Trends in annual maximum snow water equivalent and snow duration across the Wägital, Switzerland: A long-term analysis from 1943 to 2023

Abstract. Temporary storage of precipitation in mountainous regions as snow is crucial for downstream water users, including agriculture and hydroelectric power generation, and affects the climate and biogeochemical processes. The amount and duration of snow storage are changing. Snow water equivalent (SWE) has been measured at multiple sites in the pre-Alpine Wägital catchment in Switzerland around April 1^st since 1943, making it one of the longest catchment-wide SWE datasets globally. We used these data to analyse trends in SWE and to determine the annual maximum SWE (maxSWE) and duration of snow cover for each site and year using a simple degree-day model.

The model results revealed that the April 1^st measurements could occur before or after maxSWE, although maxSWE occurred more often in the week of April 1^st than in any other week. However, especially in the past decade, maxSWE occurred earlier than April 1^st. There was a general decline in the observed SWE and simulated maxSWE during the study period: positive trends dominated from the 1940s to the 1970s, followed by stronger negative trends from the 1970s onward. The strength of the overall negative trend therefore depends strongly on the chosen period. Similar patterns were observed for the snow-cover duration. Despite uncertainties in input data and model limitations, this study underscores the value of long-term datasets like those from the Wägital and a simple model for understanding trends in snow cover and storage, and to anticipate future challenges related to a reduced snow cover due to climate change.