Over the course of National Preparedness Month, we have explored the concepts of social vulnerability, community resilience, and Expected Annual Loss, all with relation to natural hazards. For the final episode in this series, we’ll see how the Federal Emergency Management Agency (FEMA) brings all three of these concepts together into a single National Risk Index (NRI).
Essentially, the NRI starts with the expected annual loss– the average loss in dollars each year from natural hazards, then scales that value up or down based on community risk factors. Higher levels of social vulnerability increase the NRI value from that baseline, while higher levels of community resilience decrease the value. Figure 1 shows the NRI at the county level statewide; categories in this map represent “natural breaks.”[1]
Figure 1: FEMA National Risk Index by County
Data Source: Federal Emergency Management Agency National Risk Index Data
This map shows that over half of Georgia counties fall into the “very low” risk category, while no counties in Georgia fall into the “very high” category relative to counties nationwide.[2] The Georgia county at highest risk from natural hazards as measured by the NRI is Chatham County, which stood out in our previous post as high risk for hurricanes and coastal flooding. Other counties on and near the coast fall into the “relatively moderate” category due to those same risks. Thomas County in south Georgia also falls in the “relatively moderate” category (despite scoring “relatively low” in terms of Expected Annual Loss), because it does not score as well on the Social Vulnerability Index or Baseline Resilience Indicators for Community Resilience measures. And the five core counties of Atlanta score in the “relatively moderate” category as well: Clayton because it has a high Social Vulnerability Index score, the others due to the magnitude of Expected Annual Loss.
Figure 2 shows the NRI at the tract level, focused on the Atlanta region. Again, categories in this map represent “natural breaks.”
Figure 2: FEMA National Risk Index by Census Tract for the Atlanta Region
Data Source: Federal Emergency Management Agency National Risk Index Data
As we see in this map, no tracts within the Atlanta region fall into the “very high” risk category.[3] The two highest risk areas as measured by this index fall in the “relatively high” category and are located downtown just north of where the connector meets I-20 and in unincorporated Cobb County between Marietta and Kennesaw. Every county in the region has at least some areas that deserve attention by virtue of falling in the “relatively moderate” category; most of these fall along the more densely populated highway corridors.
Ultimately, the NRI brings both the strengths and weaknesses of any index score. By bringing together measures of Social Vulnerability, Community Resilience, and Expected Annual Loss– each of which itself is composed of many component indicators– into a single index, the NRI helps cover various facets of risk. It paints a picture of which areas within our region require extra attention and planning to reduce natural hazard risks. But with so many measures built in, there is no way of telling what the specific needs of those areas are, or how best to craft policies to address those needs. That still requires digging into the index components, as shown in the previous posts from this series.
Want to explore further? FEMA offers an interactive mapping tool that allows you to explore the overall NRI as well as its individual component.
Notes:
[1] FEMA utilized an unsupervised machine learning technique called k-means clustering to determine appropriate categorization of geographic units by risk.
[2] The “very high” category does not appear on the legend of the county map because no Georgia counties fall into that category.
[3] Georgia has 35 Census tracts falling in the “very high” category, primaily near the coast. However, none fall within the scope of this map, which is focused on the Atlanta region.