Predicting evaporation and heat transfer of a coupled surface/subsurface problem using a simplified one-region model

Dealing with environmental flows poses significant challenges, particularly when it comes to accurately predicting mass and heat exchanges between the atmosphere and a variably saturated porous medium. In this work, we develop a non-isothermal, two-phase, two-component porous medium model equipped with physically based boundary conditions that incorporate the influence of free-flow conditions on soil evaporation and the resulting geothermal heat flux. This approach enables the use of average parameters to describe the free-flow domain, thus avoiding the need to explicitly simulate atmospheric flow while maintaining accuracy in both evaporation estimation and subsurface dynamics.

The model is validated against well-documented laboratory-scale experiments from the literature, covering a range of free-flow conditions and soil properties. It is then employed to assess the impact of soil drying dynamics on the retrievable geothermal heat flux across different soil types. The results demonstrate distinct thermal responses strongly linked to soil saturation behavior. A comparative study across different soil types and water table depths, complemented by a sensitivity analysis of free-flow parameters, reveals two distinct regimes. For shallow water tables, free-flow properties dominate, allowing for simplified groundwater modeling. In contrast, for deeper water tables, the influence of free-flow parameters becomes negligible, and a detailed representation of groundwater flow-including evaporation-is essential. The proposed approach enables accurate modeling across both regimes without the need to simulate the entire free-flow domain.