Snow model sensitivity analysis to understand spatial and temporal snow dynamics in a high-elevation catchment

In this paper, we addressed a sensitivity analysis of the snow module of the GEOtop2.0 model at point and catchment scale in a small high-elevation catchment in the Eastern Italian Alps (catchment size: 61km(2)). Simulated snow depth and snow water equivalent at the point scale were compared with measured data at four locations from 2009 to 2013. At the catchment scale, simulated snow-covered area (SCA) was compared with binary snow cover maps derived from moderate-resolution imaging spectroradiometer (MODIS) and Landsat satellite imagery. Sensitivity analyses were used to assess the effect of different model parameterizations on model performance at both scales and the effect of different thresholds of simulated snow depth on the agreement with MODIS data. Our results at point scale indicated that modifying only the snow correction factor resulted in substantial improvements of the snow model and effectively compensated inaccurate winter precipitation by enhancing snow accumulation. SCA inaccuracies at catchment scale during accumulation and melt period were affected little by different snow depth thresholds when using calibrated winter precipitation from point scale. However, inaccuracies were strongly controlled by topographic characteristics and model parameterizations driving snow albedo (snow ageing coefficient and extinction of snow albedo) during accumulation and melt period. Although highest accuracies (overall accuracy=1 in 86% of the catchment area) were observed during winter, lower accuracies (overall accuracy<0.7) occurred during the early accumulation and melt period (in 29% and 23%, respectively), mostly present in areas with grassland and forest, slopes of 20-40 degrees, areas exposed NW or areas with a topographic roughness index of -0.25 to 0m. These findings may give recommendations for defining more effective model parameterization strategies and guide future work, in which simulated and MODIS SCA may be combined to generate improved products for SCA monitoring in Alpine catchments.