Abstract
Evaporation rates and land surface temperatures can be modified by planned water availability as well as land use and land cover changes. In general, a higher evaporation rate via its associated latent heat flux yields a cooler surface. Here we demonstrate that increasing energy at the land surface necessitates more intense latent heat fluxes for the same unit degree of surface cooling. When the wet-surface temperature is around 25 °C, a unit drop in land surface temperature requires about twice as much water to evaporate than when it is only 10 °C. As a consequence, today an estimated 5 ± 3% of extra water may be needed to evaporate globally for the same cooling effect as before the industrial era when near surface air temperature over land was about 1.5 °C cooler on average. This increase is a magnitude larger than what the thermal properties of water explain.