What can we learn about multi-hazard impacts from global disaster records?

Abstract. Recent studies have reported more extreme, compounding impacts from multi-hazards than from single hazards owing to complex interrelationships of hazard, exposure, and vulnerability. However, our current understanding of multi-hazard impacts is primarily based on case studies of individual events. To complement this, we examine disaster records of the global emergency events database EM-DAT for the period 2000–2018. We develop an algorithm to identify multi-hazard events using information on associated hazards as well as spatiotemporal relationships between disaster records. We find that 35 % of events are multi-hazard events and 61 % of hazards are associated with them, based on a spatial overlap of at least 50 % and a time lag of at most 3 months. The hazards associated with multi-hazard events account for 78 % of total damages, 83 % of total people affected, and 69 % of total deaths. We also statistically compare the impacts of hazard pairs, single hazards, and combinations of two single hazards. The analysis suggests distinct patterns of compounding impacts, which vary depending on hazard and impact type. We conceptualise four archetypes (“the whole is greater than the sum of its parts”, “the whole equals the sum of its parts”, “one part determines the whole”, and “the whole and the parts are limited by total impact”) to describe these patterns and to guide the integration of multi-hazard interrelationships into risk assessments. Across all archetypes, hazard pairs have at least as much impact as single hazards, but their impact can be higher than, comparable to, or lower than the combined impact of two single hazards. The uncertainties and limitations encountered in our study highlight the need for future research to improve data on multi-hazards and their impacts.