Global Response of Evapotranspiration Ratio to Climate Conditions and Watershed Characteristics in a Changing Environment.

Understanding the complex relationship between evapotranspiration and climate conditions and land surface characteristics is important within the context of global warming and increasing anthropogenic stressors. Based on the Budyko theory, we derived general frameworks for describing how the evapotranspiration ratio (actual evapotranspiration/precipitation, AET/P) responds to changes in the aridity index (potential evapotranspiration/precipitation, PET/P) and watershed characteristics (m). The frameworks show that the sensitivity of AET/P to PET/P decreases with increasing aridity but such decreasing pattern also depends on different watershed characteristics. The sensitivity coefficient tends to be greater in the energy‐limited regimes (above 0.3) than in the water‐limited regimes. The slope of the sensitivity curve becomes steeper for larger m values (e.g., m > 2). In addition, the sensitivity of the AET/P to m shows an asymmetrical unimodal curve, while the strongest sensitivity (inflection point) of evapotranspiration ratio to m occurs at PET/P > 1. We further examined spatial patterns of these sensitivities and the relative roles of PET/P (RCPET/P) and m (RCm) to AET/P over 91 hydrological basins worldwide. The tropical humid basins present the strongest sensitivity of AET/P to PET/P, while higher sensitivity coefficients of AET/P to m can be found in very cold basins. The changes in the sensitivity of evapotranspiration ratio to PET/P and m between 1930–1970 and 1971–2008 were assessed for these basins across broad climatic gradients. Most of these basins show a positive change in RCPET/P but a negative shift in RCm in the warming world. Key Points: General frameworks are derived to describe how the evapotranspiration ratio responds to the aridity index and watershed characteristicsSensitivity of the evapotranspiration ratio to watershed characteristics (m) shows an asymmetrical unimodal curveSpatial patterns of these sensitivity coefficients and the relative roles of PET/P and m to AET/P over global basins were identified [ABSTRACT FROM AUTHOR]