A modelling approach for deriving continuous intensity-frequency and loss-frequency curves in the area of impact for robust hazard and risk assessment

Comprehensive and robust hazard and risk assessments require information beyond the current hazard map information. Current hazard mapping is usually limited to selected return periods and these return periods are commonly based on the return period of release and not the return period of impact.

We present a modelling approach, which allows to derive probability-based hazard information at any location in avalanche-prone areas. Such an event-based modelling approach provides continuous intensity-frequency-curves at any location and allows to calculate continuous loss-frequency-curves for individual objects as well as for groups of objects. It is therefore suited for comprehensive hazard and risk assessments.

The modelling approach is based on probabilistic seismic hazard analyses, which are common practice for seismic hazard and risk assessments since several decades. Continuous intensity-frequency information is required for hazard assessment and continuous loss-frequency curves are required for risk assessment. Therefore, we simulate numerous possible avalanches, covering the entire range of release volumes, from small to very large, and various possible model parameters. The probabilities of the different avalanche events are based on the exceedance probabilities of different snow accumulation heights, represented by the three-day snow accumulation, which is also the key information used for the generation of traditional hazard maps. The combined evaluation of avalanche intensities and probabilities in the area of impact allows to derive continuous intensity-frequency-curves at any given location. This approach contrasts with the common practice of assigning the return period of a single release volume to all possible outcomes of this release volume. In combination with exposed values and their vulnerability functions, this modelling approach allows to derive continuous loss-frequency-curves for comprehensive risk assessment and risk communication.

We present the simulation results from a case study in the Bernese Oberland in the Swiss Alps. The case study results highlight the advantages of this new modelling approach in hazard and risk management and the additional analyses being possible with this new modelling approach.