Temperature driven vapor fluxes in soils cause a net recharge

Temperature gradients can drive vapor diffusion by controlling vapor pressure in the soil. We studied vapor diffusion for soils in two different climates: A semiarid climate at El Cabril (Córdoba, Spain) and a subarctic climate in the Upper Tuul River basin (Mongolia). For El Cabril vapor diffusive fluxes were studied by means of the measured temperatures and an analytical model. For the second site (Upper Tuul) a physically based soil water and energy balance model was developed accounting for relevant processes such as melting-freezing of water and vapor diffusion in the soil. Results of both sites show that vapor diffuses downwards during summer and upwards during winter, while yearly averaged fluxes diffuse downwards. The overall amount is small for El Cabril, but significant for the Upper Tuul. The latter large values can be explained by the large temperature oscillations of the Mongolian climate and the freezing/thawing of subsoil layer.