Element B3
The risk assessment shall include an overall summary of each hazard and its impact on the community.
44 CFR §201.6(c)(2)(ii)
Risk analysis involves evaluating vulnerable assets, describing potential impacts, and estimating losses for each hazard. The purpose of this analysis is to help the community understand the greatest risks facing the planning area. This step occurs after hazards and assets have been identified.
Methods for analyzing risk include exposure analysis, historical analysis, and scenario analysis. These methods can be expressed qualitatively or quantitatively. Qualitative evaluations describe the types of impacts that might occur during a hazard event. The planning team, subject matter experts, stakeholders, and community members can conduct qualitative evaluations by brainstorming and discussing potential impacts. Quantitative evaluations assign values and measure the potential losses to the assets at risk.
Exposure Analysis
An exposure analysis identifies the existing and future assets located in identified hazard areas, often by using GIS for analysis and maps for visualization. You also can take into account the magnitude of the hazard, such as assets located in high, medium, or low wildfire hazard areas or assets located in different flood frequency areas (1% annual flood and 0.2% annual flood risk).
Exposure analysis can quantify the number, type, and value of structures, critical facilities, and infrastructure located in identified hazard areas, as well as assets exposed to multiple hazards. It can also be used to quantify the number of future structures and infrastructure possible in hazard prone areas based on current zoning and building codes.
Historical Analysis
Element B4
All plans must address NFIP insured structures that have been repetitively damaged by floods.
44 CFR §201.6(c)(2)(ii)
Historical analysis uses information on impacts and losses from previous hazard events to predict potential impacts and losses during a similar future event. This can be especially useful for weather-related hazards, such as severe winter storms, hail, and drought. Because of the frequency of these events, communities are more likely to have experience with and data on impacts and losses. For recent events, consider not only what was damaged, but what might have been damaged if the event had been of greater magnitude. For hazard events that have not occurred recently, consider new development and infrastructure that would now be vulnerable in a similar event.
Repetitive and Severe Repetitive Loss Properties
A repetitive loss property: an NFIP insured structure that has had at least two paid flood losses of more than $1,000 each in any 10-year period since 1978. (See NFIP Flood Insurance Manual).
Severe repetitive loss properties single or multifamily residential properties that are covered under an NFIP flood insurance policy and:
1. That have incurred flood-related damage for which 4 or more separate claims payments have been made, with the amount of each claim (including building and contents payments) exceeding $5,000, and with the cumulative amount of such claims payments exceeding $20,000; or
2. For which at least 2 separate claims payments (building payments only) have been made under such coverage, with cumulative amount of such claims exceeding the market value of the building.
3. In both instances, at least 2 of the claims must be within 10 years of each other, and claims made within 10 days of each other will be counted as 1 claim.
Source: 44 CFR §79.2(g), Definitions
The plan must address NFIP-insured structures that have been repetitively damaged by floods. The definitions for repetitive loss are below. Information on repetitive loss properties in your community can be obtained from your State NFIP coordinator or local floodplain administrator.
Scenario Analysis
Scenario analysis predicts the impacts of a particular event. Scenarios can be an especially helpful tool for low frequency, high consequence events, such as earthquakes, for which historical information is not available. Scenario analysis asks “what if” a particular event occurred and predicts potential impacts and losses in terms of monetary costs, casualties, infrastructure downtime, and other risk elements. This type of analysis can also be used to describe possible impacts for different growth and development scenarios.
Hazus, a FEMA loss estimation software, is one tool that can estimate losses for flood, earthquake, and wind hazards (for more details on Hazus, see sidebar). Loss estimations can quantify potential fatalities, injuries, direct property loss and damage, and indirect economic loss for a certain event scenario or over time (annualized loss).
Best Practices
Harris County, TX Harris County, TX was selected as a best practice because its plan estimates dollar losses to residential, commercial and critical buildings in each jurisdiction in a storm event based on different potential storm surge heights. It presents the projected losses in clear, easy-to-read tables, shown below.
Morehead City, NC
Morehead City was chosen as a best practice because its plan identified potential losses for current building values and for building values projected 5 years into the future.
Hazus
Hazus is a nationally applicable methodology for estimating potential losses from earthquakes, hurricane winds and floods. Hazus uses GIS technology to estimate physical, economic, and social impacts of disasters.
Applications for Mitigation Planning
The planning team will likely use a combination of methods for analyzing risk and express impacts both qualitatively and quantitatively, depending on the hazard and the available time, data, staff, and technical resources. For instance, analyzing flood risk could include the following:
- Develop earthquake, hurricane, or flood models to describe location, extent, and probability of the hazard across the planning area and potential impacts to critical facilities
- Conduct a cost benefit or losses avoided analysis to support a mitigation strategy
- Use Hazus GIS data inventories to model losses from other hazards such as landslide, wildfire, dam/levee failure, etc.
- Update hazard data with flood boundary, flood depth grid, earthquake shake maps, and hurricane wind data
- Update asset inventory data with population, building stock, or utility data
- Edit flood depth damage functions and stream discharges
- A description of the types of impacts that affected community assets as a result of previous flood events, including public assistance costs and insured and uninsured losses.
- Identification of the number and value of community assets located in flood hazard areas and any specific vulnerability due to physical characteristics or socioeconomic uses.
- Estimates of the physical, economic, and social impacts of a one-percent annual flood event based on a Hazus model.
- A description of future development that may be at risk to flooding based on current zoning maps.
Best Practice
New Hanover County, NC The New Hanover County hazard mitigation plan was chosen as a best practice because it does an excellent job of identifying and prioritizing hazards and clearly describes the classification system used in the plan. After the New Hanover County plan had clearly identified the relative hazards the plan then classified the hazards according to the Priority Risk Index (PRI). The purpose of the PRI is to prioritize all the potential hazards. The hazards were then grouped into three categories of high, moderate, or low risk in order to identify and prioritize mitigation opportunities. The PRI is a good practice to use when prioritizing hazards because it provides a standardized numerical value so hazards can be compared against one another (the higher the PRI value, the greater the hazard risk). PRI scores should be calculated through five categories, probability, impact, special extent, warning time, and duration. New Hanover County assigned a value to each category (1-4) based on the degree of risk. Additionally, each category was assigned a different weight. The assigned risk value for each category was multiplied by the weighting factor. The sum of all five categories equals the final PRI value, demonstrated in the equation below (the highest possible PRI value is 4.0). PRI VALUE = [(PROBABILITY x .30) + (IMPACT x .30) + (SPATIAL EXTENT x .20) + (WARNING TIME x .10) + (DURATION x .10)] The figure below summarizes the degree of risk assigned to each category for all initially identified hazards based on the application of the PRI.
Element D1
A local jurisdiction must review and revise its plan to reflect changes in development.
44 CFR §201.6(d)(3)
Element B3
The risk assessment shall include an overall summary of each hazard and its impact on the community.
44 CFR §201.6(c)(2)(ii)
Plan updates must describe changes in development that have occurred since the last plan was approved. The planning team will need to gather information from planning and building departments on recent and planned development to evaluate how vulnerability may have increased or decreased. Development in identified hazard areas and construction not built to updated building codes increase your community’s vulnerability to future hazards and disasters.
The planning team may also consider other conditions that affect vulnerability, such as climate variability, declining or increasing populations, infrastructure expansion, or economic shifts. If no changes in development occurred or did not affect the jurisdiction’s overall vulnerability, plan updates can validate the information in the previously approved plan.