Introducing hysteresis in snow depletion curves to improve the water budget of a land surface model in an Alpine catchment
Résumé
The Durance watershed (14 000 km2 ), located in the French Alps, generates 10% of French hydro-power and provides drinking water to 3 million people. The Catchment Land Surface Model (CLSM), a distributed land surface model (LSM) with a multilayer, physically-based snow model, has been applied in the upstream part of this watershed where snowfall accounts for 50% of the precipitation. The CLSM subdivides the upper Durance watershed, where elevations range from 800 m to 4000 m within 3580 km2 , into elementary catchments with an average area of 500 km2 . We first show the difference between the dynamics of the accumulation and ablation of the snow cover using MODIS images and snow depth measurements. The extent of snow cover increases faster during accumulation than during ablation because melting occurs at preferential locations. This difference corresponds to the presence of a hysteresis in the snow cover depletion curve of these catchments, and we adapted the CLSM by implementing such a hysteresis in the snow cover depletion curve of the model. Different simulations were performed to assess the influence of the parameterizations on the water budget and the evolution of the extent of the snow cover. Using 6 gauging stations, we demonstrate that introducing a hysteresis in the snow cover depletion curve improves melting dynamics. We conclude that our adaptation of the CLSM contributes to a better representation of snowpack dynamics in a LSM that enables mountainous catchments to be modeled for impact studies such as those of climate change.
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