Changes in global evaporation for the past four decades identified by the complementary evaporation principle and the Budyko framework

The complementary evaporation principle (CEP) could well explain the past changes in global evaporation while avoiding uncertainties in precipitation and soil data. However, it is still difficult to estimate the Priestley-Taylor coefficient (α) for the wet-surface evaporation without actual evaporation data. Here, we proposed an empirical approach that links the CEP and a traditional Budyko equation in order to determine α in locations where no actual evaporation (E) data are available. The CEP–Budyko combined framework enabled us to local climate conditions in α, producing more plausible E estimates in the ungauged locations. We also assessed latitudinal and temporal variations of the E estimates for the past 40 years. This study highlights that the optimal α for CEP is unlikely constant in space, since it needs to be conditioned by local climates.