Medium-Scale Multi-hazard Risk Assessment of Gravitational Processes

This section discusses the analysis of multi-hazards in a mountainous environment at a medium scale (1:25,000) using Geographic Information Systems. Although the term ‘multi-hazards’ has been used extensively in literature there are still very limited approaches to analyze the effects of more than one hazard in the same area, especially related to their interaction. The section starts with an overview of the problem of multi-hazard risk assessment, and indicates the various types of multi-hazard interactions, such as coupled events, concatenated events, and events changing the predisposing factors for other ones. An illustration is given of multi-hazards in a mountainous environment, and their interrelationships, showing triggering factors (earthquakes, meteorological extremes), contributing factors, and various multi-hazard relationships. The second part of the section gives an example of a medium scale multi-hazard risk assessment for the Barcelonnette Basin (French Alps), taking into account the hazards for landslides, debris flows, rockfalls, snow avalanches and floods. Input data requirements are discussed, as well as the limitations in relation to the use of this data for initiation modeling at a catchment scale. Simple run-out modeling is used based on the energy-line approach. Problems related to the estimation of temporal and spatial probability are presented and discussed, and methods are shown for estimating the exposure, vulnerability and risk, using risk curves that expressed the range of expected losses for different return periods. The last part presents a software tool (Multi-Risk) developed for the analysis of multi-hazard risk at a medium scale.