Assessing the impact of climate change on snow avalanche activity in France over the last 60 winters using hierarchical Bayesian change point models

This study focuses on avalanche occurrences and runout altitudes in France over the last 61 winters. For both variables, the interannual fluctuations possibly resulting from climate change are quantified using a hierarchical nonlinear analysis of variance. Bayesian inference is performed using Markov Chain Monte Carlo simulations. No systematic modifications in occurrence regime could be found, which suggests that climate change has recently had little impact on the avalanching rhythm in France. Significant temporal patterns that consist in complex combination of abrupt changes and pseudo-periodic cycles of approximately 15 years have though been highlighted. On the contrary, a change in runout altitude regime has occurred in France. Between 1946 and 1976, a decrease of 55 m has affected the mean runout altitude, but the probability of a high magnitude event has remained con-stant. After the change point, the mean runout altitude has regained its initial state, whereas the prob-ability of a high magnitude avalanche has been divided by two. Avalanche occurrences and runout altitudes are therefore differently influenced by changes in constraining climatic factors. One possible explanation is that dry snow avalanches are progressively replaced by wet snow avalanches because of climate worming, thus keeping constant the number of events, but reducing their magnitude by modifying snow rheology. To confirm this statement, further research is in progress to compare and explicitly correlate the obtained annual effects with climatic data.