Effects of Melting and Refreezing Ice in Unsaturated Soils on Groundwater Recharge

Groundwater recharge in mountainous regions is predominantly driven by snowmelt. However, shifting precipitation patterns and changes in freeze-thaw cycles due to climate change alter hydrological processes. To better understand the influence of ice dynamics in seasonally frozen soils on groundwater recharge, we evaluate two numerical models that include ice formation and melting within the soil. Specifically, we aim to quantify the partitioning of rain- and meltwater into lateral runoff and vertical infiltration.

We focus on the models PermaFOAM and PFLOTRAN, which both solve the Richards equation for unsaturated flow coupled to heat transfer equations, while using different approaches to account for ice buildup in the pore space. We apply the two models to a simplified two-dimensional hillslope cross-section, analyzing how these formulations influence hydraulic conductivity and lateral flow generation in seasonally frozen soils.  

As a next step, we plan to integrate a snowpack as a porous medium into the vadose-zone model framework, enabling a comprehensive analysis of the interplay between snowmelt, soil freezing, and preferential water flow. Our goal is to improve the understanding of water flow dynamics under transient freeze-thaw conditions in soils and overlying snowpacks. By integrating snowmelt processes into hydrological models, we aim to improve the accuracy of groundwater recharge projections in mountainous regions.