Snow avalanche impact pressure - vulnerability relations for use in risk assessment

Use of formal risk analysis to assess avalanche danger is currently limited by a lack of knowledge of how avalanche impact pressures damage structures and cause fatalities. That is, the vulnerability component of risk is poorly specified. In this paper we outline a method for deriving vulnerability values as a function of position downslope for a range of avalanche sizes. The method is based on the weighted average of vulnerability and uses an avalanche-dynamics model embedded within a statistical framework. The models seem to behave in a consistent manner. By allowing avalanche size and stopping position to vary and calculating vulnerability as a function of distance from the stopping position, vulnerability values are less approximate than the assumption of a constant vulnerability value for each individual size. When the assumptions underlying the impact pressure - vulnerability relation are perturbed, the results seem to be robust. The method outlined here should provide a way for avalanche experts to reformulate danger zones based on return period and impact pressure so that they are set within a risk framework.