Widespread Increasing Control of Water Supply on Evapotranspiration

Evapotranspiration (ET), a crucial component of water consumption in the hydrological process, is directly controlled by soil moisture (SM) and vapor pressure deficit (VPD) from the perspectives of water supply and demand. However, SM and VPD are strongly coupled through multiple physical processes, confounding their effects on ET. Here, we decouple the interaction between SM and VPD and then analyze the spatiotemporal pattern of their individual effects on ET based on multiple observation-based data sets. The results show that ET is limited by SM rather than VPD in approximately 63% of global land areas (60°S–60°N), defined as water supply-limited regions. From 1982 to 2014, the effect of SM on ET enhances significantly in 43% of the water supply-limited regions. The trends can be attributed to changes in SM and VPD themselves as well as to changes in vegetation conditions. Using the findings from the observation-based data sets as the benchmark, we show that Earth System Models (ESMs) can overall reproduce the spatial pattern of SM and VPD effects on ET but fail to capture their temporal trends. Our results highlight that the water supply and demand control on ET varies with changing environments, which should be explicitly considered when analyzing the terrestrial water cycle and land-atmosphere interaction.