Item: Incorporating a human risk factor in avalanche danger rating systems
Title: Incorporating a human risk factor in avalanche danger rating systems
Proceedings: Proceedings of the 2000 International Snow Science Workshop, October 1-6, Big Sky, Montana
Authors: Michael J. Jenkins and Elizabeth G. Hebertson, Bear River Avalanche Information Center, Logan, Utah
Abstract: Stability ratings describe the probability that natural avalanches may occur and the nature of the trigger reqUired for avalanche release. Hazard ratings describe the consequences to life and property if an avalanche is triggered. Avalanche danger rating systems use a 1-5 danger level scale that assesses the probability of natural and human triggered avalanches based on snowpack stability. There is variation in the use of the words risk, hazard, danger, but no definition considers the number and kinds of backcountry travelers and their patterns of use. The National Fire Danger Rating System (NFDRS) uses inputs of fuel, weather and topography to determine how a fire would behave (i.e. rate of spread, flame length and energy release) if ignited on a given day. Integral to the system, however is the likelihood of ignition on a particular day. Thus the final index of the NFDRS integrates potential fire behavior (hazard) with the probability of ignition (risk). This paper describes a process by which avalanche danger rating can be adjusted to account for risk where risk is a number related to the potential number and mode of travel of humans to which an area will be exposed during a given day. The proposed process is analogous to the NFDRS where avalanche triggers are considered similarly to sources of ignition. The inputs include the average number of human triggered avalanches in a forecast area, the relative contribution of each type of trigger (e.g. snowmobiler, skier, boarder etc.) and the number of triggers per day over a five-year period.
Keywords: avalanche danger rating, human risk
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