Snow and weather climatic control on snow avalanche occurrence fluctuations over 50 yr in the French Alps

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.

Projected changes of snow conditions and avalanche activity in a warming climate: the French Alps over the 2020–2050 and 2070–2100 periods

“…Sources of uncertainties and systematic errors in the estimation of certain variables are nu- merous and detailed in previous studies (e.g. Eckert et al, 2010c;Castebrunet et al, 2012).…”

“…This reanalysis, complemented for several years beyond the end date of the ERA-40 data set using large-scale meteorological fields from Météo-France operational numerical weather prediction models, covers the period from 1958 to 2009 and is referred to as the model run. For the present study, the variables given below were used, similar to those described by Castebrunet et al (2012). They concern the 23 alpine massifs (Fig.…”

“…On the other hand, this index is less sensitive in the case of instability being lower, leading to sporadic events on the massif scale, as discussed in Castebrunet et al (2012).…”

“…These results, expanding on those of Rousselot et al (2012), are then used to feed statistical models developed by Castebrunet et al (2012) to link avalanche activity and the snow and meteorological data produced by the SAFRAN-Crocus-MEPRA (Système d'Analyse Fournissant des Renseignements Adaptés à la Nivologie-CrocusModèle Expert d'aide à la Prévision du Risque d'Avalanche) model chain (see below). Hence, future changes in avalanche activity on annual/seasonal timescales are compared to the control period on the basis of natural, actually observed avalanche activity and simple but robust statistical relations.…”

A 240-year history of avalanche risk in the Vosges Mountains based on non-conventional (re)sources

“…This study takes place in a well-defined climatic context: the recent anthropogenic warming over the last few decades and the end of the Little Ice Age in the second half of the nineteenth century (Grove, 1988(Grove, , 2001. The exact effect of such changes on the spatio-temporal distribution of recorded events is difficult to determine (Eckert et al, 2010;Castebrunet et al, 2012). However, colder winter temperatures until the middle of the nineteenth century enabled the development of an important snowpack at medium (∼ 900 m a.s.l.)…”