Diverse responses of the changes in evapotranspiration and water yield to vegetation and climate change in the Yanhe River watershed

Quantifying the contribution and modes of action of climate variation and vegetation greening to evapotranspiration (ET) and water yield (WY) in the growing season of the Yanhe River Watershed (YHRW) is of great significance for scientifically managing the ecosystem in water-scarce areas. This study simulated the ET of YHRW based on the Eagleson model and analyzed the contribution, direct and indirect effects of climate variables (including precipitation (Pre), temperature (Tem), radiation (RN), relative humidity (RH), wind speed (Wind)) and vegetation on the ET and WY changes during three time periods of YHRW. The results suggested the ET in the YHRW mainly showed a downward trend from 1982 to 1999, and it turned into an increasing trend after 1999. From 1982 to 2018, ET showed an overall upward trend (2.02 mm·year⁻¹), while WY in three different study periods mainly showed a decreasing trend. Spatially, RN, Tem, and Wind were the drivers controlling ET and WY changes from 1982 to 1999. After 1999, LAI was the main controller in ET changes, while climate factors were the main contributors to WY changes. During the 1982–2018 research period, vegetation had the greatest impact on regional ET changes, while Pre dominated the WY changes. The effects of climate variation and vegetation greening on ET and WY are complex and non-independent. Tem and RH are key mediations of ET variation, while Tem and RH are key mediating factors in WY variation. We emphasize the spatial heterogeneity in water budget changes during the vegetation growth period of YHRW at different time periods, especially after large-scale vegetation greening. This finding should be considered in the planning of sustainable development in water-scarce areas in the future to make the local eco-hydrological effect the best.