Analytical model for bare soil evaporation dynamics following wetting with concurrent internal drainage

Abstract

Under natural conditions, infiltrated rainwater redistributed into the soil profile, becomes partially sheltered from surface evaporative losses relative to undrained wet surfaces. Surface evaporation rates and internal drainage dynamics are both sensitive to soil hydraulic properties and initial soil hydration state. We report a novel analytical framework for quantifying surface evaporation rates with concurrent internal drainage, considering soil properties and dynamic surface evaporation resistance. Interplay among soil hydraulic properties, boundary conditions, and atmospheric demand result in nonlinear relationships between cumulative evaporative losses and initial water content. The new analytical solution shows good agreement with laboratory column experiments and literature data. Results highlight the role of soil texture on evaporative losses and the nonlinear effects of initial wetness on evaporation. The largest evaporative losses per rainfall amount are predicted for small rainfall events over initially dry loamy soils due to the detention of infiltrated rainwater near the surface for soils with large porosity and low hydraulic conductivity. The analytical framework uses readily available parameters hence can be implemented in land surface models to explicitly consider how soil properties and rainfall event size affect surface evaporation dynamics.