The United Nations Office for Disaster Risk Reduction (UNDRR) is highlighting the growing importance of compound risk, in which multiple hazards or risk drivers interact and create impacts that can be greater than those produced by individual events.

The concept is particularly important as climate change, rapid urbanization and environmental degradation increasingly overlap. UNDRR and disaster-risk experts say these interacting pressures can make communities more vulnerable and complicate emergency response and recovery.

What Is Compound Risk?

Compound risk occurs when two or more hazards or risk factors interact, either at the same time or in succession. The combined consequences can exceed the impact expected from each hazard separately.

A heatwave, for example, can increase pressure on electricity and water supplies while also raising the risk of heat-related illness. If flooding occurs during or after such conditions, communities can face additional damage, health threats and disruptions to essential services.

The interaction between hazards is therefore an important part of modern disaster-risk planning.

Climate Change Can Increase Hazard Pressure

Climate change is one of the major drivers identified in discussions about compound risk. Rising temperatures can intensify heat-related hazards, while changing rainfall patterns can contribute to flood and drought risks in different regions.

UNDRR has warned that climate-related hazards are becoming more intense and frequent in many parts of the world. When these hazards meet high exposure and vulnerability, the likelihood of a disaster increases.

Recent research has also highlighted the growing threat of overlapping climate extremes in cities, including heatwaves, floods and droughts.

Urbanization Adds Another Layer of Risk

Rapid and poorly planned urban growth can increase exposure to hazards. Expanding cities often replace natural surfaces with roads, buildings and other infrastructure, reducing the ability of land to absorb rainfall and retain water.

Dense urban environments can also trap heat, increasing the intensity of heat exposure. UNDRR has identified urbanization, land-use decisions and infrastructure conditions as important factors in understanding modern disaster risk.

As populations and economic activity become increasingly concentrated in cities, a single extreme event can affect large numbers of people and critical infrastructure simultaneously.

Environmental Degradation Can Magnify Impacts

Damage to ecosystems can further increase disaster vulnerability. The loss of forests, wetlands and other natural systems can remove important buffers that help absorb water, reduce erosion or moderate environmental extremes.

UNDRR’s disaster-risk assessments emphasize the importance of protecting natural infrastructure and using nature-based solutions as part of broader resilience strategies.

Environmental degradation can therefore act as a risk multiplier, particularly when combined with climate-related hazards and high levels of human exposure.

Heatwaves and Floods Can Create Multiple Consequences

The combination of extreme heat and flooding illustrates why compound risk can be difficult to manage.

Heatwaves can increase illness and mortality, raise electricity demand and place pressure on water resources. Flooding can cause injuries, displacement, infrastructure damage and increased risks from waterborne diseases. When multiple pressures occur together or in close succession, essential services can face additional strain.

The consequences can extend beyond immediate physical damage, affecting healthcare systems, economic activity, ecosystems, animals and public utilities.

Disaster Planning Needs a Multi-Hazard Approach

UNDRR’s broader disaster-risk work emphasizes that governments and communities need to move beyond planning for hazards individually and consider how risks interact.

Measures such as early-warning systems, stronger infrastructure, risk-informed urban planning, ecosystem protection and improved disaster data can help reduce vulnerability before extreme events occur. UNDRR also recommends learning from previous disasters to identify the underlying factors that made their impacts more severe.

A recent UNDRR publication on urban resilience similarly emphasizes integrated planning, reliable risk information, coordinated governance, investment and community participation as important elements of preparedness.

Growing Challenge for Cities and Communities

Compound risk is becoming an increasingly important issue for disaster-management authorities because hazards do not always occur in isolation. Climate change, urban development and environmental pressures can interact across sectors and geographical areas.

Understanding these connections can help governments identify vulnerable communities, strengthen infrastructure and prepare emergency systems for multiple simultaneous or cascading impacts.

As extreme weather risks evolve, disaster preparedness will increasingly depend on anticipating not just individual hazards, but the combined effects of several risks acting together.