Abstract
Abstract. Snow avalanche activity is controlled to a large extent by snow and weather patterns. However, its response to climate fluctuations remains poorly documented. Previous studies have focused on direct extraction of trends in avalanche and winter climate data, and this study employs a time-implicit method to model annual avalanche activity in the French Alps during the 1958–2009 period from its most representative climatic drivers. Modelled snow and weather data for different elevations and aspects are considered as covariates that explain actual observed avalanche counts, modelled instability indexes, and a combination of both avalanche activity indicators. These three series present relatively similar fluctuations over the period and good consistency with historically harsh winters. A stepwise procedure is used to obtain regression models that accurately represent trends as well as high and low peaks with a small number of physically meaningful covariates, showing their climatic relevance. The activity indicators and their regression models seen as time series show, within a high interannual variability, a predominant bell-shaped pattern presumably related to a short period of colder and snowier winters around 1980, as well as a very slight but continuous increase between 1975 and 2000 concomitant with warming. Furthermore, the regression models quantify the respective weight of the different covariates, mostly temperature anomalies and south-facing snowpack characteristics to explain the trends and most of the exceptional winters. Regional differences are discussed as well as seasonal variations between winter and spring activity and confirm rather different snow and weather regimes influencing avalanche activity over the Northern and Southern Alps, depending on the season.
Highlights
Mountainous areas and high latitudes, are very sensitive to climate change
Among the 8 yr for which both the composite index (CI) and its associated regression model exceed the 80th percentile threshold at the whole Alps scale, 1962/1963 is the only winter for which the threshold is exceeded by the CI, the MEPRA index, and their regression models, but not by the Enquete Permanente sur les Avalanches ” (EPA) avalanche counts, indicating that this year was characterized by unstable snow and weather parameters rather than by actual intense activity, or possibly by only high-altitude activity missed by the EPA report
This paper has proposed a time-implicit approach for the detection of abnormal years and low-frequency trends for various indicators of natural avalanche occurrence
Summary
Mountainous areas and high latitudes, are very sensitive to climate change. Variations in mountain climate during the 20th century are fairly well documented in the European Alps and in other mountainous regions of the globe (e.g. Beniston et al, 1997). Application of runout elevations and avalanche counts from the exceptional French avalanche chronicle called the Enquete Permanente sur les Avalanches (EPA, see section) has given promising preliminary results This purely data-oriented approach is limited in that the climatic relevance of the extracted temporal signals is not guaranteed. The objective is to detect exceptional winters and trends with climatic relevance This is applied to the whole French Alps over 51 yr, based on avalanche counts from the EPA report and refined snow and weather data as well as instability indexes issued by the SAFRAN-CROCUS-MEPRA model chain (see below).
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