Estimating Evaporative Fluxes in Dry Climates

Evaporative surface fluxes can be a dominant factor in sub-surface moisture distribution and movement, especially in dry climates. Evaporation depends on both soil characteristics and atmospheric conditions, and is non-trivial to accurately measure. Consequently, evaporative fluxes are often numerically estimated. The purpose of this paper is to evaluate the predictive capability of a widely used numerical approach, and provide a method for interpreting transient evaporative fluxes from simple moisture content measurements. A parameter estimation analysis of the van Genuchten parameters α, n and Ks (saturated hydraulic conductivity) using an inverse solution and volumetric soil water content data was developed. In this study rather than using water potential data, a Tikhonov regularization method was used to deal with the ill-posed nature of the problem. The water flux was simulated using the computer program UNSAT-H. The code was then combined with the program DAKOTA (Design Analysis Kit for Optimization and Terrascale Applications) for the parameter study. By minimizing the proposed objective function through iterative calculations, the resulted evaporation from the simulation, shows a good approximation to the measured evaporation on the field.