Scenario based assessment of interrelating multi-hazards affecting the Brenner Corridor’s road infrastructure

Past events demonstrate that multi-hazard situations can lead to amplified impacts when single hazards interact. Such interrelations are often constrained within clear temporal or spatial boundaries and can be interpreted from a systemic perspective. For example, impact-chain approaches can be used to map and interrelate triggering hazards, secondary processes, and exposed elements including respective vulnerabilities. Analysing historical events therefore provides valuable insight into plausible hazard interrelations and experienced consequences relevant for present and future risk assessments.

Transferring this systemic understanding from site-specific event-based analyses to an extended spatial scale, however, remains challenging. Scale-dependent generalisation can lead to a loss of process detail, while the quantification of hazard interrelations is often based on hypothetical yet plausible scenarios rather than deterministic forecasts. In this context, the aim is not to predict specific events and respective consequences, but rather to explore potential outcomes under defined hazard interrelation assumptions.

Here, a stepwise multi-hazard risk assessment framework is applied, progressing from (i) identification of relevant hazards and their spatial and temporal interrelations, to (ii) the evaluation of exposed elements and their vulnerability, and finally (iii) the derivation of a multi-hazard risk index. The framework is applied to the transalpine Brenner Corridor between Innsbruck and Bolzano, a key European transport axis. Snow avalanches, debris flows, and river floods are combined in an interrelation-aware manner to account for co-occurrence, pre-conditioning, and trigger-related effects. Historical event analysis along the corridor indicates that debris flows dominate hazard occurrence during summer months and generally don’t interfere with motorway infrastructure, but with the federal and local roads instead.

The exposed transport infrastructure is analysed using an OpenStreetMap-based road network dataset, which is restructured into road classes including motorway, secondary, residential and unclassified roads. Functional vulnerability indices are derived to reflect differences between road segments, including structural characteristics, network redundancy, and traffic-related exposure. To capture variability in exposure, minimum, average, and maximum traffic scenarios are considered for motorway and federal road segments. The results highlight how accounting for hazard interrelations and traffic-dependent exposure alters the spatial risk index for road segments, underlining the importance of interrelation-aware multi-hazard risk assessments for critical alpine infrastructure.