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Abstract

Snow has a great importance in the Alpine region, affecting different aspects of human life and regulating the hydrological cycle. Snow can be considered as a natural freshwater reservoir, filling up in winter and emptying in spring as the melting season begins. Due to the importance of monitoring snow water equivalent (SWE) for hydropower energy production, the Italian National Electric Board (ENEL) started in 1966 a measurement campaign of snow depth (HS) and snow density. The campaign has been conducted continuously, with a homogeneous methodology, and consistently in time (from 1 February to 1 June and on 15 April) and location. Here, we use this comprehensive dataset to study the climatology of SWE in a wide portion of the Italian alps. We divided the measurement points in six macro-basins and four elevation classes of 500 m, from 1000 m to 3000 m asl. We applied a Moving Average and Running Trend Analysis (MARTA) combined with the Pettitt’s test, finding decreasing trends for both HS and SWE between 1967-2020 and change-points at the end of the 1980s, confirmed by the significant decrease of average HS and SWE in 1994-2020 compared to 1967-1993. The MARTA analysis applied to HISTALP meteorological data highlighted increasing trends for temperature, together with a change-point at the end of the 1980s. We also evaluated the correlation of maximum SWE with NAO and WeMO climatic indexes. Finally, we compared winter accumulation and summer water availability, quantifying the role of SWE in drought events in North Italy (e.g., 2022).