Too simplistic

The assumption that the diminishing snow cover in the mountains during the winter season will lead to less avalanches is too simplistic, according to a recent study for the Swiss Alps. Mere knowledge about changes in duration and depth of the seasonal snow cover is not sufficient to determine the effect of climate change on snow avalanche occurrence, the authors of this study argue. They highlight the importance of distinguishing between dry- and wet-snow avalanches.

Layering is a key factor

The stability of a snowpack not only depends on its thickness, but also on the vertical layering of the snowpack under the influence of factors such as precipitation, temperature, wind, and radiation throughout a winter season. This layering is a key factor in the formation of snow avalanches.

For wet- and dry-snow avalanches, the underlying physical processes are different. Dry-snow avalanches mostly release during or shortly after a snowstorm, or by skiers. Wet-snow avalanches, on the other hand, form when liquid water from melting or rain-on-snow events infiltrates the snowpack and reduces the strength of existing weak layers. Climate change will have a different impact on these processes, and therefore on the occurrence of wet- and dry-snow avalanches.

Less avalanches

The authors made future projections of changes in avalanche activity by feeding climate model projections into a model that simulates the vertical snow stratigraphy over time.

The study shows that the occurrence of dry-snow avalanches will indeed decline this century, but this decline will be partially compensated for by an increase in wet-snow avalanche activity. Currently, the number of avalanche days in the Swiss Alps is 45–75 per year. This number may decrease by up to 65% by the end of the century under a high-end scenario of climate change. On the other hand, under the same scenario, the number of wet-snow avalanche days may increase by up to 30%, as the snowpack is more frequently wetted and weakened by meltwater or rain.

As a result, the net effect the authors anticipate across a range of climate change scenarios is a reduction in the total avalanche activity ranging from under 10% to as much as 60% by the end of the century.

These findings are supported by observations. Rising temperatures have led to a decrease in the number and size of avalanches, and to an increase in the proportion of wet-snow avalanches.

Source: Mayer et al., 2024. Impact of climate change on snow avalanche activity in the Swiss Alps. The Cryosphere 18: 5495–5517.