Disaster risk
Disaster risk is widely recognised as the consequence of the interaction between a hazard and the characteristics that make people and places vulnerable and exposed.
What is disaster risk
There is no such thing as a natural disaster, but disasters often follow natural hazards.
Disasters are sometimes considered external shocks, but disaster risk results from the complex interaction between development processes that generate conditions of exposure, vulnerability and hazard. Disaster risk is therefore considered as the combination of the severity and frequency of a hazard, the numbers of people and assets exposed to the hazard, and their vulnerability to damage. Intensive risk is disaster risk associated with low-probability, high-impact events, whereas extensive risk is associated with high-probability, low-impact events.
Intensive risk
Disaster risk associated with low-probability, high-impact events, mainly linked to major hazards such as large earthquakes, cyclones and tsunamis.
Extensive risk
Disaster risk associated with high-probability, low-impact events — frequent, localised losses that are often hidden.
Resilience
The ability of communities, societies and systems to resist, absorb, accommodate and recover from disasters while improving wellbeing.
Disasters do not discriminate, but their impact does. They disproportionately affect the poorest and most vulnerable because they exacerbate structural inequalities.
Understanding disaster risk requires us to consider not only the hazard, our exposure and vulnerability, but also society's capacity to protect itself from disasters.
Five characteristics of disaster risk
To understand disaster risk, it is essential to recognise that it is:
- Forward looking the likelihood of loss of life, destruction and damage in a given period of time
- Dynamic: it can increase or decrease according to our ability to reduce vulnerability
- Invisible: it is comprised of not only the threat of high-impact events, but also the frequent, low-impact events that are often hidden
- Unevenly distributed around the earth: hazards affect different areas, but the pattern of disaster risk reflects the social construction of exposure and vulnerability in different countries
- Emergent and complex: many processes, including climate change and globalized economic development, are creating new, interconnected risks
Disasters threaten development
just as development creates disaster risk
Disasters are an indicator of development failures: disaster risk is a measure of the sustainability of development. Hazard, vulnerability and exposure are influenced by risk drivers, including poverty and inequality, badly planned urban development, climate change and environmental degradation.
Illustration: Risk dimensions, categories and components retrieved from Bangladesh INFORM Sub-National Risk Index 2022, UNDRR (2022)
Why does disaster risk matter?
Without action, disaster risk may increase to dangerous levels
Increasing exposure, high inequality, rapid urban development and environmental degradation are all pushing risk upward. Decades of research show disasters particularly affect the poorest and most marginalised, deepen social inequalities and harm economic growth.
Mortality risk is closely correlated with income level and quality of risk governance. While some countries have reduced deaths from floods and tropical cyclones, deaths from extensive risks are increasing — evidence of failed or skewed development and ill-adapted societies.
The private sector rarely considers disaster risk in its portfolio, yet the concentration of high-value assets in hazard areas has grown. Relative to income, low- and middle-income countries suffer the greatest losses. Disaster risk is a problem for people, businesses and governments alike. See more disaster statistics.
Hazards may be natural, but they don't have to turn into disasters. Disasters are the consequence of human decisions.
A municipal worker clears a street in Kolkata, India, after Cyclone Amphan (2020). The impacts of a hazard depend on how many people and assets lie in its path, and how prepared they are.
In most economies, 70–85% of overall investment is made by the private sector — making business decisions central to whether risk is created or reduced.
How do we measure disaster risk?
Identifying, assessing and understanding disaster risk is critical to reducing it
We measure disaster risk by analysing trends in past disaster losses — which show whether risk reduction is working — and by estimating future losses through risk assessment.
A comprehensive risk assessment considers the full range of potential events, their drivers and uncertainties. It starts with historical events, integrates forward-looking change such as climate change, and may consider rare events that science says could occur.
The three components of a risk assessment
Hazard
The probability of experiencing a certain intensity of hazard (e.g. earthquake, cyclone) at a location, including secondary perils such as liquefaction or storm surge.
Exposure
The stock of property and infrastructure exposed to a hazard, which can include socioeconomic factors.
Vulnerability
The susceptibility of exposed assets to damage. Fragility and vulnerability functions estimate damage, loss and social cost.
Ten principles for comprehensive risk assessment
Climate and disaster risks compound and cascade, so assessment needs a systemic perspective. UNDRR technical guidance (2022) proposes:
- 01Putting risk to human and ecological systems at the centre
- 02Fully accounting for the context of climate change
- 03Recognizing the complex and systemic nature of risks
- 04Applying inclusive risk governance
- 05Using multidisciplinary approaches to identify and select measures
- 06Using the concept of risk tolerance
- 07Addressing, minimising and averting risks through Nature-based Solutions
- 08Integrating risk across sectors and levels
- 09Strengthening risk communication, information and knowledge sources
- 10Using iterative and flexible processes
Four phases of a risk assessment
Following the ISO 31000 workflow:
Design the assessment to support decisions, reflecting existing goals, values and policy.
Identify relevant risks from existing knowledge and expert input.
Analyse hazards, exposure, vulnerabilities and cascading impacts, quantitatively and qualitatively.
Identify urgent actions and measures based on the risk tolerability defined by communities.
Illustration showing phases of a risk assessment, retrieved from Technical guidance on comprehensive risk assessment and planning in the context of climate change, UNDRR (2022).
Deterministic and probabilistic risk
Risk can be assessed deterministically (single or few scenarios) or probabilistically (the likelihood of all possible events). Probabilistic models “complete” historical records by recreating large numbers of synthetic events, giving a fuller picture of future risk. While data remain incomplete, these models can indicate the likely order of magnitude of risks — provided their uncertainty is recognised. Learn more.
The chart shows the median contribution of hazard, exposure and vulnerability to moderate, severe and extreme drought risk.
Hazard was the main driver in all scenarios, but exposure and vulnerability contributed more in countries where risk is increasing — highlighting the need for tailored, regional approaches.
Risk models are a representation of reality, but are only as good as the data used.
Scoring risk severity with a risk matrix
A risk matrix multiplies a likelihood score (1–5) by an impact score (1–5) to give a final risk score (1–25) for each hazard, which is then categorised into a risk level. See Strengthening risk analysis for humanitarian planning.
Illustration: Risk matrix retrieved from Strengthening risk analysis for humanitarian planning, UNDRR (2022).
Who uses risk information?
Insurance
Solvency capital of most non-life insurers is strongly influenced by catastrophe risk exposure.
Construction
Quantifying lifetime risk to buildings, bridges and critical facilities drives building codes.
Land-use and urban planning
Robust flood risk analysis drives investment in flood protection and changes in insurance.
Communities
Living memory and oral or written histories inform preparedness, evacuation and siting of facilities.
Risk is not static: it can change rapidly as hazard, exposure and vulnerability evolve. Decision makers need to engage today on the risk they face tomorrow.
How do we reduce disaster risk?
Prevent new risk, reduce existing risk and build resilience to residual risk
A country that ignores disaster risk and lets it accumulate undermines its own future development. One that invests in disaster risk reduction can reduce potential losses over time, freeing critical resources for development. Evidence from Colombia, Mexico and Nepal shows that such investment is effective.
Because businesses, the public sector and civil society all take part in creating risk, reducing it is a shared value — requiring a people-centred, multi-sector approach that builds resilience to multiple hazards and a culture of prevention.
Disaster risk reduction (DRR)
The policy objective of anticipating and reducing disaster risk.
Disaster risk management (DRM)
The implementation of DRR — building capacity to anticipate, cope with, resist and recover from disasters.
Residual risk
Risk that cannot be effectively reduced, which societies must be supported to withstand.
By strengthening capacities to absorb and recover, several countries have reduced mortality from floods and tropical cyclones, and many high-income countries have reduced extensive risk. However, losses from extensive risk are trending up in low- and middle-income countries. Explore ways to reduce and manage disaster risk.
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