Magnitude and variability of land evaporation and its components at the global scale

Abstract. A physics-based methodology is applied to estimate global land-surface evaporation from multi-satellite observations. GLEAM (Global Land-surface Evaporation: the Amsterdam Methodology) combines a wide range of remotely sensed observations within a Priestley and Taylor-based framework. Daily actual evaporation is derived at quarter degree resolution over the world’s land surface. A running water balance of the vertical profile of soil moisture in the root zone is used to estimate the effect of soil water stress on transpiration. Forest rainfall interception, evaporation from bare soil, transpiration and snow sublimation are calculated independently. The inclusion of soil moisture deficit and forest rainfall interception – by means of the Gash analytical model – leads to an improved representation of the magnitude and distribution of the latent heat flux over semiarid and forested regions. Analyses of the global results show that interception loss plays an important role in the partition of the precipitation into evaporation and water available for runoff at a continental scale. The global distribution of evaporation and its different components is analysed to understand the relative magnitude of each component over different ecosystems. This study gives new insights into the relative importance of precipitation and net radiation in driving evaporation, and how the seasonal influence of these controls varies over the different regions of the world. Precipitation is recognised as an important factor driving evaporation, not only in areas that have limited soil water availability, but also in areas of high rainfall interception and low available energy.