4.1 Meteorological and snow conditions
The four analyzed spring seasons (April-June) exhibited strong contrasts in terms of meteorological (temperature, precipitation) and snow conditions (snow depth and snow covered area) (Figure 2). April 2017 started with more than one meter of snow depth at the ultrasonic sensor of the AWS, but it melted fast in the subsequent weeks. In early May a significant portion of the catchment (40%) was snow free and with very few spots where snowpack exceeded 2 m (Figure 3). During May, no major snow events occurred and the basin was almost free of snow by 1st June. Two heavy precipitation events, mostly as rain, where observed in early and mid-May. Spring 2018 was the snowiest year. By early May, almost 1.5 m of snow depth was measured in the AWS, and by mid-May, 100% of the catchment was still covered by snow, with large areas covered by more than 3 m of snow.