Integrated Surface and Subsurface Hydrological Modeling with Snowmelt and Pore Water Freeze-Thaw.

For the simulation of winter hydrological processes a gap in the availability of flow models existed: one either had the choice between (1) physically-based and fully-integrated, but computationally very intensive, or (2) simplified and compartamentalized, but computationally less expensive, simulators. To bridge this gap, we here present the integration of a computationally efficient representation of winter hydrological processes (snowfall, snow accumulation, snowmelt, pore water freeze-thaw) in a fully-integrated surface water-groundwater flow model. This allows the efficient simulation of catchment-scale hydrological processes in locations significantly influenced by winter processes. Snow accumulation and snowmelt are based on the degree-day method and pore water freeze-thaw is calculated with a vertical heat conduction approach. This representation of winter hydrological processes is integrated into the fully-coupled surface water-groundwater flow model HydroGeoSphere. A benchmark for pore water freeze-thaw as well as two illustrative examples are provided.