Abstract
Abstract. Projecting changes in snow cover due to climate warming is important for many societal issues, including the adaptation of avalanche risk mitigation strategies. Efficient modelling of future snow cover requires high resolution to properly resolve the topography. Here, we introduce results obtained through statistical downscaling techniques allowing simulations of future snowpack conditions including mechanical stability estimates for the mid and late 21st century in the French Alps under three climate change scenarios. Refined statistical descriptions of snowpack characteristics are provided in comparison to a 1960–1990 reference period, including latitudinal, altitudinal and seasonal gradients. These results are then used to feed a statistical model relating avalanche activity to snow and meteorological conditions, so as to produce the first projection on annual/seasonal timescales of future natural avalanche activity based on past observations. The resulting statistical indicators are fundamental for the mountain economy in terms of anticipation of changes. Whereas precipitation is expected to remain quite stationary, temperature increase interacting with topography will constrain the evolution of snow-related variables on all considered spatio-temporal scales and will, in particular, lead to a reduction of the dry snowpack and an increase of the wet snowpack. Overall, compared to the reference period, changes are strong for the end of the 21st century, but already significant for the mid century. Changes in winter are less important than in spring, but wet-snow conditions are projected to appear at high elevations earlier in the season. At the same altitude, the southern French Alps will not be significantly more affected than the northern French Alps, which means that the snowpack will be preserved for longer in the southern massifs which are higher on average. Regarding avalanche activity, a general decrease in mean (20–30%) and interannual variability is projected. These changes are relatively strong compared to changes in snow and meteorological variables. The decrease is amplified in spring and at low altitude. In contrast, an increase in avalanche activity is expected in winter at high altitude because of conditions favourable to wet-snow avalanches earlier in the season. Comparison with the outputs of the deterministic avalanche hazard model MEPRA (Modèle Expert d'aide à la Prévision du Risque d'Avalanche) shows generally consistent results but suggests that, even if the frequency of winters with high avalanche activity is clearly projected to decrease, the decreasing trend may be less strong and smooth than suggested by the statistical analysis based on changes in snowpack characteristics and their links to avalanches observations in the past. This important point for risk assessment pleads for further work focusing on shorter timescales. Finally, the small differences between different climate change scenarios show the robustness of the predicted avalanche activity changes.
Highlights
In temperate mountainous areas, snow is a major component of the water cycle
We introduce results obtained through statistical downscaling techniques allowing simulations of future snowpack conditions including mechanical stability estimates for the mid and late 21st century in the French Alps under three climate change scenarios
This can be achieved by studying links between climate and snow cover for present conditions, which includes an assessment of changes already measurable using various observation series, and by quantifying changes to be expected in the future, using snow and regional climate simulations fed by global climate change scenarios
Summary
Snow is a major component of the water cycle. As an important element of the critical zone at the interface between atmosphere, geosphere, ecosystems and human societies, it has key impacts on geomorphological processes, biodiversity and the tourism industry. On the basis of these works, the current study aims at producing a detailed description of projected changes of snowpack characteristics expected in the French Alps in the mid and late 21st century, including latitudinal, altitudinal and seasonal gradients and under three greenhouse gas (GHG) emissions scenarios These results, expanding on those of Rousselot et al (2012), are used to feed statistical models developed by Castebrunet et al (2012) to link avalanche activity and the snow and meteorological data produced by the SAFRAN–Crocus–MEPRA (Système d’Analyse Fournissant des Renseignements Adaptés à la Nivologie–Crocus– Modèle Expert d’aide à la Prévision du Risque d’Avalanche) model chain (see below). Future changes in avalanche activity on annual/seasonal timescales are compared to the 1960–1990 control period on the basis of natural, observed avalanche activity and simple but robust statistical relations
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