Diminishing control of evaporation on rising land surface temperature of the Earth

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. Increasing energy at the land surface impacts global evaporation rates and surface temperatures, necessitating 5 ± 3% extra water to evaporate at the present-day for the same cooling effect, according to analysis of the latent heat flux required for surface temperature reduction through an adiabatic process.