Effects of climate change on snow cover in Swiss alpine terrains in the 21st Century

Snow is a key element in alpine terrains as it highly affects not only the surrounding environment in terms of hydrology and ecosystems of the catchment but also for socioeconomic aspects such as electricity production and winter tourism. The future changes in air temperature and precipitation as integral part of projected climate change are expected to affect the snow cover. To analyse the magnitude of this impact, in this study Snow and Climate Metrics, evaluated in two periods of the future (2020-2050 and 2069-2099), are compared to the values of the past (1971-2001). To do so, measurements data from 18 Intercantonal Measurement and Information System (IMIS) stations situated across the Swiss Alpine arc, and 6 climate change models chain, in 2 RCP scenarios (RCP2.6 and RCP8.5), from EURO-CORDEX at 50km resolution, were used. These 18 stations are spread over the Swiss Alpine Arch above 2000 m.a.s.l. and clusteredin 4 regions, 3 on the northern side (North-West, North-Center, North-East), 1 on the southern one (South). As a complete dataset including Incoming Short-Wave Radiations and precipitation, variables not directly measure ad IMIS stations, was necessary the reconstitution of the latter was carried out thanks to the use of measurements data at MeteoSwiss stations. The climate models chain were then downscaled to IMIS stations using quantiale mapping. The downscaled datasets underwent a disaggregation process from daily to hourly resolution and were subsequently fed to the physical-based snow model SNOWPACK to obtain the evolution of the snowcover from 1971 to 2099. All stations showed a future clear reduction in Snow Season Length, with, as main cause, an earlier ending, rather than a delayed starting. SSE is, in fact, expected to be 15-18 days in advance for RCP2.6 and 55 for RCP8.5, in contrast with a delay of 7-11 days for RCP2.6 and 13-22 days for RCP8.5 for SSS. Delays and anticipations are expected to result in a showertening of the SSL of 20-30 days for RCP2.6 and 80-92 days for RCP8.5 by 2069-2099. Furthermore, the snowcover is also awaited to be affected in its mean and maximum thickness. South and North-Center stations are the most affected ones, experiencing a reduction of 12-16% (16-20 [cm]) in 2020-2050, and 14-45% (20-60 [cm]) in 2069-2099. Even though an increase of precipitation in winter in expected on both sides, the reason of these changes is to be traced back mainly to the rise in temperatures along the whole year. For both RCPs and periods the Northern side is expected to experience a larger increase in air temperature and precipitation with respect to the South, however, MDTAA0 is awaited to be larger in the South, resulting in a stronger reduction in MHS on this side. The most direct impacts of the changes in the snowcover are on the hydrology of the surrounding catchments. The flux of meltwater coming from snowpacks, historically bell-shaped centered on the beginning of June with a long tail in winter, for RCP2.6 is expected to end in summer and the timing of its maximum release to be anticipated of 11-18 days, for RCP8.5 the flux becomes continuous along winter and spring and drops to 0 by the end of July, its peak is anticipated by 40 days. These impacts on the runoff behaviour can be linked to the increase in air temperature. By the end of the century, according to RCP8.5, the MDTAA0 is going to be much larger in every month causing a continuous melt of the snowpack and thus a continuous meltwater runoff from from later autumn to early summer.