Estimation of evapotranspiration based on remote sensing in Heihe River Basin

Regional evapotranspiration (ET) is an important component in water cycle and energy balance. The research on regional evapotranspiration is very important to further our understanding of the global climate change, land surface atmosphere interaction, water cycle and ecological study. However, traditional site observation is only representative of the local site scale, which can not reflect the real regional conditions. Remote sensing provides a promising way to retrieve regional evapotranspiration. Heihe River Basin is the second largest inland river basin in northwest of China, water shortage has become a crucial problem to regional ecological, environmental, economic and other related areas. The research on regional evapotranspiration is in an urgent need in this area. SEBS model, a physically based model, was selected to retrieve regional evapotranspiration. Combined with MODIS products and site observations, evapotranspiration in typical days were estimated with SEBS model. The instantaneous results were validated with flux observation data from Yingke station. In most days SEBS model have good estimation of surface fluxes, the difference between observations and estimation is limited in 50W/m. For longer time ET estimation, reference evapotranspiration fraction was selected to scale instantaneous measurements to daily and motherly evapotranspiration. Adjusted pan observations were used to validate the scaled daily results, the results indicate reference evapotranspiration fraction based method have good quality to scale daily ET. Moreover, clear spatial patterns of ET were found in Heihe River Basin. This spatial pattern is closely correlated with land use/land cover and water uses in Heihe River Basin.