Exceedance probability of multiple natural hazards: risk assessment in China’s Yangtze River Delta

In recent years, greater attention has been given to advancing the theory and practice of assessing risk from multiple hazards. Most approaches calculate multi-hazard risk by aggregating risk scores for individual hazards and ignore the combined exceedance probability of multiple hazards. We address this problem by developing a simple and practicable multi-hazard risk assessment method that uses information diffusion theory to overcome the difficulty posed by a lack of historical or spatial data on natural hazard-induced loss. China’s Yangtze River Delta region is used as a demonstrative example, and the exceedance probability distribution of multi-hazard risk to human life was calculated using natural hazard disaster life loss data for 1950–2010. Multi-hazard risk to human life is mapped as exceedance probability at different mortality rates and loss at different risk return periods using a geographical information system. Results show that Hangzhou and Ningbo are at a relatively high risk from multiple natural hazards, and Shanghai is at a relatively low risk. For scenarios of 10-, 20- and 50-year risk return periods, there are no significant changes in the risk rank of the cities; Hangzhou, Ningbo and Zhoushan are at a relatively high risk, while Shanghai is at a relatively low risk.