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< prev - next > Disaster response mitigation and rebuilding Reconstruction pcr_tool_3_learning_from_disasters (Printable PDF)
3 Disaster Risk Assessment
Important Aspects of a Risk Assessment
Important aspects of a vulnerability assessment:
• Underlying reasons of vulnerability: reasons that explain why people settle where they are and why they are
vulnerable, e.g.: the distribution of natural resources; means of livelihoods; rights to property and land; access
to institutions or influential people; access to finance; concentration of poverty; impacts of previous disasters or
• Dynamic pressures: including migration and urbanisation; pollution and loss of resources because of production
processes; weak institutions and governance; policies that are not pro-poor; housing policies; markets and
commercialisation; scientific and technological change.
• Conditions that make people vulnerable: these may have to be broken down by gender, age, religion, class, etc.
and would include shortfalls in nutrition and health; food insecurity; weak or threatened livelihoods; limited levels
of organisation and participation; limited risk awareness; poor access to information.
• Conditions that threaten people’s assets: including dangerous location; poor quality design and construction; lack
of maintenance; changes in use, such as vertical or horizontal extensions to buildings; changes in risks, e.g. a river
changing course.
Risk is defined as the probability that people
may suffer injuries or damage as a result of a
disaster. Risk may be calculated, based on three
elements: 1) the frequency and severity of a threat;
2) people’s vulnerability; and 3) the capacity of
people, communities and institutions to respond
and recover. Risks are greatest when threats are
large, people are very vulnerable, and there is a low
capacity to respond and recover.
A risk assessment is a methodology for
evaluating probable damage and loss as a result of
a disaster and to identify measures to prevent or
reduce those. It involves:
1 Knowing the disaster history and local
experience and knowledge of prevention and
coping strategies.
2 Identifying and assessing the probable Risks
and Threats within the location analysed.
Production of Threat Maps
1. Initial Inputs
• Analogical maps of the area
• Digital maps of the area
• Typing of maps
2. Field Trip
• Identification of the work area
• Identification of existing threats
• Plotting of GPS points of these threats
• Plotting of control points of the town centre
3. Preparation of threat maps
• Identification of existing threats
• Determination of physical variables (slope, soil
to use in generating the threat map
• Definition of the specific work area
• Preparation of the threat map in quantitative values
4. Analysis of the threat map
The threat map obtained in step 3 is made up out
of numbers that need to be reclassified by assigning
relative values of threat, e.g. 1=low; 2=medium; 3=high;
4=very high. For example: a community on a steep slope
receiving much rain is considered a value 4, whereas
another community on relatively flat stable terrain with
the same rain is considered a value 1.
Production of Vulnerability Maps
1. Initial Inputs
• Existing socio-economic data
• Design of vulnerability forms
2. Field trip
• Completion of vulnerability forms
3. Preparation of vulnerability map
• Preparation of a database
• Preparation of the map based on three variables:
• Accessibility to vehicles, transportation and
• Basic services in houses, such as electricity, water,
sanitation and building materials
• Capacity of local institutions
4. Analysis of the vulnerability map
A formula to associate the above three variables to a 1
to 4 range is generated, using the same classification
of values as for the threats. For example: isolated
communities accessible only via footpaths or poor
unpaved roads, with low levels of services and no CBO
or local authority presence nearby, would be classified
with a value of 4, whereas urban communities with better
access to services and a functioning local authority could
be classified with a value 1.