CPD Climate of the Past Discussions CPD 1814-9359 Copernicus GmbH Göttingen, Germany 10.5194/cpd-7-4173-2011 Snow and weather climatic control on snow avalanche occurrence fluctuations over 50 yr in the French Alps Castebrunet H. 1 2 Eckert N. 2 Giraud G. 1 Météo-France/CNRS, CNRM-GAME URA1357, CEN, Domaine Universitaire, 1441 rue de la Piscine, 38400 Saint Martin d'Hères, France Cemagref UR ETGR, 2 rue de la papeterie, 38402 Saint-Martin d'Hères, France 05 12 2011 7 6 4173 4221 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.clim-past-discuss.net/7/4173/2011/cpd-7-4173-2011.html The full text article is available as a PDF file from http://www.clim-past-discuss.net/7/4173/2011/cpd-7-4173-2011.pdf

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. Modeled snow and weather data for different elevations and aspects are considered as covariates that explain actual observed avalanche counts, modeled 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.

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