Spatio-temporal variability of avalanche risk in the French Alps

Abstract

Avalanche risk changes through time due to climate, landscape and socio-environmental transformations. These drivers exhibit space-time variations as function of local peculiarities that may alter local avalanche risk trajectories. Here, we use an integrative methodology to track the co-evolution of the socio-economic, land cover and climatic drivers of avalanche risk and its components in three upper basins of the French Alps: the Upper Maurienne valley, the Guil valley and the municipality of Valloire. The analysis, based on data from 1860 to 2017, focuses on avalanche-prone terrain defined as the maximal extension of avalanches potentially occurring on all paths of the French avalanche cadaster. Avalanche occurrence numbers have likely increased over the last decades, more strongly at higher elevation. By contrast, a quasi-complete afforestation of avalanche-prone areas took place in the Guil valley, whereas, in the Upper Maurienne and Valloire, afforestation remains incomplete. This suggests a significant increase of protection from avalanches for people downslope due to the presence of forests in the Guil valley only. In parallel, recent expansion of urban areas in avalanche-prone terrain is prominent in the Upper Maurienne, and more modest and controlled in the Guil valley and in Valloire. Hence, overall, avalanche risk for buildings and their inhabitants have locally slightly decreased over the study period in the Guil valley, remained rather stationary in Valloire and has rather strongly increased in the Upper Maurienne. This demonstrates the crucial role of local dynamics in avalanche risk evolution. Our results help in understanding the complex patterns resulting in mountain risks changing faster than ever and very differently from one location to another, which may, in turn, contribute to the development of improved disaster risk reduction strategies.