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Risk and Vulnerability Assessment Tool (RVAT)
Risk and Vulnerability Assessment Steps Hazards Analysis and Extended Discussion Print VersionWhy would I do this analysis?Essentially, a hazards analysis provides you with maps that indicate which areas in your community are most susceptible to hazards. To effectively narrow the focus of your vulnerability assessment, you must first identify the risk areas within your community. In order to obtain the most complete and comprehensive results, it is advisable that you consider all hazards facing your community. If there are data limitations , it is possible to focus your analysis on only one hazard of particular concern. Keep in mind, however, that the more risk data included in your analysis, the more opportunity there will be to focus your assessment activities in your highest-risk areas. Give me an example of something I might do in this analysis.
What are my steps?In order to locate your highest-risk areas, it may be helpful to first develop a risk-prioritization scheme. It is possible to develop such a scheme using publicly available data, although local data — data collected from local agencies — will almost always be more detailed and more accurate. For each hazard being addressed, you should research the available data pertaining to the location of high-risk areas.
What data will I need?Since the Coastal Storms Program focuses only on hazards associated with coastal storms, there are four primary data layers that will be included in this Hazards Analysis.
Where can I obtain these data and information?Every community may have unique or unusual hazards that need to be considered. Historical records and/or information from local experts and citizens can be used to provide estimates of the zones or locations potentially at risk to such events. Even if no digital (geographic information systems - GIS) data are available for your area, it is still possible to construct risk maps showing estimates of hazard extents and magnitudes using transparencies overlaid on paper maps. The Coastal Services Center has constructed two Web pages that list potential sources for Geospatial data and information. Use the following links to explore potential sources for data in and around your area. Hazard Information and Data Resources Coastal Geospatial Information: Examples of Internet Resources Who do I need to work with? What agencies can help me locate the necessary data and information?To access many of these government and organization's Web sites, view the Links page. Some potential sources of information regarding hazards in your community may include your local county and/or city emergency management office's comprehensive plan; response operations records of county and/or city emergency services organizations; flood insurance rate maps, hurricane storm surge maps, hazard computer modeling results, meteorological records from the NOAA National Weather Service, National Hurricane Center, or private weather services; geological information from the state geologist or local building inspectors; and agricultural extension agents, local and environmental organizations, and fisheries/wildlife agencies. Local (city/municipality or county level) — Planning Office/Tax Assessor, GIS Office, Emergency Management, and Non-Governmental Organizations (NGOs) such as the American Red Cross (ARC), and others. Regional (state level) — Emergency Management, Environmental Protection Office, NGOs, and others. National (federal level) — Federal Emergency Management Agency (FEMA), National Oceanic and Atmospheric Administration (NOAA), Environmental Protection Agency (EPA), U.S. Geological Survey (USGS), U.S. Army Corps of Engineers (USACE), U.S. Census Bureau, NGOs, and others. Potential Partners/Stakeholders ListLocal (county or municipality)
Regional (state or states)
National (federal)
Extended DiscussionObjective(s):Map risk areas; identify vulnerable structures and or areas Purpose:Target priority risk areas for the remaining analyses Primary Steps:
DescriptionThe difference between risk and vulnerability is an important distinction. Risk areas identify geographically (typically on maps) those areas most likely to be affected by a given hazard. People and resources located within the risk areas are considered to be at risk from hazards and may or may not be vulnerable to hazard impacts. The vulnerability of the people and resources within the risk areas is a function of their individual susceptibility to the hazard impacts. The first step toward narrowing the focus of a vulnerability assessment involves determining which hazards you will evaluate, as well as the areas potentially affected by those hazards. When selecting which hazards to include in your assessment, you may choose to compile a comprehensive list of hazards posing at least some threat to the community or a more limited list of specific hazards for which you are planning. Establishing relative priorities for your hazardsThe ideal method for assigning priorities to various hazards would be a scientific, quantifiable probability assessment. Unfortunately, probability data are not consistent among the different hazard types, nor are they always available or useable at the local level. As an alternative, communities can develop a relative priority matrix to use as a general guide for addressing different hazards. Designing such a matrix requires you to determine which factors are most critical to your community and assign weights accordingly. Factors can include hazard frequency, the amount of land typically impacted, or the magnitude of damages associated with the hazards. The purpose of this step is to initiate thought and discussion about the hazards and their potential impacts. It is a subjective exercise where the scores do not have absolute statistical significance. The comparison of hazard scores, however, will give you relative rankings that can guide your vulnerability assessment process, as well as your hazard mitigation priorities. Sample Scoring System (Relative Priority Matrix) Used in This Analysis:(Frequency + Area Impact) x Potential Damage Magnitude* = Total ScoreTable 1. Example of Relative Priority Matrix.
*The frequency, area impact, and potential damage magnitude values are typically defined by a scale of numbers ranging from 1 to 5, where 1 = low and 5 = high. In the case of this project, values were determined using input from multiple local stakeholders. All responses were summed and an average calculated, resulting in decimal values. A "multiplier" or weighting factor was then calculated by taking a rounded version of the lowest value and using that as a baseline value or "1." Remaining values are then calculated by dividing the baseline value ("1" in this case) by each rounded score value. This method is useful because it can give a much more accurate depiction of risk than scoring schemes that do not include a weighting. Risk Area Scoring MethodsAssign scores within risk areas, where possible. Within your risk areas there could be additional boundaries representing varying degrees of risk. These varying degrees of risk should be represented in your risk areas both graphically (additional boundaries on the maps) and through some type of relative scoring system (higher scores for higher risk areas). For example, hurricane storm surge maps are generally created for five different categories of storm. Category 1 storms are generally associated with the least severe winds and storm surge while Category 5 storms are considered the most severe for these hazards. Generally, those areas subject to storm surge in the lower category storms are also projected for inundation in all of the higher categories. When developing a relative priority scoring system for storm surge inundation, Category 1 storm surge areas would therefore have the highest risk of being flooded since they are at risk of inundation in all storm events. The tables below show the relative priority scoring system for natural hazard risks used in this analysis. The general concept is that locations with no consideration for risk will be given a score of 0 and each incremental increase in risk adds 1 point. A multiplier* or weighting factor is calculated by taking a rounded version of the lowest value and using that as a baseline value or "1." Tables 2 - 5. Examples of relative priority scoring system for natural hazards risk.
In this example, two of the hazards have locations with a risk score of 0 (hurricane storm surge and coastal erosion). In each case, the maximum extent of the hazard risk does not realistically include the entire county and is limited to proximity to coastal waters. The minimum risk score for each of the remaining hazards is 1 since there is some potential that each of these hazards could occur anywhere throughout each county. Data and SourcesAs mentioned previously, the more risk data that are available, the more opportunity there is to focus your vulnerability assessment activities in the highest-risk areas. It is possible, however, to develop some type of prioritization scheme using limited publicly available data and to improve upon it over time using more accurate local data. For each hazard being addressed, you should research the available data concerning the location of high-risk areas. If you have hazards with limited areas of risk (i.e., coastal erosion is limited to the land/water interface), you will want to limit your vulnerability assessment to only those areas. Similarly, if you have hazards with varying degrees of risk throughout your community (i.e., flooding can occur almost anywhere but floodplains are particularly high risk) you will want to target vulnerability assessment in your highest-risk areas. It is appropriate to refer to these designations as risk areas since they are locations you consider at risk to hazard impacts based on your best available information sources. Obviously, the better the risk data available, the more accurate your assessment will be. Establish a risk area for each hazard. Some of the risk areas are descriptive and relatively effective in targeting vulnerability assessment activities, while others are default designations, lacking useful risk data. Below are descriptions of the risk areas used in the present analysis. Hurricane Storm SurgeRisk areas for storm surge were mapped using output from the National Oceanic and Atmospheric Administration (NOAA) Hurricane Storm Surge Inundation Model, known as Sea, Lake and Overland Surges from Hurricanes (SLOSH). Find more information about SLOSH and storm surge. Hurricane storm surge zones are generally delineated according to hurricane categories on the Saffir-Simpson Hurricane Scale (Categories 1 through 5). These areas represent locations that might be impacted by storm surge events. Typically, published maps depict "worst-case" storm surge inundation, to provide a basis for evacuation decisions and for other study purposes. The surge delineations reflect simulated conditions at high tide, with an additional 1.5 feet included for oceanic values, and 1.0 foot added for inland bays and waterways. These maps do not include effects of waves (still water is assumed for model purposes), rainfall, and flooding from overflowing rivers. Locations that are subject to inundation from the lowest category storm event are considered at highest risk, as they will likely be inundated during stronger events as well. Therefore, Category 1 and 2 hurricane storm surge inundation areas are given a high-risk score of 4. Category 3 inundation areas are given a score of 3, and Category 4 and 5 inundation areas are assigned a score of 2. Because of the difficulty in making clear boundaries, a 0.25-mile buffer was established around the surge inundation zones and given a risk score of 1. All other areas of the county receive a 0, as it is highly unlikely that these areas will be impacted by surge from hurricanes. FloodRisk areas for flooding were mapped using output from the Federal Emergency Management Agency's (FEMA) Flood Insurance Rate Maps (FIRMs). The FIRMs are developed from the output of hydrologic models, identifying areas with a high potential for flooding. Find more information about FIRMs. In this analysis, a risk area score of 5 is given to the Velocity Zone (V-Zone) where coastal flooding and wave action risks are highest. The second highest score of 4 is applied to the 100-year floodplain, and a score of 3 is given to the 500-year floodplain. Areas located outside the floodplain but containing flood-prone soils are rated with a score of 2. All other areas of the county receive a score of 1, since there is at least some risk of flooding in all areas of each county. For more information about using FEMA Q3 data to assess flood hazards, including limitations, see the Q3 Frequently Asked Questions Web site. Coastal ErosionRisk area scores for erosion were determined using published reports obtained from studies conducted by the Florida Department of Environmental Protection (FDEP), using distance from the Coastal Construction Control Line (CCCL) as a baseline. A CCCL or "Control Line" defines that portion of the beach-dune system subject to severe fluctuations based on a one-hundred-year storm surge, storm waves, or other predictable weather conditions. The CCCL protects the beach/dune system from improper construction methods which could cause erosion of the system. It also protects upland property and structures, since improperly designed sites and construction can cause the destruction of the beach/dune system. Find more information about shoreline erosion estimates data and coastal erosion. Construction seaward of the CCCL is not prohibited but is regulated by specific design standards. Therefore, those areas seaward of the CCCL are assigned a 3. Those areas inland of the CCCL to a line based on the average 30-year erosion rate for the whole of both counties are assigned a score of 2. Areas between the 30-year and 50-year zones are assigned a score of 1, and the remaining areas receive a rating of 0, as there is a negligible level of erosion risk in those areas. WindRisk area scores for wind hazards were determined using data from the American Society of Civil Engineers (ASCE) 7-98, Minimum Design Loads for Buildings and Other Structures. These data provide the basis for determining wind and other loads for structures in the United States. All model building codes reference these standards. Find more information about ASCE. Areas were assigned values from 1 to 3, with the higher values reserved for those areas located closest to the coast. These data are also in accordance with various "inland wind models" which suggest that hurricane and tropical storm wind speeds decrease significantly once a storm moves inland, although the speed at which this occurs is directly correlated with a particular storm's forward speed and landfalling intensity, as well as with the general land cover of the landfall location. Summary ScoresUsing a geographic information system (GIS), the risk areas were combined and the scores were added together to create summary scores for every location in the county. These summary scores were used to develop a summary risk area map. The summary scores also provide the foundation for ranking high-risk areas in the remainder of the assessment. |
As
part of your structural analysis, you observe that one particular neighborhood
in your community has 50 homes. Using Federal Emergency Management Agency (FEMA)
"Q3" flood data (or Digital Flood Insurance Rate Map (DFIRM) data, if
available), you determine that 10 of these structures are located within the floodplain
and are therefore potentially at risk to flooding. These structures would be prime
targets for a vulnerability assessment. Luckily, seven of the structures are elevated
above the "base" or "100-year" flood elevation. The three remaining structures,
however, are not. Therefore, these structures would be considered vulnerable to
flooding. In this example, the risk area (floodplain) helped narrow the target
of the vulnerability assessment from 50 structures down to just three structures.