Identifying unrecognised risks to life from debris flows

Le résumé fourni par la source

Many debris-flow catchments pose an underappreciated hazard, especially where there are dwellings on debris-flow fans and other depositional areas. There is a need to make communities and those involved in community governance aware of situations where there may be a credible risk to life from debris flows. This needs to be simple and cheap to do, since funding is often not available to study unrecognised natural hazards. Here, we use published models to (1) estimate the threshold annual recurrence interval (ARI) for debris flows in a catchment, below which there is an unacceptable annual risk to life for the occupants of any dwellings, and (2) 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 acceptability threshold. Using four Aotearoa New Zealand (NZ) studies, we estimate a 95 % credible interval range for the ARIs of life-threatening debris flows of between 100 and 500 years. We show that given these credible intervals and precautionary but realistic assumptions about debris-flow behaviour and the vulnerability of dwellings and their occupants, catchments with no history of debris-flow activity can pose an unrecognised and unacceptable annual risk to life ( P =0.256 that the annual risk-to-life threshold of 1 in 1000 is exceeded).

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.