Swiss glacier mass loss during the 2022 drought: persistent streamflow contributions amid declining melt water volumes

Abstract

The year 2022 was extremely warm and dry in Europe, resulting in a severe hydrological drought. In Switzerland, part of Europe’s water tower, streamflow in glacier-fed rivers could have been even more reduced if the situation had not led simultaneously to extreme glacier melt. Here we analyze the role of glaciers during the 2022 drought for 88 glacierized catchments by combining streamflow and meteorological observations with estimations of snow water equivalent, actual evapotranspiration and daily glacier storage changes. We also compare the year 2022 to earlier exceptionally warm and dry years (1921, 1928, 1947, 1998, 2003 and 2018) to assess if the ongoing glacier retreat has already caused a declining meltwater supply in such extreme conditions. Results show that 60 %–80 % of the total glacier melt in 2022 came from net mass loss (imbalanced melt). During summer, the increased glacier melt could completely offset the precipitation and snowmelt deficits for catchments with around 15 % glacierization. Further downstream, the extra glacier melt in summer alleviated water input deficits by up to 5 % at Basel (Rhine) and 70 % at Porte du Scex (Rhone). Compared to past extreme years, total glacier meltwater volume has declined due to strong glacier area loss, despite higher melt rates per unit area. In 2022 versus 2003-the most comparable recent extreme summer-total glacier meltwater supply decreased in two thirds of the catchments over the entire summer, and in one third in July. In the remaining catchments, the more intense specific melt of 2022 could offset the 21 % glacier area loss since 2003. Despite these declines, relative glacier melt contributions to streamflow stayed rather constant, or even rose in some months, highlighting its ongoing importance during droughts while simultaneously raising concerns for future drought situations.