Scenario-based risk assessment of interrelating geomorphic multi-hazards - the critical road infrastructure of the Brenner Corridor

Multi-hazard interrelations can amplify impacts on critical road infrastructure, yet their assessment remains challenging because hazard processes differ in spatial footprint, timing, relations and relevance for exposed elements. A central challenge is how to operationalise such assessments while accounting for hazard interrelations and potential wider consequences. This study develops a scenario-based GIS approach for assessing interrelating multi-hazard risk along linear infrastructure systems. The framework is applied to the Brenner Corridor, a major Alpine route between northern and southern Europe, considering debris flows, avalanches and flooding. Two scenarios are modelled, representing debris-flow-avalanche and flood-debris-flow interrelations. Hazard interrelations are formalised through transparent ordinal factors representing spatial, temporal and type-based relationships. These scenario-specific hazard layers are combined with a traffic-based exposure proxy and a functional vulnerability proxy to derive a relative road-segment multi-hazard risk index. Results indicate that risk patterns are not determined by hazard overlap alone, but by the interplay between process-specific hazard footprints, road hierarchy, exposure and functional vulnerability. In the Brenner Corridor, the debris-flow-avalanche scenario affects approximately 75% of the analysed road network, whereas the flood–debris-flow scenario affects only 13% but produces higher local maximum segment hazard values. The framework complements existing single-hazard approaches by providing an integrated perspective that supports hotspot prioritisation and scenario-based planning for mountain road infrastructure.