Exposure
What is exposure?
The situation of people, infrastructure, housing, production capacities and other tangible human assets located in hazard-prone areas.
UNDRR Terminology, 2017
Exposure is one of the defining components of disaster risk. Disaster risk is the consequence of the interaction between a hazard and the characteristics that make people and places vulnerable and exposed.
Why does it matter?
If a hazard occurs in an area of no exposure, then there is no risk.
Take the example of typhoons (tropical cyclones that occur in the Pacific Ocean). In 2013, two Category 5 typhoons hit the North West Pacific within weeks of each other. The difference in impact came down to what was in their path.
Typhoon Lekima, October 2013
Winds peaked at around 240 kilometres per hour, but it caused no impact on people or assets.
Typhoon Haiyan (Yolanda), November 2013
Winds peaked at 315 kilometres per hour. It affected 11 million people, causing more than 6,000 casualties and losses of more than US$1.5 billion.
The extent to which exposed people or economic assets are actually at risk is generally determined by how vulnerable they are, as it is possible to be exposed but not vulnerable. However, increasing evidence suggests that the case of extreme hazards the degree of disaster risk is a consequence of exposure more than it is a result of vulnerability.
For instance, in the case of the 26 December 2004 Indian Ocean tsunami all those exposed to tsunamis were at risk, no matter their income, ethnicity or social class. See a related story: What if Typhoon Jebi had been stronger and taken a different path?
Disasters are not natural. They are the result of a combination of natural and non-natural factors.
What drives exposure?
People and economic assets become concentrated in hazard-prone areas, so exposure changes over time and from place to place.
This happens through processes such as population growth, migration, urbanization and economic development. Previous disasters can also drive exposure by forcing people from their lands and into increasingly unsafe areas.
Many hazard-prone areas, such as coastlines, volcanic slopes and flood plains, attract economic and urban development, offer significant economic benefits or have cultural or religious significance to the people who live there.
As more people and assets are exposed, risk in these areas becomes more concentrated. At the same time, risk spreads as cities expand and development transforms previously sparsely populated areas.
Large volumes of capital continue to flow into hazard-prone areas, significantly increasing the value of exposed economic assets. If global exposure continues to trend upwards, it may increase disaster risk to dangerous levels.
How do we measure exposure?
Count the people and assets in an area, then combine them with their vulnerability to a given hazard.
Measures of exposure can include the number of people or types of assets in an area. These can be combined with the specific vulnerability and capacity of the exposed elements to any particular hazard to estimate the quantitative risks associated with that hazard in the area of interest.
Exposure modelling has a critical role to play in risk assessment. The information used to develop exposure data sets can be derived from various sources and methods, at very different resolutions, meaning how thoroughly the data are defined.
At the local scale
High-resolution data exist, but only for specific projects. Sources include councils, household surveys, aerial photos and architectural drawings. Crowd-sourcing has become a valuable tool for collecting local data and validating global data, though it is limited by the type and quality of data.
At the national scale
Complete, geospatially linked inventories of public infrastructure are rare and not publicly available in most developing countries. Statistical offices, census data, business listings, employment figures and geographic information system (GIS) data are common sources at regional scale and above.
At the global scale
Efforts to generate globally consistent data sets have increased. At this coarsest resolution, national statistical agencies, census data, global databases and remote sensing are used.
Methodologies need to consider that exposure evolves over time, through unplanned urbanization, demographic change and building practice. Exposure data over a large geographical area (low resolution) may hide the true picture at the local level.
How do we reduce exposure?
Economic exposure in high-hazard areas is trending upwards. If we do not reverse this trend, disaster risk is set to increase.
We need to act now to reduce exposure and to build capacity and resilience in areas of growing exposure.
Where can exposure be avoided?
Land use planning and location decisions keep people and assets out of harm's way in the first place.
What if it can't be avoided?
Planning must be accompanied by structural or non-structural methods for preventing or mitigating risk.
In the Boxing Day 2004 Indian Ocean tsunami, the only possible strategy to save lives would have been to reduce exposure through timely evacuation. That depends on reliable early warning systems and effective preparedness planning, followed by compensating for loss through insurance or other risk financing instruments.
Related sections on PreventionWeb
Last updated on: 6 November 2026