Preprints
https://doi.org/10.5194/hess-2021-436
https://doi.org/10.5194/hess-2021-436

  02 Sep 2021

02 Sep 2021

Review status: this preprint is currently under review for the journal HESS.

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

Zhuoyi Tu1, Yuting Yang1, and Michael L. Roderick2 Zhuoyi Tu et al.
  • 1State Key Laboratory of Hydroscience and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing, China
  • 2Research School of Earth Sciences, Australian National University, Canberra, ACT, Australia

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.

Zhuoyi Tu et al.

Status: open (until 28 Oct 2021)

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Zhuoyi Tu et al.

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Short summary
Here we test a maximum evaporation theory that acknowledges the interdependence between radiation, surface temperature and evaporation over saturated lands. We show that the maximum evaporation approach recovers observed evaporation and surface temperature under non-water-limited conditions across a broad range of bioclimates. The implication is that the maximum evaporation concept can be used to predict potential evaporation that has long been a major difficulty in hydrological community.