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

This study examines disaster records of the global emergency events database EM-DAT for the period 2000-2018, developing an algorithm to identify multi-hazard events using information on associated hazards as well as spatiotemporal relationships. This study comes in the wake of recent reporting of the extreme, compounding impacts from multi-hazards, owing to complex interrelationships of hazard, exposure, and vulnerability. However, current understanding of multi-hazard impacts is primarily based on case studies of individual events. This study aims to broaden this scope, to improve data on multi-hazards and their impacts.

The study found 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. The analysis suggests distinct patterns of compounding impacts, which vary depending on hazard and impact type - thus, the study conceptualises four archetypes to describe these patterns:

1. "the whole is greater than the sum of its parts"
2. "the whole equals the sum of its parts"
3. "one part determines the whole"
4. "the whole and the parts are limited by total impact"