Multihazard

Multihazard refers to the coexistence or potential sequence of multiple hazards within a system or region, where hazards may occur simultaneously or in succession and interact to alter overall risk. It contrasts with single-hazard analyses that consider a lone threat in isolation. Multihazard thinking assesses physical, social, and economic vulnerabilities that shape how hazards propagate and affect communities, infrastructure, and ecosystems.

Hazard interactions can be categorized as concurrent, cascading, or compounding. Concurrent hazards occur at the same time, such as heavy rainfall during a heat event leading to riverine flooding and heat stress. Cascading hazards are triggered by an initial event, for example an earthquake triggering landslides and tsunamis or causing utility failures that worsen fire risk. Compounding hazards involve interdependent effects and feedbacks, such as drought increasing wildfire risk while reducing water supply for firefighting.

Addressing multihazard requires integrated risk assessment and planning, including hazard mapping for multiple threats, cross-sector coordination, resilience-focused design, land-use planning, and multihazard early warning systems. This approach supports emergency preparedness, evacuation planning, infrastructure design, and recovery planning.

Challenges include data gaps, uncertainties in interdependencies, modeling complex interactions, and coordinating across government agencies, municipalities, and communities. Climate change is expected to increase the frequency and intensity of several hazards, highlighting the importance of adaptive, flexible, and multihazard governance.