World of Science I Tour de CCAMM

The ground-level air temperature has risen significantly since weather records began, in Switzerland even more than the global average. According to the Swiss climate scenarios CH2018, the average annual temperature in this country will rise by a further 0.7 to 1.9 degrees by around 2060, even with consistent climate protection (CH2018, 2018). This change will noticeably alter the image of the Alps.

Higher temperatures not only cause glaciers to melt faster and permafrost to thaw, but also influence the properties of the snow cover and the flow behavior of avalanches. They also change our ecosystems. This also changes the conditions for natural hazards such as rockfalls, debris flows, landslides and avalanches. Natural disturbances such as windthrow or forest fires also have a direct impact on protective forests, which are of central importance for the safety of many Alpine regions.

Nevertheless, much is still unclear: How exactly does the changing climate influence the formation and dynamics of such mass movements? Which processes are connected and how can they reinforce each other? The WSL research program "Climate Change Impacts on Alpine Mass Movements" (CCAMM) is dedicated to precisely these questions. The researchers are investigating the most important correlations, modeling future risks and developing strategies to help mountain regions adapt to the new conditions in the best possible way (Bast, Bründl & Ortner, 2020).

The future will bring more melt forms and fewer weak layers

The simulations show that melting forms will become more common in the snowpack towards the end of the century, while the frequency of angular snow grains will decrease (Mayer et al., 2024).

Figure 1a) shows the snowpack structure in 2002 at measuring station WFJ2 (Weissfluhjoch, Davos; 2540 m above sea level). It can be seen that the snowpack is characterized by a predominance of built-up grain forms until May. Melt forms are only found in the form of thin, embedded crusts. Towards the end of winter, the proportion of rounded grains and melting forms increases more and more until the snow cover consists only of melting forms in spring and early summer.

Figure 1b) shows the simulated snow cover structure at the station in 2092, assuming the RCP8.5 (RCP = Representative Concentration Pathway) emission scenario. The RCP8.5 scenario assumes a very weak reduction in greenhouse gas emissions by the end of the century and a temperature increase of 4 - 5 °C relative to pre-industrial levels by 2100 (Michaelowa, 2016). It can be seen that the snow cover at the end of the century will be significantly more characterized by melting forms throughout the winter. In addition, the average snow depth on the Weissfluhjoch in Davos will also decrease. This trend can also be observed by the end of the century at all other stations that were analyzed as part of the project (Mayer et al., 2024).

Does less snow and fewer weak layers also mean fewer avalanches?

The type and frequency of avalanches will change significantly by the end of the 21st century. Dry snow avalanches will occur less frequently in the future, at almost all altitudes and in all climate scenarios. The decline is particularly strong in the most pessimistic scenario (RCP8.5): Here, the number of avalanche days with dry avalanches can be expected to decrease by up to 65 % (see Figure 2). The predicted higher temperatures in the snowpack mean that the temperature gradients are lower and the formation of weak layers tends to be reduced. This will also reduce the probability of dry slab avalanches in the future (Bründl & Bast, 2025).

The picture for wet snow avalanches is mixed: At lower altitudes, their number will decrease significantly, as precipitation at these altitudes will fall more frequently in the form of rain instead of snow in the future, meaning that snow cover will be present on fewer days. In higher regions above 2300 m, on the other hand, they will become more frequent, as warmer temperatures will lead to the snow cover being soaked more often in winter (Mayer et al., 2024). Under RCP8.5, wet snow activity at high altitudes initially increases significantly, but decreases again slightly towards the end of the century (see Figure 2). These opposing developments partially cancel each other out, so that the total number of avalanche days decreases only slightly by the end of the century, especially in the milder climate scenarios RCP2.6 and RCP4.5.

In the RCP8.5 scenario, however, a more significant decline is to be expected. Due to climate change, however, extreme weather events will become more frequent, which can lead to periods of extreme precipitation and thus to correspondingly pronounced avalanche activity. However, these events are very difficult to take into account in future forecasts. There is also a shift in seasonality: dry snow avalanches remain concentrated in the core winter months of January and February. In the case of wet snow avalanches, however, activity will start earlier in winter and be more evenly distributed over the months of December to March. At the same time, activity will decrease in late spring (April/May), shifting the peak of wet snow avalanches forward (Mayer et al., 2024).

Literature

Bast, A., Bründl, M. & Ortner, G. (2020). The impact of climate change on alpine mass movements: the WSL research program CCAMM, pp. 15-17.

Bründl, M. & Bast, A. (2025). WSL research program Climate Change Impacts on Alpine Mass Movements - CCAMM: Synthesis report. WSL Ber. 180. p. 404.

CH2018 (2018), CH2018 - Climate Scenarios for Switzerland, Technical Report, National Center for Climate Services, Zurich, 271 pp., ISBN: 978-3-9525031-4-0.

Mayer, S., Hendrick, M., Michel, A., Richter, B., Schweizer, J., Wernli, H. et al. (2024). Impact of climate change on snow avalanche activity in the Swiss Alps. The Cryosphere, 18(11), 5495-5517 . https://doi.org/10.5194/tc-18-5495-2024.

Michaelowa, A. (2016). Climate policy worldwide: Experiences with climate policy measures. Swiss Academies of Arts and Sciences . https://doi.org/10.5167/UZH-130447.