Elevation-dependent trends in extreme snowfall in the French Alps from 1959 to 2019

Abstract

Climate change projections indicate that extreme snowfall is expected to increase in cold areas, i.e., at high latitudes and/or high elevation, and to decrease in warmer areas, i.e., at mid-latitudes and low elevation. However, the magnitude of these contrasting patterns of change and their precise relations to elevation at the scale of a given mountain range remain poorly known. This study analyzes annual maxima of daily snowfall based on the SAFRAN reanalysis spanning the time period 1959-2019 and provided within 23 massifs in the French Alps every 300ĝ€¯m of elevation. We estimate temporal trends in 100-year return levels with non-stationary extreme value models that depend on both elevation and time. Specifically, for each massif and four elevation ranges (below 1000, 1000-2000, 2000-3000, and above 3000ĝ€¯m), temporal trends are estimated with the best extreme value models selected on the basis of the Akaike information criterion. Our results show that a majority of trends are decreasing below 2000ĝ€¯m and increasing above 2000ĝ€¯m. Quantitatively, we find an increase in 100-year return levels between 1959 and 2019 equal to +23ĝ€¯% (+32kgm-2) on average at 3500ĝ€¯m and a decrease of -10ĝ€¯% (-7kgm-2) on average at 500ĝ€¯m. However, for the four elevation ranges, we find both decreasing and increasing trends depending on location. In particular, we observe a spatially contrasting pattern, exemplified at 2500ĝ€¯m: 100-year return levels have decreased in the north of the French Alps while they have increased in the south, which may result from interactions between the overall warming trend and circulation patterns. This study has implications for natural hazard management in mountain regions.