Influence of snow surface processes on soil moisture dynamics and
streamflow generation in alpine catchments
Nander Wever1,2, Francesco Comola1, Mathias Bavay2, and Michael Lehning2,11École Polytechnique Fédérale de Lausanne (EPFL), School of Architecture, Civil and Environmental Engineering, Lausanne, Switzerland 2WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
Received: 16 Nov 2016 – Accepted for review: 12 Dec 2016 – Discussion started: 17 Jan 2017
Abstract. The assessment of flood risks in alpine, snow covered catchments requires an understanding of the linkage between the snow cover, soil and discharge in the stream network. Here, we apply the comprehensive, distributed model Alpine3D to investigate the role of soil moisture in the predisposition of a catchment to high flows from rainfall and snow melt for the Dischma catchment in East Switzerland. The recently updated soil module of the physics based, multi-layer snow cover model SNOWPACK, which solves the surface energy and mass balance in Alpine3D, is verified against soil moisture measurements at seven sites and various depths inside and in close proximity of the Dischma catchment. Measurements and simulations in such terrain are difficult and consequently, soil moisture was simulated with varying degrees of success. Differences between simulated and measured soil moisture mainly arises from an overestimation of soil freezing and an absence of a ground water description in the model. Both were found to have an influence in the soil moisture measurements. Streamflow simulations performed with a spatially-explicit hydrological model using a travel time distribution approach coupled to Alpine3D provided a closer agreement with observed streamflow at the outlet of the Dischma catchment when including 30 cm of soil layers. Performance decreased when including 2 cm or 60 cm of soil layers. This demonstrates that the role of soil moisture is important to take into account when understanding the relationship between both snowpack runoff and rainfall and catchment discharge in high alpine terrain. Runoff coefficients (i.e., ratio of rainfall over discharge) based on measurements for high rainfall and snowmelt events were found to be dependent on the simulated initial soil moisture state at the onset of an event, further illustrating the important role of soil moisture for the hydrological processes in the catchment. The runoff coefficients using simulated discharge were found to reproduce this dependency and this shows that the Alpine3D model framework can be successfully applied to assess the predisposition of the catchment to flood risks from both snowmelt and rainfall events.
Wever, N., Comola, F., Bavay, M., and Lehning, M.: Influence of snow surface processes on soil moisture dynamics and
streamflow generation in alpine catchments, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-601, in review, 2017.