Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> Following the projected increase in extreme precipitation, an increase in extreme snowfall may be expected in cold regions, e.g. for high latitudes or at high elevations. By contrast, in low/medium elevation areas, the probability to experience rainfall instead of snowfall is generally projected to increase due to warming conditions. In mountainous areas, despite the likely existence of these contrasted trends according to elevation, changes in extreme snowfall with warming remain poorly quantified. This paper assesses projected changes in heavy and extreme snowfall, i.e. in mean annual maxima and 100-year return levels, in the French Alps as a function of elevation and global warming level using a recent methodology based on non-stationary extreme value models. This methodology is applied to an ensemble of 20 adjusted GCM-RCM pairs from the EURO-CORDEX experiment under the scenario RCP8.5. available for each of the 23 massifs of the French Alps from 1951 to 2100, and every 300 m of elevations. Results are provided as relative or absolute changes computed w.r.t. current climate conditions, at the massif scale and averaged over all available massifs. Overall, mean annual maxima are projected to decrease below 3000 m and increase above 3600 m, while 100-year return levels are projected to decrease below 2400 m and increase above 3300 m. At elevations in between, values are on average projected to increase until +3 °C of global warming, and then decrease. At +4 °C, average relative changes in mean annual maxima and 100-year return levels respectively vary from −26 % (−7 kg m<sup>−2</sup>) and −15 % (−11 kg m<sup>−2</sup>) at 900 m, to +3 % (+3 kg m<sup>−2</sup>) and +8 % (+13 kg m<sup>−2</sup>) at 3600 m. Finally, for each global warming level, we compute the elevation threshold that separates contrasted trends, i.e. where the average relative change equals zero. This elevation threshold is projected to rise between +1.5 °C and +4 °C: from 3000 m to 3350 m for mean annual maxima, and from 2600 m to 3000 m for 100-year return levels. These results have implications for the management of risks related to extreme snowfall.
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