LMS Part 1 - Vulnerability Assessment
STEP 5
CONDUCTING A RISK ANALYSIS
Risk analysis and the vulnerability assessment
The final step in the vulnerability assessment process is to use the information gathered and analysis conducted to date as a basis to estimate the "risk" to which the community is exposed for each hazard. A judgment regarding the risk of a specific type of event will be an important tool for the Working Group to use later in prioritizing mitigation initiatives as they are developed from the vulnerability assessment results.
There are many ways to define risk, but for preparing mitigation strategies, "risk" can be considered as a comparison of the consequences of an incident (e.g., the number of injuries or dollar costs of damages) with the probability that such an incident could occur. In this section, an approach to the risk analysis component of the vulnerability assessment is discussed.
Information needed
Two fundamental types of information are needed to conduct a risk analysis: the probability of occurrence of an event and the consequences of its impact. Such data will be easier to obtain for some disaster types than others, and some assumptions by the Working Group are very likely to be needed to complete this process.
The vulnerability assessment process completed by the Working Group can be expected to provide an excellent basis for predicting the consequences of a specific hazard event. The results of Step Four will have equipped the Working Group with maps of the vulnerable community characteristics located within each of the delineated hazard areas, as well as those characteristics in areas vulnerable to the failure of lifeline" systems. While the Working Group will need to continue to develop information on the consequences of a specific type of hazard, the greatest challenge of Step Five is likely to be estimating the frequency with which such events can impact the county. If a reasonable prediction of the frequency of a hazard event can be developed, then it can be compared to the information regarding the consequences of the event. The results of the comparison will allow the Working Group to reach a soundly-based judgment on the relative risk represented by the range of events threatening the county. The magnitude of the risk of a hazard that is to be addressed by each initiative is an objective basis for their prioritization.
Risk information from "The Arbiter of Storms" (TAOS) analysis
The TAOS analysis by the Department will provide approximations of damages from tropical cyclone events for the Working Group to consider both in identifying mitigation initiatives and, most importantly, in prioritizing them by the level of risk. The TAOS model results will include the "return interval" or probability of occurrence of each storm scenario. These data will be used in combination with other information to provide, on a county-wide basis, the approximate number and estimated dollar value of single, multi-family and mobile homes, commercial, industrial, utility and agricultural facilities, as well as institutional and governmental facilities. These data will be provided to local planners as written tables and as data on a compact disk in a DBASEIII format.
In combination with the TAOS data, the Department will estimate the property damages likely to result in each county from different categories of tropical cyclone hazards. Additional TAOS model results, such as debris generated by a storm, can be used in estimating the overall costs for disaster recovery.
Other types of risk information needed
While the TAOS modeling effort will generate risk information by providing a comparison of frequency and approximate property damage costs regarding tropical cyclone events, to address other types of disasters and their costs, the Working Group will need to seek Out other sources of consequence and event probability information. Data to support prediction of the human and economic consequences of some types of hazard events and the frequency of occurrence of the events may be available from a range of federal, state or local sources.
To develop a comprehensive risk analysis, a Working Group would find the following types of information helpful to understand the level of risk to which the community is exposed should such an event occur:
- Historical and/or predicted frequency of occurrence of the event, categorized by the magnitude or scale of the event, if appropriate,
- The average or predictable quantifiable human costs of the event, such as the number of fatalities, injuries, or homeless victims, etc,
- The likely economic costs of the event, including both the dollar value of direct property damage, and factors such as lost wages, revenues, and taxes, business failures, etc., and
- The potential costs of long-term changes in the characteristics of the community, such as community relocation, permanent damage to valuable resources, etc.
A COMPARATIVE "RANKING" OF TORNADO RISK
Rank Total numbers of tornadoes Deaths per 10,000 sq mi Number of "killer" tornadoes Total tornado path length per 10,000 sq mi Killer tornadoes as a % of all tornadoes Annual tornadoes per 10,000 sq mi 1 Texas Massachusetts Texas Mississippi Tennessee Florida 2 Oklahoma Mississippi Oklahoma Alabama Kentucky Oklahoma 3 Florida Indiana Arkansas Oklahoma Arkansas Indiana 4 Kansas Alabama Alabama Iowa Ohio Iowa 5 Nebraska Ohio Mississippi Illinois Alabama Kansas 6 Iowa Michigan Illinois Louisiana Mississippi Delaware 7 Missouri Arkansas Missouri Kansas North Carolina Louisiana 8 Illinois Illinois Indiana Indiana Michigan Mississippi 9 South Dakota Oklahoma Louisiana Nebraska New York Nebraska 10 Louisiana Kentucky Tennessee Wisconsin Massachusetts Texas
From the Tornado Project, St. Johnsbury, VT
Period of Record: 1840 - 1995Reference sources for this type of information may be readily available in some cases; although it is very likely that the Working Group will find it necessary to use several assumptions or extrapolations to develop any quantified basis for judgment of the risk to the community represented by each type of hazard. Because the TAOS modeling will provide quantitative risk information regarding tropical cyclone hazards, the Working Group may find it practical to seek information on the probability of occurrence of other natural hazards. Several sources for such information are available on the Internet, as well as from representatives of government agencies on or accessible by the Working Group.
Examples of sources of risk information
For hazards other than hurricanes, the Internet is a very convenient starting point to gather the types of frequency and consequence data needed to conduct a comprehensive risk assessment. There are numerous websites with such data, and some examples of interest to the Working Groups of Florida
*s counties for specific hazards include:Tornado: The website of The Tornado Project (
http://www.tornadoproject.com/) has compilation of tornado strikes for each Florida county for 1950-1995 and could be used to determine an annual average number of strikes,Wildfires. The website, "Firenet" (http://sres.anu.edu.au/associated/fire/index.html) offers access to a large number of sites with data, predictive models and reference works regarding wildfires,
Severe weather: Working Groups could access (
http://www.esdim.noaa.gov/esdim/) for access to data and forecasts.Floods: The websites for FEMA National Flood Insurance Program (http://www.fema.gov/nfip/) and the Floodplain Management Association (http://www.floods.org/) can provide information regarding flood frequencies and impacts.
Hazardous Materials Incidents: Working Groups will find data regarding hazardous materials accidents reported to the Emergency Response Notification System for Region IV (the Southeast) at the website of the Chemical Emergency Preparedness Program of the US Environmental Protection Agency (http://www.epa.gov/swercepp).
Other hazards: The library of the US Army Corps of Engineers (http:libweb.wes.army.mil/usace) is a good starting point to "surf" for hazard frequency and consequence information.