Special ClimaTea


Wednesday, January 29, 2020, 12:00pm



Speaker: Lucas Vargas Zeppetello

Title: "Simple Models of Land Surface Evaporation: Theory and Applications"

Abstract: Observations show the relationship between evaporation and soil moisture generally conforms to a “two regime” framework; namely that evaporation is limited by available soil moisture in dry climates and by radiation in wet climates.  Despite its common acceptance as a pedagogical tool to understand soil moisture’s impact on evaporation, no globally uniform value of soil moisture at which a transition between the two regimes occurs has been observed.  Guided by output from a simple model of the land-atmosphere interface, we derive expressions for evaporative cooling anomalies and vapor pressure deficit that demonstrate the non-linear impact of soil moisture perturbations.  These equations show that a negative feedback between evaporation and surface temperature gives rise to the two apparent regimes without requiring a critical value of soil moisture at which the transition occurs.  As an application of these simple expressions, we present a diagnostic equation for summertime temperature variance as a function of radiation and precipitation, the two primary evaporation forcing agents.  This equation can be used to accurately model contemporary summertime temperature variance and make predictions about how variance will evolve under various climate change scenarios. Reference paper

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