Future winter snowfall and extreme snow events in the Pyrenees

Snowfall is a crucial climate variable in mountainous regions: it influences hydrological and ecosystem dynamics and has a major impact on socioeconomic activities. This study examines the future changes (2024 to 2100) in winter (December, January and February, included) snowfall and extreme snow events in the Pyrenees, using a high-resolution dataset (2.5 km) derived from multiple CMIP5 General Circulation Models (GCMs) under RCP4.5 and RCP8.5 greenhouse gas scenarios, forced with the SAFRAN model. Winter snowfall shifts are examined considering accumulated snowfall (SF), extreme snowfall (Percentile >95th; SF95) per season, and return period levels (RPs) based on fitting Generalized Extreme Value to annually maximum SF. The data indicate an overall decline in SF across the entire mountain range and at all elevations. Trend analysis reveals a statistically significant negative evolution of SF (Tau Mann-Kendall >0.3; p-value <= 0.05) for most of the mountain range under RCP8.5. Projections for the end of the 21st century (2080-2100 period) anticipate reductions ranging from -9 % (RCP4.5; 2500-3000 m) to -29 % (RCP8.5; 1000-1500 m) compared to the historical climate (1960-2006 period). SF95 projections range from +2 % (RCP4.5; 2500-3000 m) to -25 % (RCP8.5; 2500-3000 m) for the same periods. Annual maximum extreme snowfall RPs indicate decreases over the historical period, regardless of the scenario and elevation range. These changes are attributed to warming and declining precipitation (P), with maximum P reductions reaching reduction of -24 % for RCP8.5 (2080-2100 period). Differences among GCMs contribute to a variability of +/- 20 % around the average multi-model mean. These results anticipate major terrestrial ecosystem changes in the Pyrenees, including significant spatiotemporal changes in hydrological resources potentially affecting millions of people living in large lowland cities.