A FEM model for evaporation and infiltration in unsaturated soils interacting with the atmosphere

The pore water pressure in the vadose zone is controlled by the interaction between the soil and the atmosphere through evaporation and infiltration. These processes are strongly influenced by the soil's hydraulic conductivity and water retention and thermal properties (Guida et al., 2023). In this contribution, we propose a coupled model based on the mass balance equations of the air and water species by including a storage term accounting for the changes in the liquid degree of saturation and, if necessary, in porosity. Liquid water and vapour mass transport occur via advection and diffusion, respectively. Finally, the thermal energy balance is also considered, including the heat flux due to conduction and convection, to obtain the temperature field.