Techniques Used in Disaster Risk Assessment

The following list is not meant to be all-inclusive, but rather to present and explain a few of the wide range of techniques used to develop and apply disaster assessment tools.
 

• Access model
• A model that explores how an individual or groups relative resilience to disasters is impacted by differences in access to the economic or political resources needed to secure a livelihood.
• The strengths of the model are that it provides a broad view of vulnerability including root causes, it gives weight to natural hazards, and it provides a framework for looking at livelihoods and vulnerability.
• The limitation of the model, is that it is a tool for explaining vulnerability, not for measuring it. The model cannot be applied operationally without a great deal of data collection and analysis.

• Computer assisted techniques
• The use of computer software programs to automate steps of the risk management process.  For example the use of GIS and remote sensing has allowed hazard mapping to become more comprehensive.
• The limitations vary by technique; however in general there is a reliance on equipment and expertise, which may not be readily available in the communities undertaking the assessments which may widen the breach between the information produced by technical risk assessments and the understanding of risk by people.

• Cost-benefit analysis
• A process used to select countermeasures, by balancing the costs of implementing each option against the benefits derived from it. In general, the cost of managing risks needs to be equal to the benefits gained from putting the countermeasures in place.
• The benefit of this technique is the attempt to ensure public investment is directed toward those activities producing the greatest benefits for the best value for money.
• The limitations of the technique include the lack of data collection and methods that are required to capture indirect and intangible costs and benefits, legal and social responsibility requirements may override simple financial cost benefit analysis, and the possibility that its application may disadvantage certain measures or people.

• Disaster risk indexing
• A quantitative analysis technique that uses statistical indicators to measure and compare risk variables.
• Benefits of the technique are efficiency in measuring key elements of risk, repetitive application of the indictor system may allow the monitoring of disaster risk reduction progress, and because the system can be applied rapidly and with little cost it is also a useful tool for the national level to identify risk exposed communities.
• Limitations of the technique include the use of indicators that may not reflect the complex reality; local and sub-national databases are not currently using uniform data collection and analysis frameworks; lack of availability of data with a suitable coverage and accuracy; and while indexing allows a comparison of relative risk between geographic areas, it cannot be used to depict actual risk for any one area.

• Environmental impact assessment (EIA)
• A policymaking tool that provides information on the environmental impacts of activities.
• The benefits of an EIA are encouraging the private sector and individuals to consider the impacts of their actions on vulnerability factors; as part of a detailed risk assessment it can provide alternative solutions, and it could be used to reorient disaster impact assessments as planning tools.
• Limitations of the technique include the current focus on post-event impact assessment and not promoting its use as part of the planning process, although the results can feed into future planning.  In addition, there is still some way to go before EIA processes are fully mastered.

• Event-tree analysis (ETA)
• A consequence based analysis in which an event either has or has not happened or a component has or has not failed. An event tree begins with an initiating event. The consequences of the event are followed through a series of possible paths. Each path is assigned a probability of occurrence and the probability of the various possible outcomes can be calculated.
• The benefits of the technique are its value in analyzing the consequences arising from a failure or undesired event.

• Failure modes and effects analysis (FMEA)
• An analytical technique, which explores the effects of failures or malfunctions of individual components in a system - i.e. "If this part fails, in this manner, what will be the result?" The level of risk is determined by: Risk = probability of failure x severity category
• An FMEA can be used for a single point failure but can be extended to cover parallel failures and is valuable for future reviews and as a basis for other risk assessment techniques
• The limitations to the technique are that it can be a costly and time-consuming process.

• Fault-tree analysis (FTA)
• This is a graphical technique that provides a description of the combinations of possible occurrences in a system, which can result in an undesirable outcome. The most serious outcome is selected and called the Top Event. The analysis proceeds by determining how these top events can be caused by individual or combined lower level failures or events.
• The benefits of the approach are the identification of the basic causes of failures, and the investigation of the reliability and safety of complex and large systems.
• The limitations of the approach is that it does not measure probability, therefore counter measures identified by the process may not be those with the greatest potential for reducing risk.

• Geographic information system (GIS) mapping
• The use of a geographic information system, a computer-based tool, for risk or hazard mapping. GIS technology integrates database operations with the geographic analysis benefits offered by maps.
• The benefits of the technique are the increase in productivity of hazard-mapping technicians, it can give higher quality results than can be obtained manually and it can facilitate decision-making and improve coordination among agencies when efficiency is at a premium.
• The limitations of the technique include the lack of trained personnel; difficulties in exchanging data between different systems; difficulties in including social, economic and environmental variables; variability in access to computers and the quality and detail of the data required by GIS analysis.

• Geospatial analysis
• Analysis of risk information by distance, area, volume or any other spatial characteristic within geographic boundaries through GIS and hazard mapping techniques.
• The benefits of the technique are the identification of hazards and dangerous locations at varying scales from local (less than 100,000 km2), through regional (100,000 to 10 million km2) to continental (10 to 100 million km2) and a view of risk not only from a singular hazard point of view, but also from an orientation to the relative levels of exposure.
• The limitations of the technique are the same as those for GIS techniques with the added requirement for well-defined geographic boundaries (e.g., counties, municipalities, and health districts).

• Hazard mapping
• The process of mapping hazard information within a study area of varying scale, coverage, and detail.
• Mapping can be of a single hazard such as fault maps and flood plain maps or several hazard maps can be combined in a single map to give a composite picture of natural hazards.
• The benefit of the individual mapping technique is a visual form of information for decision makers and planners, which is easily understood. Multiple hazard maps provide the possibility of common mitigation technique recommendations; sub-areas requiring more information, additional assessments, or specific hazard-reduction techniques can be identified; and land-use decisions can be based on all hazard considerations simultaneously.
• The limitations of the technique are that the volume of information needed for natural hazards management, particularly in the context of integrated development planning, often exceeds the capacity of manual methods and thus drives the use of computer assisted techniques.

• Historical analysis
• The analysis of historical information to determine levels of risk based on past experiences.
• The benefits of this technique are the identification of dynamic aspects involved in vulnerability and providing the criteria to assign relative weights to different dimensions of vulnerability in risk assessment exercises.
• The limitations to the approach are the reliance on historical disaster databases and the requirement for refinement, maintenance and systematic feeding of disaster data sets.  In addition, statistics on previous disasters’ impact can be unreliable and rarely cover socio-economic aspects of the disaster; data on vulnerability is likely to be restricted to physical vulnerability, and reliance on historical assessment alone can create a false expectation of preparedness if hazards, which may not have previously occurred in the area of analysis have not been considered.