Abstract:This work presents an extensive evaluation of the Crocus snowpack model over a rugged and highly glacierized mountain catchment (Arve valley, Western Alps, France) from 1989 to 2015. The simulations were compared and evaluated using in-situ point snow depth measurements, in-situ seasonal and annual glacier surface mass balance, snow covered area evolution based on optical satellite imagery at 250 m resolution (MODIS sensor), and the annual equilibrium-line altitude of glaciers, derived from satellite images (Landsat, SPOT, and ASTER). The snowpack simulations were obtained using the Crocus snowpack model driven by the same, originally semi-distributed, meteorological forcing (SAFRAN) reanalysis using the native semi-distributed configuration, but also a fully distributed configuration. The semi-distributed approach addresses land surface simulations for discrete topographic classes characterized by elevation range, aspect, and slope. The distributed approach operates on a 250-m grid, enabling inclusion of terrain shadowing effects, based on the same original meteorological dataset. Despite the fact that the two simulations use the same snowpack model, being potentially subjected to same potential deviation from the parametrization of certain physical processes, the results showed that both approaches accurately reproduced the snowpack distribution over the study period. Slightly (although statistically significantly) better results were obtained by using the distributed approach. The evaluation of the snow cover area with MODIS sensor has shown, on average, a reduction of the Root Mean Squared Error (RMSE) from 15.2% with the semi-distributed approach to 12.6% with the distributed one. Similarly, surface glacier mass balance RMSE decreased from 1.475 m of water equivalent (W.E.) for the semi-distributed simulation to 1.375 m W.E. for the distribution. The improvement, observed with a much higher computational time, does not justify the recommendation of this approach for all applications; however, for simulations that require a precise representation of snowpack distribution, the distributed approach is suggested.

Abstract:We evaluated distributed and semi-distributed modeling approaches to 13 simulating the spatial and temporal evolution of snow and ice over an extended 14 mountain catchment, using the Crocus snowpack model. The distributed approach 15 simulated the snowpack dynamics on a 250-m grid, enabling inclusion of terrain 16 shadowing effects. The semi-distributed approach simulated the snowpack dynamics for 17 discrete topographic classes characterized by elevation range, aspect, and slope. This 18 provided a categorical simulation that was subsequently spatially re-projected over the 19 250-m grid used for the distributed simulations. The study area (the upper Arve 20 catchment, western Alps, France) is characterized by complex topography, including 21 steep slopes, an extensive glaciated area, and snow cover throughout the year. 22Simulations were carried out for the period 1989-2015 using the SAFRAN 23 meteorological forcing system. The simulations were compared using four observation 24 datasets including point snow depth measurements, seasonal and annual glacier surface 25 mass balance, snow covered area evolution based on optical satellite sensors, and the 26 annual equilibrium-line altitude of glacier zones, derived from satellite images. The 27 results showed that in both approaches the Crocus snowpack model effectively 28 reproduced the snowpack distribution over the study period. Slightly better results were 29 obtained using the distributed approach because it included the effects of shadows and 30 terrain characteristics. 31