Why study cascading and linked multi-hazards?

At least one natural hazard affects approximately 19% of the world's landcover and affect over 50% of it's population (Dilley et al, 2005). These natural hazards often cause damage to human infrastructure, casualties, economic losses, homelessness, and many other detrimental effects. Hazard risk assessments currently exist to identify areas at risk from individual natural hazards. However, many areas of the world are at risk of more than one hazard type. According to the Hotspots report, over 790 million people are exposed to more than one natural hazard globally (Dilley et al, 2005).

Multi-hazard risk assessments (MHRA) are used to assess the risk from more than one hazard affecting an area. The approach used to assess risk from these individual hazards varies between countries and studies. Generally, the risk from individual hazards are assessed and the results summed to calculate the risk from multiple hazards. This is the simplest and least data demanding method of assessing the risk from multiple hazards. However, this approach does not account for the connections between hazards.

Hazards are not independent phenomena. They are natural processes, and as such are complex and affect each other. Often an initial hazard event will cause or trigger a subsequent natural hazard to occur. This is a cascading hazard event. The figure below demonstrates some of the existing links between natural hazards.

Cascading hazards are mentioned in the literature, but descriptions and explanations are rare. Perhaps due to the monodisciplinary of research, cascading hazards have not been investigated to great extent. Natural hazard literature tends to concentrate on specialist, isolated hazards or topics. Little research has been conducted on the broad topic of cascading hazards until recently. The importance of cascading hazard research has been highlighted in recent years because of multi-hazard events of international importance (e.g. Japan earthquake and triggered tsunami, March 2011).