Testing a maximum evaporation theory over saturated land: Implications for potential evaporation estimation

Abstract

Abstract. State-of-the-art evaporation models usually assume the net radiation (Rn) and surface temperature (Ts; or near-surface air temperature) to be independent forcings on evaporation. However, Rn depends directly on Ts via outgoing longwave radiation and this creates a physical coupling between Rn and Ts that extends to evaporation. In this study, we test a maximum evaporation theory originally developed for global ocean over saturated land surfaces, which explicitly acknowledges the interactions between radiation, Ts and evaporation. Similar to the ocean surface, we find a maximum evaporation (LEmax) emerges over saturated land that represents a generic trade-off between a lower Rn and a higher evaporation fraction as Ts increases. Compared with flux site observations at the daily scale, we show that LEmax corresponds well to observed evaporation under non-water-limited conditions and that the Ts at which LEmax occurs also corresponds with the observed Ts. Our results suggest that saturated land surfaces behave essentially the same as ocean surfaces at time scales longer than a day and further imply that the maximum evaporation concept is a natural attribute of saturated land surfaces, which can be the basis of a new approach to estimating evaporation.

Energyand vapour transfer in evaporation processes over saturated bare soil and water surface‐lysimeter studies

“…Finally, previous research considered surface temperature T to be an independent external forcing that determine ‘wet surface’ evaporation (Tu et al, 2021; Yang & Roderick, 2019). The results of the present study suggest that T is a significant internal forcing for both energy and vapour transfer during the evaporation process since it influences the redistribution of energy below the evaporation surface ( G and N ), outgoing longwave radiation ( R lu ), as well as vapour gradients above the surface ( ∆e ).…”