Effects of the water retention curve on evaporation from arid soils

Water retention curves approaching infinitely negative matric potentials at residual water content are widely employed to model soil moisture dynamics. When used in numerical simulations, these retention curves fail to satisfactorily describe evaporation from arid soil (moisture-limited regime) because they do not allow the soil to dry below residual water content. We show that simple modifications can be introduced to prevent unrealistic water retention at residual water content and predict more physically sound moisture dynamics. Modified retention models that allow drying below residual predict a moisture-limited regime characterized by a thin subsurface evaporation zone and produce vapor fluxes up to 3 times larger than classical retention models. This might reduce the need to introduce empirical enhancement factors and improve the capability of modeling evaporation into the atmosphere and runoff in arid regions.