The snow avalanches risk on Alpine roads network

Road accessibility is highly strategic for the maintenance of economic activities but also for the emergency services. In mountains, snow avalanches are a particularly strong threat because, in addition to the victims and direct damage, they cause a loss of accessibility more or less prolonged when the networks are already strongly altered by seasonal closures. Specifically, risk to traffic roads caused by snow avalanches has been very rarely assessed at a regional scale. To assess the physical, human and functional vulnerabilities of road networks in three Alpine departments (Alpes-de-Haute-Provence, Hautes-Alpes, Alpes-Maritimes), the first step of this research was to geo-locate and harmonize within a GIS all information sources about the consequences of avalanches on roads. This allowed identifying the road impacts of avalanches since 1937, to characterize the intensity and typology of damages and to evaluate the functional vulnerability of networks. The second step was to produce simple risk indexes of dysfunction and isolation at this regional scale. These indicators were modeled using the graph theory in a GIS framework, integrating avalanche activity indicators derived from the past activity with the road network. The obtained output maps should facilitate the decision support for crisis management and a comparative spatial analysis at the regional scale.