Estimation of Regional Evapotranspiration Based on the Decouple Model and Remote Sensing Information --a Case Study in Beijing City and Nearby Region

Evapotranspiration (ET) is an important component of surface energy balance and a key process of hydrological cycle. Continuous and accurate estimation of regional ET is meaningful for water management, agricultural production, and climate change adaptation. Remote sensing (RS) technique is of important meaning for estimating ET on regional scale. In this study, a new method is developed to integrate the RS information and meteorological data based on the decouple model which is deduced from Penman-Monteith (PM) model. Firstly, a parameterization method for decoupling factor (omega) which is key parameter in the decouple model and could reflect the coupling relationship between the land surface and atmosphere systems is introduced. Subsequently, the decouple model is applied to inverse regional ET in Beijing City and nearby region, from 1st, May, 2013 to 31th, October, 2020. Thirdly, the inversed daily ET values are evaluated based on the measured data at Huailai station and in Badaling Forest Farm. The results show that the changing trend of estimated ET and measured ET are basically the similar. The bias value is -0.12 mm d-1, the RSME value is 0.66 mm d-1, and the correlation coefficient is 0.52. Finally, the spatiotemporal trend of water consumption in study area is analysed based on the ET estimation results. The month with the largest water consumption in 2013 is July with the quantity of 0.92 billion m3, accounting for about 22% of the regional total water consumption in growing season. The regions with high ET values agree well with the regions of high soil moisture and high air humidity as well as high biomass. These results suggest that the decouple model is with great potential to generate regional daily ET products and to support irrigation management.