Determining Risk
In the National Risk Index, risk is defined as the potential for negative impacts as a result of a natural hazard.
The risk equation behind the Risk Index includes three components: a natural hazards component (Expected Annual Loss), a consequence enhancing component (Social Vulnerability), and a consequence reduction component (Community Resilience). The datasets supporting the natural hazards and consequence reduction components have been standardized using a min-max normalization approach. The dataset supporting the consequence enhancing component was acquired in a normalized format, allowing for easy incorporation into the National Risk Index risk calculation. Using these three components, a composite Risk Index score and hazard type Risk Index scores are calculated for each community (county and Census tract) included in the Index.
Each community has a composite Risk Index score and up to 18 hazard type Risk Index scores (e.g., Tornado Risk Index score). A composite Risk Index score measures the relative risk of a community based on all 18 natural hazards included in the Index, while a hazard type Risk Index score measures the relative risk of a community for a specific hazard type.
For comprehensive details about how risk is calculated for the Risk Index, see the National Risk Index Technical Documentation.