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close this bookVulnerability and Risk Assessment - 2nd Edition (Department of Humanitarian Affairs/United Nations Disaster Relief Office - Disaster Management Training Programme - United Nations Development Programme , 1994, 70 p.)
close this folderPart 2 - Assessing risk and vulnerability
View the document(introduction...)
View the documentUsing risk in decision-making
View the documentHow is risk determined?
View the documentPresentation of risk
View the documentHazard evaluation
View the documentVulnerability evaluation
View the documentCASE STUDY - Part A
View the documentReducing vulnerability: robust societies
View the documentCASE STUDY - Part B
View the documentSUMMARY

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 people or other elements would be if they experienced some level of hazard

Each of these is not a single parameter to be evaluated, but several. Quantifying hazard probability involves assessing not only the probability of, for example, a wind storm occurring, but also the probability of occurrence of wind storms of a range of strengths. A strong windstorm will be rarer than a mild wind storm. A very strong windstorm will be rarer still.

The elements at risk consist of a wide range of things that make up our society - people's lives and their health are elements at risk; so are their economic activities, their jobs, equipment, crops and livestock. Their houses are clearly elements at risk and so are the roads and services they depend on. The community services - schools, hospitals, religious institutions - are further elements at risk. So, in many cases, is the natural environment. These elements are not easily aggregated and have to be treated as a number of separate categories - and the tangible and intangible aspects of each considered.

Vulnerability is similarly multi-dimensional. Each element - a building, a person, an activity - will be affected differently by hazards of different severity. The more severe the hazard is, the more damage will be inflicted on the element. This relationship between the severity of hazard and the degree of damage caused is the vulnerability relationship. Both hazard and vulnerability are described in more detail in subsequent sections.