Trends in avalanche problems in the French Alps between 1958 and 2020

Climate warming forces snow cover changes, which impact natural hazards such as avalanches. While significant changes of observed avalanche activity or runout distance could be documented and linked to climate drivers, little is known about potential changes of conditions in avalanche release areas as data are scarce. Using demonstrated methodology to simulate avalanche problems from reanalysis weather data, we assess how characteristics of avalanche danger evolved between 1958 and 2020 in typical release areas of the French Alps. During this period, the number of situations with natural release and the frequency of new snow situations did not change significantly at typical release area elevation at the scale of the French Alps. The frequency of persistent weak layer problems declined by about 3 days and the simulated onset date of wet-snow activity advanced by about 3 weeks. After a change point at the end of the 1980s, the frequency of new snow and the onset date of wet-snow situations changed significantly, and substantial differences between regions appeared, highlighting regional effects of climatic change. New snow situations increased by about 1 day in 10 years, in particular at higher elevations in the inner-Alpine climate regions and the wet-snow onset date advanced rapidly, by about 12 days in 10 years, in particular in the northern climate regions. Broad and regional patterns of change in avalanche problems are in line with documented atmospheric warming and changes in mean and extreme snowfall in the area. Our findings add to the already existing information on the response of avalanche activity to climate change, describing changes in avalanche danger at different spatio-temporal scales. Moreover, we provide a methodology amenable to other mountain areas of the world, where avalanche observations are lacking but input to snow cover modelling is available. In a logical next step this methodology will be applied to regional climate projections to assess future trends of avalanche danger characteristics.