Modelling Interflow in Seasonally Frozen Soils: A Comparison of Hydraulic Parameterisations

Interflow in seasonally frozen soils plays a key role in winter runoff generation and groundwater recharge. Uncertainty in the physical processes governing soil freezing has resulted in a wide range of parameterisations to capture ice-induced changes in pore-space connectivity. Although several numerical models for partially frozen soils have implemented these parameterisations, their impact on interflow development has not been systematically assessed.

In this work, we investigate how different hydraulic parameterisations of frozen soils influence interflow dynamics in sloping terrain. We compare three published parameterisations: (i) a capillary-bundle model following Watanabe and Flury (2008), (ii) an impedance-factor-based reduction of hydraulic conductivity, and (iii) a drying assumption in which ice formation reduces liquid water availability. To compare them, we developed a two-dimensional finite volume solver for coupled heat and water transport. This unified framework, implemented in JAX to enable high-performance computing in Python, allows us to isolate parameterisation effects from numerical artefacts. We conduct two-dimensional simulations to analyse the dynamics of interflow during freezing and thawing periods. The results show substantial differences in both the timing and intensity of interflow among the parameterisations.  

Our findings demonstrate that the choice of frozen-soil hydraulic parameterisation can strongly affect simulated runoff and infiltration partitioning. These results underscore the importance of parameterisation choice for hydrological modelling in cold regions with increasingly frequent midwinter melt events.

 

Watanabe K., Flury M. Capillary bundle model of hydraulic conductivity for frozen soil. Water Resour. Res., 44(12), 2008. doi:10.1029/2008WR007012.