|Vulnerability 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.)|
|Part 1 - Understanding risk|
The official definition of terms for risk assessment in natural disasters was established in an international convention agreed by an expert meeting organized by the Office of United Nations Disaster Relief Co-ordinator (UNDRO) in 1979.2
The term risk refers to the expected losses from a given hazard to a given element at risk, over a specified future time period. According to the way in which the element at risk is defined, the risk may be measured in terms of expected economic loss, or in terms of numbers of lives lost or the extent of physical damage to property.3
Risk may be expressed in terms of average expected losses, such as:
"25,000 lives lost over a 30 year period"
"75,000 houses experiencing heavy damage or destruction within 25 years"
or alternatively on a probabilistic basis:
"a 75% probability of economic losses to property exceeding 50 million dollars in the town of Puerto Nuevo within the next 10 years"
The term specific risk is used to refer to risks or loss estimations of either type which are expressed as a proportion of the total; the first two examples might also be expressed as:
"10% of the population (of the given settlement) killed by natural hazards within 30 years"
"50% of houses (in a given region) heavily damaged or destroyed in the next 25 years"
Specific risk is also used for financial losses to property, where it usually refers to the ratio of the cost of repair or reinstatement of the property to the cost of total replacement. Frequently the shorter term 'risk' is used to refer to what are strictly 'specific risks'.