SECTION 4: RISK ASSESSMENT
HISTORICAL OCCURRENCES
This section contains information on historical events, including the location and consequences of all past events on record within or near the Wake County planning area. PROBABILITY OF FUTURE OCCURRENCE This section gauges the likelihood of future occurrences based on past events and existing data. The frequency is determined by dividing the number of events observed by the number of years on record and multiplying by 100. This provides the percent chance of the event happening in any given year according to historical occurrence (e.g. 10 winter storm events over a 30-year period equates to a 33 percent chance of experiencing a severe winter storm in any given year). CLIMATE CHANGE Where applicable, this section discusses how climate change may or may not influence the risk posed by the hazard on the planning area in the future. VULNERABILITY ASSESSMENT This section quantifies, to the extent feasible using best available data, assets at risk to natural hazards and potential loss estimates. People, properties and critical facilities, and environmental assets that are vulnerable to the hazard are identified. Future development is also discussed in this section, including how exposure to the hazard may change in the future or how development may affect hazard risk. The vulnerability assessments followed the methodology described in the FEMA publication Understanding Your Risks — Identifying Hazards and Estimating Losses (August 2001). The vulnerability assessment first describes the total vulnerability and values at risk and then discusses vulnerability by hazard. Data used to support this assessment included the following: • Geographic Information System (GIS) datasets, including building footprints, topography, aerial photography, and transportation layers;
• Hazard layer GIS datasets from state and federal agencies;
• Written descriptions of inventory and risks provided by the State Hazard Mitigation Plan; and
• Written descriptions of inventory and risks provided by the previous Wake County Multi- Jurisdictional Hazard Mitigation Plan. • Exposure and vulnerability estimates provided by the North Carolina Emergency Management (NCEM) IRISK database.
• Crop insu rance claims by cause from USDA’s Risk Management Agency
Two distinct risk assessment methodologies were used in the formation of the vulnerability assessment: a quantitative analysis that relies upon best available data and technology, and a qualitative analysis that relies on local knowledge and rational decision making. Vulnerability can be quantified in those instances where there is a known, identified hazard area, such as a mapped floodplain. In these instances, the numbers and types of buildings subject to the identified hazard can be counted and their values tabulated. Where hazard risk cannot be distinctly quantified and modeled, other information can be collected in regard to the hazard area, such as the location of critical facilities, historic structures, and valued natural resources (e.g., an identified wetland or endangered species habitat). Together, this information conveys the vulnerability of that area to that hazard. The quantitative analyses for this plan involved the use of FEMA’s Hazus software, which provides modeled loss estimates for flood, earthquake, and hurricane wind, and NCEM’s IRISK database, which provides modeled damage estimates for earthquake, flood, hurricane wind, thunderstorm wind, tornado, and
Wake County, NC Multi-Jurisdictional Hazard Mitigation Plan
WSP June 2024 Page 69
Made with FlippingBook interactive PDF creator