Defining Multi-Hazard

[With reference to proposed definition in ‘Information Document on Terminology for Disaster Risk Reduction’ of ‘multi-hazard early warning system’, page 52].

UNISDR Terminology - ‘Multi-Hazard’ [Download PDF of this briefing/discussion note]

Multi-hazard is used throughout the Sendai Framework for Disaster Risk Reduction (SFDRR), but there is currently no clear definition provided by the UNISDR. The latest draft of terminology, upon which we have been invited to comment, only includes a definition for 'multi-hazard early warning system', which is a very specific application of multi-hazard methodologies. While we welcome the substance behind multi-hazard early warning definition that “hazardous events may occur simultaneously or cumulatively over time, and taking into account the potential interrelated effects.”

In theory and in practice, multi-hazard is used regularly in three ways (i) the overlay of single hazards (i.e., hazards are discrete and independent); (ii) the identification of all hazards in a place and (iii) the identification of all hazards in a place and the interactions that may occur between them (i.e. hazards have interrelations). Single hazard approaches, including the overlay of multiple single hazards that are treated independently, could potentially underestimate risk, distort management priorities or increase vulnerability to other spatially relevant hazards. Approaches that consider multiple hazards and their potential interactions, although currently challenging and an important research gap, are more representative of the natural and build environment.

Indeed, the SFDRR refers to multi-hazard in contexts other than early warning systems, for instance ‘multi-hazard management of disaster risk’ and ‘decision-making to be inclusive and risk-informed while using a multi-hazard approach’. A clear definition of 'multi-hazard' divorced from the definition of early-warning systems would therefore help researchers, practitioners and policy makers to consider the full characteristics of multi-hazards (multiple hazards and their interactions) that are common within disasters at all spatial scales. Scientists, policy makers and practitioners continue to emphasise a multi-hazard approach to disaster risk reduction. A consistent, well communicated definition and understanding of what ‘multi-hazard’ is will ultimately contribute to a better understanding of disaster risk.

Suggested Definition:

Multi-hazard [or a multi-hazard approach]: An approach that considers more than one hazard in a given place (ideally progressing to consider all known hazards) and the interrelations between these hazards, including their simultaneous or cumulative occurrence and their potential interactions. Note that to progress from hazard potential to risk, a multi-hazard approach should also consider the dynamic nature of vulnerability, for instance following a primary hazard event, exposed assets will have an increased vulnerability to subsequent hazards.

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