Evaluation of the mechanisms and performances of major satellite-based evapotranspiration models in Northwest China

Evapotranspiration (ET) is an important component of the water cycle and surface energy balance system. Accurate measurements and estimations of ET can be used to manage and allocate regional water resources and in agricultural water management under climate change. Satellite-based ET models extrapolate site ET values to regional scales, but there are uncertainties in their simulations. In this study, the use of satellite-based ET models including the Shuttleworth-Wallace-Hu (SWH), Surface Energy Balance Algorithm for Land (SEBAL), and the moderate-resolution (MOD) imaging spectroradiometer ET product (MOD16) was validated, and their applicability in Northwest China were compared. In addition, the sensitivity of these models to driving data and the correlation between the models were analyzed. Results showed that the SWH model provided superior applicability in Northwest China, followed by SEBAL and MOD16. The correlation coefficient, mean relative error, root mean square error, and index of agreement of the ET simulated by SWH compared with the eddy flux of the Haibei station were 0.90, 0.39 mm.d (-1), 0.55 mm.d(-1), and 0.87, respectively. Furthermore, the sensitivity to driving data in SWH was the highest among all models. The correlation between the models was high during the vegetation growth period but low in winter. The model simulation effects were also compared with respect to their mechanisms, and it was evident that further improvements and validation could be achieved by investigating the model structures and examining the ET estimations and critical parameters of each model.