Many populated areas are affected by a wide variety of natural hazards, such as volcanic eruptions, earthquakes, landslides, tsunamis, flooding, storms and wildfires. Many analyses of natural hazards take a single-hazards approach, which treat hazards as being separate and independent. In many cases, however, the spatial distributions of these hazards overlap and there can exist interaction relationships between hazard types.

Hazard interactions include: 
  • One hazard triggering one or more secondary hazard events (for example, an earthquake triggering a landslide or ground subsidence).
  • A series of triggering relationships forming a cascade or domino event (for example, an earthquake triggering a landslide, which dams a river and causes flooding).
  • One hazard changing the probability of an event occurring (for example, a wildfire removing vegetation and increasing the probability of landslides in the event of a major rainstorm).
  • The spatial/temporal coincidence of natural hazards, resulting in an impact greater than the sum of its component parts.
If assessing overall risk rather than the hazard potential, it is also important to consider temporal changes in vulnerability during successive hazards (for example, the destruction of buildings during an earthquake will make communities more vulnerable to hazard events such as hurricanes).
The understanding and constraining of such interaction relationships, and their impacts, are an important and topical area of research. Whilst many hazard assessment applications and research has often focused on single hazards in isolation, many populated areas, both rural and urban, are affected by multiple natural hazards with the potential for interacting relationships. An assessment that ignores these relationships has the potential to underestimate risk or increase vulnerability.

This collaborative group, drawn from multiple institutions, proposes that the holistic assessment of hazard potential must not only include the identification of all spatially relevant hazards, but also the interactions between them. This 'multi-hazard' approach gives a better understanding of the hazard potential faced by communities. Read more.