Rain on snow (ROS) events in the Italian Alps

In the Alps, numerous studies indicate that winter precipitation, measured in millimetres of water equivalent, does not exhibit any specific temporal trend. However, in recent years, the altitude of reliable snow cover has increased, whereas the snow depth on the ground, the amount of fresh snow, and the snow water equivalent (SWE) have decreased.

An investigation of the databases of Italian avalanche services affiliated with the Interregional Association for coordination and documentation of snow and avalanche problems (AINEVA), revealed an increase in rain on snow (ROS) events at all altitudes, even the highest above 2200 m. The analysis of data collected throughout the Italian Alps over a 20-year period (2006-2025) confirmed that spontaneous avalanche activity is greater on days with ROS.

Analysis conducted in the Dolomites, a range of the eastern Italian Alps, at six stations at different altitudes, further confirmed the increase in rainy days, especially in February and at medium and low altitudes. In the study area, the number of days with precipitation in the period 2016-2025 decreased by 25% compared to the previous decade, indicating more intense episodes, as total precipitation does not show significant variations. The number of snowy days decreased by 33%, further indicating a change in the snow-to-rain regime. Over the last 30 years, the snowfall limit increased by as much as 240 m in January and over 420 m in February.