Assessing rockfall risk over time: evolving scenario analysis and management of protective structures

Quantitative Risk Assessment (QRA) for rockfall hazards is a dynamic and evolving process that must consider not only the current state of the rock slope face and the elements at risk, but also how these conditions may change over time. Traditional single-scenario risk assessments often fail to capture the increasing or shifting nature of risk, potentially leading to under preparedness or inefficient allocation of mitigation resources. This study presents a time-integrated QRA framework that incorporates a comprehensive range of possible rockfall scenarios. It also proposes strategies to address their evolution, driven by natural processes such as weathering, erosion, and climate change, as well as human-induced factors such as land-use modifications and infrastructure development. To demonstrate the practical application of this methodology, two case studies at different scales, each requiring varying levels of input data accuracy, are presented. The first case study, at regional scale, applies the framework to the provincial road network of Bolzano, integrating long‑term trends in recorded rockfall arrivals, variations in traffic exposure and the time‑dependent reliability of mitigation measures into a corridor‑scale risk model. The second case study, at slope scale, examines a road section in the Eastern Alps where a windthrow event and subsequent geomorphological disturbances progressively altered block‑detachment conditions, reach probabilities and event frequencies, requiring repeated updates to the risk assessment. These examples highlight how integrating the temporal evolution of risk into QRA enhances the accuracy of hazard assessments and supports more strategic, sustainable, and cost-effective risk management.