The role of subsurface storage in snow dominated alpine catchments

In snow-dominated catchments, the hydrological response is governed by complex interactions between surface and subsurface storage that evolve throughout the snow accumulation and melt season. The water input from snowmelt has fundamentally different properties in terms of spatial and temporal patterns than rainfall input. In addition, frozen soil  comes into play. Accordingly, understanding the hydrological response of such catchments requires a shift from a too strong focus on surface processes (snow accumulation and melt patterns) to subsurface storage dynamics, soil moisture conditions, and the connectivity of flow pathways. Despite their importance, these subsurface processes are often simplified or inadequately represented in hydrological models, contributing to persistently wrong streamflow simulations in alpine catchments.

Based on field and modeling data from different case studies, we discuss the role of subsurface storage and flow paths during the snow melt season and what is required to represent them in models. A special emphasis is given to the question how understanding surface-subsurface interactions in today snow dominated catchments is of key importance to anticipate the effect of snow line shifts and eg the more frequent occurrence of rain-on-snow events.