Hydrus Modeling of Coupled Water, Vapor and Energy in Soils and at the Soil-Atmosphere Interface.

It is broadly accepted that mass and energy fluxes in the subsurface in general, and in arid and semi-arid regions in particular, are closely coupled and cannot be evaluated without considering their mutual interactions. However, only a few numerical models (if any) consider coupled water, vapor and energy transport in both the subsurface and at the soil-atmosphere interface. While the subsurface is commonly implemented in existing models, which often consider both isothermal and thermally induced water and vapor flow, the effects of slope inclination, slope azimuth, variable surface albedo and plant shading on incoming radiation and spatially variable surface mass and energy balance, and consequently soil moisture distribution, is rarely considered. In this presentation we discuss these missing elements and our attempts to implement them into the HYDRUS model. We demonstrate implications of some of their interactions, their impact on the spatial distributions of soil temperature and water content, and their effect on soil evaporation.