasonal, summer JJA) have been employed to analyze the persistence of the patterns and their characteristical time scales and seasonality. The three variables considered show a significant coupling among each other. Interestingly, most of the signal of the

Driving Factors of Understory Evapotranspiration within a Siberian Larch Forest

Science.gov (United States)

Tobio, A.; Loranty, M. M.; Kropp, H.; Pena, H., III; Alexander, H. D.; Natali, S.; Kholodov, A. L.; Spawn, S.; Farmer, S.

2017-12-01

Amplified rates of climate change are causing alterations in vegetation productivity, hydrologic cycling, and wildfire severity and intensity in arctic ecosystems. Boreal larch forests in northeastern Siberia are a critical but understudied ecosystem that are affected by these modifications. These forests cover 2.5 million km2 with densities ranging from spare to thick. The current average canopy cover is at around 17% and is expected to increase with the observed increases in vegetation productivity and wildfire. These projected changes in forest density can alter the proportional contributions of over- and understory vegetation to whole ecosystem evapotranspiration. Low density boreal forests have much higher rates of understory evapotranspiration and can contribute as much as 80% to total ecosystem evapotranspiration, while the understory in high density forests is responsible for only around 15% of total ecosystem evapotranspiration. The objective of this research is to understand why there are changes in understory evapotranspiration with varying overstory density by looking at light levels, biomass, vegetation, and air and soil differences. To better learn about these differences in understory evapotranspiration in boreal larch forests the driving factors of evapotranspiration were measured within a burn scar with varying densities of high, medium, and low. Water fluxes were conducted using the static chamber technique under different environmental conditions. Furthermore, controlling factors of evapotranspiration such as photosynethically active radiation, vapor pressure deficit, soil moisture, moss cover, biomass, and leaf area index were measured or derived. In general, we found that low density areas have highest rates of evapotranspiration due to larger amount of biomass, and increased access to light, despite low levels of soil moisture. These results can help us understand how and why total ecosystem water exchange will change in boreal larch forests

Lower responsiveness of canopy evapotranspiration rate than of leaf stomatal conductance to open-air CO2 elevation in rice.

Science.gov (United States)

Shimono, Hiroyuki; Nakamura, Hirofumi; Hasegawa, Toshihiro; Okada, Masumi

2013-08-01

An elevated atmospheric CO2 concentration ([CO2 ]) can reduce stomatal conductance of leaves for most plant species, including rice (Oryza sativa L.). However, few studies have quantified seasonal changes in the effects of elevated [CO2 ] on canopy evapotranspiration, which integrates the response of stomatal conductance of individual leaves with other responses, such as leaf area expansion, changes in leaf surface temperature, and changes in developmental stages, in field conditions. We conducted a field experiment to measure seasonal changes in stomatal conductance of the uppermost leaves and in the evapotranspiration, transpiration, and evaporation rates using a lysimeter method. The study was conducted for flooded rice under open-air CO2 elevation. Stomatal conductance decreased by 27% under elevated [CO2 ], averaged throughout the growing season, and evapotranspiration decreased by an average of 5% during the same period. The decrease in daily evapotranspiration caused by elevated [CO2 ] was more significantly correlated with air temperature and leaf area index (LAI) rather than with other parameters of solar radiation, days after transplanting, vapor-pressure deficit and FAO reference evapotranspiration. This indicates that higher air temperatures, within the range from 16 to 27 °C, and a larger LAI, within the range from 0 to 4 m(2)  m(-2) , can increase the magnitude of the decrease in evapotranspiration rate caused by elevated [CO2 ]. The crop coefficient (i.e. the evapotranspiration rate divided by the FAO reference evapotranspiration rate) was 1.24 at ambient [CO2 ] and 1.17 at elevated [CO2 ]. This study provides the first direct measurement of the effects of elevated [CO2 ] on rice canopy evapotranspiration under open-air conditions using the lysimeter method, and the results will improve future predictions of water use in rice fields. © 2013 John Wiley & Sons Ltd.

Evaluation of Daily Evapotranspiration Over Orchards Using METRIC Approach and Landsat Satellite Observations

Science.gov (United States)

He, R.; Jin, Y.; Daniele, Z.; Kandelous, M. M.; Kent, E. R.

2016-12-01

The pistachio and almond acreage in California has been rapidly growing in the past 10 years, raising concerns about competition for limited water resources in California. A robust and cost-effective mapping of crop water use, mostly evapotranspiration (ET), by orchards, is needed for improved farm-level irrigation management and regional water planning. METRIC™, a satellite-based surface energy balance approach, has been widely used to map field-scale crop ET, mostly over row crops. We here aim to apply METRIC with Landsat satellite observations over California's orchards and evaluate the ET estimates by comparing with field measurements in South San Joaquin Valley, California. Reference ET of grass (ETo) from California Irrigation Management Information system (CIMIS) stations was used to estimate daily ET of commercial almond and pistachio orchards. Our comparisons showed that METRIC-Landsat ET daily estimates agreed well with ET measured by the eddy covariance and surface renewal stations, with a RMSE of 1.25 and a correlation coefficient of 0.84 for the pistachio orchard. A slight high bias of satellite based ET estimates was found for both pistachio and almond orchards. We also found time series of NDVI was highly correlated with ET temporal dynamics within each field, but the correlation was reduced to 0.56 when all fields were pooled together. Net radiation, however, remained highly correlated with ET across all the fields. The METRIC ET was able to distinguish the differences in ET among salt- and non-salt affected pistachio orchards, e.g., mean daily ET during growing season in salt-affected orchards was lower than that of non-salt affected one by 0.87 mm/day. The remote sensing based ET estimate will support a variety of state and local interests in water use and management, for both planning and regulatory/compliance purposes, and provide the farmers observation-based guidance for site-specific and time-sensitive irrigation management.

Estimativa da evapotranspiração da cultura da mangueira no Vale do São Francisco | Estimation of the mango crop evapotranspiration in the São Francisco Valley

Directory of Open Access Journals (Sweden)

Jucicléia Soares da Silva

2016-04-01

Although irrigation is a primary factor of production, a large part of the producers still wields no technical inputs consistent with soil and climatic conditions in the São Francisco Valley. Thus, the objective of this study was to identify the relationship between climate variables and the hose from the crop evapotranspiration in all phenological phases. The experiment was conducted at the Federal Institute of Education, Science and Technology Pernambucano Backwoods, Campus Rural Zone situated in the Irrigated Perimeter Senator Nilo Coelho in Petrolina - PE, were found 1.3 hectares of mango orchard production area, the system irrigation was used for the sprinkler. For irrigation scheduling a weather station was used, with solar radiation sensors, temperature and relative humidity, barometric pressure, wind speed and direction and precipitation. To estimate the reference evapotranspiration, we used the Penman-Monteith. The evapotranspiration values of culture, were determined by reference evapotranspiration and crop coefficient for each phenological stage. The crop evapotranspiration was lower than the reference evapotranspiration in all growth stages of the mango, with the average of 3.8 and 5.3 mm/day respectively.

Incorporating field wind data to improve crop evapotranspiration parameterization in heterogeneous regions

Science.gov (United States)

Accurate parameterization of reference evapotranspiration (ET0) is necessary for optimizing irrigation scheduling and avoiding costs associated with over-irrigation (water expense, loss of water productivity, energy costs, pollution) or with under-irrigation (crop stress and suboptimal yields or qua...

Propagation of soil moisture memory to streamflow and evapotranspiration in Europe

Science.gov (United States)

Orth, R.; Seneviratne, S. I.

2013-10-01

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.

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.

Global Warming and the Summertime Evapotranspiration Regime of the Alpine Region

Energy Technology Data Exchange (ETDEWEB)

Calanca, P.; Jasper, K. [Agroscope FAL Reckenholz, Swiss Federal Research Station for Agroecology and Agriculture, CH-8046 Zuerich (Switzerland); Roesch, A.; Wild, M. [Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology, CH-8092 Zuerich (Switzerland)

2006-11-15

Changes of the summer evapotranspiration regime under increased levels of atmospheric greenhouse gases are discussed for three Alpine river basins on the basis of a new set of simulations carried out with a high-resolution hydrological model. The climate change signal was inferred from the output of two simulations with a state-of-the-art global climate model (GCM), a reference run valid for 1961-1990 and a time-slice simulation valid for 2071-2100 under forcing from the A2 IPCC emission scenario. In this particular GCM experiment and with respect to the Alpine region summer temperature was found to increase by 3 to 4C, whereas precipitation was found to decrease by 10 to 20%. Global radiation and water vapor pressure deficit were found to increase by about 5% and 2 hPa, respectively. On this background, an overall increase of potential evapotranspiration of about 20% relative to the baseline was predicted by the hydrological model, with important variations between but also within individual basins. The results of the hydrological simulations also revealed a reduction in the evapotranspiration efficiency that depends on altitude. Accordingly, actual evapotranspiration was found to increase at high altitudes and to the south of the Alps, but to decrease in low elevation areas of the northern forelands and in the inner-Alpine domain. Such a differentiation does not appear in the GCM scenario, which predicts an overall increase in evapotranspiration over the Alps. This underlines the importance of detailed simulations for the quantitative assessment of the regional impact of climate change on the hydrological cycle.

Sensitivity of annual and seasonal reference crop ...

Indian Academy of Sciences (India)

scheduling and water resources management. Ref- ... time, and refers to evapotranspiration rate from a reference ... variable per unit increase in independent variable. Sensitivity ...... Pereira L S 2007 Relating water productivity and crop.

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

Directory of Open Access Journals (Sweden)

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

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.

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

Reference Evapotranspiration Retrievals from a Mesoscale Model Based Weather Variables for Soil Moisture Deficit Estimation

Directory of Open Access Journals (Sweden)

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.

On variability of evapotranspiration

DEFF Research Database (Denmark)

Ringgaard, Rasmus

the ground water level in the meadows and by the available energy. At the spruce plantation transpiration and terception evaporation were both important. The rate of transpiration was heavily influenced by stomatal control in response to high vapor pressure deficits. In addition soil moisture stress had...... for this study. At the spruce plantation additional separate measurements of transpiration, interception evaporation and forest floor evaporation was performed. Transpiration was measured in the growing season of 2010 using Granier type TDP sap flux probes, interception was measured using net precipitation...... of evapotranspiration was controlled by crop development and by the available energy. At the meadow site soil evaporation and evaporation from free water surfaces was the most important parts of the evapotranspiration. The rate of evapotranspiration was controlled by the water level in the Skjern River which influenced...

Validating Remotely Sensed Land Surface Evapotranspiration Based on Multi-scale Field Measurements

Science.gov (United States)

Jia, Z.; Liu, S.; Ziwei, X.; Liang, S.

2012-12-01

validation experiments demonstrated that the models yield accurate estimates at flux measurement sites, the question remains whether they are performing well over the broader landscape. Moreover, a large number of RS_ET products have been released in recent years. Thus, we also pay attention to the cross-validation method of RS_ET derived from multi-source models. "The Multi-scale Observation Experiment on Evapotranspiration over Heterogeneous Land Surfaces: Flux Observation Matrix" campaign is carried out at the middle reaches of the Heihe River Basin, China in 2012. Flux measurements from an observation matrix composed of 22 EC and 4 LAS are acquired to investigate the cross-validation of multi-source models over different landscapes. In this case, six remote sensing models, including the empirical statistical model, the one-source and two-source models, the Penman-Monteith equation based model, the Priestley-Taylor equation based model, and the complementary relationship based model, are used to perform an intercomparison. All the results from the two cases of RS_ET validation showed that the proposed validation methods are reasonable and feasible.

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

Directory of Open Access Journals (Sweden)

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

Temporal variations of reference evapotranspiration and its sensitivity to meteorological factors in Heihe River Basin, China

Directory of Open Access Journals (Sweden)

Jie Zhao

2015-01-01

Full Text Available On the basis of daily meteorological data from 15 meteorological stations in the Heihe River Basin (HRB during the period from 1959 to 2012, long-term trends of reference evapotranspiration (ET0 and key meteorological factors that affect ET0 were analyzed using the Mann-Kendall test. The evaporation paradox was also investigated at 15 meteorological stations. In order to explore the contribution of key meteorological factors to the temporal variation of ET0, a sensitivity coefficient method was employed in this study. The results show that: (1 mean annual air temperature significantly increased at all 15 meteorological stations, while the mean annual ET0 decreased at most of sites; (2 the evaporation paradox did exist in the HRB, while the evaporation paradox was not continuous in space and time; and (3 relative humidity was the most sensitive meteorological factor with regard to the temporal variation of ET0 in the HRB, followed by wind speed, air temperature, and solar radiation. Air temperature and solar radiation contributed most to the temporal variation of ET0 in the upper reaches; solar radiation and wind speed were the determining factors for the temporal variation of ET0 in the middle-lower reaches.

Past and future spatiotemporal changes in evapotranspiration and effective moisture on the Tibetan Plateau

Science.gov (United States)

Yin, Yunhe; Wu, Shaohong; Zhao, Dongsheng

2013-10-01

evaporative demand has decreased worldwide during the past several decades. This trend is also noted on the Tibetan Plateau, a region that is particularly sensitive to climate change. However, patterns and trends of evapotranspiration and their relationship to drought stress on the Tibetan Plateau are complex and poorly understood. Here, we analyze spatiotemporal changes in evapotranspiration and effective moisture (defined as the ratio of actual evapotranspiration (ETa) to reference crop evapotranspiration (ETo)) based on the modified Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ). Climate data from 80 meteorological stations on the Tibetan Plateau were compiled for the period 1981-2010 and future climate projections were generated by a regional climate model through the 21st century. The results show regional trends towards decreasing ETo and statistically significant increases in ETa (p stress, because of generally increased effective moisture. Future regional differences are most pronounced in terms of effective moisture, which shows notable increases in the northwestern plateau and decreases in the southeastern plateau. Moreover, the reduced magnitude of effective moisture is likely to intensify in the long term, due mainly to increased evaporative demand.

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.

Análise espaço-temporal da evapotranspiração de referência para Minas Gerais Spatial-time analysis of evapotranspiration reference in the Minas Gerais State, Brazil

Directory of Open Access Journals (Sweden)

Luis César de Aquino Lemos Filho

2007-10-01

Full Text Available Objetivou-se com esta pesquisa, analisar a demanda hídrica em Minas Gerais, representada pela evapotranspiração de referência (ET0, durante o ano. Os valores de ET0 foram estimados pelo método de Penman-Monteith-FAO a partir de dados diários originados de registros de 42 estações climatológicas do Instituto Nacional de Meteorologia (INMET referentes a um período de 17 anos (1961 a 1978. No geral, os resultados mostraram que a ET0 é bastante variável em Minas Gerais, chegando a apresentar valores médios de 914 até valores de 1.677 mm ano-1. As maiores variações, tanto espaciais como temporais, são registradas no norte do Estado, onde também ocorrem os maiores valores de ET0. O Estado de Minas Gerais apresenta um déficit hídrico anual em aproximadamente 50% de sua área total. Os meses que apresentaram as maiores e menores demandas hídricas no Estado foram janeiro e junho, respectivamente. Em função da nítida distinção que apresentaram os dados de ET0 geoespacializados nas regiões do Estado de Minas Gerais, o conhecimento do correto valor da ET0 em cada localidade trará benefícios aos produtores no manejo da irrigação.The knowledge of information that expresses the water requirement of the plants is a fundamental issue for the irrigation process. The objective of this research was to analyze the water requirement in Minas Gerais State, Brazil, represented by the evapotranspiration reference (ET0, during the year. The ET0 values were estimated through the Penman-Monteith-FAO method starting from daily data originated by the registration of 42 climatological stations of the Instituto Nacional de Meteorologia (INMET referring to a period of 17 years (1961 to 1978. In general, the results showed that the evapotranspiration reference is plenty variable in Minas Gerais, reaching medium values from 914 to 1.677 mm year-1. The largest variations, such as spatial and temporal, are registered in the north part of the State

Drought impacts and resilience on crops via evapotranspiration estimations

Science.gov (United States)

Timmermans, Joris; Asadollahi Dolatabad, Saeid

2015-04-01

for monitoring crop health during the severe drought events. The presentation will provide results of the investigation into Droughts using time series of coarse resolution daily evapotranspiration produced from the SEBS remote sensing model, on basis of MODIS data. The evapotranspiration will be converted into drought severity using the evapotranspiration deficit index (ETDI). Afterwards the disaggregation to plot scale will be investigated. This disaggregation will be performed as a weighted filtering on basis of crop-coefficient at high resolution. These growth stage of the vegeation (needed for the estimation of the crop coefficients) are estimated on basis of Normalized Difference Vegetation Index (NDVI) using Landsat 5,7 and 8 observations. The final result of the research provides good statistical information about drought resilience and crop health.

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.

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

Directory of Open Access Journals (Sweden)

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.

Effects of changing climate on reference crop evapotranspiration over 1961-2013 in Xinjiang, China

Science.gov (United States)

Yao, Ning; Li, Yi; Sun, Changfeng

2018-01-01

To know the importance of different climate variables on reference crop evapotranspiration ( ET o), a step-by-step sensitivity analysis of ET o to single, two, and multi-climate variables ( C) was conducted. ET o in north, south, and entire Xinjiang Province, China, over 1961-2013 was estimated using the Penman-Monteith equation. Trends in the involved six Cs (i.e., minimum temperature— T min, average temperature— T ave, maximum temperature— T max, wind speed at 2 m— U 2, sunshine hour— n, and relative humidity— RH) were detected by the modified Mann-Kendall test. Nineteen scenarios of changed Cs were preset to obtain recalculated ET o values considering the actual trend in each C and the Pearson's correlation relationship between ET o and Cs. The results showed that ET o was mostly sensitive to T max, U 2, and n. Sensitivity of ET o to the two overlapped changes of T min and T max caused larger increases in ET o than T max and T ave, T ave and T max, T max and (- n), T max and RH, T max and (- U 2), and T min and T ave, but the overlapped changes (- U 2) and (- n) caused larger decreases in ET o than the other two C scenarios. The simultaneously increased T max, T min, T ave, and RH plus decreased U 2 and n had caused the actual decreases in ET o in Xinjiang. In general, the effects of decreased U 2 and n on decreasing ET o compensated the effects of increased T max on decreasing ET o in Xinjiang.

Toward a Mechanistic Understanding of Deuterium Excess as a Tracer for Evapotranspiration

Energy Technology Data Exchange (ETDEWEB)

Lai, Chun-Ta [Department of Biology, San Diego State University, San Diego, CA (United States)

2013-07-15

An understanding of atmospheric water vapour and its isotopic composition is useful for modelling effects of terrestrial evapotranspiration on regional hydrologic cycles. Previous studies showed diurnal and vertical patterns of water vapour isotope ratios ({delta}{sup 2}H{sub v} and {delta}{sup 18}O{sub v}) consistently observed in an old growth coniferous forest. Using a box model and a mass balance approach to simulate 'isoflux of d-excess', the effect of evapotranspiration on the d-excess in atmospheric water vapour is quantitatively demonstrated. The results suggest that d-excess can be mechanistically utilized to identify processes that contribute to the diurnal variation in atmospheric moisture. These new findings have implications for larger-scale predictions of precipitation across the terrestrial landscape. In this paper, I report the initial results of the {delta}{sup 2}H{sub v} and {delta}{sup 18}O{sub v} measurements using a cavity enhanced spectroscopy instrument. These recent data are consistent with the pattern observed by the conventional sampling method, providing new opportunities for studying d-excess as a tracer for evapotranspiration. (author)

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

Epistemic Uncertainty in Evaluation of Evapotranspiration and Net Infiltration Using Analogue Meteorological Data

International Nuclear Information System (INIS)

B. Faybishenko

2006-01-01

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

Sensitivity of inferred climate model skill to evaluation decisions: a case study using CMIP5 evapotranspiration

International Nuclear Information System (INIS)

Schwalm, Christopher R; Huntinzger, Deborah N; Michalak, Anna M; Fisher, Joshua B; Kimball, John S; Mueller, Brigitte; Zhang, Ke; Zhang Yongqiang

2013-01-01

Confrontation of climate models with observationally-based reference datasets is widespread and integral to model development. These comparisons yield skill metrics quantifying the mismatch between simulated and reference values and also involve analyst choices, or meta-parameters, in structuring the analysis. Here, we systematically vary five such meta-parameters (reference dataset, spatial resolution, regridding approach, land mask, and time period) in evaluating evapotranspiration (ET) from eight CMIP5 models in a factorial design that yields 68 700 intercomparisons. The results show that while model–data comparisons can provide some feedback on overall model performance, model ranks are ambiguous and inferred model skill and rank are highly sensitive to the choice of meta-parameters for all models. This suggests that model skill and rank are best represented probabilistically rather than as scalar values. For this case study, the choice of reference dataset is found to have a dominant influence on inferred model skill, even larger than the choice of model itself. This is primarily due to large differences between reference datasets, indicating that further work in developing a community-accepted standard ET reference dataset is crucial in order to decrease ambiguity in model skill. (letter)

Environmental controls on seasonal ecosystem evapotranspiration/potential evapotranspiration ratio as determined by the global eddy flux measurements

Science.gov (United States)

Chunwei Liu; Ge Sun; Steve McNulty; Asko Noormets; Yuan Fang

2017-01-01

The evapotranspiration / potential evapotranspiration (AET / PET) ratio is traditionally termed as the crop coefficient (Kc) and has been generally used as ecosystem evaporative stress index. In the current hydrology literature, Kc has been widely used as a parameter to estimate crop water demand by water managers but has...

Resolving the observer reference class problem in cosmology

Science.gov (United States)

Friederich, Simon

2017-06-01

The assumption that we are typical observers plays a core role in attempts to make multiverse theories empirically testable. A widely shared worry about this assumption is that it suffers from systematic ambiguity concerning the reference class of observers with respect to which typicality is assumed. As a way out, Srednicki and Hartle recommend that we empirically test typicality with respect to different candidate reference classes in analogy to how we test physical theories. Unfortunately, as this paper argues, this idea fails because typicality is not the kind of assumption that can be subjected to empirical tests. As an alternative, a background information constraint on observer reference class choice is suggested according to which the observer reference class should be chosen such that it includes precisely those observers who one could possibly be, given one's assumed background information.

Modelling of evapotranspiration at field and landscape scales. Abstract

DEFF Research Database (Denmark)

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

2002-01-01

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...

Evapotranspiration of a corn crop (Zea mays, L.)

International Nuclear Information System (INIS)

Calcache, M.; Engel, G.

1984-01-01

The real and potential evapotranspiration of corn crop is calculated in a field experiment. The potential evapotranspiration (PET) is estimated using the Penman Method with a Type 'A' evaporation tank. The real evapotranspiration (RET) is measured using the Mass Balance Method based on periodic calculations of the volumetric moisture of the soil using a neutron probe and the matrix potential using tensiometers. (M.A.C.) [pt

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.

Arid site water balance: evapotranspiration modeling and measurements

International Nuclear Information System (INIS)

Gee, G.W.; Kirkham, R.R.

1984-09-01

In order to evaluate the magnitude of radionuclide transport at an aird site, a field and modeling study was conducted to measure and predict water movement under vegetated and bare soil conditions. Significant quantities of water were found to move below the roo of a shallow-rooted grass-covered area during wet years at the Hanford site. The unsaturated water flow model, UNSAT-1D, was resonably successful in simulating the transient behavior of the water balance at this site. The effects of layered soils on water balance were demonstrated using the model. Models used to evaluate water balance in arid regions should not rely on annual averages and assume that all precipitation is removed by evapotranspiration. The potential for drainage at arid sites exists under conditions where shallow rooted plants grow on coarse textured soils. This condition was observed at our study site at Hanford. Neutron probe data collected on a cheatgrass community at the Hanford site during a wet year indicated that over 5 cm of water drained below the 3.5-m depth. The unsaturated water flow model, UNSAT-1D, predicted water drainage of about 5 cm (single layer, 10 months) and 3.5 cm (two layers, 12 months) for the same time period. Additional field measurements of hydraulic conductivity will likely improve the drainage estimate made by UNSAT-1D. Additional information describing cheatgrass growth and water use at the grass site could improve model predictions of sink terms and subsequent calculations of water storage within the rooting zone. In arid areas where the major part of the annual precipitation occurs during months with low average potential evapotranspiration and where soils are vegetated but are coarse textured and well drained, significant drainage can occur. 31 references, 18 figures, 1 table

Evapotranspiration studies for protective barriers: Experimental plans

International Nuclear Information System (INIS)

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

Medium-range reference evapotranspiration forecasts for the contiguous United States based on multi-model numerical weather predictions

Science.gov (United States)

Medina, Hanoi; Tian, Di; Srivastava, Puneet; Pelosi, Anna; Chirico, Giovanni B.

2018-07-01

Reference evapotranspiration (ET0) plays a fundamental role in agronomic, forestry, and water resources management. Estimating and forecasting ET0 have long been recognized as a major challenge for researchers and practitioners in these communities. This work explored the potential of multiple leading numerical weather predictions (NWPs) for estimating and forecasting summer ET0 at 101 U.S. Regional Climate Reference Network stations over nine climate regions across the contiguous United States (CONUS). Three leading global NWP model forecasts from THORPEX Interactive Grand Global Ensemble (TIGGE) dataset were used in this study, including the single model ensemble forecasts from the European Centre for Medium-Range Weather Forecasts (EC), the National Centers for Environmental Prediction Global Forecast System (NCEP), and the United Kingdom Meteorological Office forecasts (MO), as well as multi-model ensemble forecasts from the combinations of these NWP models. A regression calibration was employed to bias correct the ET0 forecasts. Impact of individual forecast variables on ET0 forecasts were also evaluated. The results showed that the EC forecasts provided the least error and highest skill and reliability, followed by the MO and NCEP forecasts. The multi-model ensembles constructed from the combination of EC and MO forecasts provided slightly better performance than the single model EC forecasts. The regression process greatly improved ET0 forecast performances, particularly for the regions involving stations near the coast, or with a complex orography. The performance of EC forecasts was only slightly influenced by the size of the ensemble members, particularly at short lead times. Even with less ensemble members, EC still performed better than the other two NWPs. Errors in the radiation forecasts, followed by those in the wind, had the most detrimental effects on the ET0 forecast performances.

The effect of different evapotranspiration methods on portraying soil water dynamics and ET partitioning in a semi-arid environment in Northwest China

OpenAIRE

Yu, L.; Zeng, Yijian; Su, Zhongbo; Cai, H.; Zheng, Z.

2016-01-01

Different methods for assessing evapotranspiration (ET) can significantly affect the performance of land surface models in portraying soil water dynamics and ET partitioning. An accurate understanding of the impact a method has is crucial to determining the effectiveness of an irrigation scheme. Two ET methods are discussed: one is based on reference crop evapotranspiration (ET0) theory, uses leaf area index (LAI) for partitioning into soil evaporation and transpiration, and...

Impact of Atmospheric Albedo on Amazon Evapotranspiration

Science.gov (United States)

Lopes, A. V.; Thompson, S. E.; Dracup, J. A.

2013-12-01

The vulnerability of the Amazon region to climate and anthropogenic driven disturbances has been the subject of extensive research efforts, given its importance in the global and regional climate and ecologic systems. The evaluation of such vulnerabilities requires the proper understanding of physical mechanisms controlling water and energy balances and how the disturbances change them. Among those mechanisms, the effects of atmospheric albedo on evapotranspiration have not been fully explored yet and are explored in this study. Evapotranspiration in the Amazon is sustained at high levels across all seasons and represents a large fraction of water and energy surface budgets. In this study, statistical analysis of data from four flux towers installed at Amazon primary forest sites was employed to quantify the impact of atmospheric albedo, mostly resulted from cloudiness, on evapotranspiration and to compare it to the effect of water limitation. Firstly, the difference in eddy-flux derived evapotranspiration at the flux towers under rainy and non-rainy antecedent conditions was tested for significance. Secondly, the same statistical comparison was performed under cloudy and clear sky conditions at hourly and daily time scales, using the reduction in incoming solar radiation as an indicator of cloudiness. Finally, the sensitivity of seasonal evapotranspiration totals to atmospheric albedo resulted from rainfall patterns is evaluated. That was done by sampling daily evapotranspiration estimates from empirical probability distribution functions conditioned to rainfall occurrence and then varying the number of dry days in each season. It was found that light limitation is much more important than water limitation in the Amazon, resulting in up to 43% reduction in daily evapotranspiration. Also, this effect varies by location and by season, the largest impact being in wet season, from December do January. Moreover, seasonal evapotranspiration totals were found to be

Spatial and temporal evapotranspiration trends after wildfire in semi-arid landscapes

Science.gov (United States)

Poon, Patrick K.; Kinoshita, Alicia M.

2018-04-01

In recent years climate change and other anthropogenic factors have contributed to increased wildfire frequency and size in western United States forests. This research focuses on the evaluation of spatial and temporal changes in evapotranspiration (ET) following the 2011 Las Conchas Fire in New Mexico (USA) using the Operational Simplified Surface Energy Balance Model (SSEBop ET). Evapotranspiration is coupled with soil burn severity and analyzed for 16 watersheds for water years 2001-2014. An average annual decrease of 120 mm of ET is observed within the regions affected by the Las Conchas Fire, and conifers were converted to grassland a year after the fire. On average, the post-fire annual ET in high, moderate, and low burn severity is lower than pre-fire ET by approximately 103-352 mm, 97-304 mm, and 91-268 mm, respectively. The ratio of post-fire evapotranspiration to precipitation (ET/P) is statistically different from pre-fire conditions (α = 0.05) in nine of the watersheds. The largest decrease in ET is approximately 13-57 mm per month and is most prominent during the summer (April to September). The observed decrease in ET contributes to our understanding of changes in water yield following wildfires, which is of interest for accurately modeling and predicting hydrologic processes in semi-arid landscapes.

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

A new reference evapotranspiration surface for the National Water Census community

Science.gov (United States)

Verdin, J. P.; Hobbins, M. T.; Senay, G. B.

2012-12-01

To meet its congressional mandate to provide water managers with accurate, up-to-date, scientifically defensible reporting on the national water cycle—the National Water Census—the USGS has developed a framework for ongoing estimation of actual evapotranspiration (ET) combining both land-based and remotely sensed (R/S) drivers and is transferable to observation-scarce regions. To provide ET at Census-required resolutions (~100-1000 m), we combine (i) an operational, long-term, high-quality, scientific record of reference crop ET (ETrc), (ii) R/S land-surface temperature (LST) and reflectance at finer spatial scales but coarser temporal scales, and (iii) the USDA Annual Cropland Data Layer as a geographic mask for cropped surfaces. Our presentation motivates this new ET framework and describes its ETrc input. The ETrc is generated by the Penman-Monteith equation, driven by hourly, 0.125-degree (~12-km) NLDAS data, from Jan 1, 1979, to within five days of the present. This is the first consistently modeled, daily, continent-wide ETrc dataset that is both up-to-date and as temporally extensive. The R/S component relies on this input to provide an ETrc magnitude at coarse scale relative to the imagery. Remote sensing of LST and/or surface reflectance permits inference of ET as a fraction of ETrc. One such method used by the USGS is the Simplified Surface Energy Balance (SSEB) approach, which adapted the hot and cold pixel approach of SEBAL/METRIC; an operational version (SSEBop) calculates ET-fraction for a given pixel and combines it with ETrc to estimate and map ET on a routine basis with a high degree of consistency at multiple spatial scales. Though these imagery options have limited temporal coverage due to the time between satellite overpasses (1 to 8 days for MODIS, 16 days for Landsat), ET-fraction so derived is stable on such time scales. Thus, as ETrc varies significantly across the diurnal cycle and inter-overpass periods, it is used to track conditions

Changes in Reference Evapotranspiration and Its Contributing Factors in Jiangsu, a Major Economic and Agricultural Province of Eastern China

Directory of Open Access Journals (Sweden)

Ronghao Chu

2017-07-01

Full Text Available Reference evapotranspiration (ETref is a key parameter of hydro-meteorological studies as well as water resource planning. In this study, we adopted the Penman–Monteith FAO 56 model to estimate ETref and through the differential equation and detrending method to determine sensitivities and the contributions of four meteorological parameters to ETref based on daily weather data from 60 stations of Jiangsu province during 1961–2015. Results reveal that ETref and its trends in the three sub-regions of the Jiangsu province had a significant spatial heterogeneity. A significant decreasing tendency of ETref (p < 0.001 was observed in the Huaibei region, while a slightly increasing tendency was identified in the Jianghuai and Sunan regions. These changes of ETref were caused by a significant increasing trend in air temperature (TA and significant decreasing trends in wind speed (WS, sunshine duration (SD as well as a non-significant change trend in actual vapor pressure (VP. However, the VP was the meteorological parameter to which ETref was most sensitive, whereas ETref was more sensitive to TA and SD in the summer but less so in the winter; the least sensitive factor, WS, had the opposite trend. Across the whole region, WS contributed most to ETref, followed by SD, while the positive contribution of TA to ETref could not offset the negative contributions of WS and SD. Although the effect of VP on changes in ETref is small, it could not be ignored, especially in the winter. The reverse relationship between increasing TA and decreasing ETref, namely the “evaporation paradox,” occurred in Jiangsu province. Thus, the outcomes of this study will contribute to thorough insight into the response to changes in ETref to the provincial water planning and management in eastern China.

Evapotranspiration and crop coefficients of corn in monoculture and intercropped with jack bean

Directory of Open Access Journals (Sweden)

Mário S. P. de Araújo

Full Text Available ABSTRACT This study was carried out to determine the evapotranspiration (ETc and crop coefficients (Kc for four stages of “Caatingueiro” corn under the climate condition of Seropédica, RJ, Brazil, using weighing lysimeters. The field trial occurred in 2015, from March 18 to June 25, in two areas cultivated with “Caatingueiro’ corn intercropped with jack bean and in monoculture. The reference evapotranspiration (ETo was estimated by the FAO-56 Penman-Monteith model and the Kc values were determined by the ratio between ETc and ETo. The Kc values obtained for the intercropping and monoculture systems, were respectively: 0.78 (I; 1.01 (II; 1.10 (III and 1.01 (IV, and 0.62 (I; 0.92 (II; 1.27 (III and 0.81 (IV, and they were different from the values presented by FAO.

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

Directory of Open Access Journals (Sweden)

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.

Effective crop evapotranspiration measurement using time-domain reflectometry technique in a sub-humid region

Science.gov (United States)

Srivastava, R. K.; Panda, R. K.; Halder, Debjani

2017-08-01

The primary objective of this study was to evaluate the performance of the time-domain reflectometry (TDR) technique for daily evapotranspiration estimation of peanut and maize crop in a sub-humid region. Four independent methods were used to estimate crop evapotranspiration (ETc), namely, soil water balance budgeting approach, energy balance approach—(Bowen ratio), empirical methods approach, and Pan evaporation method. The soil water balance budgeting approach utilized the soil moisture measurement by gravimetric and TDR method. The empirical evapotranspiration methods such as combination approach (FAO-56 Penman-Monteith and Penman), temperature-based approach (Hargreaves-Samani), and radiation-based approach (Priestley-Taylor, Turc, Abetw) were used to estimate the reference evapotranspiration (ET0). The daily ETc determined by the FAO-56 Penman-Monteith, Priestley-Taylor, Turc, Pan evaporation, and Bowen ratio were found to be at par with the ET values derived from the soil water balance budget; while the methods Abetw, Penman, and Hargreaves-Samani were not found to be ideal for the determination of ETc. The study illustrates the in situ applicability of the TDR method in order to make it possible for a user to choose the best way for the optimum water consumption for a given crop in a sub-humid region. The study suggests that the FAO-56 Penman-Monteith, Turc, and Priestley-Taylor can be used for the determination of crop ETc using TDR in comparison to soil water balance budget.

Evapotranspiration of a high-density poplar stand in comparison with a reference grass cover in the Czech–Moravian Highlands

Czech Academy of Sciences Publication Activity Database

Fischer, M.; Trnka, M.; Kučera, J.; Deckmyn, G.; Orság, M.; Sedlák, Pavel; Žalud, Z.; Ceulemans, R.

2013-01-01

Roč. 181, NOV 2013 (2013), s. 43-60 ISSN 0168-1923 Institutional support: RVO:68378289 Keywords : Evapotranspiration * Short-rotation poplar coppice * Grassland * Bowen ratio/energy balance method Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 3.894, year: 2013 http://www.sciencedirect.com/science/article/pii/S0168192313001846

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

A coupled stochastic rainfall-evapotranspiration model for hydrological impact analysis

Science.gov (United States)

Pham, Minh Tu; Vernieuwe, Hilde; De Baets, Bernard; Verhoest, Niko E. C.

2018-02-01

A hydrological impact analysis concerns the study of the consequences of certain scenarios on one or more variables or fluxes in the hydrological cycle. In such an exercise, discharge is often considered, as floods originating from extremely high discharges often cause damage. Investigating the impact of extreme discharges generally requires long time series of precipitation and evapotranspiration to be used to force a rainfall-runoff model. However, such kinds of data may not be available and one should resort to stochastically generated time series, even though the impact of using such data on the overall discharge, and especially on the extreme discharge events, is not well studied. In this paper, stochastically generated rainfall and corresponding evapotranspiration time series, generated by means of vine copulas, are used to force a simple conceptual hydrological model. The results obtained are comparable to the modelled discharge using observed forcing data. Yet, uncertainties in the modelled discharge increase with an increasing number of stochastically generated time series used. Notwithstanding this finding, it can be concluded that using a coupled stochastic rainfall-evapotranspiration model has great potential for hydrological impact analysis.

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

Science.gov (United States)

Rajib, A.; Evenson, G. R.; Golden, H. E.; Lane, C.

2017-12-01

Evapotranspiration (ET), a highly dynamic flux in wetland landscapes, regulates the accuracy of surface/sub-surface runoff simulation in a hydrologic model. Accordingly, considerable uncertainty in simulating ET-related processes remains, including our limited ability to incorporate realistic ground conditions, particularly those involved with complex land-atmosphere feedbacks, vegetation growth, and energy balances. Uncertainty persists despite using high resolution topography and/or detailed land use data. Thus, a good hydrologic model can produce right answers for wrong reasons. In this study, we develop an efficient approach for multi-variable assimilation of remotely sensed earth observations (EOs) into a hydrologic model and apply it in the 1700 km2 Pipestem Creek watershed in the Prairie Pothole Region of North Dakota, USA. Our goal is to employ EOs, specifically Leaf Area Index (LAI) and Potential Evapotranspiration (PET), as surrogates for the aforementioned processes without overruling the model's built-in physical/semi-empirical process conceptualizations. To do this, we modified the source code of an already-improved version of the Soil and Water Assessment Tool (SWAT) for wetland hydrology (Evenson et al. 2016 HP 30(22):4168) to directly assimilate remotely-sensed LAI and PET (obtained from the 500 m and 1 km Moderate Resolution Imaging Spectroradiometer (MODIS) gridded products, respectively) into each model Hydrologic Response Unit (HRU). Two configurations of the model, one with and one without EO assimilation, are calibrated against streamflow observations at the watershed outlet. Spatio-temporal changes in the HRU-level water balance, based on calibrated outputs, are evaluated using MODIS Actual Evapotranspiration (AET) as a reference. It is expected that the model configuration having remotely sensed LAI and PET, will simulate more realistic land-atmosphere feedbacks, vegetation growth and energy balance. As a result, this will decrease simulated

Long-term patterns of air temperatures, daily temperature range, precipitation, grass-reference evapotranspiration and aridity index in the USA Great Plains: Part I. Spatial trends

Science.gov (United States)

Kukal, M.; Irmak, S.

2016-11-01

Due to their substantial spatio-temporal behavior, long-term quantification and analyses of important hydrological variables are essential for practical applications in water resources planning, evaluating the water use of agricultural crop production and quantifying crop evapotranspiration patterns and irrigation management vs. hydrologic balance relationships. Observed data at over 800 sites across the Great Plains of USA, comprising of 9 states and 2,307,410 km2 of surface area, which is about 30% of the terrestrial area of the USA, were used to quantify and map large-scale and long-term (1968-2013) spatial trends of air temperatures, daily temperature range (DTR), precipitation, grass-reference evapotranspiration (ETo) and aridity index (AI) at monthly, growing season and annual time steps. Air temperatures had a strong north to south increasing trend, with annual average varying from -1 to 24 °C, and growing season average temperature varying from 8 to 30 °C. DTR gradually decreased from western to eastern parts of the region, with a regional annual and growing season averages of 14.25 °C and 14.79 °C, respectively. Precipitation had a gradual shift towards higher magnitudes from west to east, with the average annual and growing season (May-September) precipitation ranging from 163 to 1486 mm and from 98 to 746 mm, respectively. ETo had a southwest-northeast decreasing trend, with regional annual and growing season averages of 1297 mm and 823 mm, respectively. AI increased from west to east, indicating higher humidity (less arid) towards the east, with regional annual and growing season averages of 0.49 and 0.44, respectively. The spatial datasets and maps for these important climate variables can serve as valuable background for climate change and hydrologic studies in the Great Plains region. Through identification of priority areas from the developed maps, efforts of the concerned personnel and agencies and resources can be diverted towards development

The effect of crop residue layers on evapotranspiration, growth and ...

African Journals Online (AJOL)

Observations of crop growth (stalk population, stalk height, canopy cover), cane yield and evapotranspiration for these treatments were compared to that of a bare soil treatment. The data were also used to derive values of crop evaporation coefficients for different development phases and these were compared to FAO56 ...

Spatial and temporal variability of reference evapotranspiration and influenced meteorological factors in the Jialing River Basin, China

Science.gov (United States)

Herath, Imali Kaushalya; Ye, Xuchun; Wang, Jianli; Bouraima, Abdel-Kabirou

2018-02-01

Reference evapotranspiration (ETr) is one of the important parameters in the hydrological cycle. The spatio-temporal variation of ETr and other meteorological parameters that influence ETr were investigated in the Jialing River Basin (JRB), China. The ETr was estimated using the CROPWAT 8.0 computer model based on the Penman-Montieth equation for the period 1964-2014. Mean temperature (MT), relative humidity (RH), sunshine duration (SD), and wind speed (WS) were the main input parameters of CROPWAT while 12 meteorological stations were evaluated. Linear regression and Mann-Kendall methods were applied to study the spatio-temporal trends while the inverse distance weighted (IDW) method was used to identify the spatial distribution of ETr. Stepwise regression and partial correlation methods were used to identify the meteorological variables that most significantly influenced the changes in ETr. The highest annual ETr was found in the northern part of the basin, whereas the lowest rate was recorded in the western part. In the autumn, the highest ETr was recorded in the southeast part of JRB. The annual ETr reflected neither significant increasing nor decreasing trends. Except for the summer, ETr is slightly increasing in other seasons. The MT significantly increased whereas SD and RH were significantly decreased during the 50-year period. Partial correlation and stepwise regression methods found that the impact of meteorological parameters on ETr varies on an annual and seasonal basis while SD, MT, and RH contributed to the changes of annual and seasonal ETr in the JRB.

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.

Sensitivity analysis of reference evapotranspiration to sensor accuracy

Science.gov (United States)

Meteorological sensor networks are often used across agricultural regions to calculate the ASCE Standardized Reference ET Equation, and inaccuracies in individual sensors can lead to inaccuracies in ET estimates. Multiyear datasets from the semi-arid Colorado Agricultural Meteorological (CoAgMet) an...

Examining the value of global seasonal reference evapotranspiration forecasts tosupport FEWS NET's food insecurity outlooks

Science.gov (United States)

Shukla, S.; McEvoy, D.; Hobbins, M.; Husak, G. J.; Huntington, J. L.; Funk, C.; Verdin, J.; Macharia, D.

2017-12-01

The Famine Early Warning Systems Network (FEWS NET) team provides food insecurity outlooks for several developing countries in Africa, Central Asia, and Central America. Thus far in terms of agroclimatic conditions that influence food insecurity, FEWS NET's primary focus has been on the seasonal precipitation forecasts while not adequately accounting for the atmospheric evaporative demand, which is also directly related to agricultural production and hence food insecurity, and is most often estimated by reference evapotranspiration (ETo). This presentation reports on the development of a new global ETo seasonal reforecast and skill evaluation with a particular emphasis on the potential use of this dataset by the FEWS NET to support food insecurity early warning. The ETo reforecasts span the 1982-2009 period and are calculated following ASCE's formulation of Penman-Monteith method driven by seasonal climate forecasts of monthly mean temperature, humidity, wind speed, and solar radiation from NCEP's CFSv2 and NASA's GEOS-5 models. The skill evaluation using deterministic and probabilistic scores focuses on the December-February (DJF), March-May (MAM), June-August (JJA) and September-November (SON) seasons. The results indicate that ETo forecasts are a promising tool for early warning of drought and food insecurity. The FEWS NET regions with promising level of skill (correlation >0.35 at lead times of 3 months) include Northern Sub-Saharan Africa (DJF, dry season), Central America (DJF, dry season), parts of East Africa (JJA, wet Season), Southern Africa (JJA, dry season), and Central Asia (MAM, wet season). A case study over parts of East Africa for the JJA season shows that, in combination with the precipitation forecasts, ETo forecasts could have provided early warning of recent severe drought events (e.g., 2002, 2004, 2009) that contributed to substantial food insecurity in the region.

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.

Variability in understory evapotranspiration with overstory density in Siberian larch forests

Science.gov (United States)

Tobio, A.; Loranty, M. M.; Kropp, H.; Pena, H., III; Alexander, H. D.; Natali, S.; Kholodov, A. L.

2016-12-01

Arctic ecosystems are changing rapidly in response to amplified rates of climate change. Increased vegetation productivity, altered ecosystem carbon and hydrologic cycling, and increased wildfire severity are among the key responses to changing permafrost and climate conditions. Boreal larch forests in northeastern Siberia are a critical but understudied ecosystem affected by these modifications. Understory vegetation in these ecosystems, which typically have low canopy cover, may account for half of all water fluxes. Despite the potential importance of the understory for ecosystem water exchange, there has been relatively little research examining variability in understory evapotranspiration in boreal larch forests. In particular, the water balance of understory shrubs and mosses is largely undefined and could provide insight on how understory vegetation and our changing climate interact. This is especially important because both observed increases in vegetation productivity and wildfire severity could lead to increases in forests density, altering the proportional contributions of over- and understory vegetation to whole ecosystem evapotranspiration. In order to better understand variability in understory evapotranspiration we measured in larch forests with differing overstory density and permafrost conditions that likely vary as a consequence of fire severity. We used the static chamber technique to measure fluxes across a range of understory vegetation types and environmental conditions. In general, we found that the understory vegetation in low density stands transpires more than that in high density stands. This tends to be correlated with a larger amount of aboveground biomass in the low density stands, and an increase in solar radiation, due to less shading by overstory trees. These results will help us to better understand water balances, evapotranspiration variability, and productivity changes associated with climate on understory vegetation. Additionally

Simulated evapotranspiration from a landfill irrigated with landfill leachate

International Nuclear Information System (INIS)

Aronsson, P.

1996-01-01

Evapotranspiration from a landfill area, irrigated with leachate water, was simulated with the SOIL model. Three different types of vegetation (bare soil, grass ley, and willow) were used both with and without irrigation. The highest simulated evapotranspiration (604 mm) during the growing season was found from an irrigated willow stand with a high interception capacity. The lowest evapotranspiration (164 mm) was found from the bare soil. The relatively high evapotranspiration from the willow was probably caused by the high LAI (Leaf Area Index) and the low aerodynamic resistance within the willow stand. The results indicate that it is possible to reduce most of the leakage water from a landfill by irrigation of willow stands. 9 refs, 4 figs, 1 tab

Amazon river basin evapotranspiration and its influence on the rainfall in southern Brazil

Science.gov (United States)

Folegatti, M. V.; Wolff, W.

2017-12-01

Amazon river basin (ARB) presents a positive water balance, i.e. the precipitation is higher than evapotranspiration. Regarding the regional circulation, ARB evapotranspiration represents an important source of humidity for the South of Brazil. Thus, the aim of this work is to answer the question: how much is the correlation between ARB evapotranspiration and rainfall in South of Brazil? The shapefiles data of ARB and countries/states boundary were obtained through the Oak Ridge National Laboratory (ORNL) and Instituto Brasileiro de Geografia e Estatística (IBGE), respectively. According to rasters data, the precipitation was obtained from study of Numerical Terradynamic Simulation Group (NTSG) for images of Moderate Resolution Imaging Spectroradiometer (MODIS), under code MOD16A2, whereas rasters data for evapotranspiration were obtained from National Aeronautics and Space Administration (NASA) by Tropical Rainfall Measuring Mission Multi-Satellite Precipitation Analysis (TMPA), under code 3B43_V7. The products MOD16A2 and 3B43_V7 have a respective spatial resolution of 0.5º and 0.25º, and a monthly temporal resolution from January/2000 to December/2014. For ARB and South region of Brazil was calculated the mean evapotranspiration and mean precipitation through the pixels within of the respective polygons. To answer the question of this work was performed the cross-correlation analysis between these time series. We observed the highest value for the lag that corresponds the begin of spring (October), being 0.3 approximately. As a result, the mean precipitation on South region of Brazil during spring and summer was in the order of 15% to 30 %, explained by ARB evapotranspiration. For this reason, the maintenance of ARB is extremely important for water resource grant in South of Brazil.

Precipitation and evapotranspiration at the mountain lysimeter station Stoderzinken

Science.gov (United States)

Herndl, Markus; Winkler, Gerfried; Birk, Steffen

2014-05-01

Alpine water resources are highly important for the Austrian drinking water supply. In particular, the Northern Calcareous Alps contribute substantially to both the regional and the national drinking water supply. To analyse water balance, runoff and recharge in a representative mountain pasture area in the Northern Calcareous Alps a lysimeter station was established at the mountain Stoderzinken (1830 m a.s.l.) in 2005. This work examines the water balance at the lysimeter station during one summer period. Precipitation and evapotranspiration are determined using various approaches in order to identify potential errors in the measurement or interpretation of the data and thus to assess the uncertainties in the water balance components. For this purpose, data of rain gauges and a distrometer was compared with the precipitation calculated from the water balance of the lysimeter. Furthermore evapotranspiration was calculated using the HAUDE and PENMAN-MONTEITH equations for comparison. Already in previous seasons the distrometer was found to be prone to errors, which was confirmed when compared to the rain gauge data. In contrast, precipitation rates calculated from the lysimeter data were found to agree better with the rain gauge data but showed a trend to higher values. However, the approach to calculate precipitation from the lysimeter data turned out to be unsuitable for time periods with significant contribution of snow melt. Evapotranspiration calculated from lysimeter data are in good agreement with the results from the above-mentioned (semi-)empirical equations during dry periods. Furthermore the differences to the evapotranspiration calculated from the climate data correlate with the amount of precipitation. These results suggest that in alpine catchments the uncertainty in the precipitation data constitutes the major source of error in the calculation of evapotranspiration from the water balance of the lysimeter. However, it should be noted that these

Tendências recentes nos elementos do clima e suas implicações na evapotranspiração da cultura do milho em Viçosa - MG Recent trends in the weather elements and its implications in the maize crop evapotranspiration in Viçosa-MG, Brazil

Directory of Open Access Journals (Sweden)

Leonidas P. de Alencar

2011-01-01

Full Text Available A mudança nas condições climáticas tem gerado grandes preocupações em nível mundial, sendo que uma das grandes questões, neste contexto, é o aquecimento global. As alterações ocorridas nas condições climáticas podem afetar a demanda de água das plantas, porque a evapotranspiração é afetada por mudanças nos elementos climáticos. O objetivo deste trabalho foi analisar os efeitos das possíveis mudanças dos elementos do clima na evapotranspiração de referência e na evapotranspiração da cultura do milho para a região de Viçosa - MG. Mediante análise de tendência pelo teste de Mann-Kendall e da estatística do teste t da regressão linear, verificou-se o comportamento dos seguintes elementos climáticos: temperaturas máxima e mínima, insolação, velocidade do vento e umidade relativa. Observou-se uma redução na evapotranspiração de referência e da cultura do milho ao longo dos últimos 41 anos, principalmente em razão da redução da insolação e da velocidade do vento. A evapotranspiração de referência apresentou redução da ordem de 4,2 mm por ano.The change in weather conditions has caused great concern in the world and the major issue, in this context, is the global warming. The changes in climate may affect the water demand of plants, because the evapotranspiration is affected by changes in climatic elements. The objective of this study was to examine the possible effects of climatological changes in evapotranspiration and reference evapotranspiration of corn in Viçosa - MG, Brazil. Trend analysis by the Mann-Kendall statistic and student t test of the linear regression were used to study the behavior of the following weather elements: maximum and minimum temperatures, sunshine duration, wind speed and relative humidity. It was observed a reduction in the reference evapotranspiration and maize crop evapotranspiration over the recent past 41 years, mainly because of reduced solar radiation and wind

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 ...

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.

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

Directory of Open Access Journals (Sweden)

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

Potential evapotranspiration trend analysis for different climatic zones in Khyber Pakhtunkhwa, Pakistan

International Nuclear Information System (INIS)

Nazeer, M.

2012-01-01

Estimation of potential evapotranspiration (ETo) plays a significant role in the study of water resources management. The study was conducted to investigate the change in potential evapotranspiration value during the past three decade in three diverse climatic zones of Khyber Pakhtunkhwa, Pakistan. Three Districts of Khyber Pakhtunkhwa, Pakistan (Chitral, Peshawar and D. I. Khan) were selected based on their climatic diversity. Thirty years climatic data (1981-2010) obtained from Pakistan Metrological Department, Islamabad and Agriculture Research Institute, Peshawar was used. Potential evapotranspiration was determined for three decades separately, as well as on mean monthly basis. World Meteorological Organization (WMO) technique was used for trend analysis. Results revealed highest ETo in D. I. Khan followed by Peshawar and Chitral. However, in the summer months ETo value was found highest in Chitral as compared to other selected Districts. Trend analysis results showed that decrease in ETo trend was observed in all the selected Districts with the passage of time. It can be concluded that ETo values decreased as compared to past in all the selected Districts without any discrimination of physical geography and location. (author)

Evapotranspiration Estimates for a Stochastic Soil-Moisture Model

Science.gov (United States)

Chaleeraktrakoon, Chavalit; Somsakun, Somrit

2009-03-01

Potential evapotranspiration is information that is necessary for applying a widely used stochastic model of soil moisture (I. Rodriguez Iturbe, A. Porporato, L. Ridolfi, V. Isham and D. R. Cox, Probabilistic modelling of water balance at a point: The role of climate, soil and vegetation, Proc. Roy. Soc. London A455 (1999) 3789-3805). An objective of the present paper is thus to find a proper estimate of the evapotranspiration for the stochastic model. This estimate is obtained by comparing the calculated soil-moisture distribution resulting from various techniques, such as Thornthwaite, Makkink, Jensen-Haise, FAO Modified Penman, and Blaney-Criddle, with an observed one. The comparison results using five sequences of daily soil-moisture for a dry season from November 2003 to April 2004 (Udornthani Province, Thailand) have indicated that all methods can be used if the weather information required is available. This is because their soil-moisture distributions are alike. In addition, the model is shown to have its ability in approximately describing the phenomenon at a weekly or biweekly time scale which is desirable for agricultural engineering applications.

Reference evapotranspiration estimation inside greenhouses Evapotranspiração de referência estimativa em casas de vegetação

Directory of Open Access Journals (Sweden)

Carolina Fernandes

2003-01-01

Full Text Available Because of the large area occupied by a class A pan, alternative methods have been sought to estimate reference evapotranspiration (Eto inside greenhouses. The objective of this work was to compare ETo estimated by different methods inside and outside a greenhouse. A class A pan (CAPi, a reduced pan (RPi and an atmometer (Ai were installed inside a greenhouse, and another class A pan (CAPo was installed outside. ETo estimates, obtained by CAPi, RPi, and Ai were 56%, 69% and 63% of those estimated by CAPo, respectively. A simple linear regression showed positive coefficients R = 0.94 for the RPi and the CAPi, R = 0.91 for the Ai and the CAPi, R = 0.70 for the CAPi and the CAPo, R = 0.66 for the RPi and the CAPo, and R = 0.62 for the Ai and the CAPo. ETo needs to be estimated inside greenhouses and it is possible to use reduced pans or atmometers to estimate the ETo inside the greenhouse. Equipment replacement would increase the available space inside the greenhouse.Em função da área ocupada pelo tanque classe A, tem-se procurado utilizar métodos alternativos para a estimativa da evapotranspiração de referência (ETo dentro de casas de vegetação. O trabalho teve como objetivo comparar a ETo estimada pelo método do tanque classe A instalado dentro (TCAd e fora (TCAf da casa de vegetação e pelos métodos do tanque reduzido (TRED e do atmômetro (ATM instalados dentro da casa de vegetação. Os valores estimados da ETo foram comparados por análises de regressão linear simples. ETo estimada pelo TCAd, TRED e ATM correspondeu a 56%, 69% e 63% da ETo estimada pelo TCAf, respectivamente. As regressões entre os valores das ETo estimados pelo TCAd e pelos outros dois métodos apresentaram valores do coeficiente de correlação (R de 0,94 para o método do TRED e de 0,91 para o método do ATM. As regressões entre os valores das ETo estimados pelo TCAf e aqueles estimados dentro da mesma pelos diferentes métodos, apresentaram valor de R de 0

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.

Evapotranspiration of deforested areas in central and southwestern Amazonia

NARCIS (Netherlands)

Randow, von R.C.S.; Randow, C.; Hutjes, R.W.A.; Tomasella, J.; Kruijt, B.

2012-01-01

Considering the high rates of evapotranspiration of Amazonian forests, understanding the impacts of deforestation on water loss rates is important for assessing those impacts on a regional and global scale. This paper quantifies evapotranspiration rates in two different pasture sites in Amazonia and

Comparison between Evapotranspiration Fluxes Assessment Methods

Science.gov (United States)

Casola, A.; Longobardi, A.; Villani, P.

2009-11-01

Knowledge of hydrological processes acting in the water balance is determinant for a rational water resources management plan. Among these, the water losses as vapour, in the form of evapotranspiration, play an important role in the water balance and the heat transfers between the land surface and the atmosphere. Mass and energy interactions between soil, atmosphere and vegetation, in fact, influence all hydrological processes modificating rainfall interception, infiltration, evapotraspiration, surface runoff and groundwater recharge.A numbers of methods have been developed in scientific literature for modelling evapotranspiration. They can be divided in three main groups: i) traditional meteorological models, ii) energy fluxes balance models, considering interaction between vegetation and the atmosphere, and iii) remote sensing based models. The present analysis preliminary performs a study of fluxes directions and an evaluation of energy balance closure in a typical Mediterranean short vegetation area, using data series recorded from an eddy covariance station, located in the Campania region, Southern Italy. The analysis was performed on different seasons of the year with the aim to assess climatic forcing features impact on fluxes balance, to evaluate the smaller imbalance and to highlight influencing factors and sampling errors on balance closure. The present study also concerns evapotranspiration fluxes assessment at the point scale. Evapotranspiration is evaluated both from empirical relationships (Penmann-Montheit, Penmann F AO, Prestley&Taylor) calibrated with measured energy fluxes at mentioned experimental site, and from measured latent heat data scaled by the latent heat of vaporization. These results are compared with traditional and reliable well known models at the plot scale (Coutagne, Turc, Thorthwaite).

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

Directory of Open Access Journals (Sweden)

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

Spatial and temporal trends of reference crop evapotranspiration and its influential variables in Yangtze River Delta, eastern China

Science.gov (United States)

Xu, Yu; Xu, Youpeng; Wang, Yuefeng; Wu, Lei; Li, Guang; Song, Song

2017-11-01

Reference crop evapotranspiration (ETo) is one of the most important links in hydrologic circulation and greatly affects regional agricultural production and water resource management. Its variation has drawn more and more attention in the context of global warming. We used the Penman-Monteith method of the Food and Agriculture Organization, based on meteorological factors such as air temperature, sunshine duration, wind speed, and relative humidity to calculate the ETo over 46 meteorological stations located in the Yangtze River Delta, eastern China, from 1957 to 2014. The spatial distributions and temporal trends in ETo were analyzed based on the modified Mann-Kendall trend test and linear regression method, while ArcGIS software was employed to produce the distribution maps. The multiple stepwise regression method was applied in the analysis of the meteorological variable time series to identify the causes of any observed trends in ETo. The results indicated that annual ETo showed an obvious spatial pattern of higher values in the north than in the south. Annual increasing trends were found at 34 meteorological stations (73.91 % of the total), which were mainly located in the southeast. Among them, 12 (26.09 % of the total) stations showed significant trends. We saw a dominance of increasing trends in the monthly ETo except for January, February, and August. The high value zone of monthly ETo appeared in the northwest from February to June, mid-south area from July to August, and southeast coastal area from September to January. The research period was divided into two stages—stage I (1957-1989) and stage II (1990-2014)—to investigate the long-term temporal ETo variation. In stage I, almost 85 % of the total stations experienced decreasing trends, while more than half of the meteorological stations showed significant increasing trends in annual ETo during stage II except in February and September. Relative humidity, wind speed, and sunshine duration were

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.

2018-02-01

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.

Bushland Reference ET Calculator with QA/QC capabilities and iPhone/iPad application

Science.gov (United States)

Accurate daily reference evapotranspiration (ET) values are needed to estimate crop water demand for irrigation management and hydrologic modeling purposes. The USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas developed the Bushland Reference ET (BET) Calculator for calcul...

Evaluating gridded crop model simulations of evapotranspiration and irrigation using survey and remotely sensed data

Science.gov (United States)

Lopez Bobeda, J. R.

2017-12-01

The increasing use of groundwater for irrigation of crops has exacerbated groundwater sustainability issues faced by water limited regions. Gridded, process-based crop models have the potential to help farmers and policymakers asses the effects water shortages on yield and devise new strategies for sustainable water use. Gridded crop models are typically calibrated and evaluated using county-level survey data of yield, planting dates, and maturity dates. However, little is known about the ability of these models to reproduce observed crop evapotranspiration and water use at regional scales. The aim of this work is to evaluate a gridded version of the Decision Support System for Agrotechnology Transfer (DSSAT) crop model over the continental United States. We evaluated crop seasonal evapotranspiration over 5 arc-minute grids, and irrigation water use at the county level. Evapotranspiration was assessed only for rainfed agriculture to test the model evapotranspiration equations separate from the irrigation algorithm. Model evapotranspiration was evaluated against the Atmospheric Land Exchange Inverse (ALEXI) modeling product. Using a combination of the USDA crop land data layer (CDL) and the USGS Moderate Resolution Imaging Spectroradiometer Irrigated Agriculture Dataset for the United States (MIrAD-US), we selected only grids with more than 60% of their area planted with the simulated crops (corn, cotton, and soybean), and less than 20% of their area irrigated. Irrigation water use was compared against the USGS county level irrigated agriculture water use survey data. Simulated gridded data were aggregated to county level using USDA CDL and USGS MIrAD-US. Only counties where 70% or more of the irrigated land was corn, cotton, or soybean were selected for the evaluation. Our results suggest that gridded crop models can reasonably reproduce crop evapotranspiration at the country scale (RRMSE = 10%).

Potential groundwater contribution to Amazon evapotranspiration

Directory of Open Access Journals (Sweden)

Y. Fan

2010-10-01

Full Text Available Climate and land ecosystem models simulate a dry-season vegetation stress in the Amazon forest, but observations do not support these results, indicating adequate water supply. Proposed mechanisms include larger soil water store and deeper roots in nature and the ability of roots to move water up and down (hydraulic redistribution, both absent in the models. Here we provide a first-order assessment of the potential importance of the upward soil water flux from the groundwater driven by capillarity. We present a map of equilibrium water table depth from available observations and a groundwater model simulation constrained by these observations. We then present a map of maximum capillary flux these water table depths, combined with the fine-textured soils in the Amazon, can potentially support. The maps show that the water table beneath the Amazon can be shallow in lowlands and river valleys (<5 m in 36% and <10 m in 60% of Amazonia. These water table depths can potentially accommodate a maximum capillary flux of 2.1 mm day⁻¹ to the land surface averaged over Amazonia, but varies from 0.6 to 3.7 mm day⁻¹ across nine study sites.

We note that the results presented here are based on limited observations and simple equilibrium model calculations, and as such, have important limitations and must be interpreted accordingly. The potential capillary fluxes are not indicative of their contribution to the actual evapotranspiration, and they are only an assessment of the possible rate at which this flux can occur, to illustrate the power of soil capillary force acting on a shallow water table in fine textured soils. They may over-estimate the actual flux where the surface soils remain moist. Their contribution to the actual evapotranspiration can only be assessed through fully coupled model simulation of the dynamic feedbacks between soil water and groundwater with sub-daily climate forcing. The equilibrium water table

Observation and Estimation of Evapotranspiration from an Irrigated Green Roof in a Rain-Scarce Environment

Directory of Open Access Journals (Sweden)

Youcan Feng

2018-03-01

Full Text Available While the rain-driven evapotranspiration (ET process has been well-studied in the humid climate, the mixed irrigation and rain-driven ET process is less understood for green roof implementations in dry regions, where empirical observations and model parameterizations are lacking. This paper presents an effort of monitoring and simulating the ET process for an irrigated green roof in a rain-scarce environment. Annual ET rates for three weighing lysimeter test units with non-vegetated, sedums, and grass covers were 2.01, 2.52, and 2.69 mm d−1, respectively. Simulations based on the three Penman–Monteith equation-derived models achieved accuracy within the reported range of previous studies. Compared to the humid climate, the overestimation of high ET rates by existing models is expected to cause a larger error in dry environments, where the enhanced ET process caused by repeated irrigations overlapped with hot, dry conditions often occurs during summer. The studied sedum species did not show significantly lower ET rates than native species, and could not effectively take advantage of the deep moisture storage. Therefore, native species, instead of the shallow-rooted species commonly recommended in humid climates, might be a better choice for green roofs in rain-scarce environments.

Resolving the observer reference class problem in cosmology

NARCIS (Netherlands)

Friederich, Simon

2017-01-01

The assumption that we are typical observers plays a core role in attempts to make multiverse theories empirically testable. A widely shared worry about this assumption is that it suffers from systematic ambiguity concerning the reference class of observers with respect to which typicality is

Evapotranspiration of a high-density poplar stand in comparison with a reference grass cover in the Czech–Moravian Highlands

Czech Academy of Sciences Publication Activity Database

Fischer, Milan; Trnka, Miroslav; Kučera, J.; Deckmyn, G.; Orság, Matěj; Sedlák, Pavel; Žalud, Z.; Ceulemans, R.

2013-01-01

Roč. 181, NOV 2013 (2013), s. 43-60 ISSN 0168-1923 R&D Projects: GA MŠk(CZ) EE2.3.20.0248; GA MŠk(CZ) EE2.4.31.0056; GA MŠk EE2.3.30.0056; GA MŠk(CZ) ED1.1.00/02.0073 Institutional support: RVO:67179843 Keywords : Evapotranspiration * Short-rotation poplar coppice * Grassland * Bowen ratio/energy balance method Subject RIV: EH - Ecology, Behaviour Impact factor: 3.894, year: 2013

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.

Soil water sensor-based and evapotranspiration-based irrigation scheduling for soybean production on a Blackland Prairie soil in humid climate

Science.gov (United States)

In east-central Mississippi, annual rainfall was 1307 mm and reference evapotranspiration (ETo) was 1210 mm for the 120-year period from 1894 to 2014. From May to October, when major crops are typically grown in this area, monthly rainfall ranged from 72 to 118 mm, and monthly ETo from 94 to 146 mm ...

Temperature-based modeling of reference evapotranspiration using several artificial intelligence models: application of different modeling scenarios

Science.gov (United States)

Sanikhani, Hadi; Kisi, Ozgur; Maroufpoor, Eisa; Yaseen, Zaher Mundher

2018-02-01

The establishment of an accurate computational model for predicting reference evapotranspiration (ET0) process is highly essential for several agricultural and hydrological applications, especially for the rural water resource systems, water use allocations, utilization and demand assessments, and the management of irrigation systems. In this research, six artificial intelligence (AI) models were investigated for modeling ET0 using a small number of climatic data generated from the minimum and maximum temperatures of the air and extraterrestrial radiation. The investigated models were multilayer perceptron (MLP), generalized regression neural networks (GRNN), radial basis neural networks (RBNN), integrated adaptive neuro-fuzzy inference systems with grid partitioning and subtractive clustering (ANFIS-GP and ANFIS-SC), and gene expression programming (GEP). The implemented monthly time scale data set was collected at the Antalya and Isparta stations which are located in the Mediterranean Region of Turkey. The Hargreaves-Samani (HS) equation and its calibrated version (CHS) were used to perform a verification analysis of the established AI models. The accuracy of validation was focused on multiple quantitative metrics, including root mean squared error (RMSE), mean absolute error (MAE), correlation coefficient (R 2), coefficient of residual mass (CRM), and Nash-Sutcliffe efficiency coefficient (NS). The results of the conducted models were highly practical and reliable for the investigated case studies. At the Antalya station, the performance of the GEP and GRNN models was better than the other investigated models, while the performance of the RBNN and ANFIS-SC models was best compared to the other models at the Isparta station. Except for the MLP model, all the other investigated models presented a better performance accuracy compared to the HS and CHS empirical models when applied in a cross-station scenario. A cross-station scenario examination implies the

Effects of climate change on evapotranspiration over the Okavango Delta water resources

Science.gov (United States)

Moses, Oliver; Hambira, Wame L.

2018-06-01

In semi-arid developing countries, most poor people depend on contaminated surface or groundwater resources since they do not have access to safe and centrally supplied water. These water resources are threatened by several factors that include high evapotranspiration rates. In the Okavango Delta region in the north-western Botswana, communities facing insufficient centrally supplied water rely mainly on the surface water resources of the Delta. The Delta loses about 98% of its water through evapotranspiration. However, the 2% remaining water rescues the communities facing insufficient water from the main stream water supply. To understand the effects of climate change on evapotranspiration over the Okavango Delta water resources, this study analysed trends in the main climatic parameters needed as input variables in evapotranspiration models. The Mann Kendall test was used in the analysis. Trend analysis is crucial since it reveals the direction of trends in the climatic parameters, which is helpful in determining the effects of climate change on evapotranspiration. The main climatic parameters required as input variables in evapotranspiration models that were of interest in this study were wind speeds, solar radiation and relative humidity. Very little research has been conducted on these climatic parameters in the Okavango Delta region. The conducted trend analysis was more on wind speeds, which had relatively longer data records than the other two climatic parameters of interest. Generally, statistically significant increasing trends have been found, which suggests that climate change is likely to further increase evapotranspiration over the Okavango Delta water resources.

Remote Sensing of Evapotranspiration and Carbon Uptake at Harvard Forest

Science.gov (United States)

Min, Qilong; Lin, Bing

2005-01-01

A land surface vegetation index, defined as the difference of microwave land surface emissivity at 19 and 37 GHz, was calculated for a heavily forested area in north central Massachusetts. The microwave emissivity difference vegetation index (EDVI) was estimated from satellite SSM/I measurements at the defined wavelengths and used to estimate land surface turbulent fluxes. Narrowband visible and infrared measurements and broadband solar radiation observations were used in the EDVI retrievals and turbulent flux estimations. The EDVI values represent physical properties of crown vegetation such as vegetation water content of crown canopies. The collocated land surface turbulent and radiative fluxes were empirically linked together by the EDVI values. The EDVI values are statistically sensitive to evapotranspiration fractions (EF) with a correlation coefficient (R) greater than 0.79 under all-sky conditions. For clear skies, EDVI estimates exhibit a stronger relationship with EF than normalized difference vegetation index (NDVI). Furthermore, the products of EDVI and input energy (solar and photosynthetically-active radiation) are statistically significantly correlated to evapotranspiration (R=0.95) and CO2 uptake flux (R=0.74), respectively.

Drought trends indicated by evapotranspiration deficit over the contiguous United States during 1896-2013

Science.gov (United States)

Kim, Daeha; Rhee, Jinyoung

2016-04-01

Evapotranspiration (ET) has received a great attention in drought assessment as it is closely related to atmospheric water demand. The hypothetical potential ET (ETp) has been predominantly used, nonetheless it does not actually exist in the hydrologic cycle. In this work, we used a complementary method for ET estimation to obtain wet-environment ET (ETw) and actual ET (ETa) from routinely observed climatic data. By combining ET deficits (ETw minus ETa) and the structure of the Standardized Precipitation-Evapotranspiration Index (SPEI), we proposed a novel ET-based drought index, the Standardized Evapotranspiration Deficit Index (SEDI). We carried out historical drought identification for the contiguous United States using temperature datasets of the PRISM Climate Group. SEDI presented spatial distributions of drought areas similar to the Palmer Drought Severity Index (PDSI) and Standardized Precipitation Index (SPI) for major drought events. It indicates that SEDI can be used for validating other drought indices. Using the non-parametric Mann-Kendall test, we found a significant decreasing trend of SEDI (increasing drought risk) similar to PDSI and SPI in the western United States. This study suggests a potential of ET-based indices for drought quantification even with no involvement of precipitation data.

Drought assessment by evapotranspiration mapping in Twente

Science.gov (United States)

Eden, U.; Timmermans, J.; van der Velde, R.; Su, Z.

2012-04-01

). ETDI was then calculated using the estimated actual ET in combination with reference ET from Penman-Moneith. Investigations on temperature and precipitation anomalies, using SPI, are also included because of their contribution to the droughts. For this precipitation data from ground measurements were used to calculate the SPI for comparison with ETDI. Preliminary results show that SEBS ET from MODIS 1km resolution and ECMWF can be used for estimating ET for Twente region. The ET maps show that evapotranspiration in all years follow a seasonal trend with higher ET during the growing season as compared to other seasons. Investigation into ET shows small spatial variability, and investigation into SPI shows large temporal variability with 2003 and 2006 being very dry years.

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

Evapotranspiration Modeling by Linear, Nonlinear Regression and Artificial Neural Network in Greenhouse (Case study Reference Crop, Cucumber and Tomato

Directory of Open Access Journals (Sweden)

vahid Rezaverdinejad

2017-01-01

Full Text Available Introduction: Greenhouse cultivation is a steadily developing agricultural sector throughout the world. In addition, it is known that water is a major issue almost all part of the world especially for countries which have insufficient water source. With this great expansion of greenhouse cultivation, the need of appropriate irrigation management has a great importance. Accurate determination of irrigation scheduling (irrigation timing and frequency is one of the main factors in achieving high yields and avoiding loss of quality in greenhouse tomato and cucumber. To do this, it is fundamental to know the crop water requirements or real evapotranspiration. Accurate estimation on crop water requirement is needed to avoid the excess or deficit water application, with consequent impacts on nutrient availability for plants. This can be done by using appropriate method to determine the crop evapotranspiration (ETc. In greenhouse cultivation, crop transpiration is the most important energy dissipation mechanisms that influence ETc rate. There are a large number of literatures on methods to estimate ETc in greenhouses. ETc can be measured or estimated by direct or indirect methods. The most common direct method estimates ETc from measurements with weighing lysimeters. Thisalsoincludes the evaporation measuring equipment, class A pan, Piche atmometer and modified atmometer. Indirect method includes the measurement of net radiation, temperature, relative humidity, and air vapour pressure deficit. A large number of models have been developed from these measurements to estimate ETc. Due to the fast development of under greenhouse cultivation all around the world, the needs of information on how it affects ETc in greenhouses has to be known and summarized. The existing models for ETc calculation have to be studied to know whether it is reliable for greenhouse climate (hereafter, microclimate or not. Regression and artificial neural network models are two

Observing Seasonal and Diurnal Hydrometeorological Variability Within a Tropical Alpine Valley: Implications for Evapotranspiration

Science.gov (United States)

Hellstrom, R. A.; Mark, B. G.

2007-12-01

Conditions of glacier recession in the seasonally dry tropical Peruvian Andes motivate research to better constrain the hydrological balance in alpine valleys. There is an outstanding need to better understand the impact of the pronounced tropical hygric seasonality on energy and water budgets within pro-glacial valleys that channel glacier runoff to stream flow. This paper presents a novel embedded network installed in the glacierized Llanganuco valley of the Cordillera Blanca (9°S) comprising eight low-cost, discrete temperature and humidity microloggers ranging from 3470 to 4740 masl and an automatic weather station at 3850 masl. Data are aggregated into distinct dry and wet periods sampled from two full annual cycles (2004-2006) to explore patterns of diurnal and seasonal variability. The magnitude of diurnal solar radiation varies little within the valley between the dry and wet periods, while wet season near-surface air temperatures are cooler. Seasonally characteristic diurnal fluctuations in lapse rate partially regulate convection and humidity. Steep lapse rates during the wet season afternoon promote up-slope convection of warm, moist air and nocturnal rainfall events. Standardized grass reference evapotranspiration (ET0) was estimated using the FAO-56 algorithm of the United Nations Food and Agriculture Organization and compared with estimates of actual ET from the process-based BROOK90 model that incorporates more realistic vegetation parameters. Comparisons of composite diurnal cycles of ET for the wet and dry periods suggest about twice the daily ET0 during the dry period, attributed primarily to the 500% higher vapor pressure deficit and 20% higher daily total solar irradiance. Conversely, the near absence of rainfall during the dry season diminishes actual ET below that of the wet season by two orders of magnitude. Nearly cloud-free daylight conditions are critical for ET during the wet season. We found significant variability of ET with elevation

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.

Estimating wheat and maize daily evapotranspiration using artificial neural network

Science.gov (United States)

Abrishami, Nazanin; Sepaskhah, Ali Reza; Shahrokhnia, Mohammad Hossein

2018-02-01

In this research, artificial neural network (ANN) is used for estimating wheat and maize daily standard evapotranspiration. Ten ANN models with different structures were designed for each crop. Daily climatic data [maximum temperature (T max), minimum temperature (T min), average temperature (T ave), maximum relative humidity (RHmax), minimum relative humidity (RHmin), average relative humidity (RHave), wind speed (U 2), sunshine hours (n), net radiation (Rn)], leaf area index (LAI), and plant height (h) were used as inputs. For five structures of ten, the evapotranspiration (ETC) values calculated by ETC = ET0 × K C equation (ET0 from Penman-Monteith equation and K C from FAO-56, ANNC) were used as outputs, and for the other five structures, the ETC values measured by weighing lysimeter (ANNM) were used as outputs. In all structures, a feed forward multiple-layer network with one or two hidden layers and sigmoid transfer function and BR or LM training algorithm was used. Favorite network was selected based on various statistical criteria. The results showed the suitable capability and acceptable accuracy of ANNs, particularly those having two hidden layers in their structure in estimating the daily evapotranspiration. Best model for estimation of maize daily evapotranspiration is «M»ANN1 C (8-4-2-1), with T max, T min, RHmax, RHmin, U 2, n, LAI, and h as input data and LM training rule and its statistical parameters (NRMSE, d, and R2) are 0.178, 0.980, and 0.982, respectively. Best model for estimation of wheat daily evapotranspiration is «W»ANN5 C (5-2-3-1), with T max, T min, Rn, LAI, and h as input data and LM training rule, its statistical parameters (NRMSE, d, and R 2) are 0.108, 0.987, and 0.981 respectively. In addition, if the calculated ETC used as the output of the network for both wheat and maize, higher accurate estimation was obtained. Therefore, ANN is suitable method for estimating evapotranspiration of wheat and maize.

Evidence that global evapotranspiration makes a substantial contribution to the global atmospheric temperature slowdown

Science.gov (United States)

Leggett, L. Mark W.; Ball, David A.

2018-02-01

The difference between the time series trend for temperature expected from the increasing level of atmospheric CO2 and that for the (more slowly rising) observed temperature has been termed the global surface temperature slowdown. In this paper, we characterise the single time series made from the subtraction of these two time series as the `global surface temperature gap'. We also develop an analogous atmospheric CO2 gap series from the difference between the level of CO2 and first-difference CO2 (that is, the change in CO2 from one period to the next). This paper provides three further pieces of evidence concerning the global surface temperature slowdown. First, we find that the present size of both the global surface temperature gap and the CO2 gap is unprecedented over a period starting at least as far back as the 1860s. Second, ARDL and Granger causality analyses involving the global surface temperature gap against the major candidate physical drivers of the ocean heat sink and biosphere evapotranspiration are conducted. In each case where ocean heat data was available, it was significant in the models: however, evapotranspiration, or its argued surrogate precipitation, also remained significant in the models alongside ocean heat. In terms of relative scale, the standardised regression coefficient for evapotranspiration was repeatedly of the same order of magnitude as—typically as much as half that for—ocean heat. The foregoing is evidence that, alongside the ocean heat sink, evapotranspiration is also likely to be making a substantial contribution to the global atmospheric temperature outcome. Third, there is evidence that both the ocean heat sink and the evapotranspiration process might be able to continue into the future to keep the temperature lower than the level-of-CO2 models would suggest. It is shown that this means there can be benefit in using the first-difference CO2 to temperature relationship shown in Leggett and Ball (Atmos Chem Phys 15

REDRAW-Based Evapotranspiration Estimation in Chongli, North China

Science.gov (United States)

Zhang, Z.; Wang, Z.

2017-12-01

Evapotranspiration (ET) is the key component of hydrological cycle and spatial estimates of ET are important elements of atmospheric circulation and hydrologic models. Quantifying the ET over large region is significant for water resources planning, hydrologic water balances, water rights management, and water division. In this study, Evapotranspiration (ET) was estimated using REDRAW model in the Chongli on 2014. REDRAW is a satellite-based balance algorithm with reference dry and wet limits model developed to estimate ET. Remote sensing data obtained from MODIS and meteorological data from China Meteorological Data Sharing Service System were used in ET model. In order to analyze the distribution and time variation of ET over the study region, daily, monthly and yearly ET were calculated for the study area, and ET of different land cover types were calculated. In terms of the monthly ET, the figure was low in winter and high in other seasons, and reaches the maximum value in August, showing a high monthly difference. The ET value of water body was the highest and that of barren or sparse vegetation were the lowest, which accorded with local actual condition. Evaluating spatial temporal distribution of actual ET could assist to understand the water consumption regularity in region and figure out the effect from different land cover, which helped to establish links between land use, water allocation, and water use planning in study region. Due to the groundwater recession in north China, the evaluation of regional total water resources become increasingly essential, and the result of this study can be used to plan the water use. As the Chongli will prepare the ski slopes for Winter Olympics on 2022, accuracy estimation of actual ET can efficiently resolve water conflict and relieve water scarcity.

The WACMOS-ET project – Part 1: Tower-scale evaluation of four remote-sensing-based evapotranspiration algorithms

KAUST Repository

Michel, D.; Jimé nez, C.; Miralles, Diego G.; Jung, M.; Hirschi, M.; Ershadi, Ali; Martens, B.; McCabe, Matthew; Fisher, J. B.; Mu, Q.; Seneviratne, S. I.; Wood, E. F.; Ferná ndez-Prieto, D.

2016-01-01

The WAter Cycle Multi-mission Observation Strategy – EvapoTranspiration (WACMOS-ET) project has compiled a forcing data set covering the period 2005–2007 that aims to maximize the exploitation of European Earth Observations data sets for evapotranspiration (ET) estimation. The data set was used to run four established ET algorithms: the Priestley–Taylor Jet Propulsion Laboratory model (PT-JPL), the Penman–Monteith algorithm from the MODerate resolution Imaging Spectroradiometer (MODIS) evaporation product (PM-MOD), the Surface Energy Balance System (SEBS) and the Global Land Evaporation Amsterdam Model (GLEAM). In addition, in situ meteorological data from 24 FLUXNET towers were used to force the models, with results from both forcing sets compared to tower-based flux observations. Model performance was assessed on several timescales using both sub-daily and daily forcings. The PT-JPL model and GLEAM provide the best performance for both satellite- and tower-based forcing as well as for the considered temporal resolutions. Simulations using the PM-MOD were mostly underestimated, while the SEBS performance was characterized by a systematic overestimation. In general, all four algorithms produce the best results in wet and moderately wet climate regimes. In dry regimes, the correlation and the absolute agreement with the reference tower ET observations were consistently lower. While ET derived with in situ forcing data agrees best with the tower measurements (R²  =  0.67), the agreement of the satellite-based ET estimates is only marginally lower (R²  =  0.58). Results also show similar model performance at daily and sub-daily (3-hourly) resolutions. Overall, our validation experiments against in situ measurements indicate that there is no single best-performing algorithm across all biome and forcing types. An extension of the evaluation to a larger selection of 85 towers (model inputs resampled to a

The WACMOS-ET project – Part 1: Tower-scale evaluation of four remote-sensing-based evapotranspiration algorithms

KAUST Repository

Michel, D.

2016-02-23

The WAter Cycle Multi-mission Observation Strategy – EvapoTranspiration (WACMOS-ET) project has compiled a forcing data set covering the period 2005–2007 that aims to maximize the exploitation of European Earth Observations data sets for evapotranspiration (ET) estimation. The data set was used to run four established ET algorithms: the Priestley–Taylor Jet Propulsion Laboratory model (PT-JPL), the Penman–Monteith algorithm from the MODerate resolution Imaging Spectroradiometer (MODIS) evaporation product (PM-MOD), the Surface Energy Balance System (SEBS) and the Global Land Evaporation Amsterdam Model (GLEAM). In addition, in situ meteorological data from 24 FLUXNET towers were used to force the models, with results from both forcing sets compared to tower-based flux observations. Model performance was assessed on several timescales using both sub-daily and daily forcings. The PT-JPL model and GLEAM provide the best performance for both satellite- and tower-based forcing as well as for the considered temporal resolutions. Simulations using the PM-MOD were mostly underestimated, while the SEBS performance was characterized by a systematic overestimation. In general, all four algorithms produce the best results in wet and moderately wet climate regimes. In dry regimes, the correlation and the absolute agreement with the reference tower ET observations were consistently lower. While ET derived with in situ forcing data agrees best with the tower measurements (R²  =  0.67), the agreement of the satellite-based ET estimates is only marginally lower (R²  =  0.58). Results also show similar model performance at daily and sub-daily (3-hourly) resolutions. Overall, our validation experiments against in situ measurements indicate that there is no single best-performing algorithm across all biome and forcing types. An extension of the evaluation to a larger selection of 85 towers (model inputs resampled to a

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.

Evapotranspiration from two peatland watersheds

Science.gov (United States)

Roger R. Bay

1968-01-01

Measurements of precipitation, runoff, and bog water table levels have provided data for the calculation of evapotranspiration from two forested peatland watersheds near Grand Rapids, Minnesota (ca. 47? 32'N, 93? 28'W). Continuous hydrologie records were collected on one experimental bog for 6 years (1961-1966) and on the other for the past 2 years (1965-1966...

Estimating actual evapotranspiration for forested sites: modifications to the Thornthwaite Model

Science.gov (United States)

Randall K. Kolka; Ann T. Wolf

1998-01-01

A previously coded version of the Thornthwaite water balance model was used to estimate annual actual evapotranspiration (AET) for 29 forested sites between 1900 and 1993 in the Upper Great Lakes area. Approximately 8 percent of the data sets calculated AET in error. Errors were detected in months when estimated AET was greater than potential evapotranspiration. Annual...

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.

Improving evapotranspiration estimates in Mediterranean drylands

DEFF Research Database (Denmark)

Morillas, Laura; Leuning, Ray; Villagarcia, Luis

2013-01-01

An adaptation of a simple model for evapotranspiration (E) estimations in drylands based on remotely sensed leaf area index and the Penman-Monteith equation (PML model) (Leuning et al., 2008) is presented. Three methods for improving the consideration of soil evaporation influence in total evapo-...

A field evaluation of soil moisture modelling with the Soil, Vegetation, and Snow (SVS) land surface model using evapotranspiration observations as forcing data

Science.gov (United States)

Maheu, Audrey; Anctil, François; Gaborit, Étienne; Fortin, Vincent; Nadeau, Daniel F.; Therrien, René

2018-03-01

To address certain limitations with their current operational model, Environment and Climate Change Canada recently developed the Soil, Vegetation, and Snow (SVS) land surface model and the representation of subsurface hydrological processes was targeted as an area for improvement. The objective of this study is to evaluate the ability of HydroSVS, the component of SVS responsible for the vertical redistribution of water, to simulate soil moisture under snow-free conditions when using flux-tower observations of evapotranspiration as forcing data. We assessed (1) model fidelity by comparing soil moisture modelled with HydroSVS to point-scale measurements of volumetric soil water content and (2) model complexity by comparing the performance of HydroSVS to that of HydroGeoSphere, a state-of-the-art integrated surface and subsurface hydrologic model. To do this, we performed one-dimensional soil column simulations at four sites of the AmeriFlux network. Results indicate that under Mediterranean and temperate climates, HydroSVS satisfactorily simulated soil moisture (Nash-Sutcliffe efficiency between 0.26 and 0.70; R2 ≥ 0.80), with a performance comparable to HydroGeoSphere (Nash-Sutcliffe efficiency ≥0.60; R2 ≥ 0.80). However, HydroSVS performed weakly under a semiarid climate while HydroGeoSphere performed relatively well. By decoupling the magnitude and sourcing of evapotranspiration, this study proposes a powerful diagnostic tool to evaluate the representation of subsurface hydrological processes in land surface models. Overall, this study highlights the potential of SVS for hydrological applications.

Spatial variability in sensitivity of reference crop ET to accuracy of climate data in the Texas High Plains

Science.gov (United States)

A detailed sensitivity analysis was conducted to determine the relative effects of measurement errors in climate data input parameters on the accuracy of calculated reference crop evapotranspiration (ET) using the ASCE-EWRI Standardized Reference ET Equation. Data for the period of 1995 to 2008, fro...

Comparison of two recent models for estimating actual evapotranspiration using only regularly recorded data

Science.gov (United States)

Ali, M. F.; Mawdsley, J. A.

1987-09-01

An advection-aridity model for estimating actual evapotranspiration ET is tested with over 700 days of lysimeter evapotranspiration and meteorological data from barley, turf and rye-grass from three sites in the U.K. The performance of the model is also compared with the API model . It is observed from the test that the advection-aridity model overestimates nonpotential ET and tends to underestimate potential ET, but when tested with potential and nonpotential data together, the tendencies appear to cancel each other. On a daily basis the performance level of this model is found to be of the same order as the API model: correlation coefficients were obtained between the model estimates and lysimeter data of 0.62 and 0.68 respectively. For periods greater than one day, generally the performance of the models are improved. Proposed by Mawdsley and Ali (1979)

Effect of drip irrigation on yield, evapotranspiration and water use efficiency of sweet basil (Ocimum basilicum L.

Directory of Open Access Journals (Sweden)

Pejić Borivoj

2017-01-01

Full Text Available The experiments showing the effect of drip irrigation on yield, evapotranspiration and water productivity of sweet basil (Ocimum basilicum L. were conducted at the experimental field of the Alternative Crops Department, Institute of Field and Vegetable Crops, Novi Sad. Irrigation was scheduled on the basis of the water balance method. Daily evapotranspiration (ETd was computed from the reference evapotranspiration (ETo and crop coefficient (kc in May, June, July and August of 0.5, 0.6, 1.1 and 1.0, respectively. ETo was calculated using Hargreaves equation. The irrigation depth was restricted to the soil depth of 0.3 m. In other words, irrigation started when readily available water in the soil layer of 0.3 m was completely depleted by plants. The irrigation rate was 30 mm (30 l m-2 while the amount of water added by irrigation during the season was 140 mm. Basil sensitivity to water stress was determined using a yield response factor (Ky. According to the results, the yield of fresh herb of basil under irrigation (32.015 t ha-1 was higher by 9% compared to non-irrigated, control variant (29.364 t ha-1. Worthy of note, basil essential oil yield was significantly affected by irrigation (35.329/28.766 kg ha-1. The content of essential oil was significantly higher in irrigated (6.45 g kg-1 than in non-irrigated variant (5.33 g kg-1 in the first harvest, while no significant difference between irrigated and non-irrigated variants was obtained in the second harvest (6.83 and 6.62 g kg-1 , respectively. Water used on evapotranspiration in irrigation conditions (ETm was 431 mm and 270 mm in non-irrigated, control variant (ETa. The values of irrigation water use efficiency (Iwue and evapotranspiration water use efficiency (ETwue were 1.89 kg m-3 and 1.65 kg m-3 respectively. Ky value (0.22 exhibits all essential characteristics of climate conditions of 2016 rainy year. These preliminary results could be used as a good platform for basil growers in the

Water use by terrestrial ecosystems: temporal variability in rainforest and agricultural contributions to evapotranspiration in Mato Grosso, Brazil

International Nuclear Information System (INIS)

Lathuillière, Michael J; Johnson, Mark S; Donner, Simon D

2012-01-01

The state of Mato Grosso, Brazil, has experienced rapid land use changes from the expansion of rain-fed agriculture (primarily soybean and pasture). This study presents changes to evapotranspiration contributions from terrestrial ecosystems in Mato Grosso over the 2000–9 period. Instead of focusing on land use change to infer hydrologic change, in this paper we assess hydrologic changes using remote sensing, meteorological and agricultural production data to determine the rainforest, crop and pasture components of total evapotranspiration. Humid tropical rainforest evapotranspiration represented half of the state’s total evapotranspiration in 2000 despite occupying only 40% of the total land area. Annual evapotranspiration fluxes from rainforest declined at a rate of 16.2 km 3 y −1 (R 2 = 0.82, p-value < 0.01) as a result of deforestation between 2000 and 2009, representing a 25% decline in rainforest evapotranspiration since 2000. By 2009, rainforest cover accounted for only 40% of total evapotranspiration. Over the same period, crop evapotranspiration doubled, but this increase was offset by a decline in pasture evapotranspiration. Pasture fluxes were at least five times larger than crop evapotranspiration fluxes in 2000–9, with increases spatially focused at the agricultural frontier. The results highlight the expanding appropriation of soil moisture stocks for use in Mato Grosso’s rain-fed agroecosystems. (letter)

Estimations of evapotranspiration in an age sequence of Eucalyptus plantations in subtropical China.

Directory of Open Access Journals (Sweden)

Wenfei Liu

Full Text Available Eucalyptus species are widely planted for reforestation in subtropical China. However, the effects of Eucalyptus plantations on the regional water use remain poorly understood. In an age sequence of 2-, 4- and 6-year-old Eucalyptus plantations, the tree water use and soil evaporation were examined by linking model estimations and field observations. Results showed that annual evapotranspiration of each age sequence Eucalyptus plantations was 876.7, 944.1 and 1000.7 mm, respectively, accounting for 49.81%, 53.64% and 56.86% of the annual rainfall. In addition, annual soil evaporations of 2-, 4- and 6-year-old were 318.6, 336.1, and 248.7 mm of the respective Eucalyptus plantations. Our results demonstrated that Eucalyptus plantations would potentially reduce water availability due to high evapotranspiration in subtropical regions. Sustainable management strategies should be implemented to reduce water consumption in Eucalyptus plantations in the context of future climate change scenarios such as drought and warming.

Evapotranspiração e coeficiente da cultura do mamoeiro Evapotranspiration and crop coefficient of papaya

Directory of Open Access Journals (Sweden)

Robson P. Posse

2008-12-01

Full Text Available O trabalho teve como objetivos determinar a evapotranspiração da cultura (ETc e o coeficiente da cultura (Kc para o mamoeiro (Carica papaya L.. O experimento foi realizado na área de convênio UENF/PESAGRO-RIO, no município de Campos dos Goytacazes - RJ, no período de 25-4-2006 a 20-8-2007, utilizando o mamoeiro cultivar Híbrido UENF/CALIMAN01. Para a determinação da ETc e do Kc, foi utilizado lisímetro de pesagem com área superficial de 6 m². A evapotranspiração de referência (ETo foi estimada pelo método de Penman-Monteith (FAO. A evapotranspiração máxima da cultura foi de 2,9 mm dia-1, aos 229 dias após o transplantio (DAT, sendo a evapotranspiração média da cultura, em todo o período, de 1,8 mm dia ¹. O valor do Kc do mamoeiro variou linearmente de 0,63 até 1,05, do transplantio até 206 DAT. Após esse período, a variação do Kc relacionou-se inversamente com o diâmetro de copa, reduzindo-se ao valor médio mínimo de 0,81, aos 300 DAT. Considerando todo o período em estudo, obteve-se Kc médio de 0,87.This study aimed to determine the crop evapotranspiration (ETc and the crop coefficient (Kc for of UENF/CALIMAN01 papaya hybrid (Carica papaya L.. The experiment was conducted in an area of UENF/PESAGRO-RIO, in Campos dos Goytacazes, RJ, Brazil, from 4-25-2006 to 8-20-2007. To determine the ETc and Kc, a weighing lysimeter (6 m² was used. The reference evapotranspiration (ETo was determined by the Penmam-Monteith (FAO method. The maximum crop evapotranspiration was of 2.9 mm day-1, 229 days after the transplant (DAT, and the medium crop evapotranspiration during the experiment was of 1.8 mm day-1. The value of crop coefficient (Kc varied linearly from 0.63 to 1.05, the transplant to 206 DAT. After this period, the variation of Kc presented inversely relation with the canopy diameter, being reduced to a value medium minimum of 0.81, to 300 DAT. Considering the whole period of study, it was obtained an average Kc

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

Directory of Open Access Journals (Sweden)

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.

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.

Comparison of different methods for estimation of potential evapotranspiration

International Nuclear Information System (INIS)

Nazeer, M.

2010-01-01

Evapotranspiration can be estimated with different available methods. The aim of this research study to compare and evaluate the originally measured potential evapotranspiration from Class A pan with the Hargreaves equation, the Penman equation, the Penman-Montheith equation, and the FAO56 Penman-Monteith equation. The evaporation rate from pan recorded greater than stated methods. For each evapotranspiration method, results were compared against mean monthly potential evapotranspiration (PET) from Pan data according to FAO (ET/sub o/=K/sub pan X E/sub pan)), from daily measured recorded data of the twenty-five years (1984-2008). On the basis of statistical analysis between the pan data and the FAO56- Penman-Monteith method are not considered to be very significant (=0.98) at 95% confidence and prediction intervals. All methods required accurate weather data for precise results, for the purpose of this study the past twenty five years data were analyzed and used including maximum and minimum air temperature, relative humidity, wind speed, sunshine duration and rainfall. Based on linear regression analysis results the FAO56 PMM ranked first (R/sup 2/=0.98) followed by Hergreaves method (R/sup 2/=0.96), Penman-Monteith method (R/sup 2/=0.94) and Penman method (=0.93). Obviously, using FAO56 Penman Monteith method with precise climatic variables for ET/sub o/ estimation is more reliable than the other alternative methods, Hergreaves is more simple and rely only on air temperatures data and can be used alternative of FAO56 Penman-Monteith method if other climatic data are missing or unreliable. (author)

Evaluation of empirical methods to estimate reference evapotranspiration in Uberaba, State of Minas Gerais, Brazil Avaliação de métodos empíricos na estimativa devapotranspiração de referência para Uberaba - MG

Directory of Open Access Journals (Sweden)

Giovani L. de Melo

2012-10-01

Full Text Available Evapotranspiration is the process of water loss of vegetated soil due to evaporation and transpiration, and it may be estimated by various empirical methods. This study had the objective to carry out the evaluation of the performance of the following methods: Blaney-Criddle, Jensen-Haise, Linacre, Solar Radiation, Hargreaves-Samani, Makkink, Thornthwaite, Camargo, Priestley-Taylor and Original Penman in the estimation of the potential evapotranspiration when compared to the Penman-Monteith standard method (FAO56 to the climatic conditions of Uberaba, state of Minas Gerais, Brazil. A set of 21 years monthly data (1990 to 2010 was used, working with the climatic elements: temperature, relative humidity, wind speed and insolation. The empirical methods to estimate reference evapotranspiration were compared with the standard method using linear regression, simple statistical analysis, Willmott agreement index (d and performance index (c. The methods Makkink and Camargo showed the best performance, with "c" values ​​of 0.75 and 0.66, respectively. The Hargreaves-Samani method presented a better linear relation with the standard method, with a correlation coefficient (r of 0.88.A evapotranspiração é o processo de perda de água do solo vegetado devido à evaporação e à transpiração, podendo ser estimada por vários métodos empíricos. Objetivou-se, com o presente trabalho, realizar a avaliação do desempenho dos métodos de Blaney-Criddle, Jensen-Haise, Linacre, Radiação Solar, Hargreaves-Samani, Makkink, Thornthwaite, Camargo, Priestley-Taylor e Penman Original na estimativa da evapotranspiração potencial em comparação com o método-padrão Penman-Monteith (FAO56, para as condições climáticas do município de Uberaba-MG. Utilizou-se um conjunto de dados mensais de 21 anos (1990 a 2010, trabalhando-se com os elementos climáticos temperatura, umidade relativa, velocidade do vento e insolação. Os métodos empíricos para a

Modeling seasonal water balance based on catchments' hedging strategy on evapotranspiration for climate seasonality

Science.gov (United States)

Wu, S.; Zhao, J.; Wang, H.

2017-12-01

This paper develops a seasonal water balance model based on the hypothesis that natural catchments utilize hedging strategy on evapotranspiration for climate seasonality. According to the monthly aridity index, one year is split into wet season and dry season. A seasonal water balance model is developed by analogy to a two-stage reservoir operation model, in which seasonal rainfall infiltration, evapotranspiration and saturation-excess runoff is corresponding to the inflow, release and surplus of the catchment system. Then the optimal hedging between wet season and dry season evapotranspiration is analytically derived with marginal benefit principle. Water budget data sets of 320 catchments in the United States covering the period from 1980 to 2010 are used to evaluate the performance of this model. The Nash-Sutcliffe Efficiency coefficient for evapotranspiration is higher than 0.5 in 84% of the study catchments; while the runoff is 87%. This paper validates catchments' hedging strategy on evapotranspiration for climate seasonality and shows its potential application for seasonal water balance, which is valuable for water resources planning and management.

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

Directory of Open Access Journals (Sweden)

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.

Variability of Precipitation and Evapotranspiration across an Andean Paramo

Science.gov (United States)

Jaimes, J. C.; Riveros-Iregui, D.; Avery, W. A.; Gaviria, S.; Peña-Quemba, C.; Herran, G.

2012-12-01

Paramos are alpine grasslands that occur mostly in the Andes Mountains of South America. Typically soils in the paramo have a volcanic origin, which leads to high permeability and high water yield and makes the paramo a reliable drinking water supply for many highland cities. Because hydrological measurements in these humid systems are rare, current understanding of the hydrologic behavior of paramos relies on modeling studies with little validation against ground observations. We present measurements of evapotranspiration (ET) and precipitation (P) across Chingaza Paramo, near Bogotá, Colombia. This paramo supplies water for ~80% of Bogotá's population (a total of 8 million people). Meteorological variables such us air temperature, relative humidity, wind speed, precipitation, and solar radiation were monitored using five weather stations located at various elevations from 3000m to 3600m. Our results show that ET varies from 500 to 700 mm y-1 as a function of elevation, whereas precipitation commonly exceeds ET, ranging between 1500 and 1800 mm y-1. These spatial differences between P and ET make water yield highly variable across this mountainous environment. Our results demonstrate that while paramos play an important role in the hydrologic cycle of tropical environments, understanding their hydrologic behavior requires characterization and monitoring of the pronounced spatial gradients of precipitation and evapotranspiration.

Evaluation of different methods of measuring evapotranspiration as a scheduling guide for drip-irrigated cotton

International Nuclear Information System (INIS)

Rawitz, E.; Marani, A.; Mahrer, Y.; Berkovich, D.

1983-01-01

Evapotranspiration in a drip-irrigated cotton field was estimated by the energy balance method, net radiation, standard evaporation pan, evaporation pan in the field at canopy height, and by the Penman equation, and the results were compared with the soil-water balance based on neutron meter and tensiometer data from seven observation sites. Evapotranspiration according to the soil-water balance was only about 85% of that determined by the energy balance method, and this is attributed to the fact that irrigation laterals were placed every second row, and the soil-water balance was determined in the irrigated rows. The crop also utilized moisture stored from winter rains in the unirrigated inter-row spaces, which was detected by the energy balance method. Actual evapotranspiration (ET) was 96% of potential ET (Penman), and the latter equalled 98% of net radiation energy. The actual ET equalled 90% of free water evaporation from the pan in the field at canopy height, and 88% of net radiation. The high-frequency drip regime maintained ET very close to potential ET, and under these conditions the field-installed evaporation pan, or the net radiometer, are good indicators of crop water use, with the latter being adaptable to computer-controlled irrigation. (author)

Effect of Climate Extremes, Seasonal Change, and Agronomic Practices on Measured Evapotranspiration and CO2 Exchange in Sacramento-San Joaquin River Delta Alfalfa Fields

Science.gov (United States)

Clay, J.; Kent, E. R.; Leinfelder-Miles, M.; Paw U, K. T.; Little, C.; Lambert, J. J.

2017-12-01

Evapotranspiration and CO2 exchange was measured in five alfalfa fields in the Sacramento-San Joaquin River Delta region from 2016 to 2017 using eddy covariance and surface renewal methods. Seasonal changes of evapotranspiration and CO2 fluxes were compared between 2016, a drought year, and 2017, a high rainfall year. Additionally, changes in evapotranspiration and CO2 flux were investigated across various agronomic considerations, such as irrigation methods (border-check flood and sub-surface), stand life, and herbicide programs. Components of the energy balance, including net radiation, latent heat, ground heat flux, and sensible heat, were evaluated considering correlations to wind speed measured by three sonic anemometers, irrigation frequency, and crop cutting cycle. Comparisons between two different types of radiometers were also carried out. Under drought conditions, we observed higher amounts of evapotranspiration in a field having a stand life of less than two years of age compared to older stands, and in a sub-surface irrigated field compared to flood irrigated fields.

A Comparison of ASCE and FAO56 Reference Evapotranspiration at Different Subdaily Timescales: a Numerical Study

Directory of Open Access Journals (Sweden)

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

Trends in pan evaporation and actual evapotranspiration across the conterminous U.S.: paradoxical or complementary?

Science.gov (United States)

Michael T. Hobbins; Jorge A. Ramirez; Thomas C. Brown

2004-01-01

Pan evaporation (ETpan) has decreased at 64% of pans in the conterminous U.S. over the past half-century. Comparing trends in ETpan and water budget-derived actual evapotranspiration (ET*a), we observe the so-called ‘‘Pan Evaporation Paradox,’’ which we confirm is no more than a...

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

Accuracy assessment of NOAA's daily reference evapotranspiration maps for the Texas High Plains

Science.gov (United States)

The National Oceanic and Atmospheric Administration (NOAA) provides daily reference ET for the continental U.S. using climatic data from North American Land Data Assimilation System (NLDAS). This data provides large scale spatial representation for reference ET, which is essential for regional scal...

The Pattern Across the Continental United States of Evapotranspiration Variability Associated with Water Availability

Science.gov (United States)

Koster, Randal D.; Salvucci, Guido D.; Rigden, Angela J.; Jung, Martin; Collatz, G. James; Schubert, Siegfried D.

2015-01-01

The spatial pattern across the continental United States of the interannual variance of warm season water-dependent evapotranspiration, a pattern of relevance to land-atmosphere feedback, cannot be measured directly. Alternative and indirect approaches to estimating the pattern, however, do exist, and given the uncertainty of each, we use several such approaches here. We first quantify the water dependent evapotranspiration variance pattern inherent in two derived evapotranspiration datasets available from the literature. We then search for the pattern in proxy geophysical variables (air temperature, stream flow, and NDVI) known to have strong ties to evapotranspiration. The variances inherent in all of the different (and mostly independent) data sources show some differences but are generally strongly consistent they all show a large variance signal down the center of the U.S., with lower variances toward the east and (for the most part) toward the west. The robustness of the pattern across the datasets suggests that it indeed represents the pattern operating in nature. Using Budykos hydroclimatic framework, we show that the pattern can largely be explained by the relative strength of water and energy controls on evapotranspiration across the continent.

Earth Observation-Based Operational Estimation of Soil Moisture and Evapotranspiration for Agricultural Crops in Support of Sustainable Water Management

Directory of Open Access Journals (Sweden)

George P. Petropoulos

2018-01-01

Full Text Available Global information on the spatio-temporal variation of parameters driving the Earth’s terrestrial water and energy cycles, such as evapotranspiration (ET rates and surface soil moisture (SSM, is of key significance. The water and energy cycles underpin global food and water security and need to be fully understood as the climate changes. In the last few decades, Earth Observation (EO technology has played an increasingly important role in determining both ET and SSM. This paper reviews the state of the art in the use specifically of operational EO of both ET and SSM estimates. We discuss the key technical and operational considerations to derive accurate estimates of those parameters from space. The review suggests significant progress has been made in the recent years in retrieving ET and SSM operationally; yet, further work is required to optimize parameter accuracy and to improve the operational capability of services developed using EO data. Emerging applications on which ET/SSM operational products may be included in the context specifically in relation to agriculture are also highlighted; the operational use of those operational products in such applications remains to be seen.

A note on India's water budget and evapotranspiration

Indian Academy of Sciences (India)

An examination of the budget components indicates that they imply an evapo- transpiration estimate ... India; water budget; evapotranspiration; water policy; water management. J. Earth Syst. Sci. 117 ... L'Environment (2004). California. 0.41.

Dynamics of MODIS evapotranspiration in South Africa

CSIR Research Space (South Africa)

Jovanovic, Nebojsa

2015-01-01

Full Text Available of plant transpiration (T, 53%) and soil evaporation (Soil E, 39%). Evapotranspiration (ET) showed a slight tendency to decrease over the period 2000–2012 in all climatic regions, except in the south of the country (winter rainfall areas), although annual...

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.

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.

Tracking diurnal changes of photosynthesis and evapotranspiration using fluorescence, gas exchange and hyperspectral remote sensing measurements

Science.gov (United States)

Wang, S.; Zhang, L.; Guanter, L.; Huang, C.

2017-12-01

Photosynthesis and evapotranspiration (ET) are the two most important activities of vegetation and make a great contribution to carbon, water and energy exchanges. Remote sensing provides opportunities for monitoring these processes across time and space. This study focuses on tracking diurnal changes of photosynthesis and evapotranspiration over soybean using multiple measurement techniques. Diurnal changes of both remote sensing-based indicators, including active and passive chlorophyll fluorescence and biophysical-related parameters, including photosynthesis rate (photo) and leaf stomatal conductance (cond), were observed. Results showed that both leaf-level steady-state fluorescence (Fs) and canopy-level solar-induced chlorophyll fluorescence were linearly correlated to photosynthetically active radiation (PAR) during the daytime. A double-peak diurnal change curve was observed for leaf-level photo and cond but not for Fs or SIF. Photo and cond showed a strong nonlinear (second-order) correlation, indicating that photosynthesis, which might be remotely sensed by SIF, has the opportunity to track short-term changes of ET. Results presented in this report will be helpful for better understanding the relationship between remote-sensing-based indices and vegetation's biophysical processes.

Remote sensing based crop type mapping and evapotranspiration estimates at the farm level in arid regions of the globe

Science.gov (United States)

Ozdogan, M.; Serrat-Capdevila, A.; Anderson, M. C.

2017-12-01

Despite increasing scarcity of freshwater resources, there is dearth of spatially explicit information on irrigation water consumption through evapotranspiration, particularly in semi-arid and arid geographies. Remote sensing, either alone or in combination with ground surveys, is increasingly being used for irrigation water management by quantifying evaporative losses at the farm level. Increased availability of observations, sophisticated algorithms, and access to cloud-based computing is also helping this effort. This presentation will focus on crop-specific evapotranspiration estimates at the farm level derived from remote sensing in a number of water-scarce regions of the world. The work is part of a larger effort to quantify irrigation water use and improve use efficiencies associated with several World Bank projects. Examples will be drawn from India, where groundwater based irrigation withdrawals are monitored with the help of crop type mapping and evapotranspiration estimates from remote sensing. Another example will be provided from a northern irrigation district in Mexico, where remote sensing is used for detailed water accounting at the farm level. These locations exemplify the success stories in irrigation water management with the help of remote sensing with the hope that spatially disaggregated information on evapotranspiration can be used as inputs for various water management decisions as well as for better water allocation strategies in many other water scarce regions.

Estimation of Potential Evapotranspiration for a Coastal Savannah ...

African Journals Online (AJOL)

Estimation of Potential Evapotranspiration for a Coastal Savannah Environment: ... model which is the recommended standard method for estimating PET. ... model (r = 0.82) and requires only air temperature measurements as in-puts.ac ...

Trends in soil moisture and real evapotranspiration in Douro River for the period 1980-2010

Science.gov (United States)

García-Valdecasas-Ojeda, Matilde; de Franciscis, Sebastiano; Raquel Gámiz-Fortis, Sonia; Castro-Díez, Yolanda; Jesús Esteban-Parra, María

2017-04-01

This study analyzes the evolution of different hydrological variables, such as soil moisture and real evapotranspiration, for the last 30 years, in the Douro Basin, the most extensive basin in the Iberian Peninsula. The different components of the real evaporation, connected to the soil moisture content, can be important when analyzing the intensity of droughts and heat waves, and particularly relevant for the study of the climate change impacts. The real evapotranspiration and soil moisture data are provided by simulations obtained using the Variable Infiltration Capacity (VIC) hydrological model. This model is a large-scale hydrologic model and allows estimates of different variables in the hydrological system of a basin. Land surface is modeled as a grid of large and uniform cells with sub-grid heterogeneity (e.g. land cover), while water influx is local, only depending from the interaction between grid cells and local atmosphere environment. Observational data of temperature and precipitation from Spain02 dataset are used as input variables for VIC model. The simulations have a spatial resolution of about 9 km, and the analysis is carried out on a seasonal time-scale. Additionally, we compare these results with those obtained from a dynamical downscaling driven by ERA-Interim data using the Weather Research and Forecasting (WRF) model, with the same spatial resolution. The results obtained from Spain02 data show a decrease in soil moisture at different parts of the basin during spring and summer, meanwhile soil moisture seems to be increased for autumn. No significant changes are found for real evapotranspiration. Keywords: real evapotranspiration, soil moisture, Douro Basin, trends, VIC, WRF. Acknowledgements: This work has been financed by the projects P11-RNM-7941 (Junta de Andalucía-Spain) and CGL2013-48539-R (MINECO-Spain, FEDER).

On the coupling between precipitation and potential evapotranspiration: contributions to decadal drought anomalies in the Southwest China

Science.gov (United States)

Shanlei Sun; Haishan Chen; Weimin Ju; Guojie Wang; Ge Sun; Jin Huang; Hedi Ma; Chujie Gao; Wenjian Hua; Guixia Yan

2016-01-01

Under the exacerbation of climate change, cli· mate extreme events. especially for drought, happened frequently and intensively across the globe with greater spatial differences. We used the Standardized Precipitation-Evapotranspiration Index computed from the routine meteorological observations at 269 sites in Southwest China (SWC) to study the drought characteristics...

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

Directory of Open Access Journals (Sweden)

M. Ghorbanian Kerdabadi

2017-02-01

Jey and Qahab district of Isfahan. Reference evapotranspiration and actual evapotranspiration of maize were measured by evaporation pan method and volumetric soil water balance method using micro lysimeters, respectively. In order to accommodate the growing field conditions, a ditch with a depth of 25 cm, length of 240 cm and width of 300 cm were dug and micro-lysimeters were placed it in three rows (three replications with a distance of 75 cm. After preparing the treatments, four seed Maize with variety of NS540 were planted at a depth of 3-5 cm on 5 August. To reduce the oasis effect on evapotranspiration, the same corn was planted in the vicinity of the project area with 500 square meters.. Results and Discussion: The results showed that using fertilizer caused increasing of crop evapotranspiration and crop coefficient of maize. Maximum of the ten-day average evapotranspiration of maize in the silty clay loam soil with two percent fertilizer was obtained 8.76 (mm/ day on the fifth decade of growth and this value was found 45.5 percent higher than the lowest mean evapotranspiration value of the ten-day. Comparison evapotranspiration of maize in different soil fertility treatments showed that the greatest impact on increasing of maize evapotranspiration in SLF2, SCLF2, SLF2 treatments were obtained that was equal %19.1, %14.3 and %10.6, respectively (table 4. Most of the effects of fertility the crop coefficient of maize at the middle stage of growth was influenced more than other stages by the different treatments of soil fertility. Adding one and two percent of the fertilizer to treatment SCLF0 increased maize crop coefficient about 3.5 and 9.7 percent at development stage, respectively, That measured %6 and 11% for LF1 and LF2 treatments, respectively, and about 1.6 and 5.6% for SLF2 SLF1 treatment, respectively (Table 6. Comparison of maize middle crop coefficient in SLF2 and SLF1 for different soil fertility treatments showed that effect of increasing soil

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.

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...

[Variation characteristics and influencing factors of actual evapotranspiration under various vegetation types: A case study in the Huaihe River Basin, China.

Science.gov (United States)

Wu, Rong Jun; Xing, Xiao Yong

2016-06-01

The actual evapotranspiration was modelled utilizing the boreal ecosystem productivity simulator (BEPS) in Huaihe River Basin from 2001 to 2012. In the meantime, the quantitative analyses of the spatial-temporal variations of actual evapotranspiration characteristics and its influencing factors under different vegetation types were conducted. The results showed that annual evapotranspiration gradually decreased from southeast to northwest, tended to increase annually, and the monthly change for the average annual evapotranspiration was double-peak curve. The differences of evapotranspiration among vegetation types showed that the farmland was the largest contributor for the evapotranspiration of Huaihe Basin. The annual actual evapotranspiration of the mixed forest per unit area was the largest, and that of the bare ground per unit area was the smallest. The changed average annual evapotranspiration per unit area for various vegetation types indicated an increased tendency other than the bare ground, with a most significant increase trend for the evergreen broadleaf forest. The thermodynamic factors (such as average temperature) were the dominant factors affecting the actual evapotranspiration in the Huaihe Basin, followed by radiation and moisture factors.

The complementary relationship in estimation of regional evapotranspiration: An enhanced Advection-Aridity model

Science.gov (United States)

Michael T. Hobbins; Jorge A. Ramirez; Thomas C. Brown

2001-01-01

Long-term monthly evapotranspiration estimates from Brutsaert and Stricker’s Advection-Aridity model were compared with independent estimates of evapotranspiration derived from long-term water balances for 139 undisturbed basins across the conterminous United States. On an average annual basis for the period 1962-1988 the original model, which uses a Penman wind...

Operational Actual Wetland Evapotranspiration Estimation for South Florida Using MODIS Imagery

Directory of Open Access Journals (Sweden)

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.

Estimation of Evapotranspiration from Fields with and without Cover Crops Using Remote Sensing and in situ Methods

Directory of Open Access Journals (Sweden)

Christopher Hay

2012-11-01

Full Text Available Estimation of actual evapotranspiration (ETa based on remotely sensed imagery is very valuable in agricultural regions where ETa rates can vary greatly from field to field. This research utilizes the image processing model METRIC (Mapping Evapotranspiration at high Resolution with Internalized Calibration to estimate late season, post-harvest ETa rates from fields with a cover crop planted after a cash crop (in this case, a rye/radish/pea mixture planted after spring wheat. Remotely sensed EToF (unit-less fraction of grass-based reference ET, ETo maps were generated using Erdas Imagine software for a 260 km2 area in northeastern South Dakota, USA. Meteorological information was obtained from a Bowen-Ratio Energy Balance System (BREBS located within the image. Nine image dates were used for the growing season, from May through October. Five of those nine were captured during the cover crop season. METRIC was found to successfully differentiate between fields with and without cover crops. In a blind comparison, METRIC compared favorably with the estimated ETa rates found using the BREBS (ETλE, with a difference in total estimated ETa for the cover crop season of 7%.

Hydraulic and hydrological aspects of an evapotranspiration-constructed wetland combined system for household greywater treatment.

Science.gov (United States)

Filho, Fernando Jorge C Magalhães; Sobrinho, Teodorico Alves; Steffen, Jorge L; Arias, Carlos A; Paulo, Paula L

2018-05-12

Constructed wetlands systems demand preliminary and primary treatment to remove solids present in greywater (GW) to avoid or reduce clogging processes. The current paper aims to assess hydraulic and hydrological behavior in an improved constructed wetland system, which has a built-in anaerobic digestion chamber (AnC), GW is distributed to the evapotranspiration and treatment tank (CEvaT), combined with a subsurface horizontal flow constructed wetland (SSHF-CW). The results show that both the plants present in the units and the AnC improve hydraulic and volumetric efficiency, decrease short-circuiting and improve mixing conditions in the system. Moreover, the hydraulic conductivity measured on-site indicates that the presence of plants in the system and the flow distribution pattern provided by the AnC might reduce clogging in the SSHF-CW. It is observed that rainfall enables salt elimination, thus increasing evapotranspiration (ET), which promotes effluent reduction and enables the system to have zero discharge when reuse is unfeasible.

Sensitivity Modeling and Evaluation of Evapotranspiration Effects on Flow Discharge of River Owena in Nigeria

Directory of Open Access Journals (Sweden)

P.O Idogho

2015-07-01

Full Text Available Analysis of discharges, precipitation and temperature and some other meteorological-hydrological variables from 1996-2011 at the section of Owena River Basin. The evaluation, correlations, and the relationship between precipitation and discharge time series indicate a strong relationship. Minimum discharge values of 0.8 m 3 /s and 1.2 m 3 /s were observed in January and December and these values correspond to rainfall depth of 1.4 mm and 8.2 mm respectively. The average annual rainfall, river discharge were computed as 1,306.7 mm, 1,165 m 3 /s and mean temperature and evaporation of 31.1 oC and 4.6 mm. Evapotranspiration computation using pan evaporation model overestimated the evapotranspiration values by 0.5 mm and 0.21 mm over IHACRES and CROPWAT model for the total period of 15-year. Integration of the simulation outputs would be veritable in creating realistic-robust water management system for domestic and agricultural applications.

Observational evidence of the complementary relationship in regional evaporation lends strong support for Bouchet's hypothesis

Science.gov (United States)

Jorge A. Ramirez; Michael T. Hobbins; Thomas C. Brown

2005-01-01

Using independent observations of actual and potential evapotranspiration at a wide range of spatial scales, we provide direct observational evidence of the complementary relationship in regional evapotranspiration hypothesized by Bouchet in 1963. Bouchet proposed that, for large homogeneous surfaces with minimal advection of heat and moisture, potential and actual...

Persistence of evapotranspiration impacts from mountain pine beetle outbreaks in lodgepole pine forests, south-central Rocky Mountains, USA

Science.gov (United States)

Vanderhoof, Melanie; Williams, Christopher

2014-05-01

The current extent and high severity (percent tree mortality) of mountain pine beetle outbreaks across western North America have been attributed to regional climate change, specifically warmer summer and winter temperatures and drier summers. These outbreaks are widespread and have potentially persistent impacts on forest evapotranspiration. The few data-driven studies have largely been restricted by the temporal availability of remote sensing products. This study utilized multiple mountain pine beetle outbreak location datasets, both current and historical, within lodgepole pine stands in the south-central Rocky Mountains. The full seasonal evapotranspiration impact of outbreak events for decades after outbreak (0 to 60 years) and the role of outbreak severity in determining that impact were quantified. We found a 30% reduction in evapotranspiration peaking at 14-20 years post-outbreak during the spring snowmelt period, when water was not limited, but a minimal reduction in evapotranspiration during the remainder of the growing season (June - August). We also found a significant increase in evapotranspiration, relative to non-attacked stands, in intermediate aged stands (20-40 years post-disturbance) corresponding with a peak in LAI and therefore transpiration. During the snow-cover months evapotranspiration initially increased with needle fall and snag fall and corresponding increases in albedo and shortwave transmission to the surface. We found that changes in evapotranspiration during all seasons dissipated by 60 years post-attack. MODIS evapotranspiration values responded most strongly to mountain pine beetle driven changes in net radiation or available energy, and vegetation cover (e.g. LAI, fPAR and EVI). It also appears that the post-attack response of evapotranspiration may be sensitive to precipitation patterns and thus the consequences of a disturbance event may depend on the directionality of climate change conditions.

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.

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

The need of the change of the conceptualisation of hydrologic processes under extreme conditions – taking reference evapotranspiration as an example

Directory of Open Access Journals (Sweden)

S. Liu

2015-06-01

Full Text Available What a hydrological model displays is the relationships between the output and input in daily, monthly, yearly and other temporal scales. In the case of climate change or other environment changes, the input of the hydrological model may show a gradual or abrupt change. There have been numerous documented studies to explore the response of output of the hydrological models to the change of the input with scenario simulation. Most of the studies assumed that the conceptualisation of hydrologic processes will remain, which may be true for the gradual change of the input. However, under extreme conditions the conceptualisation of hydrologic processes may be completely changed. Taking an example of the Allen's formula to calculate crop reference evapotranspiration (ET0 as a simple hydrological model, we analyze the alternation of the extreme in ET0 from 1955 to 2012 at the Chongling Experimental Station located in Hebei Province, China. The relationships between ET0 and the meteorological factors for the average values, minimum (maximum values at daily, monthly and annual scales are revealed. It is found the extreme of the output can follow the extreme of the input better when their relationship is more linear. For non-liner relationship, the extreme of the input cannot at all be reflected from the extreme of the output. Relatively, extreme event at daily scale is harder to be shown than that at monthly scale. The result implicates that a routine model may not be able to catch the response to extreme events and it is even more so as we extrapolate models to higher temperature/CO2 conditions in the future. Some possible choices for the improvements are suggested for predicting hydrological extremes.

[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.

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

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 ...

Estimating Daily Evapotranspiration Based on A Model of Evapotranspiration Fraction (EF) for Mixed Pixels

Science.gov (United States)

Xin, X.; Li, F.; Peng, Z.; Qinhuo, L.

2017-12-01

Land surface heterogeneities significantly affect the reliability and accuracy of remotely sensed evapotranspiration (ET), and it gets worse for lower resolution data. At the same time, temporal scale extrapolation of the instantaneous latent heat flux (LE) at satellite overpass time to daily ET are crucial for applications of such remote sensing product. The purpose of this paper is to propose a simple but efficient model for estimating daytime evapotranspiration considering heterogeneity of mixed pixels. In order to do so, an equation to calculate evapotranspiration fraction (EF) of mixed pixels was derived based on two key assumptions. Assumption 1: the available energy (AE) of each sub-pixel equals approximately to that of any other sub-pixels in the same mixed pixel within acceptable margin of bias, and as same as the AE of the mixed pixel. It's only for a simpification of the equation, and its uncertainties and resulted errors in estimated ET are very small. Assumption 2: EF of each sub-pixel equals to the EF of the nearest pure pixel(s) of same land cover type. This equation is supposed to be capable of correcting the spatial scale error of the mixed pixels EF and can be used to calculated daily ET with daily AE data.The model was applied to an artificial oasis in the midstream of Heihe River. HJ-1B satellite data were used to estimate the lumped fluxes at the scale of 300 m after resampling the 30-m resolution datasets to 300 m resolution, which was used to carry on the key step of the model. The results before and after correction were compare to each other and validated using site data of eddy-correlation systems. Results indicated that the new model is capable of improving accuracy of daily ET estimation relative to the lumped method. Validations at 12 sites of eddy-correlation systems for 9 days of HJ-1B overpass showed that the R² increased to 0.82 from 0.62; the RMSE decreased to 1.60 MJ/m² from 2.47MJ/m²; the MBE decreased from 1.92 MJ/m² to 1

A comparison of six potential evapotranspiration methods for regional use in the Southeastern United States

Science.gov (United States)

Jianbiao Lu; Ge Sun; Steven G. McNulty; Devendra Amatya

2005-01-01

Potential evapotranspiration (PET) is an important index of hydrologic budgets at different spatial scales and is a critical variable for understanding regional biological processes. It is often an important variable in estimating actual evapotranspiration (AET) in rainfall-runoff and ecosystem modeling. However, PET is defined in different ways in the literature and...

Groundwater-supported evapotranspiration within glaciated watersheds under conditions of climate change

Science.gov (United States)

Cohen, D.; Person, M.; Daannen, R.; Locke, S.; Dahlstrom, D.; Zabielski, V.; Winter, T.C.; Rosenberry, D.O.; Wright, H.; Ito, E.; Nieber, J.L.; Gutowski, W.J.

2006-01-01

This paper analyzes the effects of geology and geomorphology on surface-water/-groundwater interactions, evapotranspiration, and recharge under conditions of long-term climatic change. Our analysis uses hydrologic data from the glaciated Crow Wing watershed in central Minnesota, USA, combined with a hydrologic model of transient coupled unsaturated/saturated flow (HYDRAT2D). Analysis of historical water-table (1970-1993) and lake-level (1924-2002) records indicates that larger amplitude and longer period fluctuations occur within the upland portions of watersheds due to the response of the aquifer system to relatively short-term climatic fluctuations. Under drought conditions, lake and water-table levels fell by as much as 2-4 m in the uplands but by 1 m in the lowlands. The same pattern can be seen on millennial time scales. Analysis of Holocene lake-core records indicates that Moody Lake, located near the outlet of the Crow Wing watershed, fell by as much as 4 m between about 4400 and 7000 yr BP. During the same time, water levels in Lake Mina, located near the upland watershed divide, fell by about 15 m. Reconstructed Holocene climate as represented by HYDRAT2D gives somewhat larger drops (6 and 24 m for Moody Lake and Lake Mina, respectively). The discrepancy is probably due to the effect of three-dimensional flow. A sensitivity analysis was also carried out to study how aquifer hydraulic conductivity and land-surface topography can influence water-table fluctuations, wetlands formation, and evapotranspiration. The models were run by recycling a wet year (1985, 87 cm annual precipitation) over a 10-year period followed by 20 years of drier and warmer climate (1976, 38 cm precipitation). Model results indicated that groundwater-supported evapotranspiration accounted for as much as 12% (10 cm) of evapotranspiration. The aquifers of highest hydraulic conductivity had the least amount of groundwater-supported evapotranspiration owing to a deep water table. Recharge

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.

Influence of soil moisture on the modelling of evapotranspiration in sparse vegetation

International Nuclear Information System (INIS)

Villagarcia, L.; Were, A.; Morillas, L.; Garcia, M.; Domingo, F.; Puigdefabregas, J.

2009-01-01

This work analyses the relevance of soil water content (θ) on the estimation of actual evapotranspiration (λE) in sparse vegetated areas. This importance is evaluated through the effect of the θ heterogeneity, both vertical and horizontal (differentiating between bare soil (bs) and soil under vegetation (s)), on λE estimates. A clumped evapotranspiration model (CM) that considers vegetation (p), bs and s as sources of evaporation, was used. This model estimates λE of the whole vegetated area, as well as the contribution of each source. (Author) 11 refs.

Comparative study of methods for potential and actual evapotranspiration determination

International Nuclear Information System (INIS)

Kolev, B.

2004-01-01

Two types of methods for potential and actual evapotranspiration determining were compared. The first type includes neutron gauge, tensiometers, gypsum blocks and lysimeters. The actual and potential evapotranspiration were calculated by water balance equation. The second type of methods used a simulation model for all calculation. The aim of this study was not only to compare and estimate the methods using. It was mainly pointed on calculations of water use efficiency and transpiration coefficient in potential production situation. This makes possible to choose the best way for water consumption optimization for a given crop. The final results find with the best of the methods could be used for applying the principles of sustainable agriculture in random region of Bulgarian territory. (author)

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

Hydrological model uncertainty due to spatial evapotranspiration estimation methods

Science.gov (United States)

Yu, Xuan; Lamačová, Anna; Duffy, Christopher; Krám, Pavel; Hruška, Jakub

2016-05-01

Evapotranspiration (ET) continues to be a difficult process to estimate in seasonal and long-term water balances in catchment models. Approaches to estimate ET typically use vegetation parameters (e.g., leaf area index [LAI], interception capacity) obtained from field observation, remote sensing data, national or global land cover products, and/or simulated by ecosystem models. In this study we attempt to quantify the uncertainty that spatial evapotranspiration estimation introduces into hydrological simulations when the age of the forest is not precisely known. The Penn State Integrated Hydrologic Model (PIHM) was implemented for the Lysina headwater catchment, located 50°03‧N, 12°40‧E in the western part of the Czech Republic. The spatial forest patterns were digitized from forest age maps made available by the Czech Forest Administration. Two ET methods were implemented in the catchment model: the Biome-BGC forest growth sub-model (1-way coupled to PIHM) and with the fixed-seasonal LAI method. From these two approaches simulation scenarios were developed. We combined the estimated spatial forest age maps and two ET estimation methods to drive PIHM. A set of spatial hydrologic regime and streamflow regime indices were calculated from the modeling results for each method. Intercomparison of the hydrological responses to the spatial vegetation patterns suggested considerable variation in soil moisture and recharge and a small uncertainty in the groundwater table elevation and streamflow. The hydrologic modeling with ET estimated by Biome-BGC generated less uncertainty due to the plant physiology-based method. The implication of this research is that overall hydrologic variability induced by uncertain management practices was reduced by implementing vegetation models in the catchment models.

Evapotranspiration and microclimate at a low-level radioactive-waste disposal site in northwestern Illinois

Science.gov (United States)

Healy, R.W.; DeVries, M.P.; Sturrock, Alex M.

1989-01-01

From July 1982 through June 1984, a study was made of the evapotranspiration and microclimate at a low-level radioactive-waste disposal site near Sheffield, Bureau County, Illinois. Vegetation at the site consists of mixed pasture grasses, primarily awnless brome (Bromus inermis) and red clover (Trifoleum pratense). Three methods were used to estimate evapotranspiration: (1) an energy budget with the Bowen ratio, (2) an aerodynamic profile, and (3) a soil-based water budget. For the aerodynamic-profile method, sensible-heat flux was estimated by a profile equation and evapotranspiration was then calculated as the residual in the energy-balance equation. Estimates by the energy-budget and aerodynamic-profile methods were computed from hourly data and then summed by days and months. Yearly estimates (for March through November) by these methods were in close agreement: 648 and 626 millimeters, respectively. Daily estimates reach a maximum of about 6 millimeters. The water-budget method produced only monthly estimates based on weekly or biweekly soil-moisture content measurements. The yearly evapotranspiration estimated by this method (which actually included only the months of April through October) was 655 millimeters. The March-through-November average for the three methods of 657 millimeters was equivalent to 70 percent of total precipitation. Continuous measurements were made of incoming and reflected shortwave radiation, incoming and emitted longwave radiation, net radiation, soil-heat flux, soil temperature, horizontal windspeed, and wet- and dry-bulb air temperature. Windspeed and air temperature were measured at heights of 0.5 and 2.0 meters (and also at 1.0 meter after September 1983). Soilmoisture content of the soil zone was measured with a gamma-attenuation gage. Annual precipitation (938 millimeters) and average temperature (10.8 degrees Celsius) at the Sheffield site were virtually identical to long-term averages from nearby National Weather Service

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 ...

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 ...

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

Science.gov (United States)

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

Estimação da evapotranspiração de referência no estado do Rio de Janeiro usando redes neurais artificiais Reference evapotranspiration estimate in Rio de Janeiro state using artificial neural networks

Directory of Open Access Journals (Sweden)

Sidney S. Zanetti

2008-04-01

Full Text Available Propor uma rede neural artificial (RNA para estimar a evapotranspiração de referência (ETo em função das coordenadas de posição geográfica e da temperatura do ar no Estado do Rio de Janeiro, motivou a realização do presente estudo. Os dados utilizados no treinamento da rede foram obtidos de 17 séries históricas de elementos climáticos localizadas nesse Estado. A ETo diária calculada pelo método de Penman-Monteith (FAO-56 foi utilizada como referência para treinar as redes. As RNAs, do tipo perceptron de múltiplas camadas, foram treinadas para estimar a ETo em função da latitude, longitude, altitude, temperatura média do ar, amplitude térmica diária e dia do ano. Após o treinamento com várias configurações de rede, selecionou-se a que apresentou o melhor desempenho, a qual é composta de apenas uma camada intermediária (com vinte neurônios e função de ativação do tipo sigmóide logística e uma camada de saída (com um neurônio e função de ativação linear. Pelos resultados obtidos conclui-se que, levando-se em consideração apenas as coordenadas de posição geográfica e a temperatura do ar, pode-se estimar a ETo (valores diários em 17 localidades do Estado do Rio de Janeiro usando uma RNA.This work was performed with the aim of proposing an artificial neural network (ANN to estimate the reference evapotranspiration (ETo as a function of geographic position coordinates and air temperature in the State of Rio de Janeiro. Data used for the network training were collected from 17 historical time series of climatic elements located in the State of Rio de Janeiro. The daily ETo calculated by Penman-Monteith (FAO-56 method was used as a reference for network training. ANNs of multilayer perceptron type were trained to estimate ETo as a function of latitude, longitude, altitude, mean air temperature, thermal daily amplitude and day of the year. After training with different network configurations, the one showing

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.

Evapotranspiration modelling of horticultural crops grown with soilless culture [Lycopersicon esculentum Mill.; Gerbera jamesonii Bolus ex Adlam

International Nuclear Information System (INIS)

Incrocci, L.; Carmassi, G.; Malorgio, F.; Pardossi, A.; Tognoni, F.

2005-01-01

This work aims at validating the evapotranspiration model developed by Baille (1994) on tomato and gerbera grown with different concentration of NaCl. Relevant to tomato, the original Baille model was adapted on daily scale and a Boltzman equation for estimating the LAI as a function of thermal day degrees was used. The model was calibrated on data collected in Spring 2004 from a soilless closed-loop tomato culture and validated on datasets collected in 2001 and 2002. Hourly data collected in Spring and Autumn 2005 from a soilless closed-loop gerbera culture grown with different irrigation water quality (0 and 10 meq lE-1 NaCl) were used. Evapotranspiration in gerbera was influenced by different water quality and by radiation levels, while in tomato those factors were negligible. In both crops a good correspondence between estimated and measured data was observed. The developed models will be implemented in a Decision Support System in order to help growers to manage the soilless closed-loop cultivation [it

Comparison of the evapotranspiration and its components before and after thinning in Japanese cedar and Japanese cypress forest

Science.gov (United States)

Tateishi, Makiko; Xiang, Yang; Matsuda, Hiroki; Saito, Takami; Sun, Haotian; Otsuki, Kyoichi; Kasahara, Tamao; Onda, Yuichi

2014-05-01

Water source area of Japan is often covered by forest, and 40 % of forest cover is coniferous plantation. Thinning has become a major tool in the management of plantation in recent years, but its effects on water cycle and its components are yet to be evaluated well. In this study, we investigated the changes in evapotranspiration and its components, including stand transpiration and canopy interception loss, after thinning in 50 years old Japanese cedar and Japanese cypress plantation at Yayama experimental catchment in Fukuoka, Japan. We established study plot in each Japanese cedar and Japanese cypress stand. Sap flow measurement was conducted for evaluating stand transpiration in each plot. Through fall and stem flow were also monitored to estimate canopy interception loss. The experiments were conducted over two years. During the measurements, 50 % of trees were thinned randomly in entire catchment, which has an area of 2.98 ha. Stem density was changed from 3945 to 1977 trees per ha after thinning. The reduction of daily stand transpiration in the studied Japanese cedar and cypress stands after thinning were 31.6 % and 48.2 % under the same condition of microclimate, respectively. These values were comparable to the changes in total sapwood area, 34.2 % and 44.5 %, and sap flow density did not change after thinning. It implies that sapwood area is a primary determinant of stand transpiration. Canopy interception ratios were 27 % and 26 % for Japanese cedar and cypress before thinning, and the ratios decreased to 24 % and 21 % after thinning, respectively. Thus, we obtained the changes in annual evapotranspiration and its components at catchment scale by using observation and models. The changes in partitioning of evapotranspiration is also discussed. The evapotranspiration before and after thinning were also compared to water balance data in this study site.

Evaluating Evapotranspiration of a crop mosaic using microwave scintillometry

Science.gov (United States)

Cohard, J. M.; Barral, H.; Coulaud, C.; Mercier, B.; Cappelaere, B.; Demarty, J.; Arpin-Pont, F.; Bradford, J.

2017-12-01

Evapotranspiration (ET) remains particularly difficult to quantify, especially on complex and heterogeneous landscapes. Since the 1990s, scintillometry has been recognized as an accurate method to estimate turbulent fluxes at km² scales compatible with a satellite pixel or a hydrological model mesh. If optic scintillometry is today considered to be an accomplished technique to measure spatially integrated sensible heat fluxes and to indirectly derive ET through the energy budget equation, very few results have been published using microwave (MW) scintillometry to derive ET more directly at km² scales for lack of reliable instruments. The recent development of new sensors operating in the microwave (MW) range and the formalization of new algorithms for the treatment of turbulent correlations revive dreams of reliable and continuous measurements of the evapotranspiration at the landscape scale. This study presents a long term evapotranspiration series measured over a crop mosaic with the combination of two scintillometers (Two-wavelength method) operating, one in the near infra-red (BLS2000, Scintec) and the other in radiofrequencies (94GHz) developed in collaboration with the Rutherford Appleton Laboratory (UK). These instruments have been installed in the Critical Zone observatory Oracle, located east of Paris in the Seine Catchment, and have run continuously since May 2016. This first ET series shows the robustness of both the MW scintillometer and the two wavelength method in this context. Scintillation ET will be presented and compared with Eddy Covariance measurements carried out on different landcover types within the scintillometer footprint, with regard to the energy balance closure.

Projected Changes in Evapotranspiration Rates over Northeast Brazil

Science.gov (United States)

Costa, Alexandre; Guimarães, Sullyandro; Vasconcelos, Francisco, Jr.; Sales, Domingo; da Silva, Emerson

2015-04-01

Climate simulations were performed using a regional model (Regional Atmospheric Modeling System, RAMS 6.0) driven by data from one of the CMIP5 models (Hadley Centre Global Environmental Model, version 2 - Earth System, HadGEM2-ES) over two CORDEX domains (South America and Central America) for the heavy-emission scenario (RCP8.5). Potential evapotranspiraion data from the RCM and from the CMIP5 global models were analyzed over Northeast Brazil, a semiarid region with a short rainy season (usually February to May in its northern portion due to the seasonal shift of the Intertropical Convergence Zone) and over which droughts are frequent. Significant changes in the potential evapotranspiration were found, with most models showing a increasing trend along the 21st century, which are expected to alter the surface water budget, increasing the current water deficit (precipitation is currently much smaller than potential evapotranspiration). Based on the projections from the majority of the models, we expect important impacts over local agriculture and water resources over Northeast Brazil.

Remote sensing estimation of evapotranspiration for SWAT Model Calibration

Science.gov (United States)

Hydrological models are used to assess many water resource problems from water quantity to water quality issues. The accurate assessment of the water budget, primarily the influence of precipitation and evapotranspiration (ET), is a critical first-step evaluation, which is often overlooked in hydro...

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...

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: DA - Hydrology ; Limnology OBOR OECD: Hydrology Impact factor: 2.533, year: 2016

High-Elevation Evapotranspiration Estimates During Drought: Using Streamflow and NASA Airborne Snow Observatory SWE Observations to Close the Upper Tuolumne River Basin Water Balance

Science.gov (United States)

Henn, Brian; Painter, Thomas H.; Bormann, Kat J.; McGurk, Bruce; Flint, Alan L.; Flint, Lorraine E.; White, Vince; Lundquist, Jessica D.

2018-02-01

Hydrologic variables such as evapotranspiration (ET) and soil water storage are difficult to observe across spatial scales in complex terrain. Streamflow and lidar-derived snow observations provide information about distributed hydrologic processes such as snowmelt, infiltration, and storage. We use a distributed streamflow data set across eight basins in the upper Tuolumne River region of Yosemite National Park in the Sierra Nevada mountain range, and the NASA Airborne Snow Observatory (ASO) lidar-derived snow data set over 3 years (2013-2015) during a prolonged drought in California, to estimate basin-scale water balance components. We compare snowmelt and cumulative precipitation over periods from the ASO flight to the end of the water year against cumulative streamflow observations. The basin water balance residual term (snow melt plus precipitation minus streamflow) is calculated for each basin and year. Using soil moisture observations and hydrologic model simulations, we show that the residual term represents short-term changes in basin water storage over the snowmelt season, but that over the period from peak snow water equivalent (SWE) to the end of summer, it represents cumulative basin-mean ET. Warm-season ET estimated from this approach is 168 (85-252 at 95% confidence), 162 (0-326) and 191 (48-334) mm averaged across the basins in 2013, 2014, and 2015, respectively. These values are lower than previous full-year and point ET estimates in the Sierra Nevada, potentially reflecting reduced ET during drought, the effects of spatial variability, and the part-year time period. Using streamflow and ASO snow observations, we quantify spatially-distributed hydrologic processes otherwise difficult to observe.

Observability of satellite launcher navigation with INS, GPS, attitude sensors and reference trajectory

Science.gov (United States)

Beaudoin, Yanick; Desbiens, André; Gagnon, Eric; Landry, René

2018-01-01

The navigation system of a satellite launcher is of paramount importance. In order to correct the trajectory of the launcher, the position, velocity and attitude must be known with the best possible precision. In this paper, the observability of four navigation solutions is investigated. The first one is the INS/GPS couple. Then, attitude reference sensors, such as magnetometers, are added to the INS/GPS solution. The authors have already demonstrated that the reference trajectory could be used to improve the navigation performance. This approach is added to the two previously mentioned navigation systems. For each navigation solution, the observability is analyzed with different sensor error models. First, sensor biases are neglected. Then, sensor biases are modelled as random walks and as first order Markov processes. The observability is tested with the rank and condition number of the observability matrix, the time evolution of the covariance matrix and sensitivity to measurement outlier tests. The covariance matrix is exploited to evaluate the correlation between states in order to detect structural unobservability problems. Finally, when an unobservable subspace is detected, the result is verified with theoretical analysis of the navigation equations. The results show that evaluating only the observability of a model does not guarantee the ability of the aiding sensors to correct the INS estimates within the mission time. The analysis of the covariance matrix time evolution could be a powerful tool to detect this situation, however in some cases, the problem is only revealed with a sensitivity to measurement outlier test. None of the tested solutions provide GPS position bias observability. For the considered mission, the modelling of the sensor biases as random walks or Markov processes gives equivalent results. Relying on the reference trajectory can improve the precision of the roll estimates. But, in the context of a satellite launcher, the roll

Coupling Evapotranspiration and Watershed Storage to Assess the Impact of Forest Disturbance on Low Flows

Science.gov (United States)

Brena Naranjo, J.; Stahl, K.; Weiler, M.

2009-05-01

Low flows are important for water-supply planning and design, and maintenance of quantity and quality of water for irrigation, recreation, and fish and wildlife conservation. There have been concerns recently that climate warming and land cover changes due to an unprecedented pine beetle epidemic in British Columbia, Canada, may cause a deterioration of water quantity during low flow periods and at certain times may become a hazard to ecosystem and to water management schemes. A study to characterize the sensitivity of the low flow regimes was performed for several mainly forested catchments located within the Fraser River basin. Here, summer low flows are maintained through the release of water from groundwater and riparian storage, lakes and wetlands, but are reduced by high evapotranspiration rates in the catchments. Since evapotranspiration in British Columbia accounts around 40% of the precipitation, the first part of this work was focused on the assessment of the relationship between the potential evapotranspiration (PET) and the actual evapotranspiration (AET) for undisturbed and disturbed landscapes which is expected to influence the hydrological behavior during the low-flow season. Through its influence on evapotranspiration, forest age appears to play an important role in the water balance. The second part of the study implemented a forest age dependent calculation of AET into a parsimonious water balance model, which was applied to simulate the sensitivity of the flow regimes of 15 non regulated watersheds to changes after the beginning of the pine beetle epidemic at a large scale. The model input was derived from disaggregated gridded 30-year climate normals. Since the geologic and topographic properties are first order controls on water storage and release of the examined catchments a framework for regionalization of these properties into ungauged catchments was developed. Furthermore, the interaction between forest disturbance and evapotranspiration

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 ...

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.

Future Projection with an Extreme-Learning Machine and Support Vector Regression of Reference Evapotranspiration in a Mountainous Inland Watershed in North-West China

Directory of Open Access Journals (Sweden)

Zhenliang Yin

2017-11-01

Full Text Available This study aims to project future variability of reference evapotranspiration (ET0 using artificial intelligence methods, constructed with an extreme-learning machine (ELM and support vector regression (SVR in a mountainous inland watershed in north-west China. Eight global climate model (GCM outputs retrieved from the Coupled Model Inter-comparison Project Phase 5 (CMIP5 were employed to downscale monthly ET0 for the historical period 1960–2005 as a validation approach and for the future period 2010–2099 as a projection of ET0 under the Representative Concentration Pathway (RCP 4.5 and 8.5 scenarios. The following conclusions can be drawn: the ELM and SVR methods demonstrate a very good performance in estimating Food and Agriculture Organization (FAO-56 Penman–Monteith ET0. Variation in future ET0 mainly occurs in the spring and autumn seasons, while the summer and winter ET0 changes are moderately small. Annually, the ET0 values were shown to increase at a rate of approximately 7.5 mm, 7.5 mm, 0.0 mm (8.2 mm, 15.0 mm, 15.0 mm decade−1, respectively, for the near-term projection (2010–2039, mid-term projection (2040–2069, and long-term projection (2070–2099 under the RCP4.5 (RCP8.5 scenario. Compared to the historical period, the relative changes in ET0 were found to be approximately 2%, 5% and 6% (2%, 7% and 13%, during the near, mid- and long-term periods, respectively, under the RCP4.5 (RCP8.5 warming scenarios. In accordance with the analyses, we aver that the opportunity to downscale monthly ET0 with artificial intelligence is useful in practice for water-management policies.

High Spatial Resolution WorldView-2 Imagery for Mapping NDVI and Its Relationship to Temporal Urban Landscape Evapotranspiration Factors

Directory of Open Access Journals (Sweden)

Hamideh Nouri

2014-01-01

Full Text Available 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

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

Value of using remotely sensed evapotranspiration for SWAT model calibration

Science.gov (United States)

Hydrologic models are useful management tools for assessing water resources solutions and estimating the potential impact of climate variation scenarios. A comprehensive understanding of the water budget components and especially the evapotranspiration (ET) is critical and often overlooked for adeq...

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

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

African Journals Online (AJOL)

This paper presents a method of determining in-situ actual evapotranspiration using water balance method in the case of maize crop grown for two seasons at the Experimental Farm of the Department of Agricultural Engineering, Federal University of Technology, Akure in a non-saturated soil condition. The crop was ...

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

African Journals Online (AJOL)

Accurately measuring evapotranspiration (ET) is essential if we are to derive reasonable estimates of production and water use for semi-arid savannas. Estimates of ET are also important in defining the health of an ecosystem and the quantity of water used by the vegetation when preparing a catchment-scale water balance.

Calcium amendment may increase hydraulic efficiency and forest evapotranspiration

Science.gov (United States)

Kevin T. Smith; Walter C. Shortle

2013-01-01

Green et al. (1) report 2 y of increased evapotranspiration (ET; calculated as the difference between total precipitation and total runoff) and decreased water yield following watershed-scale amendment of soil with wollastonite (CaSiO3) at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire. The...

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 <0.7 (0.39-0.52). However, the genetic algorithm technique was more effective with the ETa calibration while significantly

The time variability of evapotranspiration and soil water storage in long series of rainfall-runoff process

Czech Academy of Sciences Publication Activity Database

Buchtele, Josef; Tesař, Miroslav

2009-01-01

Roč. 64, č. 3 (2009), s. 575-579 ISSN 0006-3088 R&D Projects: GA MŽP(CZ) SP/1A6/151/07 Institutional research plan: CEZ:AV0Z20600510 Keywords : evapotranspiration components * evapotranspiration demand * land use * natural affection of runoff * rainfall- runoff simulation * vegetation change Subject RIV: DA - Hydrology ; Limnology Impact factor: 0.617, year: 2009

A general predictive model for estimating monthly ecosystem evapotranspiration

Science.gov (United States)

Ge Sun; Karrin Alstad; Jiquan Chen; Shiping Chen; Chelcy R. Ford; al. et.

2011-01-01

Accurately quantifying evapotranspiration (ET) is essential for modelling regional-scale ecosystem water balances. This study assembled an ET data set estimated from eddy flux and sapflow measurements for 13 ecosystems across a large climatic and management gradient from the United States, China, and Australia. Our objectives were to determine the relationships among...

Assessment of Evapotranspiration Simulation in the Malše Basin

Czech Academy of Sciences Publication Activity Database

Košková, Romana; Němečková, Soňa

2009-01-01

Roč. 4, Sp. Iss. 2 (2009), s. 111-122 ISSN 1801-5395 R&D Projects: GA AV ČR(CZ) KJB300600602 Institutional research plan: CEZ:AV0Z20600510 Keywords : hydrological modelling * evapotranspiration * SWIM model Subject RIV: DA - Hydrology ; Limnology

Improving operational land surface model canopy evapotranspiration in Africa using a direct remote sensing approach

CSIR Research Space (South Africa)

Marshall, M

2013-03-01

Full Text Available , latent energy (LE: ET energy equivalent) during the rainy season is the primary regulator after solar forcing of energy balance seasonal variability, the strength of which changes signifi- cantly across land cover types (Ramier et al., 2009). At inter... Table 1. Acronyms and their definitions in order of appearance. Acronym Definition ET Evapotranspiration LE Latent Heat LSM Land Surface Model NDVI Normalized Difference Vegetation Index PET Potential Evapotranspiration AMMA African Monsoon...

Geohydrology and evapotranspiration at Franklin Lake Playa, Inyo County, California

Energy Technology Data Exchange (ETDEWEB)

NONE

1990-12-01

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 US 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. 72 refs., 59 figs., 26 tab.

Geohydrology and evapotranspiration at Franklin Lake Playa, Inyo County, California

International Nuclear Information System (INIS)

1990-01-01

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 US 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. 72 refs., 59 figs., 26 tab

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

Directory of Open Access Journals (Sweden)

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.

Global Operational Remotely Sensed Evapotranspiration System for Water Resources Management: Case Study for the State of New Mexico

Science.gov (United States)

Halverson, G. H.; Fisher, J.; Magnuson, M.; John, L.

2017-12-01

An operational system to produce and disseminate remotely sensed evapotranspiration using the PT-JPL model and support its analysis and use in water resources decision making is being integrated into the New Mexico state government. A partnership between the NASA Western Water Applications Office (WWAO), the Jet Propulsion Laboratory (JPL), and the New Mexico Office of the State Engineer (NMOSE) has enabled collaboration with a variety of state agencies to inform decision making processes for agriculture, rangeland, and forest management. This system improves drought understanding and mobilization, litigation support, and economic, municipal, and ground-water planning through interactive mapping of daily rates of evapotranspiration at 1 km spatial resolution with near real-time latency. This is facilitated by daily remote sensing acquisitions of land-surface temperature and near-surface air temperature and humidity from the Moderate-Resolution Imaging Spectroradiometer (MODIS) instrument on the Terra satellite as well as the short-term composites of Normalized Difference Vegetation Index (NDVI) and albedo provided by MODIS. Incorporating evapotranspiration data into agricultural water management better characterizes imbalances between water requirements and supplies. Monitoring evapotranspiration over rangeland areas improves remediation and prevention of aridification. Monitoring forest evapotranspiration improves wildlife management and response to wildfire risk. Continued implementation of this decision support system should enhance water and food security.

Evaluation of land surface model simulations of evapotranspiration over a 12 year crop succession: impact of the soil hydraulic properties

Science.gov (United States)

Garrigues, S.; Olioso, A.; Calvet, J.-C.; Martin, E.; Lafont, S.; Moulin, S.; Chanzy, A.; Marloie, O.; Desfonds, V.; Bertrand, N.; Renard, D.

2014-10-01

Evapotranspiration has been recognized as one of the most uncertain term in the surface water balance simulated by land surface models. In this study, the SURFEX/ISBA-A-gs simulations of evapotranspiration are assessed at local scale over a 12 year Mediterranean crop succession. The model is evaluated in its standard implementation which relies on the use of the ISBA pedotransfer estimates of the soil properties. The originality of this work consists in explicitly representing the succession of crop cycles and inter-crop bare soil periods in the simulations and assessing its impact on the dynamic of simulated and measured evapotranspiration over a long period of time. The analysis focuses on key soil parameters which drive the simulation of evapotranspiration, namely the rooting depth, the soil moisture at saturation, the soil moisture at field capacity and the soil moisture at wilting point. The simulations achieved with the standard values of these parameters are compared to those achieved with the in situ values. The portability of the ISBA pedotransfer functions is evaluated over a typical Mediterranean crop site. Various in situ estimates of the soil parameters are considered and distinct parametrization strategies are tested to represent the evapotranspiration dynamic over the crop succession. This work shows that evapotranspiration mainly results from the soil evaporation when it is continuously simulated over a Mediterranean crop succession. The evapotranspiration simulated with the standard surface and soil parameters of the model is largely underestimated. The deficit in cumulative evapotranspiration amounts to 24% over 12 years. The bias in daily daytime evapotranspiration is -0.24 mm day-1. The ISBA pedotransfer estimates of the soil moisture at saturation and at wilting point are overestimated which explains most of the evapotranspiration underestimation. The overestimation of the soil moisture at wilting point causes the underestimation of

Daily time series evapotranspiration maps for Oklahoma and Texas panhandle

Science.gov (United States)

Evapotranspiration (ET) is an important process in ecosystems’ water budget and closely linked to its productivity. Therefore, regional scale daily time series ET maps developed at high and medium resolutions have large utility in studying the carbon-energy-water nexus and managing water resources. ...

Characterizing the Diurnal Cycle of Land Surface Temperature and Evapotranspiration at High Spatial Resolution Using Thermal Observations from sUAS.

Science.gov (United States)

Dutta, D.; Drewry, D.; Johnson, W. R.

2017-12-01

The surface temperature of plant canopies is an important indicator of the stomatal regulation of plant water use and the associated water flux from plants to atmosphere (evapotranspiration (ET)). Remotely sensed thermal observations using compact, low-cost, lightweight sensors from small unmanned aerial systems (sUAS) have the potential to provide surface temperature (ST) and ET estimates at unprecedented spatial and temporal resolutions, allowing us to characterize the intra-field diurnal variations in canopy ST and ET for a variety of vegetation systems. However, major challenges exist for obtaining accurate surface temperature estimates from low-cost uncooled microbolometer-type sensors. Here we describe the development of calibration methods using thermal chamber experiments, taking into account the ambient optics and sensor temperatures, and applying simple models of spatial non-uniformity correction to the sensor focal-plane-array. We present a framework that can be used to derive accurate surface temperatures using radiometric observations from low-cost sensors, and demonstrate this framework using a sUAS-mounted sensor across a diverse set of calibration and vegetation targets. Further, we demonstrate the use of the Surface Temperature Initiated Closure (STIC) model for computing spatially explicit, high spatial resolution ET estimates across several well-monitored agricultural systems, as driven by sUAS acquired surface temperatures. STIC provides a physically-based surface energy balance framework for the simultaneous retrieval of the surface and atmospheric vapor conductances and surface energy fluxes, by physically integrating radiometric surface temperature information into the Penman-Monteith equation. Results of our analysis over agricultural systems in Ames, IA and Davis, CA demonstrate the power of this approach for quantifying the intra-field spatial variability in the diurnal cycle of plant water use at sub-meter resolutions.

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 (ET 0 ) 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 ET 0 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 ET 0 , 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.

Analysis of reference evapotranspiration (ET0) trends under climate change in Bangladesh using observed and CMIP5 data sets

Science.gov (United States)

Rahman, Mohammad Atiqur; Yunsheng, Lou; Sultana, Nahid; Ongoma, Victor

2018-03-01

ET0 is an important hydro-meteorological phenomenon, which is influenced by changing climate like other climatic parameters. This study investigates the present and future trends of ET0 in Bangladesh using 39 years' historical and downscaled CMIP5 daily climatic data for the twenty-first century. Statistical Downscaling Model (SDSM) was used to downscale the climate data required to calculate ET0. Penman-Monteith formula was applied in ET0 calculation for both the historical and modelled data. To analyse ET0 trends and trend changing patterns, modified Mann-Kendall and Sequential Mann-Kendall tests were, respectively, done. Spatial variations of ET0 trends are presented by inverse distance weighting interpolation using ArcGIS 10.2.2. Results show that RCP8.5 (2061-2099) will experience the highest amount of ET0 totals in comparison to the historical and all other scenarios in the same time span of 39 years. Though significant positive trends were observed in the mid and last months of year from month-wise trend analysis of representative concentration pathways, significant negative trends were also found for some months using historical data in similar analysis. From long-term annual trend analysis, it was found that major part of the country represents decreasing trends using historical data, but increasing trends were observed for modelled data. Theil-Sen estimations of ET0 trends in the study depict a good consistency with the Mann-Kendall test results. The findings of the study would contribute in irrigation water management and planning of the country and also in furthering the climate change study using modelled data in the context of Bangladesh.

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

Science.gov (United States)

Liu, Xin; Wang, Sufen; Xue, Han; Singh, Vijay P

2015-01-01

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.

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

Directory of Open Access Journals (Sweden)

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.

Use of Land Surface Temperature Observations in a Two-Source Energy Balance Model Towards Improved Monitoring of Evapotranspiration and Drought

Science.gov (United States)

Hain, C.; Anderson, M. C.; Otkin, J.; Semmens, K. A.; Zhan, X.; Fang, L.; Li, Z.

2014-12-01

As the world's water resources come under increasing tension due to the 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. However, direct validation of ET models is challenging due to lack of available observations that are sufficiently representative at the model grid scale (10-100 km). Prognostic land-surface models require accurate information about observed precipitation, soil moisture storage, groundwater, and artificial controls on water supply (e.g., irrigation, dams, etc.) to reliably link rainfall to evaporative fluxes. In contrast, diagnostic estimates of ET can be generated, with no prior knowledge of the surface moisture state, by energy balance models using thermal-infrared remote sensing of land-surface temperature (LST) as a boundary condition. One such method, the Atmosphere Land Exchange Inverse (ALEXI) model provides estimates of surface energy fluxes through the use of mid-morning change in LST and radiation inputs. The LST inputs carry valuable proxy information regarding soil moisture and its effect on soil evaporation and canopy transpiration. Additionally, the Evaporative Stress Index (ESI) representing anomalies in the ratio of actual-to-potential ET has shown to be a reliable indicator of drought. ESI maps over the continental US show good correspondence with standard drought metrics and with patterns of precipitation, but can be generated at significantly higher spatial resolution due to a limited reliance on ground observations. Furthermore, ESI is a measure of actual stress rather than potential for stress, and has physical relevance to projected crop development. Because precipitation is not used in construction of the ESI, it provides an independent assessment of drought conditions and has particular utility for real-time monitoring in regions with sparse rainfall data or

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.

Estimating Actual Evapotranspiration from Satellite and Meteorological Data in Central Bolivia

NARCIS (Netherlands)

Seiler, C.; Moene, A.F.

2011-01-01

Spatial estimates of actual evapotranspiration are useful for calculating the water balance of river basins, quantifying hydrological services provided by ecosystems, and assessing the hydrological impacts of land-use practices. To provide this information, the authors estimate actual

Effects of water salinity on the correlation scale of Root density and Evapotranspiration fluxes

Science.gov (United States)

Ajeel, Ali; Saeed, Ali; Dragonetti, Giovanna; Comegna, Alessandro; Lamaddalena, Nicola; Coppola, Antonio

2015-04-01

Spatial pattern and the correlation of different soil and plant parameters were examined in a green bean field experiment carried out at the Mediterranean Agronomic Institute of Bari, Italy. The experiment aimed to evaluate the role of local processes of salt accumulation and transport which mainly influences the evapotranspiration (and thus the root uptake) processes under different water salinity levels. The experiment consisted of three transects of 30m length and 4.2 m width, irrigated with three different salinity levels (1dSm-1, 3dSm-1, 6dSm-1). Soil measurements (electrical conductivity and soil water content) were monitored along transects in 24 sites, 1 m apart by using TDR probes and Diviner 2000. Water storage measured by TDR and Diviner sensor were coupled for calculating directly the evapotranspiration fluxes along the whole soil profile under the different salinity levels imposed during the experiment. In the same sites, crop monitoring involved measurements of Leaf Area Index (LAI), Osmotic Potential (OP), Leaf Water Potential (LWP), and Root length Density (RlD). Soil and plant properties were analyzed by classical statistics, geostatistics methods and spectral analysis. Results indicated moderate to large spatial variability across the field for soil and plant parameters under all salinity treatments. Furthermore, cross-semivariograms exhibited a strong positive spatial interdependence between electrical conductivity of soil solution ECw with ET and RlD in transect treated with 3dSm-1 as well as with LAI in transect treated with 6dSm-1 at all 24 monitoring sites. Spectral analysis enabled to identify the observation window to sample the soil salinity information responsible for a given plant response (ET, OP, RlD). It is also allowed a clear identification of the spatial scale at which the soil water salinity level and distribution and the crop response in terms of actual evapotranspiration ET, RlD and OP, are actually correlated. Additionally

Maximum transpiration, reference evapotranspiration and leaf area relationships for some mango cultivars

OpenAIRE

OLIVEIRA, Greice Ximena Santos; COELHO FILHO, Maurício Antonio; PEREIRA, Francisco Adriano de Carvalho; COELHO, Eugênio Ferreira; PAZ, Vital Pedro da Silva; CASTRO NETO, Manoel Teixeira de

2009-01-01

Nas condições edafoclimáticas de Cruz da Almas - BA, na Embrapa Mandioca e Fruticultura Tropical, foi realizado um estudo no qual se relacionou a transpiração máxima (Litros m-2 folha/dia -1) de quatro variedades de mangueira (Tommy Atkins, Palmer, Haden e Van Dyke, com áreas foliares totais de 14; 8; 33 e 12 m², respectivamente) com a evapotranspiração de referência (ETo). A transpiração das plantas (L dia-1) foi estimada por meio de sensores que realizam o balanço de calor no caule (modelos...

Bacteria associated with oak and ash on a TCE-contaminated site: characterization of isolates with potential to avoid evapotranspiration of TCE.

Science.gov (United States)

Weyens, Nele; Taghavi, Safiyh; Barac, Tanja; van der Lelie, Daniel; Boulet, Jana; Artois, Tom; Carleer, Robert; Vangronsveld, Jaco

2009-11-01

Along transects under a mixed woodland of English Oak (Quercus robur) and Common Ash (Fraxinus excelsior) growing on a trichloroethylene (TCE)-contaminated groundwater plume, sharp decreases in TCE concentrations were observed, while transects outside the planted area did not show this remarkable decrease. This suggested a possibly active role of the trees and their associated bacteria in the remediation process. Therefore, the cultivable bacterial communities associated with both tree species growing on this TCE-contaminated groundwater plume were investigated in order to assess the possibilities and practical aspects of using these common native tree species and their associated bacteria for phytoremediation. In this study, only the cultivable bacteria were characterized because the final aim was to isolate TCE-degrading, heavy metal resistant bacteria that might be used as traceable inocula to enhance bioremediation. Cultivable bacteria isolated from bulk soil, rhizosphere, root, stem, and leaf were genotypically characterized by amplified rDNA restriction analysis (ARDRA) of their 16S rRNA gene and identified by 16S rRNA gene sequencing. Bacteria that displayed distinct ARDRA patterns were screened for heavy metal resistance, as well as TCE tolerance and degradation, as preparation for possible future in situ inoculation experiments. Furthermore, in situ evapotranspiration measurements were performed to investigate if the degradation capacity of the associated bacteria is enough to prevent TCE evapotranspiration to the air. Between both tree species, the associated populations of cultivable bacteria clearly differed in composition. In English Oak, more species-specific, most likely obligate endophytes were found. The majority of the isolated bacteria showed increased tolerance to TCE, and TCE degradation capacity was observed in some of the strains. However, in situ evapotranspiration measurements revealed that a significant amount of TCE and its metabolites

Changes in evapotranspiration of summer and winter crops of netted melon [Cucumis melo] grown under glass in relation to meteorological and plant-related factors

International Nuclear Information System (INIS)

Asakura, T.

1998-01-01

Measurements of evapotranspiration taken in the summer and winter on netted melon crops grown under glass were taken to characterize seasonal and daily changes. The data were compared to meteorological and plant-related factors to seek some relationships. Evapotranspiration followed a sigmoid curve until one week after pollination, and then decreased gradually during fruit growth. Cumulative evapotranspirations after transplanting were about 116 kg and 60 kg, respectively, for the summer and winter crops, whereas the peak evapotranspirations were 3.O kg plant(-1) day(-1) and 1.3 kg plant(-1) day(-1). The rapid increase h the evapotranspiration during the early stage was associated with the increase in leaf area; its gradual decrease during fruit growth was associated with a decrease in the transpiration potential of leaves. Therefore, irrigation amounts should be increased with leaf development and decreased with fruit growth. The curve of solar radiation in sunny summer days peaked at noon, whereas vapor pressure deficit usually peaked in early or mid afternoon; evapotranspirations in the afternoon had higher values than had those in the morning. In winter, vapor pressure deficit was relatively high during late afternoon and early morning because of heating, whereas it was low during the remainder of the day on account of low ventilation. These fluctuations led to a weak correlation between evapotranspiration and vapor pressure deficit. Regression analyses indicated that solar radiation was a main meteorological factor affecting evapotranspiration

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

Energy Technology Data Exchange (ETDEWEB)

Bernacchi, Carl J., E-mail: bernacch@illinois.edu [Global Change and Photosynthesis Research Unit, United States Department of Agriculture Agricultural Research Service, Urbana, IL 61801 (United States); Institute for Genomic Biology and Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Leakey, Andrew D.B. [Institute for Genomic Biology and Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States); Kimball, Bruce A. [USDA-ARS US Arid-Land Agricultural Research Center, 21881 N. Cardon Lane, Maricopa, AZ 85238 (United States); Ort, Donald R. [Global Change and Photosynthesis Research Unit, United States Department of Agriculture Agricultural Research Service, Urbana, IL 61801 (United States); Institute for Genomic Biology and Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (United States)

2011-06-15

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 ([O{sub 3}]) varied between growing seasons from 22 to 37% above background concentrations. The objective of this experiment was to examine the effects of future [O{sub 3}] on crop ecosystem energy fluxes and water use. Elevated [O{sub 3}] 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 deg. C. - Highlights: > Globally, tropospheric ozone is currently and will likely continue to increase into the future. > We examine the impact of elevated ozone on water use by soybean at the SoyFACE research facility. > High ozone grown soybean had reduced rates of evapotranspiration and higher soil moisture. > Increases in ozone have the potential to impact the hydrologic cycle where these crops are grown. - Soybean grown in elevated concentrations of ozone is shown to evapotranspire less water compared with soybean canopies grown under current atmospheric conditions.

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

International Nuclear Information System (INIS)

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

2011-01-01

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 ([O 3 ]) varied between growing seasons from 22 to 37% above background concentrations. The objective of this experiment was to examine the effects of future [O 3 ] on crop ecosystem energy fluxes and water use. Elevated [O 3 ] 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 deg. C. - Highlights: → Globally, tropospheric ozone is currently and will likely continue to increase into the future. → We examine the impact of elevated ozone on water use by soybean at the SoyFACE research facility. → High ozone grown soybean had reduced rates of evapotranspiration and higher soil moisture. → Increases in ozone have the potential to impact the hydrologic cycle where these crops are grown. - Soybean grown in elevated concentrations of ozone is shown to evapotranspire less water compared with soybean canopies grown under current atmospheric conditions.

Runoff and Evapotranspiration Sensitivities to a Changing Climate in the Western U.S.

Science.gov (United States)

Gao, M.; Xiao, M.; Lettenmaier, D. P.

2017-12-01

Climate change is likely to alter streamflow seasonal patterns, affect water availability, and otherwise pose challenges to water resources management. It is therefore important to understand how streamflow will respond to changes in climate. Previous studies have mostly focused on runoff sensitivity to precipitation (P) and temperature change, but runoff sensitivity to potential evapotranspiration (PET) is less well understood. In order to investigate how variations in precipitation and PET influence runoff, we conducted both statistical and model-based analyses of 84 near-natural basins in California, Oregon, and Washington. We obtained meteorological forcing data at 1/16 degree spatial resolution for each basin from the University of Washington/UCLA Experimental Surface Water Monitor, and observed runoff data from USGS. For the statistical method, we applied three estimators of the precipitation elasticity of runoff from previous studies. We also estimated the PET elasticity of runoff, using Penman-Monteith reference ET as a surrogate for PET. For the modelling method, we implemented the Sacramento Soil Moisture Accounting (SAC-SMA) Model, where PET is an explicit input. We performed experiments in which we changed P and PET by 1% individually to examine their effects on runoff, from which we computed the P and PET elasticities. We explore the spatial patterns in the elasticities of runoff and their relationships with basin characteristics and climatology. We also evaluate how well the statistical and model-based results meet the complementary relationship posited by Dooge (based on the Budyko Hypothesis) that the precipitation and PET elasticities of annual runoff should sum to one.

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 by...

The Social Context of Reference Work: Assessing the Effects of Gender and Communication Skill on Observers' Judgments of Competence.

Science.gov (United States)

Harris, Roma M.; Michell, B. Gillian

1986-01-01

Public library users made judgments about the competence of reference librarians whom they observed in videotaped interviews. Two social factors were varied in the interviews: the gender of the librarian, patron, and observers; and the communication behavior exhibited by the reference librarian toward the patron. Nineteen references are cited.…

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

Directory of Open Access Journals (Sweden)

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.

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

Selected micrometeorological, soil-moisture, and evapotranspiration data at Amargosa Desert Research Site in Nye County near Beatty, Nevada, 2001-05

Science.gov (United States)

Johnson, Michael J.; Mayers, C. Justin; Garcia, C. Amanda; Andraski, Brian J.

2007-01-01

Selected micrometeorological and soil-moisture data were collected at the Amargosa Desert Research Site adjacent to a low-level radio-active waste and hazardous chemical waste facility near Beatty, Nevada, 2001-05. Evapotranspiration data were collected from February 2002 through the end of December 2005. Data were col-lected in support of ongoing research to improve the understanding of hydrologic and contaminant-transport processes in arid environments. Micrometeorological data include solar radiation, net radiation, air temperature, relative humidity, saturated and ambient vapor pressure, wind speed and direction, barometric pressure, precipitation, near-surface soil temperature, soil-heat flux and soil-water content. All micrometeorological data were collected using a 10-second sampling interval by data loggers that output daily and hourly mean values. Daily maximum and minimum values are based on hourly mean values. Precipitation data output includes daily and hourly totals. Selected soil-moisture profiles at depth include periodic measurements of soil volumetric water-content measurements at nine neutron-probe access tubes to depths ranging from 5.25 to 29.25 meters. Evapotranspiration data include measurement of daily evapotranspiration and 15-minute fluxes of the four principal energy budget components of latent-heat flux, sensible-heat flux, soil-heat flux, and net radiation. Other data collected and used in equations to determine evapotranspiration include temperature and water content of soil, temperature and vapor pressure of air, and covariance values. Evapotranspiration and flux estimates during 15-minute intervals were calculated at a 0.1-second execution interval using the eddy covariance method. Data files included in this report contain the complete micrometeorological, soil-moisture, and evapotranspiration field data sets. These data files are presented in tabular Excel spreadsheet format. This report highlights selected data contained in the

Evaluating evapotranspiration for six sites in Benton, Spokane, and Yakima counties, Washington, May 1990 to September 1992

Science.gov (United States)

Tomlinson, S.A.

1996-01-01

This report evaluates evapotranspiration for six sites in Benton, Spokane, and Yakima Counties, Washington. Three sites were located on the Arid Lands Ecology Reserve in Benton County: one at a full-canopy grassland in Snively Basin (Snively Basin site), one at a sparse-canopy grassland adjacent to two weighing lysimeters (grass lysimeter site), and one at a sagebrush grassland adjacent to two weighing lysimeters (sage lysimeter site). Two sites were located on the Turnbull National Wildlife Refuge in Spokane County: one at a full-canopy grassland in a meadow (Turnbull meadow site), the other a full-canopy grassland near a marsh (Turnbull marsh site). The last site was located in a sagebrush grassland in the Black Rock Valley in Yakima County (Black Rock Valley site). The periods of study at the six sites varied, ranging from 5 months at the Black Rock Valley site to more than 2 years at the Snively Basin, grass lysimeter, and sage lysimeter sites. The periods of study were May 1990 to September 1992 for the Snively Basin, grass lysimeter, and sage lysimeter sites; May 1991 to September 1992 for the Turnbull meadow site; May 1991 to April 1992 for the Turnbull marsh site; and March to September 1992 for the Black Rock Valley site. Evapotranspiration and energy-budget fluxes were estimated for the Snively Basin site, the Turnbull meadow site, and the Black Rock Valley site using the Bowen-ratio and Penman-Monteith methods. Daily evapotranspiration for the Snively Basin site was also estimated using a deep-percolation model for the Columbia Basin. The Bowen-ratio method and weighing lysimeters were used at the grass and sage lysimeter sites. The Penman-Monteith method was used at the Turnbull marsh site. Daily evapotranspiration at the sites ranged from under 0.2 millimeter during very dry or cold periods to over 4\\x11millimeters after heavy rainfall or during periods of peak transpiration. At all sites, peak evapotranspiration occurred in spring, coinciding with

Utilizing on-farm best management practices: Managing Nitrate Leaching Using Evapotranspiration Based Irrigation Methods

Science.gov (United States)

Zaragosa, I.; Melton, F. S.; Dexter, J.; Post, K.; Haffa, A.; Kortman, S.; Spellenberg, R.; Cahn, M.

2017-12-01

In efforts to provide tools to allow farmers to optimize and quantify water usage and fertilizer applications, University of California Cooperative Extension (UCCE) developed the CropManage irrigation and nitrogen scheduling tool that provides real time evapotranspiration (ETc) based irrigation recommendations and fertilizer recommendations on a per field basis. CropManage incorporates satellite based estimates of fractional cover from web data services from the Satellite Irrigation Management Information Support (SIMS) system developed by NASA Ames Research Center in collaboration with California State University Monterey Bay (CSUMB). In this study, we conducted field trials to quantify the benefits of using these tools to support best management practices (BMPs) for irrigation and nutrient management in strawberries and lettuce in the Salinas Valley, California. We applied two different irrigation treatments based on full replacement (100%) of crop evapotranspiration (ETc), and irrigation at 130% of ETc replacement to approximate irrigation under business as usual irrigation management. Both field studies used a randomized block design with four replicates each. We used CropManage to calculate the 100% and 130% ETc replacement requirements prior to each irrigation event. We collected drainage volume and samples and analyzed them for 8500 to nitrate as (NO3-) concentrations. Experimental results for both strawberries and lettuce showed a significant decrease in the percentage of applied nitrogen leached for the 100% ETc replacement treatment against the 130% ETc replacement treatment. For strawberries, we observed that 24% of applied nitrogen was leached under the 100% ETc replacement treatment, versus 51% of applied nitrogen that was leached under the 130% ETc replacement treatment. For lettuce, we observe that 2% of the applied nitrogen leached bellow the soil profile, versus 6% of the applied nitrogen for the 130%ETc replacement treatment. In both experiments

Global Analysis of Ecosystem Evapotranspiration Response to Precipitation Deficits

Science.gov (United States)

He, Bin; Wang, Haiyan; Guo, Lanlan; Liu, Junjie

2017-12-01

Changes in ecosystem evapotranspiration (ET) due to precipitation deficits (PD) can relieve or aggravate soil moisture shortages, thus impacting drought severity. Previous findings have conflicted with regard to response of ET to PD. The present study relies on a global land ET synthesis data set (ETsyn) and observations from eddy-covariance towers (ETobs) to thoroughly examine the sensitivity of ET to PD, which is represented by the standardized precipitation index. There was a contrast in the response to PD between arid and humid ecosystems. ETsyn of arid ecosystems was typically reduced promptly in response to a reduction of precipitation, while ETsyn in humid ecosystems experienced a two-staged change: First, there was an enhancement, and then a reduction associated with persisting PD. Compared with ETsyn, ETobs suggests the occurrence of a more significant ET transition in response to PD. In arid ecosystems, ET typically negatively correlated with low PD, but this was limited by a large PD. Findings from this study are crucial for understanding the role of ET in drought evolution.

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.

Estimation of Evapotranspiration and Crop Coefficients of Tendone Vineyards Using Multi-Sensor Remote Sensing Data in a Mediterranean Environment

Directory of Open Access Journals (Sweden)

Silvia Vanino

2015-11-01

Full Text Available The sustainable management of water resources plays a key role in Mediterranean viticulture, characterized by scarcity and competition of available water. This study focuses on estimating the evapotranspiration and crop coefficients of table grapes vineyards trained on overhead “tendone” systems in the Apulia region (Italy. Maximum vineyard transpiration was estimated by adopting the “direct” methodology for ETp proposed by the Food and Agriculture Organization in Irrigation and Drainage Paper No. 56, with crop parameters estimated from Landsat 8 and RapidEye satellite data in combination with ground-based meteorological data. The modeling results of two growing seasons (2013 and 2014 indicated that canopy growth, seasonal and 10-day sums evapotranspiration values were strictly related to thermal requirements and rainfall events. The estimated values of mean seasonal daily evapotranspiration ranged between 4.2 and 4.1 mm·d−1, while midseason estimated values of crop coefficients ranged from 0.88 to 0.93 in 2013, and 1.02 to 1.04 in 2014, respectively. The experimental evapotranspiration values calculated represent the maximum value in absence of stress, so the resulting crop coefficients should be used with some caution. It is concluded that the retrieval of crop parameters and evapotranspiration derived from remotely-sensed data could be helpful for downscaling to the field the local weather conditions and agronomic practices and thus may be the basis for supporting grape growers and irrigation managers.

Comparing Three Approaches of Evapotranspiration Estimation in Mixed Urban Vegetation: Field-Based, Remote Sensing-Based and Observational-Based Methods

Directory of Open Access Journals (Sweden)

Hamideh Nouri

2016-06-01

Full Text Available Despite being the driest inhabited continent, Australia has one of the highest per capita water consumptions in the world. In addition, instead of having fit-for-purpose water supplies (using different qualities of water for different applications, highly treated drinking water is used for nearly all of Australia’s urban water supply needs, including landscape irrigation. The water requirement of urban landscapes, particularly urban parklands, is of growing concern. The estimation of evapotranspiration (ET and subsequently plant water requirements in urban vegetation needs to consider the heterogeneity of plants, soils, water, and climate characteristics. This research contributes to a broader effort to establish sustainable irrigation practices within the Adelaide Parklands in Adelaide, South Australia. In this paper, two practical ET estimation approaches are compared to a detailed Soil Water Balance (SWB analysis over a one year period. One approach is the Water Use Classification of Landscape Plants (WUCOLS method, which is based on expert opinion on the water needs of different classes of landscape plants. The other is a remote sensing approach based on the Enhanced Vegetation Index (EVI from Moderate Resolution Imaging Spectroradiometer (MODIS sensors on the Terra satellite. Both methods require knowledge of reference ET calculated from meteorological data. The SWB determined that plants consumed 1084 mm·yr−1 of water in ET with an additional 16% lost to drainage past the root zone, an amount sufficient to keep salts from accumulating in the root zone. ET by MODIS EVI was 1088 mm·yr−1, very close to the SWB estimate, while WUCOLS estimated the total water requirement at only 802 mm·yr−1, 26% lower than the SWB estimate and 37% lower than the amount actually added including the drainage fraction. Individual monthly ET by MODIS was not accurate, but these errors were cancelled out to give good agreement on an annual time step. We

Unmanned airborne thermal and mutilspectral imagery for estimating evapotranspiration in irrigated vineyards

Science.gov (United States)

Thermal-infrared remote sensing of land surface temperature (LST) provides valuable information for quantifying rootzone water availability, evapotranspiration (ET) and crop condition. This paper describes the most recent modifications applied to the robust but relatively simple LST-based energy bal...

Comparison of MODIS and SWAT evapotranspiration over a complex terrain at different spatial scales

Science.gov (United States)

Abiodun, Olanrewaju O.; Guan, Huade; Post, Vincent E. A.; Batelaan, Okke

2018-05-01

In most hydrological systems, evapotranspiration (ET) and precipitation are the largest components of the water balance, which are difficult to estimate, particularly over complex terrain. In recent decades, the advent of remotely sensed data based ET algorithms and distributed hydrological models has provided improved spatially upscaled ET estimates. However, information on the performance of these methods at various spatial scales is limited. This study compares the ET from the MODIS remotely sensed ET dataset (MOD16) with the ET estimates from a SWAT hydrological model on graduated spatial scales for the complex terrain of the Sixth Creek Catchment of the Western Mount Lofty Ranges, South Australia. ET from both models was further compared with the coarser-resolution AWRA-L model at catchment scale. The SWAT model analyses are performed on daily timescales with a 6-year calibration period (2000-2005) and 7-year validation period (2007-2013). Differences in ET estimation between the SWAT and MOD16 methods of up to 31, 19, 15, 11 and 9 % were observed at respectively 1, 4, 9, 16 and 25 km2 spatial resolutions. Based on the results of the study, a spatial scale of confidence of 4 km2 for catchment-scale evapotranspiration is suggested in complex terrain. Land cover differences, HRU parameterisation in AWRA-L and catchment-scale averaging of input climate data in the SWAT semi-distributed model were identified as the principal sources of weaker correlations at higher spatial resolution.

Comparing three approaches of evapotranspiration estimation in mixed urban vegetation; field-based, remote sensing-based and observational-based methods

Science.gov (United States)

Nouri, Hamideh; Glenn, Edward P.; Beecham, Simon; Chavoshi Boroujeni, Sattar; Sutton, Paul; Alaghmand, Sina; Nagler, Pamela L.; Noori, Behnaz

2016-01-01

Despite being the driest inhabited continent, Australia has one of the highest per capita water consumptions in the world. In addition, instead of having fit-for-purpose water supplies (using different qualities of water for different applications), highly treated drinking water is used for nearly all of Australia’s urban water supply needs, including landscape irrigation. The water requirement of urban landscapes, and particularly urban parklands, is of growing concern. The estimation of ET and subsequently plant water requirements in urban vegetation needs to consider the heterogeneity of plants, soils, water and climate characteristics. Accurate estimation of evapotranspiration (ET), which is the main component of a plant’s water requirement, in urban parks is highly desirable because this water maintains the health of green infrastructure and this in turn provides essential ecosystem services. This research contributes to a broader effort to establish sustainable irrigation practices within the Adelaide Parklands in Adelaide, South Australia.

Evapotranspiração e coeficiente de cultivo do tomate caqui cultivado em ambiente protegido Evapotranspiration and crop coefficient of Kaki tomato cultivated in greenhouse

Directory of Open Access Journals (Sweden)

Ligia S. Reis

2009-06-01

Full Text Available Os parâmetros aerodinâmicos de uma cultura cultivada em ambiente protegido podem ser considerados dependentes do nível de radiação global, temperatura do ar e umidade do ar, com base em leis exponenciais. Assim sendo se propôs com este trabalho, estimar a evapotranspiração e o coeficiente de cultivo da cultura do tomate caqui em ambiente protegido, sob irrigação por gotejamento, utilizando-se o modelo de Penman-Monteith. Os parâmetros aerodinâmicos foram medidos com sensores conectados à estação automática instalada dentro do ambiente protegido. A evapotranspiração da cultura (ETc foi determinada experimentalmente por meio de lisímetros de drenagem e a umidade do solo foi medida através de sensores instalados a uma profundidade de 20 cm. O desempenho do modelo de Penman-Monteith foi comparado aos valores decendiais do balanço hídrico nos lisímetros; já a evapotranspiração de referência foi calculada com dados externos e utilizada para o cálculo do Kc da cultura; enfim, os resultados indicaram que o modelo de Penman-Monteith subestima os valores de evapotranspiração encontrados pelo balanço hídrico nos lisímetros.The aerodynamic parameters of a crop cultivated in greenhouse can be considered dependent upon the level of global radiation, air temperature and relative humidity, based on exponential laws. Consequently, this work intends to estimate the evapotranspiration and the crop coefficient of Kaki tomato in greenhouse, under drip irrigation, using the Penman-Monteith model. The aerodynamic parameters were measured with sensors connected to the automatic station installed inside the greenhouse. The ETc was determined experimentally through drainage lysimeters and the soil water content was measured through sensors installed at a depth of 20 cm. The performance of the Penman-Monteith model was compared to decennial values of the water balance in the lysimeters, while the reference evapotranspiration was calculated

The WACMOS-ET project – Part 1: Tower-scale evaluation of four remote sensing-based evapotranspiration algorithms

KAUST Repository

Michel, D.

2015-10-20

The WACMOS-ET project has compiled a forcing data set covering the period 2005–2007 that aims to maximize the exploitation of European Earth Observations data sets for evapotranspiration (ET) estimation. The data set was used to run 4 established ET algorithms: the Priestley–Taylor Jet Propulsion Laboratory model (PT-JPL), the Penman–Monteith algorithm from the MODIS evaporation product (PM-MOD), the Surface Energy Balance System (SEBS) and the Global Land Evaporation Amsterdam Model (GLEAM). In addition, in-situ meteorological data from 24 FLUXNET towers was used to force the models, with results from both forcing sets compared to tower-based flux observations. Model performance was assessed across several time scales using both sub-daily and daily forcings. The PT-JPL model and GLEAM provide the best performance for both satellite- and tower-based forcing as well as for the considered temporal resolutions. Simulations using the PM-MOD were mostly underestimated, while the SEBS performance was characterized by a systematic overestimation. In general, all four algorithms produce the best results in wet and moderately wet climate regimes. In dry regimes, the correlation and the absolute agreement to the reference tower ET observations were consistently lower. While ET derived with in situ forcing data agrees best with the tower measurements (R² = 0.67), the agreement of the satellite-based ET estimates is only marginally lower (R² = 0.58). Results also show similar model performance at daily and sub-daily (3-hourly) resolutions. Overall, our validation experiments against in situ measurements indicate that there is no single best-performing algorithm across all biome and forcing types. An extension of the evaluation to a larger selection of 85 towers (model inputs re-sampled to a common grid to facilitate global estimates) confirmed the original findings.

AgRISTARS: Early warning and crop condition assessment. Plant cover, soil temperature, freeze, water stress, and evapotranspiration conditions

Science.gov (United States)

Wiegand, C. L. (Principal Investigator); Nixon, P. R.; Gausman, H. W.; Namken, L. N.; Leamer, R. W.; Richardson, A. J.

1981-01-01

Emissive (10.5 to 12.5 microns) and reflective (0.55 to 1.1 microns) data for ten day scenes and infrared data for six night scenes of southern Texas were analyzed for plant cover, soil temperature, freeze, water stress, and evapotranspiration. Heat capacity mapping mission radiometric temperatures were: within 2 C of dewpoint temperatures, significantly correlated with variables important in evapotranspiration, and related to freeze severity and planting depth soil temperatures.

Soil water regime and evapotranspiration of sites with trees and lawn in Moscow

NARCIS (Netherlands)

Bondarenko, V.

2009-01-01

Keywords: Urban vegetation, Tilia cordata, linden, lawn, grass, Leaf Area Index, LAI, digital image processing, evapotranspiration, water stress, electric conductivity, salinity stress, Makkink’s radiation model, deep percolation, water infiltration, runoff, modelling

Situations where

Comparing Evapotranspiration Rates Estimated from Atmospheric Flux and TDR Soil Moisture Measurements

DEFF Research Database (Denmark)

Schelde, Kirsten; Ringgaard, Rasmus; Herbst, Mathias

2011-01-01

limit estimate (disregarding dew evaporation) of evapotranspiration on dry days. During a period of 7 wk, the two independent measuring techniques were applied in a barley (Hordeum vulgare L.) field, and six dry periods were identified. Measurements of daily root zone soil moisture depletion were...

Remote estimation of a managed pine forest evapotranspiration with geospatial technology

Science.gov (United States)

S. Panda; D.M. Amatya; G Sun; A. Bowman

2016-01-01

Remote sensing has increasingly been used to estimate evapotranspiration (ET) and its supporting parameters in a rapid, accurate, and cost-effective manner. The goal of this study was to develop remote sensing-based models for estimating ET and the biophysical parameters canopy conductance (gc), upper-canopy temperature, and soil moisture for a mature loblolly pine...

Estimativa da evapotranspiração de referência em Campina Grande, Paraíba Estimate of reference evapotranspiration in the city of Campina Grande, Paraíba state, Brazil

Directory of Open Access Journals (Sweden)

Francisco de A. N. Henrique

2007-12-01

Full Text Available Deste trabalho se objetivou estimar, através de uma fórmula empírica, a evapotranspiração de referência diária no município de Campina Grande, PB (EToT, utilizando-se a amplitude térmica diária. Estimou-se, também, a ETo diária usando-se os métodos de FAO-Penman-Monteith (EToPM, Hargreaves (EToH e Linacre (EToL, sendo depois correlacionados com a EToT proposta na pesquisa, por estação do ano; para isto foram coletados valores diários das temperaturas, umidade relativa do ar, radiação solar, precipitação, pressão atmosférica e velocidade do vento a 2 m da Estação Meteorológica Automática, instalada na Universidade Federal de Campina Grande (UFCG, no período de 1 de janeiro a 31 de dezembro de 2004. Tais valores foram registrados no intervalo de 10 min. Verificou-se que as correlações da EToT com EToH, obtiveram o melhor ajuste, cujos coeficientes foram: R² = 0,7882 (no ano, R² = 0,9796 (no verão, R² = 0,8253 (no outono, R² = 0,878 (no inverno e R² = 0,914 (na primavera. Conclui-se que os métodos de EToPM e EToL não se ajustaram bem para Campina Grande, PB, o que evidencia que a EToT poderá ser utilizada na forma proposta para estimativa da ETo desta localidade. Das equações propostas, a única restrição é o EToT para o verão caso em que se recomenda o uso da equação anual.The objective of this study was to estimate, using an empiric formula, the daily reference evapotranspiration in the city of Campina Grande, Paraiba State, Brazil (EToT, using the daily thermal amplitude. The ETo was also estimated using the methods of FAO-Penman-Monteith (EToPM, Hargreaves (EToH and Linacre (EToL, being correlated later with EToT proposed in this research by season. For that, daily values of temperature, air relative humidity, solar radiation, precipitation, atmospheric pressure and wind speed at 2 m, were taken using the Automatic Meteorological Station installed in the Universidade Federal de Campina Grande (UFCG

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.

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.

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...

Isotopic estimation of the evapo-transpiration flux in a plain agricultural region (Po plain, Northern Italy)

International Nuclear Information System (INIS)

Elmi, Giovanni; Sacchi, Elisa; Zuppi, Gian Maria; Cerasuolo, Marcello; Allais, Enrico

2013-01-01

composition of the phreatic aquifer (δ 18 O = −9.0 ± 0.5 to −10.4 ± 0.3‰). In addition, the slope of the water vapour regression line (6.8) indicates evaporation under high relative humidity (R h = 95%). The isotope composition of the water vapour in the Pavia area results from three main components: moisture carried by continental cold circulation, by maritime (Atlantic and Mediterranean) circulations and by the local evapo-transpiration flux. The latter is more intense in late spring and summer, due the maximum vegetation activity but also to irrigation and rice field flooding, and to the consequent maximum rise of the water table level. The turbulence due to the dynamic nature of the troposphere mixes local atmospheric moisture with water vapour carried by advection from other regions. Even in the most obvious situations of no circulation, phenomena of exclusive local evapo-transpiration are seldom observed. Circulation of air masses from the Mediterranean and the Atlantic carry the major part of atmospheric moisture towards the Po plain, while only cold and dry air masses from the NE, which are not found in the summer, are able to completely lower the local isotopic signal of the vapour, because of the substitution effect caused by their higher density. The expected correlation between the evapo-transpiration flux intensity and the precipitation amount is significant, and little difference in the local evapo-transpiration flux is observed between 2006 and 2007. On the other hand, the isotope composition of water vapour testifies to the importance of irrigation as a source of local vapour, evidencing, even at mid-latitudes, a regional scale feedback between land use and climate

Comparison of MODIS and SWAT evapotranspiration over a complex terrain at different spatial scales

Directory of Open Access Journals (Sweden)

O. O. Abiodun

2018-05-01

Full Text Available In most hydrological systems, evapotranspiration (ET and precipitation are the largest components of the water balance, which are difficult to estimate, particularly over complex terrain. In recent decades, the advent of remotely sensed data based ET algorithms and distributed hydrological models has provided improved spatially upscaled ET estimates. However, information on the performance of these methods at various spatial scales is limited. This study compares the ET from the MODIS remotely sensed ET dataset (MOD16 with the ET estimates from a SWAT hydrological model on graduated spatial scales for the complex terrain of the Sixth Creek Catchment of the Western Mount Lofty Ranges, South Australia. ET from both models was further compared with the coarser-resolution AWRA-L model at catchment scale. The SWAT model analyses are performed on daily timescales with a 6-year calibration period (2000–2005 and 7-year validation period (2007–2013. Differences in ET estimation between the SWAT and MOD16 methods of up to 31, 19, 15, 11 and 9 % were observed at respectively 1, 4, 9, 16 and 25 km2 spatial resolutions. Based on the results of the study, a spatial scale of confidence of 4 km2 for catchment-scale evapotranspiration is suggested in complex terrain. Land cover differences, HRU parameterisation in AWRA-L and catchment-scale averaging of input climate data in the SWAT semi-distributed model were identified as the principal sources of weaker correlations at higher spatial resolution.

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...

Summer crops evapotranspiration for two climatically constrating regions of Uruguay

International Nuclear Information System (INIS)

Gimenez, L.; Garcia, M.

2011-01-01

During the growth and development of grain crops there are a series of limiting factors which prevent obtaining yields to full potential. In particular, in summer crops grown in rain fed conditions, water deficiency stands out as one of the main factors affecting yield productivity. In this study crop evapotranspiration (E Tc) was estimated as a way to assess water needs in summer crops and real evapotranspiration (E Tr) of rain fed crops that occurs under field conditions. The study consisted in estimating E Tc and E Tr of soybean G M IV and V I, corn, sorghum and sunflower in two contrasting climatic regions of Uruguay for a period of 24 years (1984/2007) using the model WinISAREG. Water needs varied. The Nina and Nino years stood out with higher and lower values of Etc respectively. Such water needs are linked to cycle duration. Daily Etc was higher in the North and total Etc was higher in the South. The Etr obtained was substantially lower than Etc and with higher variability in most agr o-climatic situations studied. Sunflower and sorghum were the crops that presented the least differences between Etc and E Tr, and soybean and corn showed the greatest differences at both locations

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...

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

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...... aspects of ET systems is their ability to evapotranspire all of the sewage discharged into the systems and the rain falling onto the systems. On an annual basis the ET should equal the amount of wastewater discharged into the system plus the amount of precipitation falling onto the system. Part......, their design, construction and management as well as operational experience are described....

Modeling of the radiative energy balance within a crop canopy for estimating evapotranspiration: Studies on a row planted soybean canopy

International Nuclear Information System (INIS)

Nakano, Y.; Hirota, O.

1990-01-01

The spatial distribution and density of the leaf area within a crop canopy were used to estimate the radiational environment and evapotranspiration. Morphological measurements were pursued on the soybean stands in the early stage of growth when the two-dimensional foliage distribution pattern existed. The rectangular tube model was used to calculate the light absorption by parallel row of crops both short-wave radiation (direct and diffuse solar radiation, and scattered radiation by plant elements) and long-wave radiation (emanated radiation from the sky, ground and leaves). The simulated profiles are in close agreement with the experimentally measured short-wave and net radiation data. The evapotranspiration of a row was calcuated using a simulated net radiation. The model calculation also agreed well with the evapotranspiration estimated by the Bowen ratio method

Estimating evapotranspiration in the central mountain region of Veracruz, Mexico

OpenAIRE

Ballinas, Mónica; Esperón-Rodríguez, Manuel; Barradas, Víctor L

2015-01-01

The global, regional and local hydrological cycle is strongly linked to vegetation distribution. The hydrological cycle is composed by precipitation, infiltration, runoff, transpiration and evaporation. Evaporation is influenced by high temperatures, high winds and low relative humidity. This work is focused on the study of evapotranspiration (ET) as the main variable of water loss in the water balance in the central mountain region of Veracruz, Mexico. ET was estimated using the Penman-Monte...

Combining Remote Sensing imagery of both fine and coarse spatial resolution to Estimate Crop Evapotranspiration and quantifying its Influence on Crop Growth Monitoring.

Science.gov (United States)

Sepulcre-Cantó, Guadalupe; Gellens-Meulenberghs, Françoise; Arboleda, Alirio; Duveiller, Gregory; Piccard, Isabelle; de Wit, Allard; Tychon, Bernard; Bakary, Djaby; Defourny, Pierre

2010-05-01

This study has been carried out in the framework of the GLOBAM -Global Agricultural Monitoring system by integration of earth observation and modeling techniques- project whose objective is to fill the methodological gap between the state of the art of local crop monitoring and the operational requirements of the global monitoring system programs. To achieve this goal, the research aims to develop an integrated approach using remote sensing and crop growth modeling. Evapotranspiration (ET) is a valuable parameter in the crop monitoring context since it provides information on the plant water stress status, which strongly influences crop development and, by extension, crop yield. To assess crop evapotranspiration over the GLOBAM study areas (300x300 km sites in Northern Europe and Central Ethiopia), a Soil-Vegetation-Atmosphere Transfer (SVAT) model forced with remote sensing and numerical weather prediction data has been used. This model runs at pre-operational level in the framework of the EUMETSAT LSA-SAF (Land Surface Analysis Satellite Application Facility) using SEVIRI and ECMWF data, as well as the ECOCLIMAP database to characterize the vegetation. The model generates ET images at the Meteosat Second Generation (MSG) spatial resolution (3 km at subsatellite point),with a temporal resolution of 30 min and monitors the entire MSG disk which covers Europe, Africa and part of Sud America . The SVAT model was run for 2007 using two approaches. The first approach is at the standard pre-operational mode. The second incorporates remote sensing information at various spatial resolutions going from LANDSAT (30m) to SEVIRI (3-5 km) passing by AWIFS (56m) and MODIS (250m). Fine spatial resolution data consists of crop type classification which enable to identify areas where pure crop specific MODIS time series can be compiled and used to derive Leaf Area Index estimations for the most important crops (wheat and maize). The use of this information allowed to characterize

Estimation of daily evapotranspiration in Northern China Plain by using MODIS/TERRA images

NARCIS (Netherlands)

Yanbo He,; Su, Z.; Jia, L.; Yuanyuan Zhang,; Roerink, G.J.; Shili Wang,; Jun Wen,; Yingyu Hou,

2005-01-01

Evapotranspiration (ET) in regional scale is not only a major component of energy and water balance, but also a linking medium between ecological system and climatic system. Due to the increased needs from hydrological, climatological and ecological communities, more interest has been paid on

Effects of elevated CO2 and vascular plants on evapotranspiration in bog vegetation

NARCIS (Netherlands)

Heijmans, M.M.P.D.; Arp, W.J.; Berendse, F.

2001-01-01

We determined evapotranspiration in three experiments designed to study the effects of elevated CO2 and increased N deposition on ombrotrophic bog vegetation. Two experiments used peat monoliths with intact bog vegetation in containers, with one experiment outdoors and the other in a greenhouse. A

Evaluation of land surface model simulations of evapotranspiration over a 12-year crop succession: impact of soil hydraulic and vegetation properties

Science.gov (United States)

Garrigues, S.; Olioso, A.; Calvet, J. C.; Martin, E.; Lafont, S.; Moulin, S.; Chanzy, A.; Marloie, O.; Buis, S.; Desfonds, V.; Bertrand, N.; Renard, D.

2015-07-01

Evapotranspiration has been recognized as one of the most uncertain terms in the surface water balance simulated by land surface models. In this study, the SURFEX/ISBA-A-gs (Interaction Sol-Biosphere-Atmosphere) simulations of evapotranspiration are assessed at the field scale over a 12-year Mediterranean crop succession. The model is evaluated in its standard implementation which relies on the use of the ISBA pedotransfer estimates of the soil properties. The originality of this work consists in explicitly representing the succession of crop cycles and inter-crop bare soil periods in the simulations and assessing its impact on the dynamics of simulated and measured evapotranspiration over a long period of time. The analysis focuses on key parameters which drive the simulation of ET, namely the rooting depth, the soil moisture at saturation, the soil moisture at field capacity and the soil moisture at wilting point. A sensitivity analysis is first conducted to quantify the relative contribution of each parameter on ET simulation over 12 years. The impact of the estimation method used to retrieve the soil parameters (pedotransfer function, laboratory and field methods) on ET is then analysed. The benefit of representing the variations in time of the rooting depth and wilting point is evaluated. Finally, the propagation of uncertainties in the soil parameters on ET simulations is quantified through a Monte Carlo analysis and compared with the uncertainties triggered by the mesophyll conductance which is a key above-ground driver of the stomatal conductance. This work shows that evapotranspiration mainly results from the soil evaporation when it is continuously simulated over a Mediterranean crop succession. This results in a high sensitivity of simulated evapotranspiration to uncertainties in the soil moisture at field capacity and the soil moisture at saturation, both of which drive the simulation of soil evaporation. Field capacity was proved to be the most

Monitoring Seasonal Evapotranspiration in Vulnerable Agriculture using Time Series VHSR Satellite Data

Science.gov (United States)

Dalezios, Nicolas; Spyropoulos, Nicos V.; Tarquis, Ana M.

2015-04-01

The research work stems from the hypothesis that it is possible to perform an estimation of seasonal water needs of olive tree farms under drought periods by cross correlating high spatial, spectral and temporal resolution (~monthly) of satellite data, acquired at well defined time intervals of the phenological cycle of crops, with ground-truth information simultaneously applied during the image acquisitions. The present research is for the first time, demonstrating the coordinated efforts of space engineers, satellite mission control planners, remote sensing scientists and ground teams to record at specific time intervals of the phenological cycle of trees from ground "zero" and from 770 km above the Earth's surface, the status of plants for subsequent cross correlation and analysis regarding the estimation of the seasonal evapotranspiration in vulnerable agricultural environment. The ETo and ETc derived by Penman-Montieth equation and reference Kc tables, compared with new ETd using the Kc extracted from the time series satellite data. Several vegetation indices were also used especially the RedEdge and the chlorophyll one based on WorldView-2 RedEdge and second NIR bands to relate the tree status with water and nutrition needs. Keywords: Evapotransipration, Very High Spatial Resolution - VHSR, time series, remote sensing, vulnerability, agriculture, vegetation indeces.

Measure and estimation of the evapotranspiration of tomato plants cultivated with organic fertilization in protected ambient / Medida e estimativa da evapotranspiração do tomateiro cultivado sob adubação orgânica em ambiente protegido

Directory of Open Access Journals (Sweden)

Viviane Aires de Paula

2010-09-01

Full Text Available The present work had the aim of determining the water consumption for tomato crop cultivated in protected ambient under organic fertilization and of evaluating the estimates of evapotranspiration and of crop coefficients (Kc in greenhouse, with the use of the methods Class A Pan, Solar Radiation, Penman and Penman-Monteith. The experiment was carried out from September/2004 to January/2005, at the Campus of Universidade Federal de Pelotas, Brazil. The organic fertilization of the soil consisted of two doses of vermicompost from bovine manure, and ‘Floradade’ tomato plants were transplanted in 4/11/2004, with 0.50 x 0.70 m spacing. In the central part of the greenhouse, a datalogger was installed in order to receive the signals originated from the agrometeorologicals sensors installed in the greenhouse. In order to determine the water consumption of the plants, the method of water balance of the soil was used associated to evapotranspirometers, constructed in the central of the polyethylene greenhouse. The water consumption of the tomato plants in the 88 days of cultivation was of 477 mm. The estimation of the evapotranspiration for the methods Class A Pan, Solar Radiation and Penman, presented high precision and had agreement with the measured values of the crop evapotranspiration. The reference evapotranspiration presented values close to the crop evapotranspiration during the crop growth with the use of the methods Class A Pan, Solar Radiation and Penman, with Kc values of 0.95; 1.02; and 1.01, respectively, while for the Penman-Monteith method the Kc was 1.41.O presente trabalho teve por objetivos determinar o consumo hídrico do tomateiro com adubação orgânica e avaliar as estimativas da evapotranspiração e do coeficiente de cultura (Kc em ambiente protegido, com o uso dos métodos do Tanque Classe A, Radiação Solar, Penman e Penman-Monteith. O experimento foi conduzido de setembro de 2004 a janeiro de 2005, no Campus da

MODIS-based global terrestrial estimates of gross primary productivity and evapotranspiration

Science.gov (United States)

Ryu, Y.; Baldocchi, D. D.; Kobayashi, H.; Li, J.; van Ingen, C.; Agarwal, D.; Jackson, K.; Humphrey, M.

2010-12-01

We propose a novel approach to quantify gross primary productivity (GPP) and evapotranspiration (ET) at global scale (5 km resolution with 8-day interval). The MODIS-based, process-oriented approach couples photosynthesis, evaporation, two-leaf energy balance and nitrogen, which are different from the previous satellite-based approaches. We couple information from MODIS with flux towers to assess the drivers and parameters of GPP and ET. Incoming shortwave radiation components (direct and diffuse PAR, NIR) under all sky condition are modeled using a Monte-Carlo based atmospheric radiative transfer model. The MODIS Level 2 Atmospheric products are gridded and overlaid with MODIS Land products to produce spatially compatible forcing variables. GPP is modeled using a two-leaf model (sunlit and shaded leaf) and the maximum carboxylation rate is estimated using albedo-Nitrogen-leaf trait relations. The GPP is used to calculate canopy conductance via Ball-Berry model. Then, we apply Penman-Monteith equation to calculate evapotranspiration. The process-oriented approach allows us to investigate the main drivers of GPP and ET at global scale. Finally we explore the spatial and temporal variability of GPP and ET at global scale.

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

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...

The Grape Remote Sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX)-a synopsis

Science.gov (United States)

Considering California’s recent multi-year drought as well as the severe droughts recently in Italy and South Africa, there is a critical need for accurate and timely evapotranspiration (ET) and crop stress information to ensure long-term sustainability of high-value value perennial crops (vineyards...

Continuous evapotranspiration monitoring and water stress at watershed scale in a Mediterranean oak savanna

Science.gov (United States)

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 ...

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...

Observations of pretreatment prostate-specific antigen doubling time in 107 patients referred for definitive radiotherapy

International Nuclear Information System (INIS)

Lee, W. Robert; Hanks, Gerald E.; Corn, Benjamin W.; Schultheiss, Timothy E.

1995-01-01

Purpose: To determine pretreatment prostate-specific antigen doubling times (PSADT) in patients referred for definitive radiotherapy. Methods and Materials: One hundred and seven patients with histologically proven nonmetastatic prostate cancer and an elevated prostate-specific antigen (PSA) who were referred for radiation therapy had three serum PSA values obtained prior to the start of definitive therapy. Prostate-specific antigen doubling times were calculated by linear regression. Results: Prostate-specific antigen values increased during the period of observation in 78 patients (73%). Forty-three patients (40%) had calculated PSADT of less than 2 years and of those patients with pretreatment serum PSA values of greater than 10 ng/mL more than 50% has calculated PSADT of less than 2 years. Conclusions: A significant minority of patients referred for radiotherapy have calculated PSADT of less than 2 years. The significance of this relatively fast growth rate is as yet undetermined, but suggests that patients referred for radiotherapy may have aggressive disease prior to treatment

Crop biomass and evapotranspiration estimation using SPOT and Formosat-2 Data

Science.gov (United States)

Veloso, Amanda; Demarez, Valérie; Ceschia, Eric; Claverie, Martin

2013-04-01

The use of crop models allows simulating plant development, growth and yield under different environmental and management conditions. When combined with high spatial and temporal resolution remote sensing data, these models provide new perspectives for crop monitoring at regional scale. We propose here an approach to estimate time courses of dry aboveground biomass, yield and evapotranspiration (ETR) for summer (maize, sunflower) and winter crops (wheat) by assimilating Green Area Index (GAI) data, obtained from satellite observations, into a simple crop model. Only high spatial resolution and gap-free satellite time series can provide enough information for efficient crop monitoring applications. The potential of remote sensing data is often limited by cloud cover and/or gaps in observation. Data from different sensor systems need then to be combined. For this work, we employed a unique set of Formosat-2 and SPOT images (164 images) and in-situ measurements, acquired from 2006 to 2010 in southwest France. Among the several land surface biophysical variables accessible from satellite observations, the GAI is the one that has a key role in soil-plant-atmosphere interactions and in biomass accumulation process. Many methods have been developed to relate GAI to optical remote sensing signal. Here, seasonal dynamics of remotely sensed GAI were estimated by applying a method based on the inversion of a radiative transfer model using artificial neural networks. The modelling approach is based on the Simple Algorithm for Yield and Evapotranspiration estimate (SAFYE) model, which couples the FAO-56 model with an agro-meteorological model, based on Monteith's light-use efficiency theory. The SAFYE model is a daily time step crop model that simulates time series of GAI, dry aboveground biomass, grain yield and ETR. Crop and soil model parameters were determined using both in-situ measurements and values found in the literature. Phenological parameters were calibrated by the

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...

Evaluation of HYDRUS-1D for Estimating Evapotranspiration of Bell Pepper Regulated by Cloud-based Fertigation System in Greenhouse

Science.gov (United States)

Ito, Y.; Honda, R.; Takesako, H.; Ozawa, K.; Kita, E.; Kanno, M.; Noborio, K.

2017-12-01

A fertile surface layer, contaminated with radiocesium resulting from the accident of the Fukushima Daiichi Nuclear Power Plant in 2011, was removed and replaced by non-fertile soil in Fukushima farmlands. In a greenhouse, we used a commercially-available cloud-based fertigation system (CBFS) for regulating an application rate of liquid fertilizer to bell pepper grown in the non-fertile soil. Although the CBFS regulates the application rate based on a weekly trend of volumetric water content (Θw) remotely measured at the soil surface using a soil moisture sensor if all applied water being consumed by plants in a greenhouse is not known. Evapotranspiration of green pepper grown with the CBFS was estimated by HYDRUS-1D. Experiments in a greenhouse were conducted in Fukushima, Japan, from September 1st to October 31st in 2016. Bell pepper plants were transplanted in the begging of June in 2016. The Penman-Monteith equation was used to estimate evapotranspiration, representing transpiration since the soil surface was covered with plastic mulch. Time domain reflectometry (TDR) probes were horizontally installed to monitor changes in Θw at 5, 10, 20, and 30 cm deep from the soil surface. The van Genuchten-Mualem hydraulic model for water and heat flow in soil was used for HYDRUS-1D. A precipitation rate for the upper boundary condition was given as an irrigation rate. We assumed wind speed was always 0.6 m s-1 for the Penman-Monteith equation. The amount of evapotranspiration estimated with the Penman-Monteith equation agreed well with the amount of irrigated water measured. The evapotranspiration simulated with HYDRUS-1D agreed well with that estimated with the Penman-Monteith equation. However, Θw at all depth were underestimated with Hydrus-1D by approximately 0.05 m3 m-3 and differences of Θw between measured and estimated with HYDRYS-1D became larger at deeper the soil depths. This might be attributed to larger water flow occurred because of a free drainage used

Analysis of Evapotranspiration and Modified Fournier Index in the municipality of Ahuacatlan, Nayarit, Mexico.

Directory of Open Access Journals (Sweden)

García-Ramírez, E.I.

2016-01-01

Full Text Available There is a global concern to know the trends on climate variables to prevent natural disasters and adapt measures in diverse productive activities. The objective of this work was to analyze the effect that potential evapotranspiration (ETo and modified Fournier index (MFi have on soil erosion, in the municipality of Ahuacatlan Nayarit during the period 1980-2009. Climatological records of precipitation and maximum and minimum temperatures were taken from the official website of the National Meteorological Service; a data cleaning and data quality control was performed using RClimdex software; data processing and variable calculation was carried by the Moclic software. Regarding the ETo variable, no significant changes were observed annually but a considered increasing trend in the months of july and august. A significant trend towards an increase was observed annually for the MFi. It was found that july, august, june and september were the months that most affect such trend. An increase in the ETo and MFi variables was found during july, which can cause higher damage on the soil.

Modelling insights on the partition of evapotranspiration components across biomes

Science.gov (United States)

Fatichi, Simone; Pappas, Christoforos

2017-04-01

Recent studies using various methodologies have found a large variability (from 35 to 90%) in the ratio of transpiration to total evapotranspiration (denoted as T:ET) across biomes or even at the global scale. Concurrently, previous results suggest that T:ET is independent of mean precipitation and has a positive correlation with Leaf Area Index (LAI). We used the mechanistic ecohydrological model, T&C, with a refined process-based description of soil resistance and a detailed treatment of canopy biophysics and ecophysiology, to investigate T:ET across multiple biomes. Contrary to observation-based estimates, simulation results highlight a well-constrained range of mean T:ET across biomes that is also robust to perturbations of the most sensitive parameters. Simulated T:ET was confirmed to be independent of average precipitation, while it was found to be uncorrelated with LAI across biomes. Higher values of LAI increase evaporation from interception but suppress ground evaporation with the two effects largely cancelling each other in many sites. These results offer mechanistic, model-based, evidence to the ongoing research about the range of T:ET and the factors affecting its magnitude across biomes.

Stochastic model for simulating Souris River Basin precipitation, evapotranspiration, and natural streamflow

Science.gov (United States)

Kolars, Kelsey A.; Vecchia, Aldo V.; Ryberg, Karen R.

2016-02-24

The Souris River Basin is a 61,000-square-kilometer basin in the Provinces of Saskatchewan and Manitoba and the State of North Dakota. In May and June of 2011, record-setting rains were seen in the headwater areas of the basin. Emergency spillways of major reservoirs were discharging at full or nearly full capacity, and extensive flooding was seen in numerous downstream communities. To determine the probability of future extreme floods and droughts, the U.S. Geological Survey, in cooperation with the North Dakota State Water Commission, developed a stochastic model for simulating Souris River Basin precipitation, evapotranspiration, and natural (unregulated) streamflow. Simulations from the model can be used in future studies to simulate regulated streamflow, design levees, and other structures; and to complete economic cost/benefit analyses.Long-term climatic variability was analyzed using tree-ring chronologies to hindcast precipitation to the early 1700s and compare recent wet and dry conditions to earlier extreme conditions. The extended precipitation record was consistent with findings from the Devils Lake and Red River of the North Basins (southeast of the Souris River Basin), supporting the idea that regional climatic patterns for many centuries have consisted of alternating wet and dry climate states.A stochastic climate simulation model for precipitation, temperature, and potential evapotranspiration for the Souris River Basin was developed using recorded meteorological data and extended precipitation records provided through tree-ring analysis. A significant climate transition was seen around1970, with 1912–69 representing a dry climate state and 1970–2011 representing a wet climate state. Although there were some distinct subpatterns within the basin, the predominant differences between the two states were higher spring through early fall precipitation and higher spring potential evapotranspiration for the wet compared to the dry state.A water

In situ measurements for calculating evapotranspiration values using neutron moisture meter

International Nuclear Information System (INIS)

El-Gendy, R.W.; El-Moniem, M.; Massoud, M.

2000-01-01

Field experiment was conducted at the Wadi Sudr area, south Sinai, Egypt. Two types of residual animal farm (i.e., goat and camel)used wheat crop, beside control (no manure). The neutron scattering method and tensiometers were used to calculate the components of soil moisture depletion, evapotranspiration (ET) and drainage rate (DR). Evapotranspiration (ET) was determined by four methods, i.e, soil moisture depletion (SMD), Active rooting depth (ARD) at 80% SMD, active rooting depth (ARD) at zero hydraulic potential gradient (dh/dz = 0) and Blaney - Criddle formula (climatically data) using published crop coefficient (Kc) ET values for goat and camel residuals and control treatments were found to be 5.59, 5.54 and 6.80; 4.48, 4.43 and 5.44; 5.01, 4.11 and 11.66 and 4.5 mm day 1 for all treatments using the previous four methods respectively. The data obtained also showed that ET values under organic manure treatments were lower than control treatment, while the dry weight of wheat crop was higher in the manure-treated plots relative to the control. These less irrigation water requirements are needed to be applied to manure-treated plots and this should reduce the opportunity of soil deterioration if saline water is used

Estimation of the regional evapotranspiration through remote sensing

International Nuclear Information System (INIS)

Vives, L.; Rivas, R.; Wohl Coelho, O.; Schirmbeck, J.; Valor, E.

2004-01-01

This proposal deals with a new methodology capable of estimating variations in time and space of the evapotranspiration rate, which is one of the main processes controlling recharge to the Guarani Aquifer System (GAS). Such a methodology is being applied to the dos Sinos River Basin, Rio Grande do Sul, Brazil, which is in a region where groundwater from the GAS is heavily used for industrial and urban purposes. The investigations are being carried out by researchers of the Flat Plains Hydrology Institute (National University of the Center Buenos Aires Province, Azul, Argentina) and the Center of Exact and Technological Sciences (University of dos Simos River Valley, UNISINOS, Sao Leopoldo, Rio Grande do Sul, Brazil) [es

Variabilidade local e regional da evapotranspiração estimada pelo algoritmo SEBAL Local and regional variability of evapotranspiration estimated by SEBAL algorithm

Directory of Open Access Journals (Sweden)

Luis C. J. Moreira

2010-12-01

Full Text Available Em face da importância em conhecer a evapotranspiração (ET para uso racional da água na irrigação no contexto atual de escassez desse recurso, algoritmos de estimativa da ET a nível regional foram desenvolvidos utilizando-se de ferramentas de sensoriamento remoto. Este estudo objetivou aplicar o algoritmo SEBAL (Surface Energy Balance Algorithms for Land em três imagens do satélite Landsat 5, do segundo semestre de 2006. As imagens correspondem a áreas irrigadas, floresta nativa densa e a Caatinga do Estado do Ceará (Baixo Acaraú, Chapada do Apodi e Chapada do Araripe. Este algoritmo calcula a evapotranspiração horária a partir do fluxo de calor latente, estimado como resíduo do balanço de energia na superfície. Os valores de ET obtidos nas três regiões foram superiores a 0,60 mm h-1 nas áreas irrigadas ou de vegetação nativa densa. As áreas de vegetação nativa menos densa apresentaram taxa da ET horária de 0,35 a 0,60 mm h-1, e valores quase nulos em áreas degradadas. A análise das médias de evapotranspiração horária pelo teste de Tukey a 5% de probabilidade permitiu evidenciar uma variabilidade significativa local, bem como regional no Estado do Ceará.In the context of water resources scarcity, the rational use of water for irrigation is necessary, implying precise estimations of the actual evapotranspiration (ET. With the recent progresses of remote-sensed technologies, regional algorithms estimating evapotranspiration from satellite observations were developed. This work aimed at applying the SEBAL algorithm (Surface Energy Balance Algorithms for Land at three Landsat-5 images during the second semester of 2006. These images cover irrigated areas, dense native forest areas and caatinga areas in three regions of the state of Ceará (Baixo Acaraú, Chapada do Apodi and Chapada do Araripe. The SEBAL algorithm calculates the hourly evapotranspiration from the latent heat flux, estimated from the surface energy

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...

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...

Topographic effects on solar radiation distribution in mountainous watersheds and their influence on reference evapotranspiration estimates at watershed scale

Directory of Open Access Journals (Sweden)

C. Aguilar

2010-12-01

Full Text Available Distributed energy and water balance models require time-series surfaces of the climatological variables involved in hydrological processes. Among them, solar radiation constitutes a key variable to the circulation of water in the atmosphere. Most of the hydrological GIS-based models apply simple interpolation techniques to data measured at few weather stations disregarding topographic effects. Here, a topographic solar radiation algorithm has been included for the generation of detailed time-series solar radiation surfaces using limited data and simple methods in a mountainous watershed in southern Spain. The results show the major role of topography in local values and differences between the topographic approximation and the direct interpolation to measured data (IDW of up to +42% and −1800% in the estimated daily values. Also, the comparison of the predicted values with experimental data proves the usefulness of the algorithm for the estimation of spatially-distributed radiation values in a complex terrain, with a good fit for daily values (R² = 0.93 and the best fits under cloudless skies at hourly time steps. Finally, evapotranspiration fields estimated through the ASCE-Penman-Monteith equation using both corrected and non-corrected radiation values address the hydrologic importance of using topographically-corrected solar radiation fields as inputs to the equation over uniform values with mean differences in the watershed of 61 mm/year and 142 mm/year of standard deviation. High speed computations in a 1300 km² watershed in the south of Spain with up to a one-hour time scale in 30 × 30 m² cells can be easily carried out on a desktop PC.

Comparison of hydrological simulations of climate change using perturbation of observations and distribution-based scaling

DEFF Research Database (Denmark)

Van Roosmalen, Lieke Petronella G; Sonnenborg, Torben; Jensen, Karsten Høgh

2011-01-01

of the HIRHAM4 regional climate model (RCM). The aim of this study was to determine whether the choice of bias-correction method, applied to the RCM data, aff ected the projected hydrological changes. One method consisted of perturbation of observed data (POD) using climate change signals derived from the RCM......Projected climate change eff ects on groundwater and stream discharges were investigated through simulations with a distributed, physically based, surface water–groundwater model. Input to the hydrological model includes precipitation, reference evapotranspiration, and temperature data...... the simulations using both methods, only small differences between the projected changes in hydrological variables for the scenario period were found. Mean annual recharge increased by 15% for the DBS method and 12% for POD, and drain flow increased by 24 and 19%, respectively, while the increases in base flow...

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.

Estimating crop yields and crop evapotranspiration distributions from remote sensing and geospatial agricultural data

Science.gov (United States)

Smith, T.; McLaughlin, D.

2017-12-01

Growing more crops to provide a secure food supply to an increasing global population will further stress land and water resources that have already been significantly altered by agriculture. The connection between production and resource use depends on crop yields and unit evapotranspiration (UET) rates that vary greatly, over both time and space. For regional and global analyses of food security it is appropriate to treat yield and UET as uncertain variables conditioned on climatic and soil properties. This study describes how probability distributions of these variables can be estimated by combining remotely sensed land use and evapotranspiration data with in situ agronomic and soils data, all available at different resolutions and coverages. The results reveal the influence of water and temperature stress on crop yield at large spatial scales. They also provide a basis for stochastic modeling and optimization procedures that explicitly account for uncertainty in the environmental factors that affect food production.

Comparative study of in situ methods for potential and actual evapotranspiration determination and their calculation by simulation model

International Nuclear Information System (INIS)

Kolev, B.

2006-01-01

Four in situ methods for potential and actual evapotranspiration determining were compared: neutron gauge, tensiometers, gypsum blocks and lysimeters. The actual and potential evapotranspiration were calculated by water balance equation and by using a simulation model for their determination. The aim of this study was mainly pointed on calculations of water use efficiency and transpiration coefficient in potential production situation. This makes possible to choose the best way for water consumption optimization for a given crop. The final results find with the best of the methods could be used for applying the principles of sustainable agricultural production in random object of Bulgarian agricultural area

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

A System Dynamics Approach to Modeling Future Climate Scenarios: Quantifying and Projecting Patterns of Evapotranspiration and Precipitation in the Salton Sea Watershed

Directory of Open Access Journals (Sweden)

Michael E. Kjelland

2014-01-01

Full Text Available The need for improved quantitative precipitation forecasts and realistic assessments of the regional impacts of natural climate variability and climate change has generated increased interest in regional (i.e., systems-scale climate simulation. The Salton Sea Stochastic Simulation Model (S4M was developed to assist planners and residents of the Salton Sea (SS transboundary watershed (USA and Mexico in making sound policy decisions regarding complex water-related issues. In order to develop the S4M with a higher degree of climate forecasting resolution, an in-depth analysis was conducted regarding precipitation and evapotranspiration for the semiarid region of the watershed. Weather station data were compiled for both precipitation and evapotranspiration from 1980 to 2004. Several logistic regression models were developed for determining the relationships among precipitation events, that is, duration and volume, and evapotranspiration levels. These data were then used to develop a stochastic weather generator for S4M. Analyses revealed that the cumulative effects and changes of ±10 percent in SS inflows can have significant effects on sea elevation and salinity. The aforementioned technique maintains the relationships between the historic frequency distributions of both precipitation and evapotranspiration, and not as separate unconnected and constrained variables.

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

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

KAUST Repository

Wang, Lixin; Niu, Shuli; Good, Stephen P.; Soderberg, Keir; McCabe, Matthew; Sherry, Rebecca A.; Luo, Yiqi; Zhou, Xuhui; Xia, Jianyang; Caylor, Kelly K.

2013-01-01

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

Water productivity using SAFER - Simple Algorithm for Evapotranspiration Retrieving in watershed

Directory of Open Access Journals (Sweden)

Daniel N. Coaguila

Full Text Available ABSTRACT The Cabeceira Comprida stream’s watershed, located in Santa Fé do Sul, São Paulo state, has great environmental importance. It is essential for supplying water to the population and generating surpluses for sewage dilution. This study aimed to evaluate the annual performance of the components of water productivity from Landsat-8 images of 2015, using the Simple Algorithm for Evapotranspiration Retrieving (SAFER, calculating the actual evapotranspiration (ETa, biomass (BIO and water productivity (WP. The annual averages of ETa, BIO and WP were 1.03 mm day-1, 36.04 kg ha-1 day-1 and 3.19 kg m-3, respectively. The average annual values of ETa for land use and occupation were 1.40, 1.23, 1.05, 0.97 and 1.08 mm day-1 for the remaining forest (RF, invasive species (IS, pasture (Pa, annual crop (AC and perennial crop (PC, respectively, with BIO of 57.64, 46.10, 36.78, 32.69, 40.03 kg ha-1 day-1 for RF, IS, Pa, AC and PC, respectively, resulting in WP of 3.94, 3.59, 3.25, 3.09, 3.35 kg m-3 for RF, IS, Pa, AC and PC, respectively. The ETa, BIO and WP adjust to the seasonality of the region, and RF and IS stood out with the highest values.

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.

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.

Evapotranspiration and crop coefficient of drip irrigated watermelon in Piaui coastline, Brazil Evapotranspiração e coeficiente de cultivo da melancia irrigada por gotejamento no litoral do Piauí

Directory of Open Access Journals (Sweden)

Edson A. Bastos

2012-06-01

Full Text Available The knowledge of the evapotranspiration (ETc and crop coefficient (Kc is fundamental to plan and to manage the irrigation of any crop. The aim of this study was to determine the daily and hourly evapotranspiration of drip irrigated watermelon (Citrullus Lanatus, var. Crimson Sweet and crop coefficient (Kc in each crop development phase. The experiment was carried out in an experimental area of 1.27 ha of Embrapa Mid-North, localized in Parnaíba (02°54'S, 41°47'W and 46 m above of sea, State of Piauí, Brazil, from September to November, 2006. Electronic weighing lysimeters of 1.5 m x 1.5 m wide and long and 1.0 m deep were used to obtain the evapotranspiration. The plants were drip irrigated with a lateral row per plant row and drippers spaced 0.5 m from each other. The reference evapotranspiration (ETo was estimated using the Penman-Monteith equation from the climatic data obtained by electronic sensors. The total evapotranspiration during the watermelon crop cycle cultivated in the state of Piauí was 233.87 mm, with mean values of 3.7 mm day-1, minimum of 1.18 and maximum of 8.14 mm day-1. The Kc of the drip irrigated watermelon was 0.18 in the initial stage of crop growth; 0.18 to 1.3, in crop development stage; 1.3 in the intermediate stage and 0.43 in the final stage.O conhecimento da evapotranspiração e do coeficiente de cultivo (Kc é fundamental para dimensionar e manejar a irrigação de qualquer cultura. O objetivo deste trabalho foi determinar a evapotranspiração (ETc diária e horária da melancia (Citrullus lanatus Schrad, var. Crimson Sweet irrigada por gotejamento e o Kc em cada fase de desenvolvimento da cultura. O estudo foi conduzido em uma área experimental de 1,27 ha da Embrapa Meio-Norte, localizada em Parnaíba - PI (02° 54'S, 41° 47'W e 46 m de altitude, no período de setembro a novembro de 2006. Utilizaram-se quatro lisímetros de pesagem eletrônica de 1,5 m x 1,5 m de largura e comprimento com 1,0 m de

Post-Fire Evapotranspiration and Net Ecosystem Exchange over A Semi-Arid Grassland in Arizona

Science.gov (United States)

Krishnan, P.; Meyers, T. P.; Heuer, M.

2015-12-01

The seasonal and interannual variability of evapotranspiration (E) and net ecosystem exchange (NEE) following a fire disturbance over a semi -arid grassland located on the Audubon Research Ranch in south western Arizona (31.5907N, 110.5104W, elevation 1496 m), USA, and their relationships to environmental variables were examined using continuous measurements of water vapour and CO2 fluxes made from first week of June 2002 to 2009 using the eddy covariance technique. The research ranch was established in 1969 as an ecological research preserve and it is now one of the largest ungrazed, privately managed grassland sites in Arizona. A wild fire occurred in April - May 2002, and burned all the standing vegetation and litter on in research ranch (~38,000 acres) including 500 acres of grassland. The mean annual temperature and precipitation (P) at this site were ~16 deg C and ~370 mm, respectively. More than 60% of the annual P was received during the North American monsoon period (July-September) with the lowest annual P in the drought years of 2004 and 2009. Drastic changes in albedo, vegetation growth and evapotranspiration occurred following the onset of the monsoon season in July. The ecosystem was mostly a carbon sink during monsoon period. Daily total evapotranspiration during July-August increased from 2 mm d-1 in 2002 to >3 mm d-1 in 2007. The mean annual E over the site was during 2003 -2009 was 352 ±75 mm. With the onset of monsoon the ecosystem turned to carbon sink in 2002, with daily total net ecosystem exchange (NEE) varying up to ~vegetation index, longest monsoon growing season and the highest annual and July-September P. The interannual variations in annual E and NEE were mostly controlled by annual P, July-September NDVI and growing season length during 2002-2009.

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...

SOLAR-ISS: A new reference spectrum based on SOLAR/SOLSPEC observations

Science.gov (United States)

Meftah, M.; Damé, L.; Bolsée, D.; Hauchecorne, A.; Pereira, N.; Sluse, D.; Cessateur, G.; Irbah, A.; Bureau, J.; Weber, M.; Bramstedt, K.; Hilbig, T.; Thiéblemont, R.; Marchand, M.; Lefèvre, F.; Sarkissian, A.; Bekki, S.

2018-03-01

Context. Since April 5, 2008 and up to February 15, 2017, the SOLar SPECtrometer (SOLSPEC) instrument of the SOLAR payload on board the International Space Station (ISS) has performed accurate measurements of solar spectral irradiance (SSI) from the middle ultraviolet to the infrared (165 to 3088 nm). These measurements are of primary importance for a better understanding of solar physics and the impact of solar variability on climate. In particular, a new reference solar spectrum (SOLAR-ISS) is established in April 2008 during the solar minima of cycles 23-24 thanks to revised engineering corrections, improved calibrations, and advanced procedures to account for thermal and aging corrections of the SOLAR/SOLSPEC instrument. Aims: The main objective of this article is to present a new high-resolution solar spectrum with a mean absolute uncertainty of 1.26% at 1σ from 165 to 3000 nm. This solar spectrum is based on solar observations of the SOLAR/SOLSPEC space-based instrument. Methods: The SOLAR/SOLSPEC instrument consists of three separate double monochromators that use concave holographic gratings to cover the middle ultraviolet (UV), visible (VIS), and infrared (IR) domains. Our best ultraviolet, visible, and infrared spectra are merged into a single absolute solar spectrum covering the 165-3000 nm domain. The resulting solar spectrum has a spectral resolution varying between 0.6 and 9.5 nm in the 165-3000 nm wavelength range. We build a new solar reference spectrum (SOLAR-ISS) by constraining existing high-resolution spectra to SOLAR/SOLSPEC observed spectrum. For that purpose, we account for the difference of resolution between the two spectra using the SOLAR/SOLSPEC instrumental slit functions. Results: Using SOLAR/SOLSPEC data, a new solar spectrum covering the 165-3000 nm wavelength range is built and is representative of the 2008 solar minimum. It has a resolution better than 0.1 nm below 1000 nm and 1 nm in the 1000-3000 nm wavelength range. The new

Evapotranspiration and crop coefficient of oil palm (Elaeis guineensis Jacq.) on the main nursery in a greenhouse

Science.gov (United States)

Sigalingging, R.; Sumono; Rahmansyah, N.

2018-02-01

The estimation of crop water requirement is an important part of oil palm plantation because fruit yield of oil palm can be affected by water stress. Evapotranspiration and crop coefficient of oil palm using Tenera variety at 7-12 months old was determined. Soil texture was sandy loam with 73.8 % sand, 10.8 % silt, 15.77 % clay and 1.41 % organic matter. The results showed that the oil palm getting older decreased significantly in bulk density, particle density and porosity of soil caused the root of oil palm enlarged (19.42 g to 53.37 g). This was indicated by increased the dry root weight. On the other hand, the value of evapotranspiration and crop coefficient increased significantly, that was 1.85 to 2.00 mm/day and 0.8 to 0.87 respectively.

Reference Evapotranspiration Variation Analysis and Its Approaches Evaluation of 13 Empirical Models in Sub-Humid and Humid Regions: A Case Study of the Huai River Basin, Eastern China

Directory of Open Access Journals (Sweden)

Meng Li

2018-04-01

Full Text Available Accurate and reliable estimations of reference evapotranspiration (ET0 are imperative in irrigation scheduling and water resource planning. This study aims to analyze the spatiotemporal trends of the monthly ET0 calculated by the Penman–Monteith FAO-56 (PMF-56 model in the Huai River Basin (HRB, eastern China. However, the use of the PMF-56 model is limited by the insufficiency of climatic input parameters in various sites, and the alternative is to employ simple empirical models. In this study, the performances of 13 empirical models were evaluated against the PMF-56 model by using three common statistical approaches: relative root-mean-square error (RRMSE, mean absolute error (MAE, and the Nash–Sutcliffe coefficient (NS. Additionally, a linear regression model was adopted to calibrate and validate the performances of the empirical models during the 1961–2000 and 2001–2014 time periods, respectively. The results showed that the ETPMF increased initially and then decreased on a monthly timescale. On a daily timescale, the Valiantzas3 (VA3 was the best alternative model for estimating the ET0, while the Penman (PEN, WMO, Trabert (TRA, and Jensen-Haise (JH models showed poor results with large errors. Before calibration, the determination coefficients of the temperature-based, radiation-based, and combined models showed the opposite changing trends compared to the mass transfer-based models. After calibration, the performance of each empirical model in each month improved greatly except for the PEN model. If the comprehensive climatic datasets were available, the VA3 would be the recommended model because it had a simple computation procedure and was also very well correlated linearly to the PMF-56 model. Given the data availability, the temperature-based, radiation-based, Valiantzas1 (VA1 and Valiantzas2 (VA2 models were recommended during April–October in the HRB and other similar regions, and also, the mass transfer-based models were

Characteristics and Impact Factors of Parameter Alpha in the Nonlinear Advection-Aridity Method for Estimating Evapotranspiration at Interannual Scale in the Loess Plateau

Science.gov (United States)

Zhou, H.; Liu, W.; Ning, T.

2017-12-01

Land surface actual evapotranspiration plays a key role in the global water and energy cycles. Accurate estimation of evapotranspiration is crucial for understanding the interactions between the land surface and the atmosphere, as well as for managing water resources. The nonlinear advection-aridity approach was formulated by Brutsaert to estimate actual evapotranspiration in 2015. Subsequently, this approach has been verified, applied and developed by many scholars. The estimation, impact factors and correlation analysis of the parameter alpha (αe) of this approach has become important aspects of the research. According to the principle of this approach, the potential evapotranspiration (ETpo) (taking αe as 1) and the apparent potential evapotranspiration (ETpm) were calculated using the meteorological data of 123 sites of the Loess Plateau and its surrounding areas. Then the mean spatial values of precipitation (P), ETpm and ETpo for 13 catchments were obtained by a CoKriging interpolation algorithm. Based on the runoff data of the 13 catchments, actual evapotranspiration was calculated using the catchment water balance equation at the hydrological year scale (May to April of the following year) by ignoring the change of catchment water storage. Thus, the parameter was estimated, and its relationships with P, ETpm and aridity index (ETpm/P) were further analyzed. The results showed that the general range of annual parameter value was 0.385-1.085, with an average value of 0.751 and a standard deviation of 0.113. The mean annual parameter αe value showed different spatial characteristics, with lower values in northern and higher values in southern. The annual scale parameter linearly related with annual P (R2=0.89) and ETpm (R2=0.49), while it exhibited a power function relationship with the aridity index (R2=0.83). Considering the ETpm is a variable in the nonlinear advection-aridity approach in which its effect has been incorporated, the relationship of

Astrometric observations of Saturn's satellites from McDonald Observatory, 1972. [using reference stars

Science.gov (United States)

Abbot, R. I.; Mulholland, J. D.; Shelus, P. J.

1974-01-01

Observations of Saturn's satellites were reduced by means of secondary reference stars obtained by reduction of Palomar Sky Survey (PSS) plates. This involved the use of 39 SAO stars and plate overlap technique to determine the coordinates of 59 fainter stars in the satellite field. Fourteen plate constants were determined for each of the two PSS plates. Comparison of two plate measurement and reduction techniques on the satellite measurements demonstrate the existence of a serious background gradient effect and the utility of microdensitometry to eliminate this error source in positional determinations of close satellites.

Evapotranspiration versus oxygen intrusion: which is the main force in alleviating bioclogging of vertical-flow constructed wetlands during a resting operation?

Science.gov (United States)

Hua, Guofen; Chen, Qiuwen; Kong, Jun; Li, Man

2017-08-01

Clogging is the most significant challenge limiting the application of constructed wetlands. Application of a forced resting period is a practical way to relieve clogging, particularly bioclogging. To reveal the alleviation mechanisms behind such a resting operation, evapotranspiration and oxygen flux were studied during a resting period in a laboratory vertical-flow constructed wetland model through physical simulation and numerical model analysis. In addition, the optimum theoretical resting duration was determined based on the time required for oxygen to completely fill the pores, i.e., formation of a sufficiently thick and completely dry layer. The results indicated that (1) evapotranspiration was not the key factor, but was a driving force in the alleviation of bioclogging; (2) the rate of oxygen diffusion into the pores was sufficient to oxidize and disperse the flocculant biofilm, which was essential to alleviate bioclogging. This study provides important insights into understanding how clogging/bioclogging can be alleviated in vertical-flow constructed wetlands. Graphical abstract Evapotranspiration versus oxygen intrusion in alleviating bioclogging in vertical flow constructed wetlands.

Large-scale lysimeter site St. Arnold, Germany: analysis of 40 years of precipitation, leachate and evapotranspiration

Directory of Open Access Journals (Sweden)

N. Harsch

2009-03-01

Full Text Available This study deals with a lysimetrical-meteorological data series collected on the large-scale lysimeter site "St. Arnold", Germany, from November 1965 to April 2007. The particular relevance of this data rests both upon its perdurability and upon the fact that the site is comprised of a grassland basin, an oak/beech and a pine basin.

Apart from analyzing long term trends of the meteorological measurements, the primary objective of this study is to investigate the water balance in grassland and forested basins, in particular comparing the precipitation term to leachate quantities and potential and actual evapotranspiration. The latter are based upon the Penman and the Penman-Monteith approaches, respectively.

The main results of this survey are that, on a long-term average, the grassland basin turns more than half (53% of its annually incoming precipitation into leachate and only 36% into water vapour, while the deciduous forest exhibits a ratio of 37% for leachate and 56% for evapotranspiration, and the evergreen coniferous forest shows the highest evaporation rate (65% and the lowest leachate rate (26%.

Concerning these water balances, considerable differences both between basins and between seasons stand out. While summer periods exhibit high evapotranspiration rates for the forests and moderate ones for the grassland, winter periods are characterised by considerable leachate quantities for grassland and the deciduous forest and moderate ones for the coniferous forest. Following the analysis of the climatic development in St. Arnold, trends towards a milder and more humid regional climate were detected.

Avaliação do Kt para estimativa da evapotranspiração de referência (ETo em Campos dos Goytacazes, RJ Evaluation of "Class A" pan coefficients to estimate the referential evapotranspiration in Campos dos Goytacazes, RJ

Directory of Open Access Journals (Sweden)

Barbara dos S. Esteves

2010-03-01

Full Text Available Neste trabalho foram avaliados diferentes métodos de determinação do coeficiente do tanque (Kt, para a estimativa diária da evapotranspiração de referência (ETo utilizando o método do tanque Classe A (TCA. Foram avaliadas as metodologias propostas por Allen et al. (1998, Bernardo et al., (1996, Cuenca (1989 e Snyder (1992; os valores da ETo diária estimados foram correlacionados com os estimados pelo método de Penman-Monteith parametrizado (FAO-56. Para a estimativa da ETo foi utilizado uma série histórica de 10 anos de dados coletados em uma estação automática, modelo Thies Clima, instalada na Estação Evapotranspirométrica da Universidade Estadual do Norte Fluminense Darcy Ribeiro (UENF. Os resultados obtidos, considerando-se as diferentes metodologias para o cálculo do Kt, mostrou um bom desempenho do método do tanque Classe A para a estimativa de valores diários da ETo (coeficientes r² > 0,79 e D > 0,90. As metodologias propostas por Cuenca (1989, Bernardo et al. (1996 e Allen (1998 apresentaram o mesmo índice de concordância (D = 0,95. O menor erro médio absoluto (EMA = 0,50 foi obtido pelo método de Cuenca (1989 que também mostrou a maior eficiência (EF = 0,81.In this work, different methods of determination of pan coefficient (Kp for a daily estimation of referential evapotranspiration (ETo using the "Class A" pan method (TCA were analyzed. Methodologies proposed by Allen et al. (1998, Bernardo et al. (1996, Cuenca (1989 and Snyder (1992 were evaluated, and values of daily ETo estimated using TCA were compared to ones estimated by Penman-Monteith (FAO-56. A ten years historical series of data collected from an automatic station, Thies Clima model, was used installed at evapotranspiration station of Universidade Estadual do Norte Fluminense (UENF. A good fulfillment of Class A pan to estimate daily values of ETo by different ways to calculate Kp (R² > 0.79 and D > 0.90 was verified, with Cuenca (1989, Bernardo

Use of geostationary satellite imagery in optical and thermal bands for the estimation of soil moisture status and land evapotranspiration

Science.gov (United States)

Ghilain, N.; Arboleda, A.; Gellens-Meulenberghs, F.

2009-04-01

satellites is the close monitoring of the diurnal variation of the land surface temperature. This feature reinforced the statistical strength of empirical methods. An empirical method linking land surface morning heating rates and the fraction of the vegetation cover, also known as a ‘Triangle method' (Gillies et al, 1997) is examined. This method is expected to provide an estimation of a root-zone soil moisture index. The sensitivity of the method to wind speed, soil type, vegetation type and climatic region is explored. Moreover, the impact of the uncertainty of LST and FVC on the resulting soil moisture estimates is assessed. A first impact study of using remotely sensed soil moisture index in the energy balance model is shown and its potential benefits for operational monitoring of evapotranspiration are outlined. References García-Haro, F.J., F. Camacho-de Coca, J. Meliá, B. Martínez (2005) Operational derivation of vegetation products in the framework of the LSA SAF project. Proceedings of the EUMETSAT Meteorological Satellite Conference Dubrovnik (Croatia) 19-23 Septembre. Gellens-Meulenberghs, F., Arboleda, A., Ghilain, N. (2007) Towards a continuous monitoring of evapotranspiration based on MSG data. Proceedings of the symposium on Remote Sensing for Environmental Monitoring and Change Detection. IAHS series. IUGG, Perugia, Italy, July 2007, 7 pp. Ghilain, N., Arboleda, A. and Gellens-Meulenberghs, F., (2008) Improvement of a surface energy balance model by the use of MSG-SEVIRI derived vegetation parameters. Proceedings of the 2008 EUMETSAT meteorological satellite data user's conference, Darmstadt, Germany, 8th-12th September, 7 pp. Gillies R.R., Carlson T.N., Cui J., Kustas W.P. and Humes K. (1997), Verification of the triangle method for obtaining surface soil water content and energy fluxes from remote measurements of Normalized Difference Vegetation Index (NDVI) and surface radiant temperature, International Journal of Remote Sensing, 18, pp. 3145

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

Directory of Open Access Journals (Sweden)

Giovanni Ravazzani

Full Text Available 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.

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.

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.

Validation of global evapotranspiration product (MOD16) using flux tower data in the African savanna, South Africa

CSIR Research Space (South Africa)

Ramoelo, Abel

2014-08-01

Full Text Available Globally, water is an important resource required for the survival of human beings. Water is a scarce resource in the semi-arid environments, including South Africa. In South Africa, several studies have quantified evapotranspiration (ET...

Long-term potential and actual evapotranspiration of two different forests on the Atlantic Coastal Plain

Science.gov (United States)

Devendra Amatya; S. Tian; Z. Dai; Ge Sun

2016-01-01

A reliable estimate of potential evapotranspiration (PET) for a forest ecosystem is critical in ecohydrologic modeling related with water supply, vegetation dynamics, and climate change and yet is a challenging task due to its complexity. Based on long-term on-site measured hydro-climatic data and predictions from earlier validated hydrologic modeling studies...

Reference resolution in multi-modal interaction: Preliminary observations

NARCIS (Netherlands)

González González, G.R.; Nijholt, Antinus

2002-01-01

In this paper we present our research on multimodal interaction in and with virtual environments. The aim of this presentation is to emphasize the necessity to spend more research on reference resolution in multimodal contexts. In multi-modal interaction the human conversational partner can apply

Application of a MODIS Soil Moisture-Evapotranspiration (MOD-SMET) Model to Evaluate Landscape and Hydrologic Recovery after the High Park Fire in Colorado, USA

Science.gov (United States)

Blount, W. K.; Hogue, T. S.; Franz, K.; Knipper, K. R.

2017-12-01

Accurate estimation of evapotranspiration (ET) is critical for the management of water resources, especially in water-stressed regions. ET accounts for approximately 60% of terrestrial precipitation globally and approaches 100% of annual rainfall in arid ecosystems, where transpiration becomes the dominant term. ET is difficult to measure due to its spatiotemporal variation, which requires adequate data coverage. While new remote sensing-based ET products are available at a 1 km spatial resolution, including the Operational Simplified Surface Energy Balance model (SSEBop) and the MODIS Global Evapotranspiration Project (MOD16), these products are available at monthly and 8-day temporal resolutions, respectively. To better understand the changing dynamics of hydrologic fluxes and the partitioning of water after land cover disturbances and to identify statically significant trends, more frequent observations are necessary. Utilizing the recently developed MODIS Soil Moisture-Evapotranspiration (MOD-SMET) model, daily temporal resolution is achieved. This presentation outlines the methodology of the MOD-SMET model and compares SSEBop, MOD16, and MOD-SMET ET estimates over the High Park Fire burn scar in Colorado, USA. MOD-SMET estimates are used to identify changes in fluxes and partitioning of the water cycle after a wildfire and during recovery in the High Park Fire near Fort Collins, Colorado. Initial results indicate greenness and ET from all three models decrease post-fire, with higher statistical confidence in high burn areas and spatial patterns that closely align with burn severity. MOD-SMET improves the ability to resolve statistically significant changes in ET following wildfires and better understand changes in the post-fire water budget. Utilizing this knowledge, water resource managers can better plan for, and mitigate, the short- and long-term impacts of wildfire on regional water supplies.

Evapotranspiration partitioning in the highest alpine meadow zones through in-situ chamber and dual stable water isotope approaches

Science.gov (United States)

Cui, J.; Tian, L.

2017-12-01

Understanding plant functionality within the water cycles of grassland ecosystems is crucial for obtaining both regional water balance and plant adaptability in the context of ongoing climate change. The transpiration to evapotranspiration ratio (T/ET) is an indicator of plant's contribution to ecosystem water cycle. In this study, we used high-frequency laser spectroscopy (L2130-i), three custom-built chambers, and eddy covariance techniques, to constrain the role played by plants in evapotranspiration over an alpine meadow ecosystem in the central Tibetan Plateau (TP). Three different sizes of chambers are used to direct measure the isotopic compositions in evapotranspiration (δET), evaporation (δE) and transpiration (δT). The consistent T/ET between δ18O and δD manifests that chamber and dual isotope tracers are robust methods to estimate T/ET in alpine meadow zone. Sensitivity analysis shows that the isotopic composition of evapotranspiration is the main contributor to, and the uncertainty source for, the T/ET estimate. The influence of meteorological and biotic factors on T/ET is also discussed. The results from this study indicate that plants play an important role in the water cycles of alpine meadow ecosystems despite the sparse distribution of plant cover. We also synthesized the published T/ET data over the entire TP region, and found a good relation between T/ET and leaf area index (LAI). Moreover, soil water content played some role in controlling T/ET beyond the LAI in arid/semiarid regions such as the TP. More than half of the TP is covered by grassland, but its low biomass and shallow rooting depth make it very vulnerable to climate change variables such as air temperature warming and variations in precipitation. Given the crucial role played by plants in an ecosystem's water cycle, any variations in grassland cover are likely to exert a critical impact on the regional hydrological cycle, and even the regional climate.

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

Mapping Evapotranspiration in the Sacramento San Joaquin Delta using simulated ECOSTRESS Thermal Data: Validation and Inter-comparison

Science.gov (United States)

Wong, A.; Jin, Y.; He, R.; Hulley, G.; Fisher, J.; Lee, C. M.; Rivera, G.; Hook, S. J.; Medellin-Azuara, J.; Kent, E. R.; Paw U, K. T.; Gao, F.; Lund, J. R.

2017-12-01

Irrigation accounts for 80% of human freshwater consumption, and most of it return to the atmosphere through evapotranspiration (ET). In California, where our water resources are limited and heavily utilized, the need for a cost-effective, timely, and consistent spatial estimate of crop ET, from the farm to watershed level, is becoming increasingly important. The ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS), to be launched in mid-2018, will provide the most detailed and accurate temperature measurements ever acquired from space and thus unique opportunities for estimating ET at the farm scale. We simulated the ECOSTRESS thermal data at a 70 m resolution using VIIRS thermal observations and ASTER emissivity data in the Sacramento-San Joaquin Delta region for the 2016 water year. Three remote sensing based ET methods were then applied to estimate ET using simulated ECOSTRESS data and optical data from Landsat and VIIRS, including Priestley-Taylor approaches developed by the Jet Propulsion Laboratory (PT-JPL) and by UC Davis (PT-UCD), and the Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) model. We compared these three sets of ET estimates with field measurements at sixteen sites over five crop types (Alfalfa, Corn, Pasture, Tomato, and Beardless Wheat). Good agreement was found between satellite-based estimates and field measurements. Our results demonstrate that thermal data from the upcoming ECOSTRESS mission will reduce the uncertainty in ET estimates. A continuous monitoring of the dynamics and spatial heterogeneity of consumptive water use at a field scale will help prepare and inform to adaptively manage water, canopy, and planting density to maximize yield with least amount of water.

Assessing groundwater storage changes using remote sensing-based evapotranspiration and precipitation at a large semiarid basin scale

NARCIS (Netherlands)

Gokmen, M.; Vekerdy, Z.; Lubczynski, M.; Timmermans, J.; Batelaan, Okke; Verhoef, W.

2013-01-01

A method is presented that uses remote sensing (RS)-based evapotranspiration (ET) and precipitation estimates with improved accuracies under semiarid conditions to quantify a spatially distributed water balance, for analyzing groundwater storage changes due to supplementary water uses. The method is

A New Method to Quantify the Isotopic Signature of Leaf Transpiration: Implications for Landscape-Scale Evapotranspiration Partitioning Studies

Science.gov (United States)

Wang, L.; Good, S. P.; Caylor, K. K.

2010-12-01

Characterizing the constituent components of evapotranspiration is crucial to better understand ecosystem-level water budgets and water use dynamics. Isotope based evapotranspiration partitioning methods are promising but their utility lies in the accurate estimation of the isotopic composition of underlying transpiration and evaporation. Here we report a new method to quantify the isotopic signature of leaf transpiration under field conditions. This method utilizes a commercially available laser-based isotope analyzer and a transparent leaf chamber, modified from Licor conifer leaf chamber. The method is based on the water mass balance in ambient air and leaf transpired air. We verified the method using “artificial leaves” and glassline extracted samples. The method provides a new and direct way to estimate leaf transpiration isotopic signatures and it has wide applications in ecology, hydrology and plant physiology.

Evapotranspiration Power Law in Self-Organized and Human-Managed Ecosystems

Science.gov (United States)

Zeng, R.; Cai, X.

2017-12-01

Natural systems display a profound degree of self-organization, often apparent even to the untrained eye. However, in this age of increased coupling among human and natural systems, it is unclear to what degree natural organization principles continue to govern human-managed landscapes. Here we present an emerging characteristic of terrestrial evapotranspiration (ET), one of the key components of the water cycle and energy budget, adhered to by both naturally organized and intensively managed landscapes. We find that ET variance and ET mean for ecosystems throughout the world with diverse climate conditions, vegetation structures, and land covers and land uses organize themselves according to a specific power law curve. From multi-source observations, the ET power law curve stands true through varying spatial scales, from field to region. Moreover, a phenomenon of similar ecosystems gravitating toward particular segments of the power law curve, suggests that the feature of self-optimization of ecosystems establishes the ET power law together with climatic conditions. Perhaps surprisingly, we find that landscapes persistently follow the power law curve even upon human-induced transition from rain-fed to irrigated agriculture in the American High Plains and from wetland to agricultural land in American Midwest. As such, the ET power law can be an informative tool for predicting consequences of anthropogenic disturbances to the hydrologic cycle and understanding constraints to sustainable land use.

Relações entre transpiração máxima, evapotranspiração de referência e área foliar em quatro variedades de mangueira Maximum transpiration, reference evapotranspiration and leaf area relationships for some mango cultivars

Directory of Open Access Journals (Sweden)

Greice Ximena Santos Oliveira

2009-03-01

Full Text Available Nas condições edafoclimáticas de Cruz da Almas - BA, na Embrapa Mandioca e Fruticultura Tropical, foi realizado um estudo no qual se relacionou a transpiração máxima (Litros m-2 folha/dia -1 de quatro variedades de mangueira (Tommy Atkins, Palmer, Haden e Van Dyke, com áreas foliares totais de 14; 8; 33 e 12 m², respectivamente com a evapotranspiração de referência (ETo. A transpiração das plantas (L dia-1 foi estimada por meio de sensores que realizam o balanço de calor no caule (modelos SAG13; SGB9; SGB16; SGB19 e SGB25, Dynamax Inc. dispostos nos sentidos norte (N, sul (S, leste (E, oeste (W e centro (C de cada planta. A transpiração por unidade de área foliar (Lm-2 folha dia-1 variou em média de 1,58 ao longo do período estudado, e linearmente com o aumento da área foliar total da planta, independentemente da variedade estudada. A transpiração (Litros m-2 folha/dia -1 variou de 0,36 a 3,00, dependendo da demanda atmosférica. A transpiração máxima (T das quatro variedades de mangueira (Litros m-2 folha/dia -1 relacionouse linearmente com a ETo (T = 0,44. ETo; r² = 0,78, sendo um excelente subsídio para o manejo de irrigação por gotejamento nesta cultura.A study relating maximum transpiration (L m-2 leaf day-1 to reference evapotranspiration (ETo for four mango cultivars (Tommy Atkins, Palmer, Haden and Van Dyke, with 14 m², 8 m², 33 m² and 12 m² of leaf area, respectively was carried out at Embrapa Cassava and Tropical Fruits, in the conditions of Cruz da Almas-BA. Plant transpiration (L. day-1 was estimated by heat balance sensors that were installed on the shoots (models SAG13; SGB9; SGB16; SGB19 e SGB25, Dynamax Inc.. The sensors were installed to the North (N, South (S, East (E, West (W and Center(C of each plant. The transpiration per unity leaf area (L.m-2.day-1 varied about 1.58 in average along the studied period and it also varied linearly with the increase in total leaf area, regardless the studied

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.

Water cycle observations in forest watersheds of Cambodia

Science.gov (United States)

Shimizu, A.; Tamai, K.; Kabeya, N.; Shimizu, T.; Iida, S. I.

2015-12-01

The Lower Mekong River flows through Cambodia, where forests cover ~60% of the country and are believed to have a marked effect on the water cycle. These tropical seasonal forests in the Cambodian flat lands are very precious in the Indochinese Peninsula as few forests of this type remain. However, few hydrological observations have been conducted in these areas. In Cambodia, deciduous and evergreen forests make up 42% and 33% of the total forest area, respectively. We established experimental watersheds both in deciduous and evergreen forests containing meteorological observation towers in Cambodia and collected various observational data since 2003 (O'Krieng, deciduous forest watershed including a 30-m-high observation tower, 2,245 km2; Stung Chinit, evergreen forest watershed including a 60-m-high observation tower, 3,700 km2 including three small watersheds). The basic data from these sites included various kinds of information related to the composition of vegetation, soil characteristics, etc. Hydrologic data was collected and linked to the above data; the main hydrologic research results follow. The water budget for each watershed was determined using an observational rainfall and runoff dataset. The evapotranspiration rate in an evergreen forest was obtained using various observational methods including the Bowen energy-balance ratio and the bandpass eddy covariance method. The annual evapotranspiration of evergreen forests, estimated using the Bowen energy-balance ratio method and water balance, was about 1100-1200 mm, corresponding to 70-80% of annual rainfall. While considering the importance of the presence of evergreen forest, we conducted sap flow measurements to analyze the transpiration process that maintains water uptake through root systems that reach to depths exceeding 8 m. Characteristics of the evaporation from the forest floor that form an important element of the evaporation system were estimated in both evergreen and deciduous forests.

A method of camera calibration in the measurement process with reference mark for approaching observation space target

Science.gov (United States)

Zhang, Hua; Zeng, Luan

2017-11-01

Binocular stereoscopic vision can be used for space-based space targets near observation. In order to solve the problem that the traditional binocular vision system cannot work normally after interference, an online calibration method of binocular stereo measuring camera with self-reference is proposed. The method uses an auxiliary optical imaging device to insert the image of the standard reference object into the edge of the main optical path and image with the target on the same focal plane, which is equivalent to a standard reference in the binocular imaging optical system; When the position of the system and the imaging device parameters are disturbed, the image of the standard reference will change accordingly in the imaging plane, and the position of the standard reference object does not change. The camera's external parameters can be re-calibrated by the visual relationship of the standard reference object. The experimental results show that the maximum mean square error of the same object can be reduced from the original 72.88mm to 1.65mm when the right camera is deflected by 0.4 degrees and the left camera is high and low with 0.2° rotation. This method can realize the online calibration of binocular stereoscopic vision measurement system, which can effectively improve the anti - jamming ability of the system.

Mapping daily evapotranspiration at field scales over rainfed and irrigated agricultural areas using remote sensing data fusion

Science.gov (United States)

A continuous monitoring of daily evapotranspiration (ET) at field scale can be achieved by combining thermal infrared remote sensing data information from multiple satellite platforms. Here, an integrated approach to field scale ET mapping is described, combining multi-scale surface energy balance e...

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

2018-05-01

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.

Projecting the potential evapotranspiration by coupling different formulations and input data reliabilities: The possible uncertainty source for climate change impacts on hydrological regime

Science.gov (United States)

Wang, Weiguang; Li, Changni; Xing, Wanqiu; Fu, Jianyu

2017-12-01

Representing atmospheric evaporating capability for a hypothetical reference surface, potential evapotranspiration (PET) determines the upper limit of actual evapotranspiration and is an important input to hydrological models. Due that present climate models do not give direct estimates of PET when simulating the hydrological response to future climate change, the PET must be estimated first and is subject to the uncertainty on account of many existing formulae and different input data reliabilities. Using four different PET estimation approaches, i.e., the more physically Penman (PN) equation with less reliable input variables, more empirical radiation-based Priestley-Taylor (PT) equation with relatively dependable downscaled data, the most simply temperature-based Hamon (HM) equation with the most reliable downscaled variable, and downscaling PET directly by the statistical downscaling model, this paper investigated the differences of runoff projection caused by the alternative PET methods by a well calibrated abcd monthly hydrological model. Three catchments, i.e., the Luanhe River Basin, the Source Region of the Yellow River and the Ganjiang River Basin, representing a large climatic diversity were chosen as examples to illustrate this issue. The results indicated that although similar monthly patterns of PET over the period 2021-2050 for each catchment were provided by the four methods, the magnitudes of PET were still slightly different, especially for spring and summer months in the Luanhe River Basin and the Source Region of the Yellow River with relatively dry climate feature. The apparent discrepancy in magnitude of change in future runoff and even the diverse change direction for summer months in the Luanhe River Basin and spring months in the Source Region of the Yellow River indicated that the PET method related uncertainty occurred, especially in the Luanhe River Basin and the Source Region of the Yellow River with smaller aridity index. Moreover, the

Field note: comparative efficacy of a woody evapotranspiration landfill cover following the removal of aboveground biomass.

Science.gov (United States)

Schnabel, William; Munk, Jens; Byrd, Amanda

2015-01-01

Woody vegetation cultivated for moisture management on evapotranspiration (ET) landfill covers could potentially serve a secondary function as a biomass crop. However, research is required to evaluate the extent to which trees could be harvested from ET covers without significantly impacting their moisture management function. This study investigated the drainage through a six-year-old, primarily poplar/cottonwood ET test cover for a period of one year following the harvest of all woody biomass exceeding a height of 30 cm above ground surface. Results were compared to previously reported drainage observed during the years leading up to the coppice event. In the first year following coppice, the ET cover was found to be 93% effective at redirecting moisture during the spring/summer season, and 95% effective during the subsequent fall/winter season. This was slightly lower than the 95% and 100% efficacy observed in the spring/summer and fall/winter seasons, respectively, during the final measured year prior to coppice. However, the post-coppice efficacy was higher than the efficacy observed during the first three years following establishment of the cover. While additional longer-term studies are recommended, this project demonstrated that woody ET covers could potentially produce harvestable biomass while still effectively managing aerial moisture.

Impact and consequences of evapotranspiration changes on water resources availability in the arid Zhangye Basin, China

NARCIS (Netherlands)

Jin, X.; Schaepman, M.E.; Clevers, J.G.P.W.; Su, Z.

2009-01-01

Evapotranspiration (ET) plays an important role in the hydrological cycle and it is essential to estimate ET accurately for the evaluation of available water resources. This is most important in arid and semi-arid regions. In this paper, the long-term changes in daily ET in the semi-arid Zhangye

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

The combined geodetic network adjusted on the reference ellipsoid – a comparison of three functional models for GNSS observations

Directory of Open Access Journals (Sweden)

Kadaj Roman

2016-12-01

Full Text Available The adjustment problem of the so-called combined (hybrid, integrated network created with GNSS vectors and terrestrial observations has been the subject of many theoretical and applied works. The network adjustment in various mathematical spaces was considered: in the Cartesian geocentric system on a reference ellipsoid and on a mapping plane. For practical reasons, it often takes a geodetic coordinate system associated with the reference ellipsoid. In this case, the Cartesian GNSS vectors are converted, for example, into geodesic parameters (azimuth and length on the ellipsoid, but the simple form of converted pseudo-observations are the direct differences of the geodetic coordinates. Unfortunately, such an approach may be essentially distorted by a systematic error resulting from the position error of the GNSS vector, before its projection on the ellipsoid surface. In this paper, an analysis of the impact of this error on the determined measures of geometric ellipsoid elements, including the differences of geodetic coordinates or geodesic parameters is presented. Assuming that the adjustment of a combined network on the ellipsoid shows that the optimal functional approach in relation to the satellite observation, is to create the observational equations directly for the original GNSS Cartesian vector components, writing them directly as a function of the geodetic coordinates (in numerical applications, we use the linearized forms of observational equations with explicitly specified coefficients. While retaining the original character of the Cartesian vector, one avoids any systematic errors that may occur in the conversion of the original GNSS vectors to ellipsoid elements, for example the vector of the geodesic parameters. The problem is theoretically developed and numerically tested. An example of the adjustment of a subnet loaded from the database of reference stations of the ASG-EUPOS system was considered for the preferred functional

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...

Calibração regional e local da equação de Hargreaves para estimativa da evapotranspiração de referência Regional and local calibration of Hargreaves equation for estimating reference evapotranspiration

Directory of Open Access Journals (Sweden)

Diego Simões Fernandes

2012-06-01

Full Text Available A equação de Penman-Monteith FAO-56 (EToPM tem sido recomendada pela FAO, Organização para a Alimentação e Agricultura das Nações Unidas (ONU, como padrão para estimar a evapotranspiração de referência (ETo. Essa equação requer muitas variáveis que não estão disponíveis na maioria das estações meteorológicas no Brasil central. Por outro lado, a equação de Hargreaves é considerada simples e demanda somente dados de temperatura máxima e mínima para estimar a ETo. Entretanto, essa equação requer um ajuste local. Esse estudo analisa a possibilidade de utilizar a equação de Hargreaves ajustada para estimar a ETo no estado de Goiás. Para isso, os parâmetros empíricos, HC (coeficiente empírico de Hargreaves e HE (expoente empírico de Hargreaves, da equação de Hargreaves foram ajustados considerando dois processos, ajuste local (HGR - Hargreaves ajuste local e ajuste regional (HGL - Hargreaves ajuste regional. Para o HGL, os parâmetros empíricos foram ajustados para cada estação meteorológica. Já, para o HGR, os parâmetros empíricos foram ajustados considerando conjuntamente os dados de todas as estações meteorológicas. A equação de Hargreaves ajustada para ambos os processos, local e regional, apresentou valores de ERQM de 17,95 e 21,93%, respectivamente, considerando o conjunto total de dados climáticos. A equação de Hargreaves ajustada localmente ou regionalmente é uma opção para estimar os valores diários de ETo no Estado de Goiás em locais em que a disponibilidade de dados climáticos é limitada.The FAO-56 Penman-Monteith equation (EToPM has been recommended by the Food and Agriculture Organization (FAO of the United Nations as the standard equation for estimating reference evapotranspiration (ETo. The FAO-56 PM equation requires numerous weather data that are not available in most of the stations of Brazil central. On the other hand, the Hargreaves equation is a more simple equation for

Evaluating the use of sharpened land surface temperature for daily evapotranspiration estimation over irrigated crops in arid lands

KAUST Repository

Rosas, Jorge

2014-12-01

Satellite remote sensing provides data on land surface characteristics, useful for mapping land surface energy fluxes and evapotranspiration (ET). Land-surface temperature (LST) derived from thermal infrared (TIR) satellite data has been reliably used as a remote indicator of ET and surface moisture status. However, TIR imagery usually operates at a coarser resolution than that of shortwave sensors on the same satellite platform, making it sometimes unsuitable for monitoring of field-scale crop conditions. This study applies the data mining sharpener (DMS; Gao et al., 2012) technique to data from the Moderate Resolution Imaging Spectroradiometer (MODIS), which sharpens the 1 km thermal data down to the resolution of the optical data (250-500 m) based on functional LST and reflectance relationships established using a flexible regression tree approach. The DMS approach adopted here has been enhanced/refined for application over irrigated farming areas located in harsh desert environments in Saudi Arabia. The sharpened LST data is input to an integrated modeling system that uses the Atmosphere-Land Exchange Inverse (ALEXI) model and associated flux disaggregation scheme (DisALEXI) in conjunction with model reanalysis data and remotely sensed data from polar orbiting (MODIS) and geostationary (MSG; Meteosat Second Generation) satellite platforms to facilitate daily estimates of evapotranspiration. Results are evaluated against available flux tower observations over irrigated maize near Riyadh in Saudi Arabia. Successful monitoring of field-scale changes in surface fluxes are of importance towards an efficient water use in areas where fresh water resources are scarce and poorly monitored. Gao, F.; Kustas, W.P.; Anderson, M.C. A Data Mining Approach for Sharpening Thermal Satellite Imagery over Land. Remote Sens. 2012, 4, 3287-3319.

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

surface fluxes using MODIS data; and (ii) provide insights about the factors most affecting the accuracy of results. Factors considered included the type of climatic control on evapotranspiration, λE, (i.e. water-limited vs. energy-limited), the quality of Tair estimates, the heterogeneity of land cover...

[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.

Evapotranspiration estimates and consequences due to errors in the determination of the net radiation and advective effects

International Nuclear Information System (INIS)

Oliveira, G.M. de; Leitao, M. de M.V.B.R.

2000-01-01

The objective of this study was to analyze the consequences in the evapotranspiration estimates (ET) during the growing cycle of a peanut crop due to the errors committed in the determination of the radiation balance (Rn), as well as those caused by the advective effects. This research was conducted at the Experimental Station of CODEVASF in an irrigated perimeter located in the city of Rodelas, BA, during the period of September to December of 1996. The results showed that errors of the order of 2.2 MJ m -2 d -1 in the calculation of Rn, and consequently in the estimate of ET, can occur depending on the time considered for the daily total of Rn. It was verified that the surrounding areas of the experimental field, as well as the areas of exposed soil within the field, contributed significantly to the generation of local advection of sensible heat, which resulted in the increase of the evapotranspiration [pt

Carrier phase altimetry using Zeppelin based GNSS-R observations and water gauge reference data

Science.gov (United States)

Semmling, Maximilian; Schön, Steffen; Beckheinrich, Jamila; Beyerle, Georg; Ge, Maorong; Wickert, Jens

2014-05-01

The increasing number of transmitters in global navigation satellite systems (GNSS), like GPS, Galileo, Glonass or Compass, provide observations with an increasing coverage for positioning but also for remote sensing. A space based GNSS remote sensing application is radio occultation, a limb sounding method. Globally distributed vertical profiles of temperature, water vapour and electron density are provided operationally for weather forecast and ionospheric monitoring. Another application is GNSS reflectometry (GNSS-R) that is currently developed especially for ocean remote sensing. The high reflection coefficient of water is crucial for GNSS-R. This study presents a method that uses GNSS phase observations for lake altimetry with the potential for ocean application. Phase observations are deduced from a GORS (GNSS Occultaction Reflectometry Scatterometry) receiver in Master-Slave-Configuration. The Master sampling dedicated for direct signal acquisition is connected to an up-looking antenna with right hand circular polarization (RHCP). Two Slave samplings dedicated for acquisition of the reflected signals are connected to down-looking antennas with right- and left-hand circular polarization (RHCP and LHCP). Based on in-phase and quad-phase (I, Q) sample components, an altimetric phase residual is retrieved. This residual can be related to the height of the reflecting surface. An altimetric challenge arises from the unknown ambiguity of phase residuals that introduces a height bias. The presented study uses ancillary data deduced from water gauges to mitigate the ambiguity bias. Reference tracks are formed by linear surface height interpolation between the water gauge stations. At crossover points of reflection tracks with reference tracks a phase ambiguity estimate is determined for bias mitigation. For this study airborne GNSS measurements were conducted aboard a Zeppelin NT (New Technology) airship with a geodetic receiver for navigation and a GORS receiver for

Unravelling spatio-temporal evapotranspiration patterns in topographically complex landscapes

Science.gov (United States)

Metzen, Daniel; Sheridan, Gary; Nyman, Petter; Lane, Patrick

2016-04-01

Vegetation co-evolves with soils and topography under a given long-term climatic forcing. Previous studies demonstrated a strong eco-hydrologic feedback between topography, vegetation and energy and water fluxes. Slope orientation (aspect and gradient) alter the magnitude of incoming solar radiation resulting in larger evaporative losses and less water availability on equator-facing slopes. Furthermore, non-local water inputs from upslope areas potentially contribute to available water at downslope positions. The combined effect of slope orientation and drainage position creates complex spatial patterns in biological productivity and pedogenesis, which in turn alter the local hydrology. In complex upland landscapes, topographic alteration of incoming radiation can cause substantial aridity index (ratio of potential evapotranspiration to precipitation) variations over small spatial extents. Most of the upland forests in south-east Australia are located in an aridity index (AI) range of 1-2, around the energy limited to water limited boundary, where forested systems are expected to be most sensitive to AI changes. In this research we aim to improve the fundamental understanding of spatio-temporal evolution of evapotranspiration (ET) patterns in complex terrain, accounting for local topographic effects on system properties (e.g. soil depth, sapwood area, leaf area) and variation in energy and water exchange processes due to slope orientation and drainage position. Six measurement plots were set-up in a mixed species eucalypt forest on a polar and equatorial-facing hillslope (AI ˜1.3 vs. 1.8) at varying drainage position (ridge, mid-slope, gully), while minimizing variations in other factors, e.g. geology and weather patterns. Sap flow, soil water content, incoming solar radiation and throughfall were continuously monitored at field sites spanning a wide range of soil depth (0.5 - >3m), maximum tree heights (17 - 51m) and LAI (1.2 - 4.6). Site-specific response curves

A scaling approach to Budyko's framework and the complementary relationship of evapotranspiration in humid environments: case study of the Amazon River basin

Science.gov (United States)

Carmona, A. M.; Poveda, G.; Sivapalan, M.; Vallejo-Bernal, S. M.; Bustamante, E.

2016-02-01

This paper studies a 3-D state space representation of Budyko's framework designed to capture the mutual interdependence among long-term mean actual evapotranspiration (E), potential evapotranspiration (Ep) and precipitation (P). For this purpose we use three dimensionless and dependent quantities: Ψ = E ⁄ P, Φ = Ep ⁄ P and Ω = E ⁄ Ep. This 3-D space and its 2-D projections provide an interesting setting to test the physical soundness of Budyko's hypothesis. We demonstrate analytically that Budyko-type equations are unable to capture the physical limit of the relation between Ω and Φ in humid environments, owing to the unfeasibility of Ep ⁄ P = 0 when E ⁄ Ep → 1. Using data from 146 sub-catchments in the Amazon River basin we overcome this inconsistency by proposing a physically consistent power law: Ψ = kΦe, with k = 0.66, and e = 0.83 (R2 = 0.93). This power law is compared with two other Budyko-type equations. Taking into account the goodness of fits and the ability to comply with the physical limits of the 3-D space, our results show that the power law is better suited to model the coupled water and energy balances within the Amazon River basin. Moreover, k is found to be related to the partitioning of energy via evapotranspiration in terms of Ω. This suggests that our power law implicitly incorporates the complementary relationship of evapotranspiration into the Budyko curve, which is a consequence of the dependent nature of the studied variables within our 3-D space. This scaling approach is also consistent with the asymmetrical nature of the complementary relationship of evapotranspiration. Looking for a physical explanation for the parameters k and e, the inter-annual variability of individual catchments is studied. Evidence of space-time symmetry in Amazonia emerges, since both between-catchment and between-year variability follow the same Budyko curves. Finally, signs of co-evolution of catchments are explored by linking spatial

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

Directory of Open Access Journals (Sweden)

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.

Relationship between drought severity and observed regional yields in the Czech Republic

Science.gov (United States)

Hlavinka, Petr; Semerádová, Daniela; Balek, Jan; Možný, Martin; Žalud, Zdeněk; Trnka, Miroslav

2015-04-01

Although the Czech Republic is not generally characterized as a drought prone region within European context, drought occurs and is one of the most important climatic extremes in terms of economic damages. Crop production is highly sensitive to soil water availability and the rainfed agriculture almost dominantly prevails in the Czech Republic. Generally we can observe trends towards drier conditions with more often and more severe drought episodes. Based on this, the impact analyzes are very important. The relationship between drought episodes (with various timing and severity) and observed decrease of yields at district level (NUTS4) during the period from 2000 to 2014 was analyzed within submitted study. The observed yields of spring barley, winter wheat and oilseed winter rape from 14 districts were used (210 seasons are included). All districts are positioned within southeastern part of the Czech Republic and represent various agro-climatic conditions. The regressions between various drought indicators (as independent variables) and yields (dependent variable) were established. For this purpose the several drought indicators in monthly time step were derived as spatial average for arable land (each district separately). The difference between precipitation and reference evapotranspiration (ET0), average soil moisture content available for crops up to 40 cm and 100 cm depth, percent of time with soil moisture below 50 % and below 30 % of available soil moisture up to 100 cm depth were used. For reference evapotranspiration (ET0) and soil water estimates SoilClim model was used. This software is the main module used within Drought monitoring system in the Czech Republic (www.intersucho.cz). Within this study SoilClim was used in resolution 500 x 500 meters within grids of arable land. The soil water holding capacity as well as vegetation development was considered. By this way the yield losses due to various drought intensity was identified and compared. In case

Mechanisms of water supply and vegetation demand govern the seasonality and magnitude of evapotranspiration in Amazonia and Cerrado

NARCIS (Netherlands)

Christoffersen, B.O.; Restrepo-Coupe, N.; Arain, M.A.; Baker, I.T.; Cestaro, B.P.; Ciais, P.; Fisher, J.B.; Galbraith, D.; Guan, X.; Hurk, van den B.; Kruijt, B.

2014-01-01

Evapotranspiration (E) in the Amazon connects forest function and regional climate via its role in precipitation recycling However, the mechanisms regulating water supply to vegetation and its demand for water remain poorly understood, especially during periods of seasonal water deficits In this

Coeficientes médios da equação de Angström-Prescott, radiação solar e evapotranspiração de referência em Brasília Angström-Prescott equation mean coefficients, solar radiation and reference crop evapotranspiration in Brasília

Directory of Open Access Journals (Sweden)

Karla Daniele e Silva Dornelas

2006-08-01

Full Text Available O objetivo deste trabalho foi estimar os coeficientes médios a e b da equação de Angström-Prescott, em Brasília, e seus efeitos sobre o cálculo da radiação solar global (Rs e da evapotranspiração de referência (ETo. Foram utilizados dados da estação meteorológica da Embrapa Hortaliças, do período de 1978 a 2003. Os coeficientes médios foram determinados por análise de regressão linear, no período todo e em períodos mensais e anuais. Utilizando-se o coeficiente calculado e os propostos pela FAO (0,25 e 0,50 estimaram-se Rs e ETo, e avaliaram-se os seus desempenhos. Os coeficientes médios mensais a variaram de 0,241 a 0,345, e b de 0,430 a 0,515. Os coeficientes médios anuais a e b foram 0,278 e 0,498, e os do período geral foram 0,282 e 0,490, respectivamente. A performance entre esses coeficientes na estimativa da radiação não diferiu. No mês de julho, foram verificados as piores estimativas e os piores desempenhos. Com as estimativas de Rs e os coeficientes médios calculados, as estimativas de ETo não diferiram dos observados, tendo-se constatado um ótimo desempenho, independentemente do coeficiente utilizado. Dependendo do tipo de aplicação final dos dados, recomenda-se utilizar, por sua simplicidade, os coeficientes médios obtidos para o período geral.The objective of this work was to estimate Angström-Prescott equation mean coefficients in Brasília, DF, Brazil, and their effects on the calculations of global radiation (Rs and reference crop evapotranspiration (ETo. It was used meteorological data from Embrapa Hortaliças weather station, from 1978 to 2003. The mean coefficients were determined by linear regression analysis considering monthly, annual and total periods. Using the calculated coefficients for different periods and those provided by FAO (0.25 and 0.50, Rs and ETo were estimated and their performances were evaluated. Monthly mean coefficient a varied from 0.241 to 0.345, and b from 0.430 to 0

Precipitation and soil impacts on partitioning of subsurface moisture in Avena barbata: Observations from a greenhouse experiment

Energy Technology Data Exchange (ETDEWEB)

Salve, R.; Torn, M.S.

2011-03-01

The primary objective of this study was to assess the impact of two grassland soils and precipitation regimes on soil-moisture dynamics. We set up an experiment in a greenhouse, and monitored soil moisture dynamics in mesocosms planted with Avena barbata, an annual species found in California grasslands. By repeating the precipitation input at regular intervals, we were able to observe plant manipulation of soil moisture during well-defined periods during the growing season. We found that the amount of water partitioned to evapotranspiration, seepage, and soil storage varied among different growth stages. Further, both soil type and precipitation regimes had a significant impact on redistributing soil moisture. Whereas in the low-precipitation treatments most water was released to the atmosphere as evapotranspiration, major losses from the high-precipitation treatment occurred as gravity drainage. Observations from this study emphasize the importance of understanding intra-seasonal relationships between vegetation, soil, and water.

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 OBOR OECD: Environmental sciences (social aspects to be 5.7)

Diurnal Dynamics of Wheat Evapotranspiration Derived from Ground-Based Thermal Imagery

Directory of Open Access Journals (Sweden)

Hella Ellen Ahrends

2014-10-01

Full Text Available The latent heat flux, one of the key components of the surface energy balance, can be inferred from remotely sensed thermal infrared data. However, discrepancies between modeled and observed evapotranspiration are large. Thermal cameras might provide a suitable tool for model evaluation under variable atmospheric conditions. Here, we evaluate the results from the Penman-Monteith, surface energy balance and Bowen ratio approaches, which estimate the diurnal course of latent heat fluxes at a ripe winter wheat stand using measured and modeled temperatures. Under overcast conditions, the models perform similarly, and radiometric image temperatures are linearly correlated with the inverted aerodynamic temperature. During clear sky conditions, the temperature of the wheat ear layer could be used to predict daytime turbulent fluxes (root mean squared error and mean absolute error: 20–35 W∙m−2, r2: 0.76–0.88, whereas spatially-averaged temperatures caused underestimation of pre-noon and overestimation of afternoon fluxes. Errors are dependent on the models’ ability to simulate diurnal hysteresis effects and are largest during intermittent clouds, due to the discrepancy between the timing of image capture and the time needed for the leaf-air-temperature gradient to adapt to changes in solar radiation. During such periods, we suggest using modeled surface temperatures for temporal upscaling and the validation of image data.

Regional Analysis of Remote Sensing Based Evapotranspiration Information

Science.gov (United States)

Geli, H. M. E.; Hain, C.; Anderson, M. C.; Senay, G. B.

2017-12-01

Recent research findings on modeling actual evapotranspiration (ET) using remote sensing data and methods have proven the ability of these methods to address wide range of hydrological and water resources issues including river basin water balance for improved water resources management, drought monitoring, drought impact and socioeconomic responses, agricultural water management, optimization of land-use for water conservations, water allocation agreement among others. However, there is still a critical need to identify appropriate type of ET information that can address each of these issues. The current trend of increasing demand for water due to population growth coupled with variable and limited water supply due to drought especially in arid and semiarid regions with limited water supply have highlighted the need for such information. To properly address these issues different spatial and temporal resolutions of ET information will need to be used. For example, agricultural water management applications require ET information at field (30-m) and daily time scales while for river basin hydrologic analysis relatively coarser spatial and temporal scales can be adequate for such regional applications. The objective of this analysis is to evaluate the potential of using an integrated ET information that can be used to address some of these issues collectively. This analysis will highlight efforts to address some of the issues that are applicable to New Mexico including assessment of statewide water budget as well as drought impact and socioeconomic responses which all require ET information but at different spatial and temporal scales. This analysis will provide an evaluation of four remote sensing based ET models including ALEXI, DisALEXI, SSEBop, and SEBAL3.0. The models will be compared with ground-based observations from eddy covariance towers and water balance calculations. Remote sensing data from Landsat, MODIS, and VIIRS sensors will be used to provide ET

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)...

Mapping evapotranspiration trends using MODIS and SEBAL model in a data scarce and heterogeneous landscape in Eastern Africa

NARCIS (Netherlands)

Kiptala, J.K.; Mohamedi, Y.; Mul, M.L.; Van der Zaag, P.

2013-01-01

Evapotranspiration (ET) accounts for a substantial amount of the water use in river basins particular in the tropics and arid regions. However, accurate estimation still remains a challenge especially in large spatially heterogeneous and data scarce areas including the Upper Pangani River Basin in

The role of evapotranspiration in the groundwater hydrochemistry of an arid coastal wetland (Península Valdés, Argentina)

International Nuclear Information System (INIS)

Alvarez, María del Pilar; Carol, Eleonora; Dapeña, Cristina

2015-01-01

Coastal wetlands are complex hydrogeological systems, in which saline groundwater usually occurs. Salinity can be attributed to many origins, such as dissolution of minerals in the sediments, marine contribution and evapotranspiration, among others. The aim of this paper is to evaluate the processes that condition the hydrochemistry of an arid marsh, Playa Fracasso, located in Patagonia, Argentina. A study of the dynamics and geochemistry of the groundwater was carried out in each hydrogeomorphological unit, using major ion and isotope ( 18 O and 2 H) data, soil profiles descriptions and measurements, and recording of water tables in relation to the tidal flow. Water balances and analytical models based on isotope data were used to quantify the evaporation processes and to define the role of evaporation in the chemical composition of water. The results obtained show that the groundwater salinity of the marsh comes mainly from the tidal inflow, to which the halite and gypsum dissolution is added. These mineral facies are the result of the total evaporation of the marine water flooding that occurs mostly at the spring high tides. The isotope relationships in the fan and bajada samples show the occurrence of evaporation processes. Such processes, however, are not mainly responsible for the saline content of groundwater, which is actually generated by the dissolution of the typical evaporite facies of the arid environment sediments. It is concluded that the evapotranspiration processes condition groundwater quality. This is not only due to the saline enrichment caused by the evapotranspiration of shallow water, but also because such processes are the main drivers of the formation of soluble salts, which are then incorporated into the water by groundwater or tidal flow. - Highlights: • Tidal inflow and evapotranspiration processes condition the salinity of the marsh. • The total evaporation of marine water led the halite and gypsum precipitation. • The dissolution

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

Plant cover, soil temperature, freeze, water stress, and evapotranspiration conditions. [south Texas

Science.gov (United States)

Wiegand, C. L.; Nixon, P. R.; Gausman, H. W.; Namken, L. N.; Leamer, R. W.; Richardson, A. J. (Principal Investigator)

1981-01-01

Emissive and reflective data for 10 days, and IR data for 6 nights in south Texas scenes were analyzed after procedures were developed for removing cloud-affected data. HCMM radiometric temperatures were: within 2 C of dewpoint temperatures on nights when air temperature approached dewpoint temperatures; significantly correlated with variables important in evapotranspiration; and, related to freeze severity and planting depth soil temperatures. Vegetation greenness indexes calculated from visible and reflective IR bands of NOAA-6 to -9 meteorological satellites will be useful in the AgRISTARS program for seasonal crop development, crop condition, and drought applications.

Surface energy balance and actual evapotranspiration of the transboundary Indus Basin estimated from satellite measurements and the ETLook model

NARCIS (Netherlands)

Bastiaanssen, W.G.M.; Cheema, M.J.M.; Immerzeel, W.W.; Mittenburg, I.J.; Pelgrum, H.

2012-01-01

The surface energy fluxes and related evapotranspiration processes across the Indus Basin were estimated for the hydrological year 2007 using satellite measurements. The new ETLook remote sensing model (version 1) infers information on actual Evaporation (E) and actual Transpiration (T) from

The use of neutron probes to determine evapotranspiration

International Nuclear Information System (INIS)

Can, O.; Kurttas, Y. S. K.

2009-01-01

Water is an essential requirement for life on the planet. It is often the single most limiting factor in crop and livestock production. Water is a scarce resource in many urban and rural environments worldwide. According to the FAO, the global demand for fresh water is doubling every 21 years. The quality of the finite water supplies is also under threat from industrial, agricultural and domestic sources of pollution. The majority of crops are grown under rain-fed conditions and adequate water supply is the main factor limiting crop production in semi-arid and sub-humid regions. On the other hand, currently 20% of the world's arable land is under irrigation providing 35 to 40% of all agricultural production. Irrigation mismanagement poses a serious threat to the environment through groundwater pollution and salinization. It is therefore, essential that water resources be used efficiently by regular monitoring of soil-water status in the unsaturated zone. The neutron depth probe, a nuclear-based technique, is utilized worldwide for this purpose. For a given region, the water balance is given by I+P-(D+ET)-R=±ΔS where P is the rainfall integrated over Δt (mm), I is the irrigation integrated over Δt (mm), ET is the evapotranspiration integrated over Δt (mm), R is the runoff integrated over Δt (mm), D is the water draining from the soil at depth L integrated over Δt (mm), and ΔS is the change in soil-water storage in layer during the interval Δt (mm) The most commonly used values of Δt are a few days, a week, a month, and a year. The increase or decrease of soil moisture in a given soil depth, can easily monitor with neutron probes. When the neutron probe calibration is done, the amount of moisture in the soil at the desired frequency and depth can be learned quickly. In 2006 a study for the evapotranspiration of satsuma mandarin tree has been identified. In a irrigation period (01-31.08.2006) for four soil layer, ET : 78,04 mm. in 0-30 cm depth, ET: 50,01 mm

Comparison of sap flux, moisture flux tower and MODIS enhanced vegetation index methods for estimating riparian evapotranspiration

Science.gov (United States)

Nagler, Pamela L.; Glenn, Edward P.; Morino, Kiyomi; Neale, Christopher M.U; Cosh, Michael H.

2010-01-01

Riparian evapotranspiration (ET) was measured on a salt cedar (Tamarix spp.) dominated river terrace on the Lower Colorado River from 2007 to 2009 using tissue-heat-balance sap flux sensors at six sites representing very dense, medium dense, and sparse stands of plants. Salt cedar ET varied markedly across sites, and sap flux sensors showed that plants were subject to various degrees of stress, detected as mid-day depression of transpiration and stomatal conductance. Sap flux results were scaled from the leaf level of measurement to the stand level by measuring plant-specific leaf area index and fractional ground cover at each site. Results were compared to Bowen ratio moisture tower data available for three of the sites. Sap flux sensors and flux tower results ranked the sites the same and had similar estimates of ET. A regression equation, relating measured ET of salt cedar and other riparian plants and crops on the Lower Colorado River to the Enhanced Vegetation Index from the MODIS sensor on the Terra satellite and reference crop ET measured at meteorological stations, was able to predict actual ET with an accuracy or uncertainty of about 20%, despite between-site differences for salt cedar. Peak summer salt cedar ET averaged about 6 mm d-1 across sites and methods of measurement.

Evapotranspiração da cultura da melancia irrigada com água de diferentes salinidades Evapotranspiration of watermelon irrigated with different salinity waters

Directory of Open Access Journals (Sweden)

Vladimir B. Figueirêdo

2009-06-01

Full Text Available Sabe-se que a determinação precisa da evapotranspiração da cultura (ETc é de grande importância para o uso eficiente da água, principalmente em regiões áridas e semiáridas onde se faz necessária a utilização de água salina para irrigação. O objetivo deste trabalho foi determinar a evapotranspiração da melancia, cultivar Mickylee, com o uso de diferentes níveis de salinidade da água de irrigação. O experimento foi conduzido na Fazenda Experimental da Alagoinha, pertencente à Universidade Federal Rural do Semiárido, Mossoró - RN. Os níveis de salinidade da água de irrigação foram: S1 = 0,55; S2 = 1,65; S3 = 2,35; S4 = 3,5, e S5 = 4,5 dS m-1, sendo os tratamentos dispostos no delineamento de blocos ao acaso, com quatro repetições. A determinação da evapotranspiração de referência (ETo foi realizada pelo método FAO-Penmam-Monteith, e a ETc, pelas leituras obtidas em lisímetros de pesagem, instalados nos tratamentos S1 e S5. Os resultados mostraram que a ETc da melancia diminui com o aumento da salinidade da água aplicada e que a evapotranspiração total durante o ciclo foi de 245 e 214 mm, respectivamente, para os tratamentos S1 e S5. Os valores médios de Kc obtidos para cada fase fenológica foram 0,23; 0,68; 1,12; 0,90 e 0,24; 0,61; 0,98 e 0,78, respectivamente, para as águas S1 e S5.The knowledge of crop evapotranspiration (ETc is very important for efficient water use in irrigated crops, mainly in arid and semi-arid regions, where the use of saline water is common. The objective of this study was to determine watermelon crop evapotranspiration (cv. Mickylee in plants submitted to different irrigation water salinity levels. The experiment was carried out at the Experimental field of the Semi-Arid Federal Rural University, Mossoró, RN, Brazil. The irrigation water salinity levels were of S1 = 0.55; S2 = 1.65; S3 = 2.35; S4 = 3.5 and S5 = 4.5 dS m-1, with the treatments set up in randomized blocks with

Surface temperature and evapotranspiration: application of local scale methods to regional scales using satellite data

International Nuclear Information System (INIS)

Seguin, B.; Courault, D.; Guerif, M.

1994-01-01

Remotely sensed surface temperatures have proven useful for monitoring evapotranspiration (ET) rates and crop water use because of their direct relationship with sensible and latent energy exchange processes. Procedures for using the thermal infrared (IR) obtained with hand-held radiometers deployed at ground level are now well established and even routine for many agricultural research and management purposes. The availability of IR from meteorological satellites at scales from 1 km (NOAA-AVHRR) to 5 km (METEOSAT) permits extension of local, ground-based approaches to larger scale crop monitoring programs. Regional observations of surface minus air temperature (i.e., the stress degree day) and remote estimates of daily ET were derived from satellite data over sites in France, the Sahel, and North Africa and summarized here. Results confirm that similar approaches can be applied at local and regional scales despite differences in pixel size and heterogeneity. This article analyzes methods for obtaining these data and outlines the potential utility of satellite data for operational use at the regional scale. (author)

REM-3D Reference Datasets: Reconciling large and diverse compilations of travel-time observations

Science.gov (United States)

Moulik, P.; Lekic, V.; Romanowicz, B. A.

2017-12-01

A three-dimensional Reference Earth model (REM-3D) should ideally represent the consensus view of long-wavelength heterogeneity in the Earth's mantle through the joint modeling of large and diverse seismological datasets. This requires reconciliation of datasets obtained using various methodologies and identification of consistent features. The goal of REM-3D datasets is to provide a quality-controlled and comprehensive set of seismic observations that would not only enable construction of REM-3D, but also allow identification of outliers and assist in more detailed studies of heterogeneity. The community response to data solicitation has been enthusiastic with several groups across the world contributing recent measurements of normal modes, (fundamental mode and overtone) surface waves, and body waves. We present results from ongoing work with body and surface wave datasets analyzed in consultation with a Reference Dataset Working Group. We have formulated procedures for reconciling travel-time datasets that include: (1) quality control for salvaging missing metadata; (2) identification of and reasons for discrepant measurements; (3) homogenization of coverage through the construction of summary rays; and (4) inversions of structure at various wavelengths to evaluate inter-dataset consistency. In consultation with the Reference Dataset Working Group, we retrieved the station and earthquake metadata in several legacy compilations and codified several guidelines that would facilitate easy storage and reproducibility. We find strong agreement between the dispersion measurements of fundamental-mode Rayleigh waves, particularly when made using supervised techniques. The agreement deteriorates substantially in surface-wave overtones, for which discrepancies vary with frequency and overtone number. A half-cycle band of discrepancies is attributed to reversed instrument polarities at a limited number of stations, which are not reflected in the instrument response history

Estimating crop coefficients for corn during an evapotranspiration experiment on an oxisol in Brazil Determinação de coeficientes de cultura para o milho durante um experimento de evapotranspiração em um oxisol do Brasil

Directory of Open Access Journals (Sweden)

M.M. Villagra

1994-08-01

Full Text Available Soil water balance components were measured during two periods (from 1989 to 1991 on a Dark Red Latosol (oxisol in Piracicaba,SP, Brazil. The change in soil water storage and the soil water fluxes at the lower limit of the rooting zone were calculated for a transect of 25 observation plots. Hydraulic head gradients were determined by tensiometer measurements. Soil water flux densities were estimated through Darcy's equation. The actual evapotranspiration of the crops and weeds and the actual evaporation of bare soil were obtained from the water balance equation and this for two periods under different crop rotations. For the first period the sequence was bare soil-corn-weeds and for the second period it was stubble mulch-weeds-corn. For assessing the crop coefficients the potential evapotranspiration was calculated according to two different methods. The first method was based on the modified Penman equation with grass as a reference crop, to obtain this way reference coefficients, and the second method was based on the pan "A" evaporation data in order to obtain pan coefficients. These coefficients were compared with the tabulated crop coefficients. In general when there was no shortage of water during the corn growth, the crop coefficients k c"A" and k c ref were very close to the k c values.Os componentes do balanço hídrico foram medidos durante dois períodos (de 1989 a 1991 em terra roxa estruturada, em Piracicaba,SP, Brasil. As variações de armazenamento de água e os fluxos de água no solo no limite inferior da zona radicular foram calculados para uma transeção de 25 parcelas experimentais. Gradientes hidráulicos foram determinados por meio de medidas tensiométricas. Densidades de fluxo de água foram estimadas através da equação de Darcy. A evapotranspiração atual das culturas e das ervas daninhas e a evaporação atual do solo nú foram obtidas da equação do balanço hídrico, para dois períodos, sob diferentes rota

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.

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.

Peru Water Resources: Integrating NASA Earth Observations into Water Resource Planning and Management in Perus La Libertad Region

Science.gov (United States)

Padgett-Vasquez, Steve; Steentofte, Catherine; Holbrook, Abigail

2014-01-01

Developing countries often struggle with providing water security and sanitation services to their populations. An important aspect of improving security and sanitation is developing a comprehensive understanding of the country's water budget. Water For People, a non-profit organization dedicated to providing clean drinking water, is working with the Peruvian government to develop a water budget for the La Libertad region of Peru which includes the creation of an extensive watershed management plan. Currently, the data archive of the necessary variables to create the water management plan is extremely limited. Implementing NASA Earth observations has bolstered the dataset being used by Water For People, and the METRIC (Mapping EvapoTranspiration at High Resolution and Internalized Calibration) model has allowed for the estimation of the evapotranspiration values for the region. Landsat 8 imagery and the DEM (Digital Elevation Model) from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor onboard Terra were used to derive the land cover information, and were used in conjunction with local weather data of Cascas from Peru's National Meteorological and Hydrological Service (SENAMHI). Python was used to combine input variables and METRIC model calculations to approximate the evapotranspiration values for the Ochape sub-basin of the Chicama River watershed. Once calculated, the evapotranspiration values and methodology were shared Water For People to help supplement their decision support tools in the La Libertad region of Peru and potentially apply the methodology in other areas of need.

Drought stress impact on vegetable crop yields in the Elbe River lowland between 1961 and 2014

Czech Academy of Sciences Publication Activity Database

Potopová, V.; Štěpánek, Petr; Farda, Aleš; Türkott, L.; Zahradníček, Pavel; Soukup, J.

2016-01-01

Roč. 42, č. 1 (2016), s. 127-143 ISSN 0211-6820 R&D Projects: GA MŠk(CZ) LD14043; GA ČR GA13-19831S Institutional support: RVO:67179843 Keywords : standardized precipitation evapotranspiration index * drought stress * reference evapotranspiration * crop evapotranspiration * crop coefficient * Czech Republic Subject RIV: EH - Ecology, Behaviour

Controls of evapotranspiration and CO2 fluxes from scots pine by surface conductance and abiotic factors.

Directory of Open Access Journals (Sweden)

Tianshan Zha

Full Text Available Evapotranspiration (E and CO2 flux (Fc in the growing season of an unusual dry year were measured continuously over a Scots pine forest in eastern Finland, by eddy covariance techniques. The aims were to gain an understanding of their biological and environmental control processes. As a result, there were obvious diurnal and seasonal changes in E, Fc , surface conductance (gc , and decoupling coefficient (Ω, showing similar trends to those in radiation (PAR and vapour pressure deficit (δ. The maximum mean daily values (24-h average for E, Fc , gc , and Ω were 1.78 mmol m(-2 s(-1, -11.18 µmol m(-2 s(-1, 6.27 mm s(-1, and 0.31, respectively, with seasonal averages of 0.71 mmol m(-2 s(-1, -4.61 µmol m(-2 s(-1, 3.3 mm s(-1, and 0.16. E and Fc were controlled by combined biological and environmental variables. There was curvilinear dependence of E on gc and Fc on gc . Among the environmental variables, PAR was the most important factor having a positive linear relationship to E and curvilinear relationship to Fc , while vapour pressure deficit was the most important environmental factor affecting gc . Water use efficiency was slightly higher in the dry season, with mean monthly values ranging from 6.67 to 7.48 μmol CO2 (mmol H2O(-1 and a seasonal average of 7.06 μmol CO2 (μmol H2O(-1. Low Ω and its close positive relationship with gc indicate that evapotranspiration was sensitive to surface conductance. Mid summer drought reduced surface conductance and decoupling coefficient, suggesting a more biotic control of evapotranspiration and a physiological acclimation to dry air. Surface conductance remained low and constant under dry condition, supporting that a constant value of surface constant can be used for modelling transpiration under drought condition.

Microwave implementation of two-source energy balance approach for estimating evapotranspiration

Directory of Open Access Journals (Sweden)

T. R. H. Holmes

2018-02-01

Full Text Available A newly developed microwave (MW land surface temperature (LST product is used to substitute thermal infrared (TIR-based LST in the Atmosphere–Land Exchange Inverse (ALEXI modeling framework for estimating evapotranspiration (ET from space. ALEXI implements a two-source energy balance (TSEB land surface scheme in a time-differential approach, designed to minimize sensitivity to absolute biases in input records of LST through the analysis of the rate of temperature change in the morning. Thermal infrared retrievals of the diurnal LST curve, traditionally from geostationary platforms, are hindered by cloud cover, reducing model coverage on any given day. This study tests the utility of diurnal temperature information retrieved from a constellation of satellites with microwave radiometers that together provide six to eight observations of Ka-band brightness temperature per location per day. This represents the first ever attempt at a global implementation of ALEXI with MW-based LST and is intended as the first step towards providing all-weather capability to the ALEXI framework. The analysis is based on 9-year-long, global records of ALEXI ET generated using both MW- and TIR-based diurnal LST information as input. In this study, the MW-LST (MW-based LST sampling is restricted to the same clear-sky days as in the IR-based implementation to be able to analyze the impact of changing the LST dataset separately from the impact of sampling all-sky conditions. The results show that long-term bulk ET estimates from both LST sources agree well, with a spatial correlation of 92 % for total ET in the Europe–Africa domain and agreement in seasonal (3-month totals of 83–97 % depending on the time of year. Most importantly, the ALEXI-MW (MW-based ALEXI also matches ALEXI-IR (IR-based ALEXI very closely in terms of 3-month inter-annual anomalies, demonstrating its ability to capture the development and extent of drought conditions. Weekly ET output

The conversion of grasslands to forests in Southern South America: Shifting evapotranspiration, stream flow and groundwater dynamics

Science.gov (United States)

Jobbagy, E. G.; Nosetto, M. D.; Pineiro, G.; Farley, K. A.; Palmer, S. M.; Jackson, R. B.

2005-12-01

Vegetation changes, particularly those involving transitions between tree- and grass-dominated systems, often modify evaporation as a result of plant-mediated shifts in moisture access and demand. The establishment of tree plantations (fast growing eucalypts and pines) on native grasslands is emerging as a major land-use change, particularly in the Southern Hemisphere, where cheap land and labor, public subsidies, and prospective C sequestration rewards provide converging incentives. What are the hydrological consequences of grassland afforestation? How are crucial ecosystem services such as fresh water supply and hydrological regulation being affected? We explore these questions focusing on a) evapotranspiration, b) stream flow, and c) groundwater recharge-discharge patterns across a network of paired stands and small watershed occupied by native grassland and tree plantation in Argentina and Uruguay. Radiometric information obtained from Landsat satellite images was used to estimate daily evapotranspiration in >100 tree plantations and grasslands stands in the humid plains of the Uruguay River (mean annual precipitation, MAP= 1350 mm). In spite of their lower albedo, tree plantations were 0.5 C° cooler than grasslands. Energy balance calculations suggested 80% higher evapotranspiration in afforested plots with relative differences becoming larger during dry periods. Seasonal stream flow measurements in twelve paired watershed (50-500 Ha) in the hills of Comechingones (MAP= 800 mm) and Minas (MAP= 1200 mm) showed declining water yields following afforestation. Preliminary data in Cordoba showed four-fold reductions of base flow in the dry season and two-fold reductions of peak flow after storms. A network of twenty paired grassland-plantation stands covering a broad range of sediment textures in the Pampas (MAP= 1000 mm, typical groundwater depth= 1-5 m) showed increased groundwater salinity in afforested stands (plantation:grassland salinity ratio = 1.2, 10, and

Potential of Electric Power Production from Microbial Fuel Cell (MFC) in Evapotranspiration Reactor for Leachate Treatment Using Alocasia macrorrhiza Plant and Eleusine indica Grass

Science.gov (United States)

Zaman, Badrus; Wardhana, Irawan Wisnu

2018-02-01

Microbial fuel cell is one of attractive electric power generator from nature bacterial activity. While, Evapotranspiration is one of the waste water treatment system which developed to eliminate biological weakness that utilize the natural evaporation process and bacterial activity on plant roots and plant media. This study aims to determine the potential of electrical energy from leachate treatment using evapotranspiration reactor. The study was conducted using local plant, namely Alocasia macrorrhiza and local grass, namely Eleusine Indica. The system was using horizontal MFC by placing the cathodes and anodes at different chamber (i.e. in the leachate reactor and reactor with plant media). Carbon plates was used for chatode-anodes material with size of 40 cm x 10 cm x1 cm. Electrical power production was measure by a digital multimeter for 30 days reactor operation. The result shows electric power production was fluctuated during reactor operation from all reactors. The electric power generated from each reactor was fluctuated, but from the reactor using Alocasia macrorrhiza plant reach to 70 μwatt average. From the reactor using Eleusine Indica grass was reached 60 μwatt average. Electric power production fluctuation is related to the bacterial growth pattern in the soil media and on the plant roots which undergo the adaptation process until the middle of the operational period and then in stable growth condition until the end of the reactor operation. The results indicate that the evapotranspiration reactor using Alocasia macrorrhiza plant was 60-95% higher electric power potential than using Eleusine Indica grass in short-term (30-day) operation. Although, MFC system in evapotranspiration reactor system was one of potential system for renewable electric power generation.

Evapotranspiration dynamics along elevational and disturbance gradients at Mt. Kilimanjaro

Science.gov (United States)

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

2015-04-01

each. Minor data gaps are introduced by particular environmental conditions (e.g. strong winds, fog) and external power failure, and a random forest-based approach has been successfully implemented to impute missing values. Visual inspection revealed that ET rates on study sites below the forest belt (3500 m a.s.l.) in magnitude and diurnal variation. Diurnal ET variation on the lower elevated research plots followed the course of the sun, with maximum values in the early afternoon and minimum values during sunrise and sunset. Maximum evapotranspirative net water loss occurred on the selected grassland sites, followed by maize, coffee, and minimum values on savanna. The study sites located above the forest belt, however, showed maximum ET rates coinciding with sunrise, whilst ET remained almost constantly low during the remaining hours of sunlight. We tentatively suggest that tree density regulates net water loss on the lower elevated research plots, while water scarcity is of subordinate importance. As for the high-lying sites, maximum ET rates directly after sunrise indicate an immediate sublimation of ice accumulated in the soil during night and subsequently attenuated water loss as a result of limited water availability. However, further analysis steps need to be performed in order to draw more reliable conclusions on the observed ET patterns.

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; Choi, Minha

2016-01-01

product of MOD16 evapotranspiration was raised from cropland regions. Overall, this study revealed the performance and suitability of two distinctive remote sensing approaches for characterizing the footprints of water fluxes in the Korean peninsula

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...

Drivers of soil drying in the Czech Republic between 1961 and 2012

Czech Academy of Sciences Publication Activity Database

Trnka, M.; Brázdil, R.; Balek, J.; Semerádová, D.; Hlavinka, P.; Možný, M.; Štepánek, P.; Dobrovolný, P.; Zahradníček, P.; Dubrovský, Martin; Eitzinger, J.; Fuchs, B.; Svoboda, M.; Hayes, M.; Žalud, Z.

2015-01-01

Roč. 35, č. 9 (2015), s. 2664-2675 ISSN 0899-8418 Institutional support: RVO:68378289 Keywords : pan evaporation * soil moisture * reference evapotranspiration * drought climatology * water balance * observed climate change Subject RIV: DG - Athmosphere Sciences, Meteorology Impact factor: 3.609, year: 2015 http://onlinelibrary.wiley.com/doi/10.1002/joc.4167/abstract

Numerical evaluation of monofil and subtle-layered evapotranspiration (ET) landfill caps

International Nuclear Information System (INIS)

Wilson, G.V.; Henley, M.; Valceschini, R.

1998-01-01

The US Department of Energy/Nevada Operations Office (DOE/NV) has identified the need to design a low-level waste (LLW) closure cap for the arid conditions at the Nevada Test Site (NTS). As a result of concerns for subsidence impacting the cover, DOE/NV redesigned the LLW cover from one containing a 'hard' infiltration barrier that would likely fail, to a 'soft' (ET) cover that is sufficiently deep to accommodate the hydrologic problems of subsidence. An ET cover is one that does not contain hydrologic barrier layers but relies on soil-water retention and sufficient thickness to store water until evapotranspiration (ET) can remove the moisture. Subtle layering within an ET cap using the native soil could be environmentally beneficial and cost effective

United States Climate Reference Network (USCRN) Raw Observations from Datalogger

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Datalogger files are raw USCRN data. However, instead of being collected via satellite, the raw data are collected from station dataloggers (also referred to as...

Micrometeorological, evapotranspiration, and soil-moisture data at the Amargosa Desert Research site in Nye County near Beatty, Nevada, 2006-11

Science.gov (United States)

Arthur, Jonathan M.; Johnson, Michael J.; Mayers, C. Justin; Andraski, Brian J.

2012-01-01

This report describes micrometeorological, evapotranspiration, and soil-moisture data collected since 2006 at the Amargosa Desert Research Site adjacent to a low-level radio-active waste and hazardous chemical waste facility near Beatty, Nevada. Micrometeorological data include precipitation, solar radiation, net radiation, air temperature, relative humidity, saturated and ambient vapor pressure, wind speed and direction, barometric pressure, near-surface soil temperature, soil-heat flux, and soil-water content. Evapotranspiration (ET) data include latent-heat flux, sensible-heat flux, net radiation, soil-heat flux, soil temperature, air temperature, vapor pressure, and other principal energy-budget data. Soil-moisture data include periodic measurements of volumetric water-content at experimental sites that represent vegetated native soil, devegetated native soil, and simulated waste disposal trenches - maximum measurement depths range from 5.25 to 29.25 meters. All data are compiled in electronic spreadsheets that are included with this report.

Estimating evapotranspiration and groundwater flow from water-table fluctuations for a general wetland scenario

Science.gov (United States)

Weber, Lisa C.; Wiley, Michael J.; Wilcox, Douglas A.

2016-01-01

The use of diurnal water-table fluctuation methods to calculate evapotranspiration (ET) and groundwater flow is of increasing interest in ecohydrological studies. Most studies of this type, however, have been located in riparian wetlands of semi-arid regions where groundwater levels are consistently below topographic surface elevations and precipitation events are infrequent. Current methodologies preclude application to a wider variety of wetland systems. In this study, we extended a method for estimating sub-daily ET and groundwater flow rates from water-level fluctuations to fit highly dynamic, non-riparian wetland scenarios. Modifications included (1) varying the specific yield to account for periodic flooded conditions and (2) relating empirically derived ET to estimated potential ET for days when precipitation events masked the diurnal signal. To demonstrate the utility of this method, we estimated ET and groundwater fluxes over two growing seasons (2006–2007) in 15 wetlands within a ridge-and-swale wetland complex of the Laurentian Great Lakes under flooded and non-flooded conditions. Mean daily ET rates for the sites ranged from 4.0 mm d−1 to 6.6 mm d−1. Shallow groundwater discharge rates resulting from evaporative demand ranged from 2.5 mm d−1 to 4.3 mm d−1. This study helps to expand our understanding of the evapotranspirative demand of plants under various hydrologic and climate conditions. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.

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

Directory of Open Access Journals (Sweden)

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.

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.

Potential of Electric Power Production from Microbial Fuel Cell (MFC in Evapotranspiration Reactor for Leachate Treatment Using Alocasia macrorrhiza Plant and Eleusine indica Grass

Directory of Open Access Journals (Sweden)

Zaman Badrus

2018-01-01

Full Text Available Microbial fuel cell is one of attractive electric power generator from nature bacterial activity. While, Evapotranspiration is one of the waste water treatment system which developed to eliminate biological weakness that utilize the natural evaporation process and bacterial activity on plant roots and plant media. This study aims to determine the potential of electrical energy from leachate treatment using evapotranspiration reactor. The study was conducted using local plant, namely Alocasia macrorrhiza and local grass, namely Eleusine Indica. The system was using horizontal MFC by placing the cathodes and anodes at different chamber (i.e. in the leachate reactor and reactor with plant media. Carbon plates was used for chatode-anodes material with size of 40 cm x 10 cm x1 cm. Electrical power production was measure by a digital multimeter for 30 days reactor operation. The result shows electric power production was fluctuated during reactor operation from all reactors. The electric power generated from each reactor was fluctuated, but from the reactor using Alocasia macrorrhiza plant reach to 70 μwatt average. From the reactor using Eleusine Indica grass was reached 60 μwatt average. Electric power production fluctuation is related to the bacterial growth pattern in the soil media and on the plant roots which undergo the adaptation process until the middle of the operational period and then in stable growth condition until the end of the reactor operation. The results indicate that the evapotranspiration reactor using Alocasia macrorrhiza plant was 60-95% higher electric power potential than using Eleusine Indica grass in short-term (30-day operation. Although, MFC system in evapotranspiration reactor system was one of potential system for renewable electric power generation.

Evapotranspiration and heat fluxes over a small forest - a study using modelling and measurements

DEFF Research Database (Denmark)

Sogachev, Andrey; Dellwik, Ebba; Boegh, Eva

2013-01-01

are very often used for calibration of forest parameters or model constants, further use of these parameters without a proper interpretation in mesoscale or global circulation models can result in serious bias of estimates of modelled evapotranspiration or heat fluxes from the given area. In the present...... work, we apply the atmospheric boundary layer (ABL) model SCADIS with enhanced turbulence closure including buoyancy for investigation of the spatial distribution of latent and sensible heat vertical fluxes over patchy forested terrain in Denmark during selected days in the summer period. The approach...

IMOS National Reference Stations: A Continental-Wide Physical, Chemical and Biological Coastal Observing System

Science.gov (United States)

Lynch, Tim P.; Morello, Elisabetta B.; Evans, Karen; Richardson, Anthony J.; Rochester, Wayne; Steinberg, Craig R.; Roughan, Moninya; Thompson, Peter; Middleton, John F.; Feng, Ming; Sherrington, Robert; Brando, Vittorio; Tilbrook, Bronte; Ridgway, Ken; Allen, Simon; Doherty, Peter; Hill, Katherine; Moltmann, Tim C.

2014-01-01

Sustained observations allow for the tracking of change in oceanography and ecosystems, however, these are rare, particularly for the Southern Hemisphere. To address this in part, the Australian Integrated Marine Observing System (IMOS) implemented a network of nine National Reference Stations (NRS). The network builds on one long-term location, where monthly water sampling has been sustained since the 1940s and two others that commenced in the 1950s. In-situ continuously moored sensors and an enhanced monthly water sampling regime now collect more than 50 data streams. Building on sampling for temperature, salinity and nutrients, the network now observes dissolved oxygen, carbon, turbidity, currents, chlorophyll a and both phytoplankton and zooplankton. Additional parameters for studies of ocean acidification and bio-optics are collected at a sub-set of sites and all data is made freely and publically available. Our preliminary results demonstrate increased utility to observe extreme events, such as marine heat waves and coastal flooding; rare events, such as plankton blooms; and have, for the first time, allowed for consistent continental scale sampling and analysis of coastal zooplankton and phytoplankton communities. Independent water sampling allows for cross validation of the deployed sensors for quality control of data that now continuously tracks daily, seasonal and annual variation. The NRS will provide multi-decadal time series, against which more spatially replicated short-term studies can be referenced, models and remote sensing products validated, and improvements made to our understanding of how large-scale, long-term change and variability in the global ocean are affecting Australia's coastal seas and ecosystems. The NRS network provides an example of how a continental scaled observing systems can be developed to collect observations that integrate across physics, chemistry and biology. PMID:25517905

IMOS National Reference Stations: a continental-wide physical, chemical and biological coastal observing system.

Directory of Open Access Journals (Sweden)

Tim P Lynch

Full Text Available Sustained observations allow for the tracking of change in oceanography and ecosystems, however, these are rare, particularly for the Southern Hemisphere. To address this in part, the Australian Integrated Marine Observing System (IMOS implemented a network of nine National Reference Stations (NRS. The network builds on one long-term location, where monthly water sampling has been sustained since the 1940s and two others that commenced in the 1950s. In-situ continuously moored sensors and an enhanced monthly water sampling regime now collect more than 50 data streams. Building on sampling for temperature, salinity and nutrients, the network now observes dissolved oxygen, carbon, turbidity, currents, chlorophyll a and both phytoplankton and zooplankton. Additional parameters for studies of ocean acidification and bio-optics are collected at a sub-set of sites and all data is made freely and publically available. Our preliminary results demonstrate increased utility to observe extreme events, such as marine heat waves and coastal flooding; rare events, such as plankton blooms; and have, for the first time, allowed for consistent continental scale sampling and analysis of coastal zooplankton and phytoplankton communities. Independent water sampling allows for cross validation of the deployed sensors for quality control of data that now continuously tracks daily, seasonal and annual variation. The NRS will provide multi-decadal time series, against which more spatially replicated short-term studies can be referenced, models and remote sensing products validated, and improvements made to our understanding of how large-scale, long-term change and variability in the global ocean are affecting Australia's coastal seas and ecosystems. The NRS network provides an example of how a continental scaled observing systems can be developed to collect observations that integrate across physics, chemistry and biology.

PHOTOMETRIC OBSERVATIONS OF SELECTED, OPTICALLY BRIGHT QUASARS FOR SPACE INTERFEROMETRY MISSION AND OTHER FUTURE CELESTIAL REFERENCE FRAMES

International Nuclear Information System (INIS)

Ojha, Roopesh; Zacharias, Norbert; Hennessy, Gregory S.; Gaume, Ralph A.; Johnston, Kenneth J.

2009-01-01

Photometric observations of 235 extragalactic objects that are potential targets for the Space Interferometry Mission (SIM) are presented. Mean B, V, R, I magnitudes at the 5% level are obtained at 1-4 epochs between 2005 and 2007 using the 1 m telescopes at Cerro Tololo Inter-American Observatory and the Naval Observatory Flagstaff Station. Of the 134 sources that have V magnitudes in the Veron and Veron-Cetty catalog, a difference of over 1.0 mag is found for the observed-catalog magnitudes for about 36% of the common sources, and 10 sources show over 3 mag difference. Our first set of observations presented here form the basis of a long-term photometric variability study of the selected reference frame sources to assist in mission target selection and to support QSO multicolor photometric variability studies in general.

Calibration and evaluation of the FAO56-Penman-Monteith, FAO24-radiation, and Priestly-Taylor reference evapotranspiration models using the spatially measured solar radiation across a large arid and semi-arid area in southern Iran

Science.gov (United States)

Didari, Shohreh; Ahmadi, Seyed Hamid

2018-05-01

Crop evapotranspiration (ET) is one of the main components in calculating the water balance in agricultural, hydrological, environmental, and climatological studies. Solar radiation (Rs) supplies the available energy for ET, and therefore, precise measurement of Rs is required for accurate ET estimation. However, measured Rs and ET and are not available in many areas and they should be estimated indirectly by the empirical methods. The Angström-Prescott (AP) is the most popular method for estimating Rs in areas where there are no measured data. In addition, the locally calibrated coefficients of AP are not yet available in many locations, and instead, the default coefficients are used. In this study, we investigated different approaches for Rs and ET calculations. The daily measured Rs values in 14 stations across arid and semi-arid areas of Fars province in south of Iran were used for calibrating the coefficients of the AP model. Results revealed that the calibrated AP coefficients were very different and higher than the default values. In addition, the reference ET (ET o ) was estimated by the FAO56 Penman-Monteith (FAO56 PM) and FAO24-radiation methods by using the measured Rs and were then compared with the measured pan evaporation as an indication of the potential atmospheric demand. Interestingly and unlike many previous studies, which have suggested the FAO56 PM as the standard method in calculation of ET o , the FAO24-radiation with the measured Rs showed better agreement with the mean pan evaporation. Therefore, the FAO24-radiation with the measured Rs was used as the reference method for the study area, which was also confirmed by the previous studies based on the lysimeter data. Moreover, the accuracy of calibrated Rs in the estimation of ET o by the FAO56 PM and FAO24-radiation was investigated. Results showed that the calibrated Rs improved the accuracy of the estimated ET o by the FAO24-radiation compared with the FAO24-radiation using the measured

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.

Calibration of a distributed hydrologic model for six European catchments using remote sensing data

Science.gov (United States)

Stisen, S.; Demirel, M. C.; Mendiguren González, G.; Kumar, R.; Rakovec, O.; Samaniego, L. E.

2017-12-01

While observed streamflow has been the single reference for most conventional hydrologic model calibration exercises, the availability of spatially distributed remote sensing observations provide new possibilities for multi-variable calibration assessing both spatial and temporal variability of different hydrologic processes. In this study, we first identify the key transfer parameters of the mesoscale Hydrologic Model (mHM) controlling both the discharge and the spatial distribution of actual evapotranspiration (AET) across six central European catchments (Elbe, Main, Meuse, Moselle, Neckar and Vienne). These catchments are selected based on their limited topographical and climatic variability which enables to evaluate the effect of spatial parameterization on the simulated evapotranspiration patterns. We develop a European scale remote sensing based actual evapotranspiration dataset at a 1 km grid scale driven primarily by land surface temperature observations from MODIS using the TSEB approach. Using the observed AET maps we analyze the potential benefits of incorporating spatial patterns from MODIS data to calibrate the mHM model. This model allows calibrating one-basin-at-a-time or all-basins-together using its unique structure and multi-parameter regionalization approach. Results will indicate any tradeoffs between spatial pattern and discharge simulation during model calibration and through validation against independent internal discharge locations. Moreover, added value on internal water balances will be analyzed.

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

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...

Analysis of the Arctic system for freshwater cycle intensification: Observations and expectations

Science.gov (United States)

Rawlins, M.A.; Steele, M.; Holland, M.M.; Adam, J.C.; Cherry, J.E.; Francis, J.A.; Groisman, P.Y.; Hinzman, L.D.; Huntington, T.G.; Kane, D.L.; Kimball, J.S.; Kwok, R.; Lammers, R.B.; Lee, C.M.; Lettenmaier, D.P.; McDonald, K.C.; Podest, E.; Pundsack, J.W.; Rudels, B.; Serreze, Mark C.; Shiklomanov, A.; Skagseth, O.; Troy, T.J.; Vorosmarty, C.J.; Wensnahan, M.; Wood, E.F.; Woodgate, R.; Yang, D.; Zhang, K.; Zhang, T.

2010-01-01

Hydrologic cycle intensification is an expected manifestation of a warming climate. Although positive trends in several global average quantities have been reported, no previous studies have documented broad intensification across elements of the Arctic freshwater cycle (FWC). In this study, the authors examine the character and quantitative significance of changes in annual precipitation, evapotranspiration, and river discharge across the terrestrial pan-Arctic over the past several decades from observations and a suite of coupled general circulation models (GCMs). Trends in freshwater flux and storage derived from observations across the Arctic Ocean and surrounding seas are also described. With few exceptions, precipitation, evapotranspiration, and river discharge fluxes from observations and the GCMs exhibit positive trends. Significant positive trends above the 90% confidence level, however, are not present for all of the observations. Greater confidence in the GCM trends arises through lower interannual variability relative to trend magnitude. Put another way, intrinsic variability in the observations tends to limit confidence in trend robustness. Ocean fluxes are less certain, primarily because of the lack of long-term observations. Where available, salinity and volume flux data suggest some decrease in saltwater inflow to the Barents Sea (i.e., a decrease in freshwater outflow) in recent decades. A decline in freshwater storage across the central Arctic Ocean and suggestions that large-scale circulation plays a dominant role in freshwater trends raise questions as to whether Arctic Ocean freshwater flows are intensifying. Although oceanic fluxes of freshwater are highly variable and consistent trends are difficult to verify, the other components of the Arctic FWC do show consistent positive trends over recent decades. The broad-scale increases provide evidence that the Arctic FWC is experiencing intensification. Efforts that aim to develop an adequate

Evapotranspiration estimation using a parameter-parsimonious energy partition model over Amazon basin

Science.gov (United States)

Xu, D.; Agee, E.; Wang, J.; Ivanov, V. Y.

2017-12-01

The increased frequency and severity of droughts in the Amazon region have emphasized the potential vulnerability of the rainforests to heat and drought-induced stresses, highlighting the need to reduce the uncertainty in estimates of regional evapotranspiration (ET) and quantify resilience of the forest. Ground-based observations for estimating ET are resource intensive, making methods based on remotely sensed observations an attractive alternative. Several methodologies have been developed to estimate ET from satellite data, but challenges remained in model parameterization and satellite limited coverage reducing their utility for monitoring biodiverse regions. In this work, we apply a novel surface energy partition method (Maximum Entropy Production; MEP) based on Bayesian probability theory and nonequilibrium thermodynamics to derive ET time series using satellite data for Amazon basin. For a large, sparsely monitored region such as the Amazon, this approach has the advantage methods of only using single level measurements of net radiation, temperature, and specific humidity data. Furthermore, it is not sensitive to the uncertainty of the input data and model parameters. In this first application of MEP theory for a tropical forest biome, we assess its performance at various spatiotemporal scales against a diverse field data sets. Specifically, the objective of this work is to test this method using eddy flux data for several locations across the Amazonia at sub-daily, monthly, and annual scales and compare the new estimates with those using traditional methods. Analyses of the derived ET time series will contribute to reducing the current knowledge gap surrounding the much debated response of the Amazon Basin region to droughts and offer a template for monitoring the long-term changes in global hydrologic cycle due to anthropogenic and natural causes.

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.

Effect of readily available water deficit in soil on maize yield and evapotranspiration

Directory of Open Access Journals (Sweden)

Pejić Borivoj

2010-01-01

Full Text Available An investigation was carried out at Rimski Šančevi experiment field of Institute of Field and Vegetable Crops, Novi Sad on calcareous chernozem soil on the loess terrace, in the period 2000-2007, and included irrigated variant (T1 and non-irrigated i.e. control variant (T0. NS-640, maize hybrid from the FAO maturity group 600, was analyzed. Readily available soil water deficit (RASWD in the layer of 60 cm in the course of growing season and actual evapotranspiration (ETa were calculated by the water balance method. Water consumption for potential evapotranspiration (ETm in individual months and the growing season were calculated by the bioclimatic procedure, using hydrophytothermic indexes. The correlation analysis revealed highly significant dependences of maize yield (Y on RASWD (r = -0.941 and the amount of precipitation (P in August (r = 0.931. Statistically significant dependence was also found between Y and RASWD (r = -0.765 and P (r = 0.768 in July and August. The obtained results indicate that maize production in Vojvodina under the rainfed conditions is unreliable, and that it is correlated with weather conditions, especially with the amount and distribution of precipitation. The statistically significant correlation obtained between Y and ETa (r = 0.755 confirms that water supply is the basic prerequisite which allows the other production factors to be realized. Significantly higher maize yields in the T1 variant (13.517 t ha-1 in relation to the T0 variant (11.210 t ha-1 indicate clearly that under the climatic conditions of Vojvodina high and stable yields of maize can be achieved only in irrigation. .

An observational study of complications in chickenpox with special reference to unusual complications in an apex infectious disease hospital, Kolkata, India

Directory of Open Access Journals (Sweden)

A K Kole

2013-01-01

Full Text Available Background: Chickenpox can cause serious complications and even death in persons without any risk factors. Aims: To observe the different complications with special reference to unusual complications of chickenpox and their outcomes. Materials and Methods: The present study was a prospective observational study where 300 patients suffering from chickenpox were evaluated with special reference to unusual complications and outcomes. Results: The usual complications of chickenpox commonly observed were acute hepatitis in 30 (10% and cerebellar ataxia in 22 patients (7.3%, whereas common unusual complications were acute pancreatitis in 45 (15%, hemorrhagic rash in 10 (3.3%, Guillain-Barrι syndrome in 4 (1.3%, disseminated intravascular coagulation in 4 (1.3%, necrotizing fasciitis in 4 (1.3%, and acute renal failure in 3 patients (1%. It had been observed that most of these unusual complications occurred in patients without any risk factor. A total of 18 patients (6% died in this study and of them 12 patients (4% died due to unusual complications. Conclusions: Compulsory childhood varicella vaccination including vaccination of risk groups and susceptible individuals are all essential to reduce the incidence of chickenpox, associated complications, and subsequent death.

Surface Renewal Application for Estimating Evapotranspiration: A Review

Directory of Open Access Journals (Sweden)

Yongguang Hu

2018-01-01

Full Text Available The estimation of evapotranspiration (ET is essential for meteorological modeling of surface exchange processes, as well as for the agricultural practice of irrigation management. Hitherto, a number of methods for estimation of ET at different temporal scales and climatic conditions are constantly under investigation and improvement. One of these methods is surface renewal (SR. Therefore, the premise of this review is to present recent developments and applications of SR for ET measurements. The SR method is based on estimating the turbulent exchange of sensible heat flux between plant canopy and atmosphere caused by the instantaneous replacement of air parcels in contact with the surface. Additional measurements of net radiation and soil heat flux facilitate extracting ET using the shortened energy balance equation. The challenge, however, is the calibration of SR results against direct sensible heat flux measurements. For the classical SR method, only air temperature measured at high frequency is required. In addition, a new model suggests that the SR method could be exempted from calibration by measuring additional micrometeorological variables. However, further improvement of the SR method is required to provide improved results in the future.

Estimating Evapotranspiration from an Improved Two-Source Energy Balance Model Using ASTER Satellite Imagery

Directory of Open Access Journals (Sweden)

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.

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.

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

The influence of the surface roughness parameterization on remote sensing-based estimates of evapotranspiration from vineyards

Science.gov (United States)

Alfieri, J. G.; Kustas, W. P.; Gao, F.; Nieto, H.; Prueger, J. H.; Hipps, L.

2017-12-01

Because the judicious application of water is key to ensuring berry quality, information regarding evapotranspiration (ET) is critical when making irrigation and other crop management decisions for vineyards. Increasingly, wine grape producers seek to use remote sensing-based models to monitor ET and inform management decisions. However, the parameterization schemes used by these models do not fully account for the effects of the highly-structured canopy architecture on either the roughness characteristics of the vineyard or the turbulent transport and exchange within and above the vines. To investigate the effects of vineyard structure on the roughness length (zo) and displacement height (do) of vineyards, data collected from 2013 to 2016 as a part of the Grape Remote Sensing Atmospheric Profiling and Evapotranspiration Experiment (GRAPEX), an ongoing multi-agency field campaign conducted in the Central Valley of California, was used. Specifically, vertical profiles (2.5 m, 3.75 m, 5 m, and 8 m, agl) of wind velocity collected under near-neutral conditions were used to estimate do and zo and characterize how these roughness parameters vary in response changing environmental conditions. The roughness length was found to vary as a function of wind direction. It increased sigmoidally from a minimum near 0.15 m when the wind direction was parallel to the vine rows to a maximum between 0.3 m and 0.4 m when the winds were perpendicularly to the rows. Similarly, do was found responds strongly to changes in vegetation density as measured via leaf area index (LAI). Although the maximum varied from year-to-year, do increased rapidly after bud break in all cases and then remained constant for the remainder of the growing season. A comparison of the model output from the remote sensing-based two-source energy balance (TSEB) model using the standard roughness parameterization scheme and the empirical relationships derived from observations indicates a that the modeled ET

Evaluation of Clear-Sky Incoming Radiation Estimating Equations Typically Used in Remote Sensing Evapotranspiration Algorithms

Directory of Open Access Journals (Sweden)

Ted W. Sammis

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 components of net radiation are obtained from remote sensing data, while the incoming shortwave (RS and longwave (RL components are typically estimated from weather data using empirical equations. This study evaluates the accuracy of empirical equations commonly used in remote sensing ET algorithms for estimating RS and RL radiation. Evaluation is carried out through comparison of estimates and observations at five sites that represent different climatic regions from humid to arid. Results reveal (1 both RS and RL estimates from all evaluated equations well correlate with observations (R2 ≥ 0.92, (2 RS estimating equations tend to overestimate, especially at higher values, (3 RL estimating equations tend to give more biased values in arid and semi-arid regions, (4 a model that parameterizes the diffuse component of radiation using two clearness indices and a simple model that assumes a linear increase of atmospheric transmissivity with elevation give better RS estimates, and (5 mean relative absolute errors in the net radiation (Rn estimates caused by the use of RS and RL estimating equations varies from 10% to 22%. This study suggests that Rn estimates using recommended incoming radiation estimating equations could improve ET estimates.

A null-parameter formula for storage-evapotranspiration relationship based on generalized proportionality hypothesis and its applications

Science.gov (United States)

Han, P. F.; Wang, X. S.; Istanbulluoglu, E.

2017-12-01

Different formulas have been developed to estimate the mean annual evapotranspiration ratio (E/P) at catchment scale from the mean annual aridity index (Ep/P) based on the Budyko framework. A major challenge in using the Budyko framework for the inter-annual behaviors of a catchment is the missed storage in these formulas. Efforts have been contributed to modify the formulas for estimating the annual E/P from both of the annual Ep/P and the change in storage, leading to a significant increase in the number of empirical parameters. In this paper we develop a null-parameter formula of the storage-evapotranspiration relationship based on a new interpretation of the proportionality hypothesis, which takes the storage in the soil-plant-atmosphere continuum (SPAC) as the accessible water for the evapotranspiration processes. According to the formula, the annual E/P depends on the annual Ep/P and S/P values where S is the initial SPAC storage in a year. The difference between the S values of two years represents the inter-annual change in storage in the SPAC system. An annual water balance model including groundwater storage for a basin is required to estimate the annual runoff and S/P from year to year. We develop a tri-parameters model using this null-parameter formula to minimize the number of parameters and successfully applied to investigate the NLRB basin in Nebraska, USA. For mean annual water balance, the tri-parameters model results in one-parameter formulas to estimate both of the mean annual E/P and S/P so that the status of storage can be included in the Budyko framework. The tri-parameters model is further extended to a twin-zones model for the effect of irrigation in croplands and applied to reconstruct the hydrological behaviors in the natural state for 12 catchments in Illinois, USA, with different cropland areas. It is found in the Illinois examples (where Ep/P is less than 2) that the annual E/P increases with the increasing Ep/P almost in a linear

Evapotranspiration partitioning, stomatal conductance, and components of the water balance: A special case of a desert ecosystem in China

Science.gov (United States)

Zhao, Wenzhi; Liu, Bing; Chang, Xuexiang; Yang, Qiyue; Yang, Yuting; Liu, Zhiling; Cleverly, James; Eamus, Derek

2016-07-01

Partitioning evapotranspiration (ET) into its components reveals details of the processes that underlie ecosystem hydrologic budgets and their feedback to the water cycle. We measured rates of actual evapotranspiration (ETa), canopy transpiration (Tc), soil evaporation (Eg), canopy-intercepted precipitation (EI), and patterns of stomatal conductance of the desert shrub Calligonum mongolicum in northern China to determine the water balance of this ecosystem. The ETa was 251 ± 8 mm during the growing period, while EI, Tc, and Eg accounted for 3.2%, 63.9%, and 31.3%, respectively, of total water use (256 ± 4 mm) during the growing period. In this unique ecosystem, groundwater was the main water source for plant transpiration and soil evaporation, Tc and exceeded 60% of the total annual water used by desert plants. ET was not sensitive to air temperature in this unique desert ecosystem. Partitioning ET into its components improves our understanding of the mechanisms that underlie adaptation of desert shrubs, especially the role of stomatal regulation of Tc as a determinant of ecosystem water balance.

A Terrestrial Reference Frame realised on the observation level using a GPS-LEO satellite constellation

Science.gov (United States)

Koenig, Daniel

2018-02-01

Applying a one-step integrated process, i.e. by simultaneously processing all data and determining all satellite orbits involved, a Terrestrial Reference Frame (TRF) consisting of a geometric as well as a dynamic part has been determined at the observation level using the EPOS-OC software of Deutsches GeoForschungsZentrum. The satellite systems involved comprise the Global Positioning System (GPS) as well as the twin GRACE spacecrafts. Applying a novel approach, the inherent datum defect has been overcome empirically. In order not to rely on theoretical assumptions this is done by carrying out the TRF estimation based on simulated observations and using the associated satellite orbits as background truth. The datum defect is identified here as the total of all three translations as well as the rotation about the z-axis of the ground station network leading to a rank-deficient estimation problem. To rectify this singularity, datum constraints comprising no-net translation (NNT) conditions in x, y, and z as well as a no-net rotation (NNR) condition about the z-axis are imposed. Thus minimally constrained, the TRF solution covers a time span of roughly a year with daily resolution. For the geometric part the focus is put on Helmert transformations between the a priori and the estimated sets of ground station positions, and the dynamic part is represented by gravity field coefficients of degree one and two. The results of a reference solution reveal the TRF parameters to be estimated reliably with high precision. Moreover, carrying out a comparable two-step approach using the same data and models leads to parameters and observational residuals of worse quality. A validation w.r.t. external sources shows the dynamic origin to coincide at a level of 5 mm or better in x and y, and mostly better than 15 mm in z. Comparing the derived GPS orbits to IGS final orbits as well as analysing the SLR residuals for the GRACE satellites reveals an orbit quality on the few cm level

Earth observation based assessment of the water production and water consumption of Nile Basin agro-ecosystems

Science.gov (United States)

Bastiaanssen, Wim G.M.; Karimi, Poolad; Rebelo, Lisa-Maria; Duan, Zheng; Senay, Gabriel; Muthuwatte, Lal; Smakhtin, Vladimir

2014-01-01

The increasing competition for water resources requires a better understanding of flows, fluxes, stocks, and the services and benefits related to water consumption. This paper explains how public domain Earth Observation data based on Moderate Resolution Imaging Spectroradiometer (MODIS), Second Generation Meteosat (MSG), Tropical Rainfall Measurement Mission (TRMM) and various altimeter measurements can be used to estimate net water production (rainfall (P) > evapotranspiration (ET)) and net water consumption (ET > P) of Nile Basin agro-ecosystems. Rainfall data from TRMM and the Famine Early Warning System Network (FEWS-NET) RainFall Estimates (RFE) products were used in conjunction with actual evapotranspiration from the Operational Simplified Surface Energy Balance (SSEBop) and ETLook models. Water flows laterally between net water production and net water consumption areas as a result of runoff and withdrawals. This lateral flow between the 15 sub-basins of the Nile was estimated, and partitioned into stream flow and non-stream flow using the discharge data. A series of essential water metrics necessary for successful integrated water management are explained and computed. Net water withdrawal estimates (natural and humanly instigated) were assumed to be the difference between net rainfall (Pnet) and actual evapotranspiration (ET) and some first estimates of withdrawals—without flow meters—are provided. Groundwater-dependent ecosystems withdraw large volumes of groundwater, which exceed water withdrawals for the irrigation sector. There is a strong need for the development of more open-access Earth Observation databases, especially for information related to actual ET. The fluxes, flows and storage changes presented form the basis for a global framework to describe monthly and annual water accounts in ungauged river basins.

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.

Assessment of evapotranspiration and soil water content in the Kysuca River basin (Slovakia) using a rainfall-runoff model

Czech Academy of Sciences Publication Activity Database

Košková, Romana; Němečková, Soňa; Sitková, Z.

2008-01-01

Roč. 4, č. 1 (2008), s. 012002 ISSN 1755-1315. [Conference of the Danubian Countries /24./. Bled, 02.06.2008-04.06.2008] R&D Projects: GA AV ČR(CZ) KJB300600602 Institutional research plan: CEZ:AV0Z20600510 Keywords : hydrological modelling * soil water content * evapotranspiration * SWIM model Subject RIV: DA - Hydrology ; Limnology http://www.iop.org/EJ/abstract/1755-1315/4/1/012002

Explaining the evaporation paradox in Jiangxi Province of China: Spatial distribution and temporal trends in potential evapotranspiration of Jiangxi Province from 1961 to 2013

Directory of Open Access Journals (Sweden)

Xianghui Lu

2016-03-01

Full Text Available Evaporation acts as an important component and a key control factor in land hydrological processes. In order to analyze the trend of change on potential evapotranspiration from 1961 to 2013 and to discuss the existence of the evaporation paradox in Jiangxi province, China, monthly meteorological data spanning the years 1961–2013 were analyzed in this study, where the data were collected from 15 national meteorological stations in Jiangxi Province. The Penman–Monteith equation was employed to compute the potential evapotranspiration (ET0. Spatial interpolation and data mining technology were used to analyze the spatial and temporal changes of ET0 and air temperature, with the effort to explain the evaporation paradox. By solving the total differential and the partial derivatives coefficients of the independent variables in Penman–Monteith equation, the cause of the paradox was quantitatively evaluated. The results showed that the annual ET0 had been decreasing significantly in Jiangxi Province since 1979, whereas the air temperature had been rising significantly, presenting the evaporation paradox. The decreases in sunshine duration and wind speed reduced ET0 by 0.207 mm and 0.060 mm, respectively, accounting for 92.3% and 26.7% of the total ET0, respectively. It is concluded that sunshine duration and wind speed are the main causes to the decrease in potential evapotranspiration in Jiangxi Province.

Quantum frames of reference

International Nuclear Information System (INIS)

Kaufherr, T.

1981-01-01

The idea that only relative variables have physical meaning came to be known as Mach's principle. Carrying over this idea to quantum theory, has led to the consideration of finite mass, macroscopic reference frames, relative to which all physical quantities are measured. During the process of measurement, a finite mass observer receives a kickback, and this reaction of the measuring device is not negligible in quantum theory because of the quantization of the action. Hence, the observer himself has to be included in the system that is being considered. Using this as the starting point, a number of thought experiments involving finite mass observers is discussed which have quantum uncertainties in their time or in their position. These thought experiments serve to elucidate in a qualitative way some of the difficulties involved, as well as pointing out a direction to take in seeking solutions to them. When the discussion is extended to include more than one observer, the question of the covariance of the theory immediately arises. Because none of the frames of reference should be preferred, the theory should be covariant. This demand expresses an equivalence principle which here is extended to include reference frames which are in quantum uncertainties relative to each other. Formulating the problem in terms of canonical variables, the ensueing free Hamiltonian contains vector and scalar potentials which represent the kick that the reference frame receives during measurement. These are essentially gravitational type potentials, resulting, as it were, from the extension of the equivalence principle into the quantum domain

Evolution of evapotranspiration and water stress of oak savanna vegetation in the Iberian Peninsula (2001-2015

Directory of Open Access Journals (Sweden)

M. P. González-Dugo

2017-12-01

Full Text Available The objective of this work is to provide new insights about the effect of soil water deficit on the vegetation of Mediterranean oak savanna. The evolution of evapotranspiration (ET and vegetation water stress over this ecosystem, in the Iberian Peninsula, has been monitored for fifteen years through the application of a remote sensing thermal-based energy balance model. The Surface Energy Balance System (SEBS has been applied, on a monthly timescale from January 2001 to December 2015, using input satellite and meteorological reanalysis databases. The model performance has been evaluated under these conditions by comparison with field measurements. The estimation of energy fluxes yielded reasonable agreements with observations (RMSD=14-20 W·m–2 for the radiative fluxes and RMSD=26-29 W·m–2 for the turbulent ones and have led to characterize the main drought events occurred during the study period, and to quantify their effects on the vegetation coverage and production. The most generalized and severe events (2004/2005 and 2011/2012 and their impact on different vegetation strata, oaks and grasslands, are further analyzed.

Actual evapotranspiration estimation in a Mediterranean mountain region by means of Landsat-5 TM and TERRA/AQUA MODIS imagery and Sap Flow measurements in Pinus sylvestris forest stands.

Science.gov (United States)

Cristóbal, J.; Poyatos, R.; Ninyerola, M.; Pons, X.; Llorens, P.

2009-04-01

Evapotranspiration monitoring has important implications on global and regional climate modelling, as well as in the knowledge of the hydrological cycle and in the assessment of environmental stress that affects forest and agricultural ecosystems. An increase of evapotranspiration while precipitation remains constant, or is reduced, could decrease water availability for natural and agricultural systems and human needs. Consequently, water balance methods, as the evapotranspiration modelling, have been widely used to estimate crop and forest water needs, as well as the global change effects. Nowadays, radiometric measurements provided by Remote Sensing and GIS analysis are the technologies used to compute evapotranspiration at regional scales in a feasible way. Currently, the 38% of Catalonia (NE of the Iberian Peninsula) is covered by forests, and one of the most important forest species is Scots Pine (Pinus sylvestris) which represents the 18.4% of the area occupied by forests. The aim of this work is to model actual evapotranspiration in Pinus sylvestris forest stands, in a Mediterranean mountain region, using remote sensing data, and compare it with stand-scale sap flow measurements measured in the Vallcebre research area (42° 12' N, 1° 49' E), in the Eastern Pyrenees. To perform this study a set of 30 cloud-free TERRA-MODIS images and 10 Landsat-5 TM images of path 198 and rows 31 and 32 from June 2003 to January 2005 have been selected to perform evapotranspiration modelling in Pinus sylvestris forest stands. TERRA/AQUA MODIS images have been downloaded by means of the EOS Gateway. We have selected two different types of products which contain the remote sensing data we have used to model daily evapotranspiration, daily LST product and daily calibrated reflectances product. Landsat-5 TM images have been corrected by means of conventional techniques based on first order polynomials taking into account the effect of land surface relief using a Digital

Spatio-temporal variability of evapotranspiration and energy fluxes over Heihe River Basin, China

Science.gov (United States)

Xu, Z.; Liu, S.; Xu, T.; Song, L.; Wang, X.

2017-12-01

Evapotranspiration (ET) is an essential component of energy and water budgets and is an important process in the soil-plant-atmosphere continuum (SPAC). Some important ecosystem parameters and processes, such as soil moisture, vegetation productivity, ecosystem energy, water, and nutrient budgets, are influenced by ET. The Heihe River Basin (HRB) is the second largest inland river, with an area of approximately 140,000 km2. A diverse land covers are distributing in HRB, which is characterized by distinct cold and arid landscapes, glaciers, frozen soil, alpine meadow, forest, irrigated crops, riparian ecosystem, and desert from upstream to downstream. Up to now, there was not a quantitative characterization of ET and energy flux over HRB; therefore, special attention should be paid on this term. A comprehensive hydrometeorological observatory was established since 2008 and completed in 2013. The network included 3 superstations and 18 ordinary stations, covering the main underlying surfaces in the basin, including alpine meadow, cropland, desert, wetland, frozen soil, Tamarix chinensis, and Populus euphratica, etc. Reliable data were obtained after the routine instrument maintenance and carefully data processing. ET and energy flux observations were made more than 5 years (2012-2017) using eddy covariance (EC) systems and large aperture scintillometers (LAS), and the seasonal and interannual variability of ET and its influencing factors were quantitatively analyzed with ET in main underlying surfaces of 400-580 mm in alpine meadow (upstream), 600-700 mm in cropland (midstream), 500-650 mm in riparian forest (downstream), 40 mm in desert (downstream). Meanwhile, the spatial distributions of ET were investigated based on site observations using machine learning techniques. Further, ET partitioning (evaporation (E) and transpiration (T)) was acquired through a method of underlying water use efficiency based on EC observations. The spatial variations of E and T were

Case study of a full-scale evapotranspiration cover

Science.gov (United States)

McGuire, Patrick E.; Andraski, Brian J.; Archibald, Ryan E.

2009-01-01

The design, construction, and performance analyses of a 6.1ha evapotranspiration (ET) landfill cover at the semiarid U.S. Army Fort Carson site, near Colorado Springs, Colo. are presented. Initial water-balance model simulations, using literature reported soil hydraulic data, aided selection of borrow-source soil type(s) that resulted in predictions of negligible annual drainage (⩽1mm∕year). Final construction design was based on refined water-balance simulations using laboratory determined soil hydraulic values from borrow area natural soil horizons that were described with USDA soil classification methods. Cover design components included a 122cmthick clay loam (USDA), compaction ⩽80% of the standard Proctor maximum dry density (dry bulk density ∼1.3Mg∕m3), erosion control measures, top soil amended with biosolids, and seeding with native grasses. Favorable hydrologic performance for a 5year period was documented by lysimeter-measured and Richards’-based calculations of annual drainage that were all <0.4mm∕year. Water potential data suggest that ET removed water that infiltrated the cover and contributed to a persistent driving force for upward flow and removal of water from below the base of the cover.

Berry's phase factors in moving frames of reference and their observable effects

International Nuclear Information System (INIS)

Sun Changpu; Zhang Linzhi

1990-01-01

Under non-relativistic conditions, the properties of adiabatic solutions of the Schroedinger equation in moving frame of reference and the behaviours of the corresponding Berry's Phase are analysed. Two cases of translation and rotation are discussed in detail, which show that the existence of Berry's phase depends on the choice of frame of reference. While Bitter and Dubbers's experiment is explained by the first-order approximation in the discussion. The non-adiabatic effects in this experiment are predicted by the second-order approximation when the adiabatic condition is broken

Quantifying the Components of Evapotranspiration from Plant Communities, Soil Evaporation and Plant Transpiration, with Oxygen-18 Isotopes and Micrometeorology

Energy Technology Data Exchange (ETDEWEB)

Denmead, Tom [CSIRO Centre for Environmental Mechanics, GPO Box 821, Canberra, ACT 2601 (Australia); Heng, Lee; Nguyen, Long [Soil and Water Management and Crop Nutrition Section, IAEA (Austria); Zeeman, Matthias [Karlsruhe Institute of Technology, Garmisch-Partenkirchen (Germany); Mayr, Leo; Arrillaga, Jose Luis [Soil and Water Management and Crop Nutrition Laboratory, IAEA (Austria); Cepuder, Peter [Department of Water-Atmosphere-Environment, Institute for Hydraulics and Rural Water Management (BOKU), Vienna (Austria)

2013-01-15

The Keeling plot (Keeling, 1961) approach has been shown to provide an estimate of the relative proportions of water vapour emanating from evaporation (E) from soil, and transpiration (T) from the plant canopy (Moreira et. al., 1997; Williams et al., 2004). This estimate can be used in conjunction with measurements of the net water vapour flux and evapotranspiration (ET), to quantify the E and T components using an Inverse Lagrangian (IL) approach based on canopy turbulence (Raupach, 1989), which allows the identification of water vapour in the different canopy layers (Denmead et al., 2005). A study was carried out on a wheat crop over a 3-day period in April (daily temperatures ranged from 14-23''oC) at the BOKU experimental field outside Vienna to provide an independent check of the relative proportions of soil evaporation (E) and plant transpiration (T) estimated by the Keeling plot {sigma}{sup 18}O isotope analysis and by the application of the IL model of water vapour transport in plant canopies. The eddy covariance instrumentation to measure ET was provided by the Karlsruhe Institute of Technology at Garmisch-Partenkirchen, Germany. Transpiration rates, estimated by the {sigma}{sup 18}O isotopic technique were similar to those derived from Inverse Lagrangian analyses. indicating that the IL and isotopic analyses gave essentially the same partitioning of evapotranspiration into E and T. The use of the IL analysis to determine water vapour in different segments of the canopy is illustrated. In these observations the soil was dry (9-12 %) and soil evaporation was small. The eddy covariance approach confirmed the correctness of the IL analysis for the total water loss from the canopy (to within 6%) (data not shown). The IL and the isotopic analyses gave essentially the same partitioning of ET into E and T for 3 days on a dry soil. The isotopic analysis using {sigma}{sup 18}O gave E/ET {approx} 4% and T/ET {approx} 96%, while IL analysis gave corresponding figures

Modeling actual evapotranspiration with routine meteorological variables in the data-scarce region of the Tibetan Plateau: Comparisons and implications

Science.gov (United States)

Ma, Ning; Zhang, Yinsheng; Xu, Chong-Yu; Szilagyi, Jozsef

2015-08-01

Quantitative estimation of actual evapotranspiration (ETa) by in situ measurements and mathematical modeling is a fundamental task for physical understanding of ETa as well as the feedback mechanisms between land and the ambient atmosphere. However, the ETa information in the Tibetan Plateau (TP) has been greatly impeded by the extremely sparse ground observation network in the region. Approaches for estimating ETa solely from routine meteorological variables are therefore important for investigating spatiotemporal variations of ETa in the data-scarce region of the TP. Motivated by this need, the complementary relationship (CR) and Penman-Monteith approaches were evaluated against in situ measurements of ETa on a daily basis in an alpine steppe region of the TP. The former includes the Nonlinear Complementary Relationship (Nonlinear-CR) as well as the Complementary Relationship Areal Evapotranspiration (CRAE) models, while the latter involves the Katerji-Perrier and the Todorovic models. Results indicate that the Nonlinear-CR, CRAE, and Katerji-Perrier models are all capable of efficiently simulating daily ETa, provided their parameter values were appropriately calibrated. The Katerji-Perrier model performed best since its site-specific parameters take the soil water status into account. The Nonlinear-CR model also performed well with the advantage of not requiring the user to choose between a symmetric and asymmetric CR. The CRAE model, even with a relatively low Nash-Sutcliffe efficiency (NSE) value, is also an acceptable approach in this data-scarce region as it does not need information of wind speed and ground surface conditions. In contrast, application of the Todorovic model was found to be inappropriate in the dry regions of the TP due to its significant overestimation of ETa as it neglects the effect of water stress on the bulk surface resistance. Sensitivity analysis of the parameter values demonstrated the relative importance of each parameter in the

Satellite retrieval of actual evapotranspiration in the Tibetan Plateau: Components partitioning, multidecadal trends and dominated factors identifying

Science.gov (United States)

Wang, Weiguang; Li, Jinxing; Yu, Zhongbo; Ding, Yimin; Xing, Wanqiu; Lu, Wenjun

2018-04-01

As the only connecting term between water balance and energy budget in the earth-atmospheric system, evapotranspiration (ET) is considered the most excellent indicator for the activity for the water and energy cycle. Under the background of global change, regional ET estimates, components partitioning as well as their spatial and temporal patterns recognition are of great importance in understanding the hydrological processes and improving water management practices. This is particularly true for the Tibetan Plateau (TP), one of most sensitive and vulnerable region in response to the environment change in the earth. In this study, with flux site observation data and monthly ET data from the monthly water balance method incorporating the terrestrial water storage changes from the Gravity Recovery and Climate Experiment satellite (GRACE) production as the multiple validations, the long-term daily ET in the TP was retrieved by a modified Penman-Monteith-Leuning (PML) model with considering evapotranspiration over snow covered area during 1982-2012. The spatial and temporal changes of partitioned three components of ET, i.e., soil evaporation (Es), transpiration through the stomata of plant (Ec) and canopy interception (Ei), were investigated in the TP. Meanwhile, how the ET components contribute to ET changes and respond to the change in environmental factors in the TP was revealed and discussed. The results indicate that Es dominates ET in most areas of the TP with the mean annual ratio of 65.7%, except southeastern regions where the vegetation coverage is high. Although regional average ET and three main components all present obvious increase trends during the past decades, high spatial heterogeneity for their trends are identified in the TP. Moreover, a mixed changing pattern can be apparently found for Es in southeastern area, Ec and Ei in northwestern and southeastern area. Spatially, the ET variation are mainly attributed to change in Es, followed by Ec and Ei

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

2017-02-21

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/m 3 . 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.

Evapotranspiration from drained wetlands: drivers, modeling, storage functions, and restoration implications

Science.gov (United States)

Shukla, S.; Wu, C. L.; Shrestha, N.

2017-12-01

Abstract Evapotranspiration (ET) is a major component of wetland and watershed water budgets. The effect of wetland drainage on ET is not well understood. We tested whether the current understanding of insignificant effect of drainage on ET in the temperate region wetlands applies to those in the sub-tropics. Eddy covariance (EC) based ET measurements were made for two years at two previously drained and geographically close wetlands in the Everglades region of Florida. One wetland was significantly drained with 97% of its storage capacity lost. The other was a more functional wetland with 42% of storage capacity lost. Annual average ET at the significantly drained wetland was 836 mm, 34% less than the function wetland (1271 mm) and the difference was statistically significant (p = 0.001). Such differences in wetland ET in the same climatic region have not been observed. The difference in ET was mainly due to drainage driven differences in inundation and associated effects on net radiation (Rn) and local relative humidity. Two daily ET models, a regression (r2 = 0.80) and a Relevance Vector Machine (RVM) model (r2 = 0.84), were developed with the latter being more robust. These models, when used in conjunction with hydrologic models, improved ET predictions for drained wetlands. Predictions from an integrated model showed that more intensely drained wetlands at higher elevation should be targeted for restoration of downstream flows (flooding) because they have the ability to loose higher water volume through ET which increases available water storage capacity of wetlands. Daily ET models can predict changes in ET for improved evaluation of basin-scale effects of restoration programs and climate change scenarios.

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

Best Reference Practices are Not Observed in Telephone Ready Reference Services. A review of: Agosto, Denise A. and Holly Anderton. “Whatever Happened to ‘Always Cite the Source?’” Reference & User Services Quarterly 47.1 (2007: 44-54.

Directory of Open Access Journals (Sweden)

Julie McKenna

2008-06-01

and year (author, edition, page number, publisher and place of publication not required.Each reference transaction was noted to record whether the answer was correct and to define the nature of source citing that occurred. Other notes were kept to describe other respondent behaviors and attitudes demonstrated during the transaction.Main Results – 93.6% of the answers to the 125 reference questions were correct. Complete citations were provided seventimes (5.6% and partial citations were provided an additional thirty-one times (24.8%. In 68% of the 125 transactions, no source citation information was provided. There was a corresponding relationship between the difficulty of the reference question and the respondent’s provision of any citation source (either a complete or incomplete citation source. Sources were generally not provided for simple questions even though the practice of citing is expected for all levels of questions. The practice of citing in order to reveal the path to the answer so that the user may become independent in the future was not observed. In addition, five “negative closure” techniques were employed by respondents. These included unmonitored referral; immediate referral away from the service; articulating that the encounter would not be successful at the start; shutting down the transaction either by tone of voice or by use of phrase that precluded any further interaction with the user; or claiming that the information did not exist or was not available. A reliance on digital formats rather than print sources was found.Conclusion – The accuracy rate of the answers to the questions was very high (93.6%, but other aspects of the service were considered to be less than satisfactory. The Reference and User Services Association (RUSA Guidelines, considered the best practices for reference service, were not observed and in particular, the source citation rule was not followed.

Performance of the METRIC model in estimating evapotranspiration fluxes over an irrigated field in Saudi Arabia using Landsat-8 images

Science.gov (United States)

Madugundu, Rangaswamy; Al-Gaadi, Khalid A.; Tola, ElKamil; Hassaballa, Abdalhaleem A.; Patil, Virupakshagouda C.

2017-12-01

Accurate estimation of evapotranspiration (ET) is essential for hydrological modeling and efficient crop water management in hyper-arid climates. In this study, we applied the METRIC algorithm on Landsat-8 images, acquired from June to October 2013, for the mapping of ET of a 50 ha center-pivot irrigated alfalfa field in the eastern region of Saudi Arabia. The METRIC-estimated energy balance components and ET were evaluated against the data provided by an eddy covariance (EC) flux tower installed in the field. Results indicated that the METRIC algorithm provided accurate ET estimates over the study area, with RMSE values of 0.13 and 4.15 mm d-1. The METRIC algorithm was observed to perform better in full canopy conditions compared to partial canopy conditions. On average, the METRIC algorithm overestimated the hourly ET by 6.6 % in comparison to the EC measurements; however, the daily ET was underestimated by 4.2 %.

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

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.

Evapotranspiration (ET) covers.

Science.gov (United States)

Rock, Steve; Myers, Bill; Fiedler, Linda

2012-01-01

Evapotranspiration (ET) cover systems are increasingly being used at municipal solid waste (MSW) landfills, hazardous waste landfills, at industrial monofills, and at mine sites. Conventional cover systems use materials with low hydraulic permeability (barrier layers) to minimize the downward migration of water from the surface to the waste (percolation), ET cover systems use water balance components to minimize percolation. These cover systems rely on soil to capture and store precipitation until it is either transpired through vegetation or evaporated from the soil surface. Compared to conventional membrane or compacted clay cover systems, ET cover systems are expected to cost less to construct. They are often aesthetic because they employ naturalized vegetation, require less maintenance once the vegetative system is established, including eliminating mowing, and may require fewer repairs than a barrier system. All cover systems should consider the goals of the cover in terms of protectiveness, including the pathways of risk from contained material, the lifecycle of the containment system. The containment system needs to be protective of direct contact of people and animals with the waste, prevent surface and groundwater water pollution, and minimize release of airborne contaminants. While most containment strategies have been based on the dry tomb strategy of keeping waste dry, there are some sites where adding or allowing moisture to help decompose organic waste is the current plan. ET covers may work well in places where complete exclusion of precipitation is not needed. The U.S. EPA Alternative Cover Assessment Program (ACAP), USDOE, the Nuclear Regulatory Commission, and others have researched ET cover design and efficacy, including the history of their use, general considerations in their design, performance, monitoring, cost, current status, limitations on their use, and project specific examples. An on-line database has been developed with information

Precipitation collection and evapo(transpi)ration of living wall systems : A comparative study between a panel system and a planter box system

NARCIS (Netherlands)

van de Wouw, P.M.F.; Ros, E.J.M.; Brouwers, H.J.H.

2017-01-01

By reducing the quantity of precipitation reaching the ground, a green façade can contribute to a more natural way of rainwater drainage. Additionally, it provides shadowing, insulation, and evapotranspiration (ET) of water enabling it to reduce the heat load of a building. The collection of

Quantitative estimation of land surface evapotranspiration in Taiwan based on MODIS data

Directory of Open Access Journals (Sweden)

Che-sheng Zhan

2011-09-01

Full Text Available Land surface evapotranspiration (ET determines the local and regional water-heat balances. Accurate estimation of regional surface ET provides a scientific basis for the formulation and implementation of water conservation programs. This study set up a table of the momentum roughness length and zero-plane displacement related with land cover and an empirical relationship between land surface temperature and air temperature. A revised quantitative remote sensing ET model, the SEBS-Taiwan model, was developed. Based on Moderate Resolution Imaging Spectroradiometer (MODIS data, SEBS-Taiwan was used to simulate and evaluate the typical actual daily ET values in different seasons of 2002 and 2003 in Taiwan. SEBS-Taiwan generally performed well and could accurately simulate the actual daily ET. The simulated daily ET values matched the observed values satisfactorily. The results indicate that the net regional solar radiation, evaporation ratio, and surface ET values for the whole area of Taiwan are larger in summer than in spring, and larger in autumn than in winter. The results also show that the regional average daily ET values of 2002 are a little higher than those of 2003. Through analysis of the ET values from different types of land cover, we found that forest has the largest ET value, while water areas, bare land, and urban areas have the lowest ET values. Generally, the Northern Taiwan area, including Ilan County, Nantou County, and Hualien County, has higher ET values, while other cities, such as Chiayi, Taichung, and Tainan, have lower ET values.

Assessment of aquifer properties, evapotranspiration, and the effects of ditching in the Stoney Brook watershed, Fond du Lac Reservation, Minnesota, 2006-9

Science.gov (United States)

Jones, Perry M.; Tomasek, Abigail A.

2015-01-01

The U.S. Geological Survey, in cooperation with the Fond du Lac Band of Lake Superior Chippewa, assessed hydraulic properties of geologic material, recharge, and evapotranspiration, and the effects of ditching on the groundwater resources in the Stoney Brook watershed in the Fond du Lac Reservation. Geologic, groundwater, and surface-water data were collected during 2006–9 to estimate hydrologic properties in the watershed. Streamflow and groundwater levels in the shallow glacial deposits in the Stoney Brook watershed were analyzed to estimate groundwater-flow directions, groundwater recharge, and evapotranspiration within the watershed and to assess the effect of ditches on surrounding groundwater resources. Groundwater, streamflow, and precipitation data collected during the study (2006–9) can be used to update the U.S. Department of Agriculture’s Natural Resource Conservation Service and Fond du Lac Resource Management Division surface-water models, which are used to evaluate the effect of proposed adjustments to the ditching system on streamflow on wild rice production and aquatic habitats.

SEBAL-based Daily Actual Evapotranspiration Forecasting using Wavelets Decomposition Analysis and Multivariate Relevance Vector Machines

Science.gov (United States)

Torres, A. F.

2011-12-01

Agricultural lands are sources of food and energy for population around the globe. These lands are vulnerable to the impacts of climate change including variations in rainfall regimes, weather patterns, and decreased availability of water for irrigation. In addition, it is not unusual that irrigated agriculture is forced to divert less water in order to make it available for other uses, e.g. human consumption and others. As part of implementation of better policies for water control and management, irrigation companies and water user associations have been implemented water conveyance and distribution monitoring systems along with soil moisture sensors networks in the last decades. These systems allow them to manage and distribute water among the users based on their requirements and water availability while collecting information about actual soil moisture conditions in representative crop fields. In spite of this, requested water deliveries by farmers/water users is based typically on total water share, traditions and past experience on irrigation, which in most cases do not correspond to the actual crop evapotranspiration, already affected by climate change. Therefore it is necessary to provide actual information about the crop water requirements to water users/managers, so they can better quantify the required vs. available water for the irrigation events along the irrigation season. To estimate the actual evapotranspiration in a spatial extent the Sensitivity Analysis of the Surface Energy Balance Algorithm for Land (SEBAL) algorithm has demonstrated its effectiveness using satellite or airborne data. Nonetheless the estimation is restricted to the day when the geospatial information was obtained. Without information of precise future daily water crop demand there is a continuous challenge for the implementation of better water distribution and management policies in the irrigation system. The purpose of this study is to investigate the plausibility of using

Evapotranspiration and crop coefficient for potato in organic farming Evapotranspiração e coeficiente de cultivo da batata em sistema agroecológico de produção

Directory of Open Access Journals (Sweden)

Daniel F. de Carvalho

2013-02-01

Full Text Available The aim of this study was to quantify the water consumption and the crop coefficients (Kc for the potato (Solanum tuberosum L., in Seropédica, Rio de Janeiro (RJ, Brazil, under organic management, and to simulate the crop evapotranspiration (ETc using the Kc obtained in the field and the ones recommended by the Food and Agriculture Organization (FAO. The water consumption was obtained through soil water balance, using TDR probes installed at 0.15m and 0.30m deep. At the different stages of development, the Kc was determined by the ratio of ETc and reference evapotranspiration, obtained by Penman-Monteith FAO 56. The crop coefficients obtained were 0.35, 0.45, 1.29 and 0.63. The accumulated ETc obtained in the field was 109.6 mm, while the ETc accumulated from FAO's Kc were 142.2 and 138mm, respectively, considering the classical values and the values adjusted to the local climatic conditions. The simulation of water consumption based on meteorological data of historical series from 1961 to 2007 provided higher value of ETc when compared with the one obtained in the field. From the meteorological data of historical series, it was observed that the use of Kc recommended by FAO may overestimate the amount of irrigation water by 9%, over the same growing season.O trabalho foi desenvolvido visando a quantificar, sob manejo agroecológico, o consumo hídrico e os kcs para a cultura da batata (Solanum tuberosum L., em Seropédica (RJ, e a simular a evapotranspiração da cultura (ETc, utilizando os kcs obtidos e os kcs preconizados pela FAO. O consumo hídrico foi obtido por meio do balanço hídrico do solo, utilizando sondas de TDR instaladas a 0,15 e 0,30 m de profundidade. Nas diferentes fases de desenvolvimento, o kc foi determinado pela razão entre a ETc e a evapotranspiração de referência, obtida por Penman-Monteith FAO 56. Os kcs obtidos foram 0,35; 0,45; 1,29 e 0,63. A ETc acumulada obtida em campo foi de 109,6 mm, enquanto as ETcs

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...

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).

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

KAUST Repository

Mueller, B.; Hirschi, M.; Jimenez, C.; Ciais, P.; Dirmeyer, P.A.; Dolman, A.J.; Fisher, J.B.; Jung, M.; Ludwig, F.; Maignan, F.; Miralles, D.G.; McCabe, Matthew; Reichstein, M.; Sheffield, J.; Wang, K.; Wood, E.F.; Zhang, Y.; Seneviratne, S.I.

2013-01-01

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).

Validation of MODIS Data for localized spatio-temporal evapotranspiration mapping

International Nuclear Information System (INIS)

Nadzri, M I; Hashim, M

2014-01-01

Advancement in satellite remote sensing sensors allows evapo-transpiration (ET) from land surfaces to be derived from selected reflectance and emmitance in visible and thermal infrared wavelengths, such as using Moderate Solution Imaging Spectrometer (MODIS). In this paper, we report the validation of recent MODIS-generated higher-order global terrestrial ET product 16A2. The main focus of this paper is to devise the follow-up calibration for the localised region covering the entire Malaysia peninsular. The validation is carried out locally by dividing the study area into 3 distinct climatological regions based on the influence to monsoons, and using multi-temporal MODIS data acquired in 2000-2009. The results, evidently show the local effects still inherit in the MODIS 16A2 products; with varying R2 within the 3 local climatological regions established (Northwest = 0.49 South = 0.47, and Southwest = 0.52; all with P < 0.001). The accuracy of each region validated is within + RMSE 43mm for monthly ET. With P value in acceptable range, the correction is useable for further usage

Partitioning evapotranspiration using long-term carbon dioxide and water vapor fluxes

Science.gov (United States)

Scott, Russell L.; Biederman, Joel A.

2017-07-01

The separate components of evapotranspiration (ET) elucidate the pathways and time scales over which water is returned to the atmosphere, but ecosystem-scale measurements of transpiration (T) and evaporation (E) remain elusive. We propose a novel determination of E and T using multiyear eddy covariance estimates of ET and gross ecosystem photosynthesis (GEP). The method is applicable at water-limited sites over time periods during which a linear regression between GEP (abscissa) and ET (ordinate) yields a positive ET axis intercept, an estimate of E. At four summer-rainfall semiarid sites, T/ET increases to a peak coincident with maximum GEP and remains elevated as the growing season progresses, consistent with previous, direct measurements. The seasonal course of T/ET is related to increasing leaf area index and declining frequency of rainy days—an index of the wet surface conditions that promote E—suggesting both surface and climatic controls on ET partitioning.

Scaling Potential Evapotranspiration with Greenhouse Warming (Invited)

Science.gov (United States)

Scheff, J.; Frierson, D. M.

2013-12-01

Potential evapotranspiration (PET) is a supply-independent measure of the evaporative demand of a terrestrial climate, of basic importance in climatology, hydrology, and agriculture. Future increases in PET from greenhouse warming are often cited as key drivers of global trends toward drought and aridity. The present work computes recent and business-as-usual-future Penman-Monteith (i.e. physically-based) PET fields at 3-hourly resolution in 14 modern global climate models. The %-change in local annual-mean PET over the upcoming century is almost always positive, modally low double-digit in magnitude, usually increasing with latitude, yet quite divergent between models. These patterns are understood as follows. In every model, the global field of PET %-change is found to be dominated by the direct, positive effects of constant-relative-humidity warming (via increasing vapor pressure deficit and increasing Clausius-Clapeyron slope.) This direct-warming term very accurately scales as the PET-weighted (warm-season daytime) local warming, times 5-6% per degree (related to the Clausius-Clapeyron equation), times an analytic factor ranging from about 0.25 in warm climates to 0.75 in cold climates, plus a small correction. With warming of several degrees, this product is of low double-digit magnitude, and the strong temperature dependence gives the latitude dependence. Similarly, the inter-model spread in the amount of warming gives most of the spread in this term. Additional spread in the total change comes from strong disagreement on radiation, relative-humidity, and windspeed changes, which make smaller yet substantial contributions to the full PET %-change fields.

Improving satellite-based post-fire evapotranspiration estimates in semi-arid regions

Science.gov (United States)

Poon, P.; Kinoshita, A. M.

2017-12-01

Climate change and anthropogenic factors contribute to the increased frequency, duration, and size of wildfires, which can alter ecosystem and hydrological processes. The loss of vegetation canopy and ground cover reduces interception and alters evapotranspiration (ET) dynamics in riparian areas, which can impact rainfall-runoff partitioning. Previous research evaluated the spatial and temporal trends of ET based on burn severity and observed an annual decrease of 120 mm on average for three years after fire. Building upon these results, this research focuses on the Coyote Fire in San Diego, California (USA), which burned a total of 76 km2 in 2003 to calibrate and improve satellite-based ET estimates in semi-arid regions affected by wildfire. The current work utilizes satellite-based products and techniques such as the Google Earth Engine Application programming interface (API). Various ET models (ie. Operational Simplified Surface Energy Balance Model (SSEBop)) are compared to the latent heat flux from two AmeriFlux eddy covariance towers, Sky Oaks Young (US-SO3), and Old Stand (US-SO2), from 2000 - 2015. The Old Stand tower has a low burn severity and the Young Stand tower has a moderate to high burn severity. Both towers are used to validate spatial ET estimates. Furthermore, variables and indices, such as Enhanced Vegetation Index (EVI), Normalized Difference Moisture Index (NDMI), and the Normalized Burn Ratio (NBR) are utilized to evaluate satellite-based ET through a multivariate statistical analysis at both sites. This point-scale study will able to improve ET estimates in spatially diverse regions. Results from this research will contribute to the development of a post-wildfire ET model for semi-arid regions. Accurate estimates of post-fire ET will provide a better representation of vegetation and hydrologic recovery, which can be used to improve hydrologic models and predictions.

The surface renewal method for better spatial resolution of evapotranspiration measurements

Science.gov (United States)

Suvocarev, K.; Fischer, M.; Massey, J. H.; Reba, M. L.; Runkle, B.

2017-12-01

Evaluating feasible irrigation strategies when water is scarce requires measurements or estimations of evapotranspiration (ET). Direct observations of ET from agricultural fields are preferred, and micrometeorological methods such as eddy covariance (EC) provide a high quality, continuous time series of ET. However, when replicates of the measurements are needed to compare irrigation strategies, the cost of such experiments is often prohibitive and limits experimental scope. An alternative micrometeorological approach to ET, the surface renewal (SR) method, may be reduced to a thermocouple and a propeller anemometer (Castellvi and Snyder, 2009). In this case, net radiation, soil and sensible heat flux (H) are measured and latent heat flux (an energy equivalent for ET) is estimated as the residual of the surface energy-balance equation. In our experiment, thermocouples (Type E Fine-Wire Thermocouple, FW3) were deployed next to the EC system and combined with mean horizontal wind speed measurements to obtain H using SR method for three weeks. After compensating the temperature signal for non-ideal frequency response in the wavelet half-plane and correcting the sonic anemometer for the flow distortion (Horst et al., 2015), the SR H fluxes compared well to those measured by EC (r2 = 0.9, slope = 0.92). This result encouraged us to install thermocouples over 16 rice fields under different irrigation treatments (continuous cascade flood, continuous multiple inlet rice irrigation, alternate wetting and drying, and furrow irrigation). The EC measurements with net radiometer and soil heat flux plates are deployed at three of these fields to provide a direct comparison. The measurement campaign will finish soon and the data will be processed to evaluate the SR approach for ET estimation. The results will be used to show better spatial resolution of ET measurements to support irrigation decisions in agricultural crops.

Assessing Crop Coefficients for Natural Vegetated Areas Using Satellite Data and Eddy Covariance Stations

Directory of Open Access Journals (Sweden)

Chiara Corbari

2017-11-01

Full Text Available The Food and Agricultural Organization (FAO method for potential evapotranspiration assessment is based on the crop coefficient, which allows one to relate the reference evapotranspiration of well irrigated grass to the potential evapotranspiration of specific crops. The method was originally developed for cultivated species based on lysimeter measurements of potential evapotranspiration. Not many applications to natural vegetated areas exist due to the lack of available data for these species. In this paper we investigate the potential of using evapotranspiration measurements acquired by micrometeorological stations for the definition of crop coefficient functions of natural vegetated areas and extrapolation to ungauged sites through remotely sensed data. Pastures, deciduous and evergreen forests have been considered and lower crop coefficient values are found with respect to FAO data.

Assessing Crop Coefficients for Natural Vegetated Areas Using Satellite Data and Eddy Covariance Stations.

Science.gov (United States)

Corbari, Chiara; Ravazzani, Giovanni; Galvagno, Marta; Cremonese, Edoardo; Mancini, Marco

2017-11-18

The Food and Agricultural Organization (FAO) method for potential evapotranspiration assessment is based on the crop coefficient, which allows one to relate the reference evapotranspiration of well irrigated grass to the potential evapotranspiration of specific crops. The method was originally developed for cultivated species based on lysimeter measurements of potential evapotranspiration. Not many applications to natural vegetated areas exist due to the lack of available data for these species. In this paper we investigate the potential of using evapotranspiration measurements acquired by micrometeorological stations for the definition of crop coefficient functions of natural vegetated areas and extrapolation to ungauged sites through remotely sensed data. Pastures, deciduous and evergreen forests have been considered and lower crop coefficient values are found with respect to FAO data.

A structural SVM approach for reference parsing.

Science.gov (United States)

Zhang, Xiaoli; Zou, Jie; Le, Daniel X; Thoma, George R

2011-06-09

Automated extraction of bibliographic data, such as article titles, author names, abstracts, and references is essential to the affordable creation of large citation databases. References, typically appearing at the end of journal articles, can also provide valuable information for extracting other bibliographic data. Therefore, parsing individual reference to extract author, title, journal, year, etc. is sometimes a necessary preprocessing step in building citation-indexing systems. The regular structure in references enables us to consider reference parsing a sequence learning problem and to study structural Support Vector Machine (structural SVM), a newly developed structured learning algorithm on parsing references. In this study, we implemented structural SVM and used two types of contextual features to compare structural SVM with conventional SVM. Both methods achieve above 98% token classification accuracy and above 95% overall chunk-level accuracy for reference parsing. We also compared SVM and structural SVM to Conditional Random Field (CRF). The experimental results show that structural SVM and CRF achieve similar accuracies at token- and chunk-levels. When only basic observation features are used for each token, structural SVM achieves higher performance compared to SVM since it utilizes the contextual label features. However, when the contextual observation features from neighboring tokens are combined, SVM performance improves greatly, and is close to that of structural SVM after adding the second order contextual observation features. The comparison of these two methods with CRF using the same set of binary features show that both structural SVM and CRF perform better than SVM, indicating their stronger sequence learning ability in reference parsing.

Hysteresis responses of evapotranspiration to meteorological factors at a diel timescale: patterns and causes.

Directory of Open Access Journals (Sweden)

Han Zheng

Full Text Available Evapotranspiration (ET is an important component of the water cycle in terrestrial ecosystems. Understanding the ways in which ET changes with meteorological factors is central to a better understanding of ecological and hydrological processes. In this study, we used eddy covariance measurements of ET from a typical alpine shrubland meadow ecosystem in China to investigate the hysteresis response of ET to environmental variables including air temperature (Ta, vapor pressure deficit (VPD and net radiation (Rn at a diel timescale. Meanwhile, the simulated ET by Priestly-Taylor equation was used to interpret the measured ET under well-watered conditions. Pronounced hysteresis was observed in both Ta and VPD response curves of ET. At a similar Ta and VPD, ET was always significantly depressed in the afternoon compared with the morning. But the hysteresis response of ET to Rn was not evident. Similar hysteresis patterns were also observed in the Ta/VPD response curves of simulated ET. The magnitudes of the measured and simulated hysteresis loops showed similar seasonal variation, with relatively smaller values occurring from May to September, which agreed well with the lifetime of plants and the period of rainy season at this site. About 62% and 23% of changes in the strength of measured ET-Ta and ET-VPD loops could be explained by the changes in the strength of simulated loops, respectively. Thus, the time lag between Rn and Ta/VPD is the most important factor generating and modulating the ET-Ta/VPD hysteresis, but plants and water status also contribute to the hysteresis response of ET. Our research confirmed the different hysteresis in the responses of ET to meteorological factors and proved the vital role of Rn in driving the diel course of ET.

Evapotranspiration and water balance in a hot pepper (Capsicum frutescens L.) field during a dry season in the tropics

Science.gov (United States)

Laban, S.; Oue, H.; Rampisela, D. A.

2018-05-01

Evapotranspiration and water balance in a hot pepper (Capsicum frutescens L.) field during the 2nd dry season were analyzed in this study. Actual evapotranspiration (ET) was estimated by Bowen Ratio Energy Budget (BREB) method, potential evaporation (EP) was calculated by Penman method, and irrigation volume of water was measured manually. Meteorological instruments were installed in the experimental field during hot pepper cultivation. Leaf area index increased during the growing stages where the highest LAI of 1.65 in the generative stage. The daily average of ET was 1.94 and EP was 6.71 mm resulting in low Kc. The Kc values were significantly different between stage to stage under T-test analysis (α = 0.05). Moreover, Kc in every stage could be related to soil water content (SWC) in logarithmic function. Totally, ET during hot pepper cultivation was 179.19 mm, while rainfall was 180.0 mm and irrigation water was 27.42 mm. However, there was a water shortages during vegetative and generative stages. This study suggested that consumptive water of hot pepper was complimented by soil and groundwater under the condition of water shortages in the vegetative and generative stages during the 2nd dry season.

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.

Estimation of potential and actual evapotranspiration of boreal forest ecosystems in the European part of Russia during the Holocene

International Nuclear Information System (INIS)

Olchev, A; Novenko, E

2011-01-01

A simple regression model for calculating annual actual evapotranspiration (ET) and potential evapotranspiration (PET), as well as annual transpiration (TR) of mature boreal forests grown in the European part of Russia in the Holocene using paleoclimatic and paleobotanical data (air temperature, precipitation, forest species compositions) is presented. The model is based on nonlinear approximations of annual values of ET, TR and PET obtained by the Levenberg–Marquardt method using the results of numerical simulations of ET, TR and PET provided by a process-based Mixfor-SVAT model for forests with different species compositions under various thermal and moistening conditions. The results of ET, TR and PET reconstructions for the Holocene show large variability and high correlation with the air temperature pattern. Minimal values of ET and PET are obtained for the Younger Dryas cold phase (11.0–10.0 14 C kyr BP) when ET varied between 320 and 370 mm yr −1 and PET varied between 410 and 480 mm yr −1 . During the Late Atlantic periods of the Holocene (4.5–5.1 14 C kyr BP), ET and PET reached maximal values (ET: 430–450 mm yr −1 and PET: 550–570 mm yr −1 ).

On the downscaling of actual evapotranspiration maps based on combination of MODIS and landsat-based actual evapotranspiration estimates

Science.gov (United States)

Singh, Ramesh K.; Senay, Gabriel B.; Velpuri, Naga Manohar; Bohms, Stefanie; Verdin, James P.

2014-01-01

 Downscaling is one of the important ways of utilizing the combined benefits of the high temporal resolution of Moderate Resolution Imaging Spectroradiometer (MODIS) images and fine spatial resolution of Landsat images. We have evaluated the output regression with intercept method and developed the Linear with Zero Intercept (LinZI) method for downscaling MODIS-based monthly actual evapotranspiration (AET) maps to the Landsat-scale monthly AET maps for the Colorado River Basin for 2010. We used the 8-day MODIS land surface temperature product (MOD11A2) and 328 cloud-free Landsat images for computing AET maps and downscaling. The regression with intercept method does have limitations in downscaling if the slope and intercept are computed over a large area. A good agreement was obtained between downscaled monthly AET using the LinZI method and the eddy covariance measurements from seven flux sites within the Colorado River Basin. The mean bias ranged from −16 mm (underestimation) to 22 mm (overestimation) per month, and the coefficient of determination varied from 0.52 to 0.88. Some discrepancies between measured and downscaled monthly AET at two flux sites were found to be due to the prevailing flux footprint. A reasonable comparison was also obtained between downscaled monthly AET using LinZI method and the gridded FLUXNET dataset. The downscaled monthly AET nicely captured the temporal variation in sampled land cover classes. The proposed LinZI method can be used at finer temporal resolution (such as 8 days) with further evaluation. The proposed downscaling method will be very useful in advancing the application of remotely sensed images in water resources planning and management.

Observations of increased tropical rainfall preceded by air passage over forests.

Science.gov (United States)

Spracklen, D V; Arnold, S R; Taylor, C M

2012-09-13

Vegetation affects precipitation patterns by mediating moisture, energy and trace-gas fluxes between the surface and atmosphere. When forests are replaced by pasture or crops, evapotranspiration of moisture from soil and vegetation is often diminished, leading to reduced atmospheric humidity and potentially suppressing precipitation. Climate models predict that large-scale tropical deforestation causes reduced regional precipitation, although the magnitude of the effect is model and resolution dependent. In contrast, observational studies have linked deforestation to increased precipitation locally but have been unable to explore the impact of large-scale deforestation. Here we use satellite remote-sensing data of tropical precipitation and vegetation, combined with simulated atmospheric transport patterns, to assess the pan-tropical effect of forests on tropical rainfall. We find that for more than 60 per cent of the tropical land surface (latitudes 30 degrees south to 30 degrees north), air that has passed over extensive vegetation in the preceding few days produces at least twice as much rain as air that has passed over little vegetation. We demonstrate that this empirical correlation is consistent with evapotranspiration maintaining atmospheric moisture in air that passes over extensive vegetation. We combine these empirical relationships with current trends of Amazonian deforestation to estimate reductions of 12 and 21 per cent in wet-season and dry-season precipitation respectively across the Amazon basin by 2050, due to less-efficient moisture recycling. Our observation-based results complement similar estimates from climate models, in which the physical mechanisms and feedbacks at work could be explored in more detail.

Regional evapotranspiration estimation based on a two-layer remote-sensing scheme in Shahe River basin

International Nuclear Information System (INIS)

Yin, Jian; Wang, Huixiao

2014-01-01

Land surface evapotranspiration (ET) derived from remote sensing data has significant meaning for plant growth monitoring, crop yield assessment, disaster monitoring and understanding energy and water cycle in river basin area and surrounding regions. In the study, we developed a land surface ET remote sensing retrieval system to estimate the daily ET in Shahe river basin using the TM/ETM+ images. The system is based on the two-layer ET model and includes three parts: inversion of the evaporation ration using two-layer model, calculation of total daily net radiation, and estimation of daily ET based on evaporation fraction method. The results show that the average daily ET is about 2.28mm of the typical days in spring, and 2.97mm in summer, 1.59mm in autumn, and 0.5mm in winter. The ET in upstream areas covered by forest is higher than that in the downstream covered by settlement and farmland. In summer the difference of ET between the upper reaches and lower reaches is smaller compared to the other three seasons. The measurements by large aperture scintillometer and eddy correlation instrument were used for validation. By comparing the observed data with the estimated data, we found the estimation system had a high precision with the relative error between 0 and 16% (mean error of 11.1%), and the variance 0.77mm

Turfgrass water consumption on green and fairway as a function of turfgrass species and day number after irrigation to field capacity

DEFF Research Database (Denmark)

Aamlid, T S; Kvalbein, A; Kusliene, Gedrime

Worldwide, lack of irrigation water is a serious threat to the turfgrass sector. The objective of this research was to determine crop coefficients (Kc), i.e. the ratio between actual and reference evapotranspiration, for cool season turfgrasses on greens and fairways.......Worldwide, lack of irrigation water is a serious threat to the turfgrass sector. The objective of this research was to determine crop coefficients (Kc), i.e. the ratio between actual and reference evapotranspiration, for cool season turfgrasses on greens and fairways....

Evapotranspiration of rubber (Hevea brasiliensis) cultivated at two plantation sites in Southeast Asia

Science.gov (United States)

Giambelluca, Thomas W.; Mudd, Ryan G.; Liu, Wen; Ziegler, Alan D.; Kobayashi, Nakako; Kumagai, Tomo'omi; Miyazawa, Yoshiyuki; Lim, Tiva Khan; Huang, Maoyi; Fox, Jefferson; Yin, Song; Mak, Sophea Veasna; Kasemsap, Poonpipope

2016-02-01

To investigate the effects of expanding rubber (Hevea brasiliensis) cultivation on water cycling in Mainland Southeast Asia (MSEA), evapotranspiration (ET) was measured within rubber plantations at Bueng Kan, Thailand, and Kampong Cham, Cambodia. After energy closure adjustment, mean annual rubber ET was 1211 and 1459 mm yr-1 at the Thailand and Cambodia sites, respectively, higher than that of other tree-dominated land covers in the region, including tropical seasonal forest (812-1140 mm yr-1), and savanna (538-1060 mm yr-1). The mean proportion of net radiation used for ET by rubber (0.725) is similar to that of tropical rainforest (0.729) and much higher than that of tropical seasonal forest (0.595) and savanna (0.548). Plant area index (varies with leaf area changes), explains 88.2% and 73.1% of the variance in the ratio of latent energy flux (energy equivalent of ET) to potential latent energy flux (LE/LEpot) for midday rain-free periods at the Thailand and Cambodia sites, respectively. High annual rubber ET results from high late dry season water use, associated with rapid refoliation by this brevideciduous species, facilitated by tapping of deep soil water, and by very high wet season ET, a characteristic of deciduous trees. Spatially, mean annual rubber ET increases strongly with increasing net radiation (Rn) across the three available rubber plantation observation sites, unlike nonrubber tropical ecosystems, which reduce canopy conductance at high Rn sites. High water use by rubber raises concerns about potential effects of continued expansion of tree plantations on water and food security in MSEA.

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...

Analysis of Dynamic Spatiotemporal Changes in Actual Evapotranspiration and Its Associated Factors in the Pearl River Basin Based on MOD16

Directory of Open Access Journals (Sweden)

Tao Zhang

2017-11-01

Full Text Available Evapotranspiration is an important part of the hydrological cycle, surface energy balance and global climate system. Due to spatial heterogeneity, the trends in actual evapotranspiration (ET and its associated factors vary in different regions. Because direct measurements of ET are limited over large areas, remote sensing provides an efficient method of ET spatial analysis, and standard data products are available at the global scale. This study uses the monthly MOD16 ET dataset and daily meteorological data to analyze the dynamic spatiotemporal changes in ET and its associated factors in the Pearl River Basin (PRB from 2000 to 2014. The results of the study are as follows. (1 Over time and space, annual ET exhibited a slight increasing trend from 2000 to 2014, with an average value of approximately 946.56 mm/a. ET considerably varied at the monthly and seasonal scales, and in July displayed the highest monthly ET of approximately 119.57 mm, accounting for 36.37% of the annual ET. (2 ET displayed obvious spatial heterogeneity. Specifically, the west was a low-ET region, and moderate and high ET values were interspersed in the central and eastern PRB. Moreover, the rate of change of ET ranged from −13.99 mm/a to 12.81 mm/a in space, and 46.25% of the basin exhibited an increasing trend. (3 Dynamic changes in ET were mainly associated with temperature and relative humidity (RH. Additionally, energy-related elements and wind speed were positively correlated with ET, and temperature was the most influential factor of ET in some months (February–March and September–November. RH was the most important factor in other months but negatively correlated with ET in June and July. Affected by the actual environmental condition, qualitative changes were observed in the correlation between RH and ET in different months. The positive and negative spatial correlations between ET and its associated factors changed in different regions and in different

In situ measurements of tritium evapotranspiration (³H-ET) flux over grass and soil using the gradient and eddy covariance experimental methods and the FAO-56 model.

Science.gov (United States)

Connan, O; Maro, D; Hébert, D; Solier, L; Caldeira Ideas, P; Laguionie, P; St-Amant, N

2015-10-01

The behaviour of tritium in the environment is linked to the water cycle. We compare three methods of calculating the tritium evapotranspiration flux from grassland cover. The gradient and eddy covariance methods, together with a method based on the theoretical Penmann-Monteith model were tested in a study carried out in 2013 in an environment characterised by high levels of tritium activity. The results show that each of the three methods gave similar results. The various constraints applying to each method are discussed. The results show a tritium evapotranspiration flux of around 15 mBq m(-2) s(-1) in this environment. These results will be used to improve the entry parameters for the general models of tritium transfers in the environment. Copyright © 2015 Elsevier Ltd. All rights reserved.

Comment on 'Shang S. 2012. Calculating actual crop evapotranspiration under soil water stress conditions with appropriate numerical methods and time step. Hydrological Processes 26: 3338-3343. DOI: 10.1002/hyp.8405'

Science.gov (United States)

Yatheendradas, Soni; Narapusetty, Balachandrudu; Peters-Lidard, Christa; Funk, Christopher; Verdin, James

2014-01-01

A previous study analyzed errors in the numerical calculation of actual crop evapotranspiration (ET(sub a)) under soil water stress. Assuming no irrigation or precipitation, it constructed equations for ET(sub a) over limited soil-water ranges in a root zone drying out due to evapotranspiration. It then used a single crop-soil composite to provide recommendations about the appropriate usage of numerical methods under different values of the time step and the maximum crop evapotranspiration (ET(sub c)). This comment reformulates those ET(sub a) equations for applicability over the full range of soil water values, revealing a dependence of the relative error in numerical ET(sub a) on the initial soil water that was not seen in the previous study. It is shown that the recommendations based on a single crop-soil composite can be invalid for other crop-soil composites. Finally, a consideration of the numerical error in the time-cumulative value of ET(sub a) is discussed besides the existing consideration of that error over individual time steps as done in the previous study. This cumulative ET(sub a) is more relevant to the final crop yield.