Exploratory analysis of the annual risk to life from debris flows
Abstract. Debris flows are hazardous yet often unrecognised and poorly understood by the public and natural hazards community. Some catchments generate debris flows with average recurrence intervals (ARIs) <10 years, but most debris flow catchments have ARIs ranging from decades to millennia. Consequently, many debris flow catchments pose an underappreciated hazard, especially where there are dwellings on debris flow fans and other depositional areas.
Here, we describe how to use simple and well-accepted methods to:
- Make a preliminary identification of catchments that are susceptible to debris flows.
- Estimate the threshold ARI for debris flows in a catchment below which there is an unacceptable annual risk to life for the occupiers of any dwellings.
- Identify the "window of non-recognition" where debris flows are sufficiently infrequent within a catchment that it is not recognised as susceptible, yet frequent enough that the risk to life exceeds the accepted threshold.
- Explore the influence of the important parameters driving the annual risk to life from debris flows.
We show that, given precautionary but realistic assumptions about debris flow hazards and the vulnerability of dwellings and their occupants, catchments with no history of debris flow activity can pose an unrecognised and unacceptable risk to life.
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