Landslide life-loss risk quantification based on historical fatalities

Life-loss risk estimates inform decisions that have dramatic impacts on individuals and communities in landslide hazard zones. Literature provides methods for making these estimates through multiplication of site-specific parameters. However, there is no method in the literature for calibrating those estimates, and regional context is needed to make efficient, fair, and affordable decisions. Therefore, we developed methods to quantify risk to individuals and groups based on regional historical fatality and hazard zone population data. The methods can be used to evaluate the accuracy of large sets of site-specific risk estimates, to assign quantitative risk values to buildings and hazard zones at a regional scale, to develop a long-term regional budget for landslide risk management, or to inform selection of a risk tolerance threshold that can inform where limited resources are invested in landslide mitigation. An example of the methods is provided for a case study of residential landslide risk in British Columbia, Canada. It estimates that there are between a few hundred and a few thousand people living with individual risk exceeding 100 micromorts (1 in 10 000) per year, and between 70 and 370 landslide hazard zones with annual probable life loss greater than 1E–3 (1 death in 1000 years), based on a historical fatality rate of 0.4 to 1.4 deaths per year across the entire province.