An operational model for estimating Regional Evapotranspiration through Surface Energy Partitioning (RESEP)

Considerable work has been done on estimating surface energy fluxes and thus evapotranspiration at regional scale using remote sensing technique. Approaches currently used for estimating regional evapotranspiration are either based on empirical models or utilize a surface energy balance approach. The operationalization of these models has not been successful, because of the complexities involved in the procedure, strong dependence of heat transfer coefficient on a number of local meteorological parameters and accuracy at regional scale. This paper presents a remote sensing based simplified operational procedure to estimate sensible heat flux incorporating the local meteorological conditions. The model utilizes the surface reflectance in visible, infrared and thermal bands to generate surface albedo, surface temperature and leaf area index and thus surface energy fluxes to determine regional evapotranspiration. The developed model (Regional Evapotranspiration through Surface Energy Partitioning-RESEP) is applied to a part of the Western Yamuna Canal command in the State of Haryana, India to illustrate the methodology. The proposed procedure is computationally simple with reasonable accuracy of results. For a well-watered crop, average evapotranspiration by the proposed model is estimated as 2.1 mm day(-1), whereas using Penman-Monteith equation it is calculated as 1.9 mm day(-1). The error involved in estimating evapotranspiration by the proposed model is calculated to be about 10%, which is acceptable for most cases.