Evaluating the accuracy of satellite-derived evapotranspiration estimates acquired during conditions of water stress |
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| Authors: | S Gokool Es Riddell C Jarmain Kt Chetty G Feig H Thenga |
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| Affiliation: | 1. School of Agricultural, Earth and Environmental Sciences, Centre for Water Resources Research (CWRR), University of KwaZulu-Natal, Pietermaritzburg, South Africashaedengokool@gmail.com;3. School of Agricultural, Earth and Environmental Sciences, Centre for Water Resources Research (CWRR), University of KwaZulu-Natal, Pietermaritzburg, South Africa;4. Conservation Management, South African National Parks, Skukuza, South Africa;5. Independent Researcher, University of Stellenbosch, Stellenbosch, South Africa;6. Expanded Freshwater and Terrestrial Environmental Observation Network (EFTEON), South Africa;7. Natural Resources and the Environment, Council for Scientific and Industrial Research (CSIR), Pretoria, South Africa |
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| Abstract: | ABSTRACTSurface energy balance models such as the surface energy balance system (SEBS) assume that the influence of soil moisture and biophysical parameters on evapotranspiration (ET), are implicitly encompassed in model input variables such as the land surface temperature. This simplification may generally be suitable for environments in which the available energy constrains ET but may prove to be inadequate during suboptimal environmental conditions. To address this limitation, the SEBSESF approach was proposed to better represent the influence of environmental stress on surface energy fluxes, using an empirically derived calibration factor to adjust the evaporative fraction previously determined in SEBS. SEBSESF was evaluated by comparing the modelled ET estimates against Eddy Covariance ET measurements (ECET) at two sites, with contrasting environmental conditions. Comparisons between ECET and modelled ET indicated that the implementation of SEBSESF resulted in an improved correlation between ECET and modelled ET estimates, as well as an increase in the percentage of modelled ET estimates within an acceptable accuracy range (± 15 to 30%). Overall, the results of the study demonstrate how potential improvements in the mapping of ET within arid and semi-arid environments can be achieved by accounting for environmental stress. This in turn provides an opportunity to better understand and quantify energy and water fluxes, using satellite-based ET estimation approaches. |
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