Abstract
Rising air temperatures and increasingly intense precipitation are being observed in the Swiss Alps. These changes strongly affect the evolution of the temperature regime and the dynamics of mountain permafrost. Changes occur at different rates depending on ground ice content. Long-term monitoring reveals progressive warming and degradation of permafrost and accelerating rock glacier velocities. This study analyses changes occurring in ice-rich (excess-ice) and ice-poor mountain permafrost in Switzerland between 1997 and 2019 on the basis of ground temperature and rock glacier dynamics measurements carried out by the WSL Institute for Snow and Avalanche Research SLF at seven sites. Long-term borehole data indicate an increase of ground temperatures at all depths, in particular at ice-poor and nearly snow-free sites. Active layers are thickening at most sites and prolonged periods of active layer thaw are observed. Long autumn zero curtains are observed in ice-rich permafrost, possibly leading to an overall acceleration of rock glaciers. All these changes point towards ongoing permafrost warming and permafrost degradation in future.
Highlights
On a global scale, permafrost temperatures increased by approximately 0.3◦C during the last decade (Biskaborn et al, 2019)
We show a detailed analysis of ground temperatures measured in 9 SLF boreholes at 7 sites located between approximately 2400 m and 3600 m a.s.l. in different regions of the Swiss Alps and in different landforms with varying ice contents (Table 1 and Figure 1): rock walls and crests, talus slopes, and rock glaciers
The same applies for Switzerland, where the air temperature increase is strong at MeteoSwiss automatic weather stations above 1000 m a.s.l
Summary
Permafrost temperatures increased by approximately 0.3◦C during the last decade (Biskaborn et al, 2019). Rising ground temperatures (Biskaborn et al, 2019; PERMOS, 2019), active layer thickening, varying ice- and water contents (Mollaret et al, 2019) and strongly increasing rock glacier deformation rates (PERMOS, 2019) have been observed in the (Swiss) Alps during the last two decades and are attributed to climate warming. Higher water contents contribute to the acceleration of rock glaciers (Wirz et al, 2016; Buchli et al, 2018; Cicoira et al, 2019b). Shortterm accelerations of rock glaciers are caused by intense summer rainfall (Jansen and Hergarten, 2006; Wirz et al, 2014; Kenner et al, 2017a), while on an annual basis the duration of the freezing period in the active layer controls the water budget and is decisive for rock glacier velocity
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