Energy partitioning dynamics of drying terrestrial surfaces

The dynamics of radiative energy partitioning on drying terrestrial surfaces reflects the strong coupling between evaporation and surface temperature that shapes latent and sensible heat fluxes. We used a new pore-scale analytical model that explicitly links evaporative fluxes with temperature dynamics of drying surfaces. Model predictions were in good agreement with measured evaporation rates and surface temperature variations observed during drying of a homogeneous sand surface. The model was extended to heterogeneous surfaces by considering responses of representative elements of a complex surface and weighing relative contributions to formulate area-averaged fluxes. Notwithstanding the small scale basis of the model, the fully coupled surface energy balance provides a physically-based framework for predicting the Bowen ratio and the Priestley-Taylor alpha (Priestley and Taylor, 1972) for a range of boundary conditions using readily available input variables (radiation, air temperature, etc.). Analyses show that a is not constant (typically assumed as alpha = 1.26), it decreases with surface drying and increasing net radiation, and increases with increasing wind speed. The physically-based predictability offers new opportunities for generalization of algorithms that rely on remotely sensed surface temperature to estimate surface fluxes. (C) 2014 Elsevier B.V. All rights reserved.