Loss in snow storage in the Alps: attribution to elevation bands and meteorological drivers
Assigned Session: FS 3.115: Drought in mountain regions
Abstract ID: 3.12546 | Not reviewed | Requested as: Talk | TBA | TBA
Raul Wood (1,2,3)
Manuela, Brunner (1,2,3)
(1) WSL Institute for Snow and Avalanche Research SLF, Fluelastr. 11, 7260, Davos, CH
(2) Institute for Atmospheric and Climate Science, ETH Zurich, Universitätstrasse 16, 8006 Zurich, CH
(3) Climate Change, Extremes and Natural Hazards in Alpine Regions Research Center CERC, Fluelastr. 11, 7260, Davos, CH
Abstract
Another low snow year in the European Alps marks the rapid decline in Alpine snowpack and fuels the emerging topic of snow droughts. Such snow droughts can have serious hydrological consequences, as highlighted by the prolonged hydrological drought in northern Italy in 2022. Snow storage is expected to decrease and the number of snow droughts to increase in response to rising temperatures. However, it is not yet clear whether a decline in snow storage and the occurrence of low-snow years are solely caused by rising temperatures or whether changes in precipitation patterns also play an important role.
Here, we use gridded snow products for Switzerland and Austria to quantify (1) changes in catchment snow water equivalent (SWE), since 1961 and attribute these changes to SWE deficits from low to high elevation bands; (2) the occurrence, dynamics, and meteorologic drivers of low-snow years, i.e. years with annual maximum SWE below the 30th percentile; and (3) the persistence of low-snow conditions and the predictability of annual maximum SWE.
Our results show a median loss of total annual catchment SWE of approx. 20 % across 251 catchments in Switzerland and Austria over the period 1962-2023, with a marked regime shift at the end of the 1980s. All elevation ranges experience a loss in SWE, but most of the catchment SWE loss (approx. 60%) can be attributed to the loss in mid-elevation SWE (1200-2100m). Further, we see an increase in the fraction of area under low-snow conditions in all elevation bands. Thereby, low-snow years are connected to precipitation deficits, especially at higher elevations (>2100m). At lower and mid-elevations, warm temperature anomalies are additionally important to explain low-snow years. Further, low-snow years are characterized by a high persistence of low-snow conditions, starting three months (median) before the climatological period of maximum SWE. SWE deficits are to large parts accumulated during November-January and by January there already exists a 60% chance of predicting the SWE conditions at the end of winter . These results showcase the potential for a better seasonal snow prediction and will help to constrain future projections of SWE and associated hydrological impacts.
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