The DRI enables the calculation of the average risk of death per country in large- and medium-scale disasters associated with earthquakes, tropical cyclones and floods, based on data from 1980 to 2000. It also enables the identification of a number of socio-economic and environmental variables that are correlated with risk to death and which may point to causal processes of disaster risk.

In the DRI, countries are indexed for each hazard type according to their degree of physical exposure, their degree of relative vulnerability and their degree of risk.

The pioneering Disaster Risk Index (DRI) Analysis Tool measures the relative vulnerability of countries to three key natural hazards — earthquake, tropical cyclone and flood — and identifies development factors that contribute to risk, and shows in quantitative terms, just how the effects of disasters can be either reduced or exacerbated by policy choices. Our hope is that the toolx will both help generate renewed interest in this critical development issue and help bring together stakeholders around more careful and coherent planning to mitigate the impact of future disasters.

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Underlying the DRI is the concept that disaster risk is not caused by hazardous events per se, but rather is historically constructed through human activities and processes. As such the risk of death in a disaster is only partially dependent on the presence of physical phenomenon such as earthquakes, tropical cyclones and floods. In the DRI, risk refers exclusively to the risk of loss of life and excludes other facets of risk, such as risk to livelihood and to the economy. This is because of a lack of datasets available at the global scale with national resolution.

For an extreme physical event to be hazardous, by definition there has to be a subject to experience the hazard or the threat. For example, people, infrastructure and economic activities have to be located in an area where earthquakes occur. In the DRI, this relationship is expressed through the concept of physical exposure, referring to the number of people located in areas where hazardous events occur combined with the frequency of hazard events. Physical exposure is not an indicator of vulnerability, but is a condition sine qua non for disaster risk to exist. Without people exposed to hazardous events, there is no risk to human life.

Clearly however, greater physical exposure leads to greater loss of life. Assuming no change in other developmental conditions, a fivefold increase in the population living in a given flood plain would lead to a fivefold increase in mortality due to floods. Very high physical exposure in many countries reflects the concentration of population in hazard prone areas, itself a characteristic of the development process.

Physical exposure, however, is insufficient to explain risk. Countries with similar levels of physical exposure to a given hazard experience have widely differing levels of risk.

Vulnerability is the concept that explains why, with a given level of physical exposure, people are more or less at risk. In theory, vulnerability is modified by coping capacity and adaptive capacity. In the DRI, coping and adaptation are assumed to have been active in shaping recorded risk. Vulnerability brings together all these elements of human process in a single concept.

In the DRI, vulnerability refers to the different variables that make people less able to absorb the impact and recover from a hazard event. These may be economic (such as lack of reserves or low asset levels); social (such as the absence of social support mechanisms or weak social organisation); technical (such as poorly constructed, unsafe housing); and environmental (such as the fragility of ecosystems).

The way vulnerability is used in the DRI means that it also includes variables that may increase the severity, frequency, extension and unpredictability of a hazard. For example, deforestation may increase flood and landslide hazard in some contexts and destruction of coastal mangroves may increase cyclone hazard. Thus, those development activities that influence hazard as well as those that influence human vulnerability are represented in the DRI as vulnerability.

Included in the vulnerability index of the DRI are also those factors that may decrease vulnerability, such as appropriate development and urban planning, and specific actions to mitigate disaster losses, such as disaster preparedness and early warning systems.

In the DRI, it is assumed that the factors that make people vulnerable to earthquakes are not necessarily the same as those that make people vulnerable to floods or cyclones. Each corresponds to particular configurations of development activities. Due to the hazard specificity of people’s vulnerability, it is not conceptually possible to arrive at a global multi-hazard indicator of vulnerability.Rather the vulnerability indicators suggested by the DRI are always hazard specific.

The risk of death in a natural disaster is a function of physical exposure to a hazardous event and vulnerability to the hazard. People are more or less vulnerable to a given hazard depending on a range of social, economic, cultural, political and physical variables. The DRI has used the number of people actually killed by each hazard type in each country as a proxy for manifest risk. In other words, the occurrence of past disasters manifests, by definition, the existence of conditions of physical exposure and vulnerability.

The DRI, therefore, was able to calculate the relative vulnerability of a country to a given hazard by dividing the number of people killed by the number exposed. When more people are killed with respect to the number exposed, the relative vulnerability to the hazard in question is higher.

Disasters affect people’s lives and livelihoods in many ways. Depending on the type of hazard, houses may be damaged or destroyed, crops may be lost and land may be eroded or washed away. Social infrastructure such as schools, hospitals and community centres may be destroyed, economic activities may be directly or indirectly affected, family members may suffer from illness or injury and be unable to work or study, and lives may be lost. Therefore, the risk of mortality is only one aspect of disaster risk. Many disasters cause enormous social and economic impact without serious mortality. This is particularly so for slow-onset disasters associated with drought.

The use of deaths as a proxy for manifest risk, therefore, strictly limits the analysis of disaster risk to human development. Deaths do not capture human development losses and can only point to comparative orders of magnitude in vulnerability and loss. An economic outcome of disaster risk should complement the current approach based on human losses. Not only are disaster risk trends in industrialised countries not addressed when using mortality calibrated models, but the different economic impacts among different types of hazards skew disaster risk trends within least developed countries.

In the DRI, mortality was chosen as a proxy indicator for disaster risk because reliable data on other aspects of disaster risk (people affected, economic impact) is not available in global level disaster databases. The DRI used the EM-DAT database (see Technical Annex), the only global disaster database in the public domain. While mortality is an indicator of broader risk to human development, the DRI only represents risk to loss of life and cannot be inferred to represent other physical, social and economic aspects of risk.

Disaster risk can be represented as a continuum from, at one extreme, the risk from everyday hazards (such as contaminated water supplies, poor sanitation, house fires and dangerous working and living environments) to, at the other extreme, the risk associated with infrequent catastrophic hazard events, such as major earthquakes or cyclones that devastate entire countries and regions. In between these two extremes lie the risks associated with frequently occurring small-scale hazard events (such as highly localised landslides, flash floods and debris flows) and periodic mediumscale hazard events.

Publicly available global data on disaster impact is currently only available for large- and medium-scale disaster events, defined as those involving more than 10 deaths, 100 affected and/or a call for international assistance. As the DRI is based on this data, it does not represent risk associated with small-scale and everyday disasters. At the same time, a recent study undertaken for the ISDR Working Group 3 on Risk, Vulnerability and Impact Assessment, indicates that international reporting may not be capturing all the medium- scale disaster events that occur. Nevertheless, and taking into account these data limitations, we consider that for the purposes of an Index constructed with a global level of observation and a national level of resolution, the large- and medium-scale disasters captured in international databases represent a very good sample of overall disaster risk.

At the global level, and with respect to large- and medium-scale disasters, the three hazard types analysed in the DRI (plus drought, presented here as a work in progress) account for approximately 94 percent of total mortality.Nevertheless, in individual countries, other hazards may have an important local impact and are not considered in the DRI. For example: landslides, debris flows and fires.

At the same time, primary hazards may trigger a range of secondary hazard events. Earthquakes, for example, often provoke landslides and fires and tropical cyclones cause sea surges and flooding. The DRI only represents the primary hazard events as recorded in global disaster databases, even when in some cases the majority of loss may be associated with a range of different hazard types triggered by the primary event.

The DRI has been calibrated using data from the period 1980-2000 because it was considered that access to information before that period was less reliable. This, however, weights the work in favour of countries that suffered catastrophic disaster events with large loss of life in the two decades under analysis and against countries that suffered such events in the 1970s, for example, but not since then.

At an early stage, volcanic eruptions were excluded from the DRI analysis because of the need to differentiate locally between different types of volcanic hazard.Data for such a task exists and could be compiled into an international database.

The DRI has run statistical regression analysis comparing some 26 socio-economic and environmental variables with risk levels in order to identify possible indicators of vulnerability.

Clearly the variables that could be tested are those that were available in global datasets. This implies that there may be other variables that potentially might help build a better correlation with risk, but for which no global datasets were available at the time of production of the DRI. The choice of vulnerability indicators presented in the DRI, therefore, is limited by available data. It is hoped that in the future more direct indicators of national vulnerability might be available, for example, soil types or the proportion of earthquake resistant buildings per country for earthquake hazard.

The logarithmic base of the model can highlight longterm trends, but does not allow predictive casualties to be made. Small differences in the vulnerability indicator figures can mask major changes in disaster risk.