Reanalysis of 44 Yr of Climate in the French Alps (1958–2002): Methodology, Model Validation, Climatology, and Trends for Air Temperature and Precipitation

TLDR

Since the early 1990s, Météo‑France has employed an automated system that combines three numerical models to simulate meteorological parameters, snow cover, and avalanche risk across French alpine regions. To overcome the lack of long‑term snow observations, the authors used the SAFRAN–Crocus–MEPRA model chain—normally applied to operational avalanche forecasting—to conduct and validate retrospective climate analyses for 1958–2002. The resulting 2‑m temperature and precipitation climatology indicates a temperate French Alpine climate governed by westerly flow, with a roughly linear altitude dependence, an overall ~1 °C rise in near‑surface temperature during 1958–2002—most pronounced between 1500–2000 m and correlated with the North Atlantic Oscillation—while precipitation variability precludes clear trend detection.

Abstract

Abstract Since the early 1990s, Météo-France has used an automatic system combining three numerical models to simulate meteorological parameters, snow cover stratification, and avalanche risk at various altitudes, aspects, and slopes for a number of mountainous regions in France. Given the lack of sufficient directly observed long-term snow data, this “SAFRAN”–Crocus–“MEPRA” (SCM) model chain, usually applied to operational avalanche forecasting, has been used to carry out and validate retrospective snow and weather climate analyses for the 1958–2002 period. The SAFRAN 2-m air temperature and precipitation climatology shows that the climate of the French Alps is temperate and is mainly determined by atmospheric westerly flow conditions. Vertical profiles of temperature and precipitation averaged over the whole period for altitudes up to 3000 m MSL show a relatively linear variation with altitude for different mountain areas with no constraint of that kind imposed by the analysis scheme itself. Over the observation period 1958–2002, the overall trend corresponds to an increase in the annual near-surface air temperature of about 1°C. However, variations are large at different altitudes and for different seasons and regions. This significantly positive trend is most obvious in the 1500–2000-m MSL altitude range, especially in the northwest regions, and exhibits a significant relationship with the North Atlantic Oscillation index over long periods. Precipitation data are diverse, making it hard to identify clear trends within the high year-to-year variability.