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close this bookAn Overview of Disaster Management (Department of Humanitarian Affairs/United Nations Disaster Relief Office - United Nations Development Programme , 1992, 136 p.)
close this folderChapter 8. Vulnerability and risk assessment 1
View the document(introduction...)
View the documentRisk management
View the documentRisk probability
View the documentAcceptable levels of risk
View the documentAssessing risk and vulnerability
View the documentHow is risk determined?
View the documentVulnerability evaluation
View the documentReducing vulnerability for displaced persons


1 This chapter has been drawn from the UNDP/UNDRO training module Vulnerability and Risk Assessment written by A.W. Coburn. R.J.S. Spence and A. Pomonis

This chapter considers the nature of risk; discusses the techniques by which natural hazards and the accompanying risk of future losses can be estimated; and it discusses the ways in which future risk estimates can be used to assist the choice of the optimum disaster mitigation strategy.

First, let us review the definitions of the key terms. Risk is the expected lives lost, persons injured, property damaged, and economic activity disrupted due to a particular hazard. Risk is the probability of a disaster occurring and resulting in a particular level of loss.

Risk assessment determines the scale of the estimated losses which can be anticipated in particular areas during a specified time period.

Risk management

One of the underlying principles of this training module is that most people working in development are involved in disaster management at one time or another. Even if you, as a generalist or a sectoral specialist, do not have an active role to play in some of the other disaster phases, you do play an important role when it comes to risk management. The design of development projects should include an exercise in risk management.

The overall task of risk management must include both an estimation of the magnitude of a particular risk and an evaluation of how important to us the risk is. The process of risk management therefore has two parts: risk assessment and risk evaluation. Risk assessment requires the quantification of the risk from data and understanding the processes involved. Risk evaluation is the judgment that a society places on the risks that face them in deciding what to do about them.

Risk probability

Risks are often quantified in generalized ways. For example, there is a probability of an individual dying in any one year of: 1 in 200 if he or she smokes 10 cigarettes a day; 1 in 23,000 in an earthquake in Iran; and 1 in 10,000,000 of being hit by lightning in the USA. Such gross risk estimates can be useful for comparative purposes, but usually conceal large variations in the risk to individuals or different regions. In the case of Iran, people who live closer to an earthquake fault are at greater risk than those that live far away. Similarly, people who live in poorly constructed masonry houses near a fault are more at risk than those who may live nearby in well built wood structures.

The first step in risk management, therefore, is quantifying the probability of the risk. The second step is evaluating the risk, that is, passing judgment on how serious it is. The importance a community places on the risk of a disaster is likely to be influenced by the type and level of other everyday risks it faces. Even if the risk from a natural hazard is quite significant, it is unlikely to compare, for example, with the risk of child mortality in a society with minimal primary health care. Villages in the hazardous mountain valleys of Northern Pakistan, regularly afflicted by floods, earthquakes, and landslides, do not perceive disaster mitigation to be one of their priorities. Their priorities are protection against the greater risks of disease and irrigation failures.

As societies develop economically, risk reduction is likely to assume greater importance to them. Development itself can increase the likelihood of disasters, but as societies become richer more resources can be made available to invest in some degree of protection. Protection of the development process itself becomes a disaster mitigation issue.

Acceptable levels of risk

Many risks are associated with benefits. Living close to a volcano may bring the benefit of fertile soils for good agriculture. Generally, though, the exposure to natural and environmental hazards does not have any specific benefit associated with it - the exposure is a simple consequence of living or working in a particular location. This can have the effect of making such risks less acceptable than those from which some benefit is obtained. Generally the acceptable levels of risk appear to increase according to the benefits derived from being exposed to it. However, the acceptable level of risk appears to decrease over time as more people become exposed to a particular type of risk.

Assessing risk and vulnerability

The estimation of probably future losses is a matter of increasing interest to those concerned with development planning in hazard-prone regions. Fundamental to disaster preparedness and mitigation planning is an understanding of what to expect. This needs to be quantified, if only in a crude and approximate way, in terms of the degree of risk faced, the size of event that is likely, and the consequences of an event if it occurs.

The calculation of risk generally needs to consider several types of loss. The most common parameter of loss, and the one most easily dealt with, is economic cost. Cost is widely used because many types of loss can be converted into economic cost. Effects which are considered in terms of economic costs are known as tangible losses. But there are a range of other effects resulting from disasters which are important but which cannot be converted into a monetary equivalent, and these are referred to as intangible losses.

A full consideration of risk would include a complete range of effects, both tangible and intangible, and of several qualitatively different types. The range of undesirable consequences of natural hazards what we might consider as loss parameters are listed in Table 1.

Table 1 Loss parameters for risk analysis







Number of people

Loss of economically active individuals

Social and psychological effects on remaining community


Number and injury severity

Medical treatment needs, temporary loss of economic activity by productive individuals

Social and psychological.
Pain and recovery

Physical damage

Inventory of damaged elements, by number and damage level

Replacement and repair cost

Cultural losses

Emergency operations

Volume of manpower, man-days employed, equipment and resources expended for relief

Mobilization costs, investment in preparedness capability

Stress and overwork in relief participants

Disruption to economy

Number of working days lost, volume of production lost

Value of lost production

Opportunities, competitiveness, reputation

Social disruption

Number of displaced persons, homeless

Temporary housing, relief, economic production

Psychological, Social contacts, cohesion, community morale

Environmental impact

Scale and severity

Clean-up costs, repair cost

Consequences of poorer environment, health risks, risk of future disaster

How is risk determined?

There are three essential components in the determination of risk, each of which should be separately quantified:

a) the hazard occurrence probability: the likelihood of experiencing any natural or technological hazard at a location or in a region

b) the elements at risk: identifying and making an inventory of people or buildings or other elements which would be affected by the hazard if it occurred, and where required, estimating their economic value

c) the vulnerability of the elements at risk: how damaged the buildings or injured the people or other elements would be if they experienced some level of hazard.


There is a variety of methods of presenting the above information to illustrate the data describing risk. These can often be represented on a map. This is an essential tool in evaluating development projects because you can see if a project site is located in an area of high risk.

An example of mapping is the Potential Loss Study. This consists of mapping the effect of expected hazard occurrence probability across a region or country. It shows the location of communities likely to suffer heavy losses. The effect of the hazard of each area is calculated for each of the communities within those areas to identify the “Communities Most at Risk”. This shows, for example, which towns or villages are likely to suffer highest losses, which should be priorities for loss-reduction programs, and which are likely to need most aid or rescue assistance in the event of a major disaster.

The following is an example of potential loss mapping. It presents risk as the levels of losses that would occur if a certain level of hazard were to occur at all the locations simultaneously. In this case the type of loss plotted (Map 4) is urban earthquake casualties in Turkey. Casualties are defined as those people whose houses are liable to be totally destroyed by the largest expected earthquake - a measure used because it has been found in Turkey to correlate closely with the numbers of killed and injured. The potential loss plotted in each location is derived from three other types of geographically varying data, which are shown in Maps 1,2 and 3. (See figure. 8.1)

Figure 8.1 Potential loss study

Map 1 shows the earthquake hazard in terms of the maximum intensity of earthquake which might possible occur there.


Map 2 shows the elements at risk - in this case the total size of the urban population. Larger towns and dries are plotted individually, and are identified by circles whose area represents the population. The population in the smaller towns of 2,000 to 25,000 population is shown in the form of a population density. Other elements at risk could be mapped in a similar way.

2 - ELEMENTS AT RISK (population)

Map 3 shows one aspect of the vulnerability of those elements at risk. The casualties are caused by the collapse of buildings. The vulnerability of a building depends primarily on the type of construction. A useful approximate classification of the building types in Turkey divides them into just three types: rubble and adobe walls, brick and timber walls, and reinforced concrete frame. An estimate has been made about the expected proportions of buildings that will collapse.


Map 4 shows the analysis of the three preceding maps for each location. This is derived by estimating the numbers of people living in each building type, (from Maps 2 and 3) and then estimating the potential proportion of collapsed buildings of each type if the largest earthquake were to occur there. The total potential casualties are obtained by adding those from all three building types.

4 - CASUALTY RISK (potential loss of life)

Vulnerability evaluation

Vulnerability is the propensity of things to be damaged by a hazard. People’s lives and health are at risk directly from the destructive effects of the hazard. Their incomes and livelihood are at risk because of the destruction of the buildings, crops, livestock or equipment which these depend on. Each type of hazard puts a somewhat different set of elements at risk. Most of disaster mitigation work is focused on reducing vulnerability, and in order to act to reduce vulnerability, development planners need an understanding of which elements are most at risk from the principal hazards which have been identified.

Vulnerability assessment is the process of estimating the vulnerability to potential disaster hazards of specified elements at risk. For general socio-economic purposes it involves consideration of all significant elements in society, including physical, social and economic considerations, and the extent to which essential services will be able to continue functioning.

As we have noted in Chapter 1 the root causes of vulnerability to disasters in developing countries are poverty and inequitable development. Rapid population growth, urban or mass migration, inequitable patterns of land ownership, lack of education, and subsistence agriculture on marginal lands lead to vulnerable conditions such as unsafe siting of buildings and settlements, unsafe homes, deforestation, malnutrition, unemployment, underemployment, and illiteracy.

It is the interface between these vulnerable conditions and natural hazards such as an earthquake, tropical storm, drought, and heavy rains, that results in a disaster or protracted emergency. (See Fig. 1.1)

Vulnerability derived from poverty can best be addressed by long-term development projects targeted at the underlying reasons that large population groups remain poor, while at the same time introducing measure to mitigate disaster effects.

Vulnerability may also be a result of factors more easily solved by specific risk reduction measures. These factors include inappropriate building codes and materials, and a lack of public awareness. However, many of these measures depend on the extent of a society’s development. For example, it is unrealistic to expect building codes to be enforced where governments do not have staff and resources to carry out inspections. Likewise, public awareness depends, to some extent, on the community’s educational level and the availability of communication facilities, which are frequently deficient in developing countries.

Vulnerability and risk assessment is the link between development project implementation and disaster mitigation. In UNDP, for example, a proposed project should be examined against the vulnerability and risk of the project location. If the location or the nature of the project design are inherently vulnerable to disasters, then the location should be reconsidered or disaster mitigation/risk reduction measures must be taken. (See Chapter 13 for additional discussion on how this may be achieved.)

Reducing vulnerability for displaced persons

Much of the preceding discussion on vulnerability and risk relates more to sudden onset disasters than slow onset disasters and population displacements. Nevertheless, much of the assessment process and technologies apply to these situations. For example, mapping of hazards is also of prime concern to identify areas subject to drought, or even civil conflict. Meeting the needs of a migrating population or one recently arrived at a new location will be assisted by mapping the best routes and survival resources along the way. Strategies for vulnerability reduction in zones of conflict might include development inputs which can reduce the conflict, such as installing water points for nomads in areas where water is a scarce resource subject to competition.

These topics are discussed in more detail in the special topic modules “Disaster Mitigation” and “Vulnerability and Risk Assessment.”

In summary, because hazards tend to be uncontrollable, much mitigation work is centered on reducing vulnerability. Improved economic conditions reduce many aspects of vulnerability and a sound economy may in many cases be the best defense against disasters and emergencies.

Q. Imagine that you are working for an agency responsible for the economic development of a community in an area where tropical storms occur. You want to do an analysis of the most appropriate types of projects to achieve economic development. As part of your analysis how would you conduct a risk and vulnerability assessment?

A. ___________________________________________________________



Step one: Review the history of tropical storms to estimate the probability of one occurring during the lifetime of your project.

Step two: Inventory the elements at risk.

Step three: Determine the vulnerability of the elements at risk by estimating

a) how badly damaged the buildings might be.
b) the number of people potentially killed or injured.

c) the level of disruption or employment or the economic base of your project