A global quantitation of factors affecting evapotranspiration variability

Abstract Scientific viewpoints on the long-term hydrological responses to factors other than climatic change remain controversial and yet the impacts of these factors are often neglected at the short-term (such as monthly and annual) timescale. We developed an analytical method to decompose evapotranspiration (E) variability to the variability of precipitation (P), potential evapotranspiration (E0), total water storage change (ΔS), and catchment characteristics (n), such as vegetation, soil and climate seasonality. Global assessment showed that P enhanced E variability in most regions, while restrained E variability in some extremely humid regions. E0 controlled monthly E variability in most the energy-constrained regions. ΔS had much larger impacts on E variability at monthly scale compared to the annual scale, and restrained E variability in many arid regions (P/E0 0.66), especially at annual scale. The dominant factors of E variability varied with timescales and regions. At a global scale, P and catchment characteristics are the dominant factors controlling global E variability at monthly and annual scales, respectively; In humid regions, however, the impacts of E0 on monthly E variability are generally larger than the impacts of precipitation and catchment characteristics. We highlight the necessity to consider the impacts of catchment characteristics even at the short-term timescales, otherwise the simulation and attribution of E variability would be significantly underestimated.