SUMMARY

ASSESSING RISK AND VULNERABILITY

Quantification of the level of risk is an essential aspect of both preparedness planning and mitigation planning

By UN definition, the term risk refers to the expected losses from a particular hazard to a specified element at risk in a particular future time period. Loss may be estimated in terms of human lives, or buildings destroyed or in financial terms.

There are 3 essential components to the quantification of risk:

Hazard occurrence probability, defined as the probability of occurrence of a specified natural hazard at a specified severity level in a specified future tune period

Elements at risk, an inventory of those people or artifacts which are exposed to the hazard and

Vulnerability, the degree of loss to each element should a hazard of a given severity occur.

The probability of occurrence of the extreme levels of natural hazards which may cause a disaster maybe estimated by statistical extrapolation from data on the normal levels of occurrence. The accuracy of such estimates depends on the amount and completeness of data and the period of time over which it has been collected. Historical records can be an invaluable source of information.

Recurrence frequency and intensity of most natural hazards varies from place to place - hazard mapping may be used to show this variation. For some, notably geological hazards, detailed local mapping (micro-zoning) can be used to establish local variations and assist land-use planning decisions. For others only coarse mapping of geographical areas at risk is possible.

Vulnerability assessment involves first identifying all the elements which may be at risk from a particular hazard. Local knowledge may be used to complete the inventory, and census data to enumerate the elements at risk

Loss functions in the form of vulnerability curves or damage probability matrices may be obtained for some elements at risk (buildings, people) based on past experience elsewhere.

Many aspects of vulnerability are unquantifiable, and these should not be overlooked.

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 disaster.

Risk is compiled from hazard and vulnerability data and from the inventory of elements at risk. A variety of ways of presenting risk are available such as f:N curves, scenario mapping, potential loss mapping and annualized risk.

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