September is National Preparedness Month, a time to remember that safety of our families and communities during emergencies and disasters hinges on preparing for them. Where within the Atlanta region do vulnerable populations reside? How does our region’s potential for resilience to natural disasters such as extreme weather events compare to the rest of the country? And what types of natural hazards pose the greatest threat to our region? We will address these questions over a series of four blog posts. This entry will focus on the location of vulnerable populations.
The Centers for Disease Control and Prevention (CDC) provides us with one way of examining vulnerable populations through its Social Vulnerability Index, or SVI.[1] The SVI utilizes 16 indicators from the U.S. Census Bureau’s American Community Survey grouped into four “themes” or domains: socioeconomic status; household characteristics; racial & ethnic minority status; and housing type & transportation. The logic behind many of these indicators is quite intuitive. For example, people with disabilities will have a harder time relocating during a disaster; people lacking access to a vehicle may not have the means to evacuate; and mobile homes are typically more vulnerable to damage than other types of housing structures.
The SVI is available for counties, Census tracts, and (starting with the most recent release, 2022) ZIP Code Tabulation Areas.[2] Figure 1 presents the SVI statewide by county.[3]
Figure 1: CDC Social-Vulnerability Index for Georgia Counties
Data Source: Centers for Disease Control, County Level Social Vulnerability Index
Figure 1 above shows a fairly strong north-south divide in the state: with the exception of Chattooga and Clayton counties, all of the high vulnerability counties are located in middle and south Georgia. Looking at the 11-county ARC region, Clayton is the lone county in the high vulnerability group; DeKalb and Rockdale are considered medium-high vulnerability; Douglas, Fulton, and Gwinnett are low-medium vulnerability, and the remaining five counties (Cobb, Cherokee, Fayette, Forsyth, and Henry) are classified as low vulnerability.
But there is also important variation within counties. Figure 2 below concentrates on the ARC region and presents data at the Census tract level.
Figure 2: CDC Social-Vulnerability Index for Atlanta Tracts
Data Source: Centers for Disease Control, Tract Level Social Vulnerability Index
Figure 2 above reveals pockets of high vulnerability areas within the Atlanta region. These include a band running southeast from northeastern Douglas County through south Cobb and south Atlanta, and covering much of Clayton County, then moving northeast into central DeKalb, and finally along I-20 into Rockdale County. Other high vulnerability communities are located in central Cobb, along the Buford Highway corridor through Gwinnett County, and central Cherokee.
How do the four themes of social vulnerability correlate with the overall SVI? Let’s look at each in descending order of correlation.
The first theme is socioeconomic status, presented below in Figure 3.[4]
Figure 3: Socioeconomic Status Theme within CDC Social-Vulnerability Index for Atlanta Tracts
Data Source: Centers for Disease Control, Tract Level Social Vulnerability Index
Among Georgia tracts, the socioeconomic theme correlates strongly with the overall SVI index (r=.89).[5] Its distribution is therefore very similar to the overall index itself. The main differences are the heavier pockets of high vulnerability populations along the I-20 and Buford Highway corridor.
In second place, the Housing Type theme[6] correlates at .79 with the overall SVI. The distribution of this theme is presented in Figure 4 below.
Figure 4: Housing Type Theme within CDC Social-Vulnerability Index for Atlanta Tracts
Data Source: Centers for Disease Control, Tract Level Social Vulnerability Index
Again, we see above similar geographic patterns between this theme and the overall SVI, but also some differences worth noting. For example, a number of tracts along the Buford Highway corridor in the highest risk category for the overall SVI are now only in the medium-high group for household characteristics. We see the same phenomenon in Clayton County. These differences can be attributed, in part, to the fact that mobile homes are relatively uncommon in our region as compared to the state as a whole.
Next, we have the Household Characteristics theme, as displayed in Figure 5, which correlates at .65 with the overall SVI statewide.[7]
Figure 5: Household Characteristics Theme within CDC Social-Vulnerability Index for Atlanta Tracts
Data Source: Centers for Disease Control, Tract Level Social Vulnerability Index
Comparing the distribution of high vulnerability Census tracts on this dimension with the overall SVI score, we see some notable differences. While Fayette County has no tracts in the high vulnerability group for the overall SVI, it has several in the high vulnerability category within this theme, in part due to higher rates of elderly population. Similarly, a number of tracts along the Buford Highway corridor in Gwinnett County are in the most vulnerable category for the overall SVI but are only in the medium-high category for this theme. Again, this is largely explained by the age profile of the population in these areas.
Finally, Figure 6 below shows the Racial & Ethnic Minority Status[8] theme.
Figure 6: Racial & Ethnic Minority Status Theme within CDC Social-Vulnerability Index for Atlanta Tracts
Data Source: Centers for Disease Control, Tract Level Social Vulnerability Index
With a correlation of .51, this theme still exhibits a moderate relationship with the overall SVI. But that relationship to the SVI is much weaker than for any other themes. In particular, we see that the Census tracts scoring high on this dimension form much more coherent blocks.
In sum, the Social Vulnerability Index can alert us to which parts of our community may have needs both leading up to and after an emergency or disaster. But when designing specific interventions, one must dig deeper into which components caused an area to score high.[9] For example, areas with large elderly populations may require special transportation or medical attention. But an area with many people with low English language proficiency might require extra interpreters and materials written in other languages.
In the next episode in this series, we will examine the concept of community resilience.
Want to explore further? The CDC offers an interactive map of SVI: https://www.atsdr.cdc.gov/place-health/php/svi/svi-interactive-map.html
Notes:
[1] The idea of constructing and mapping a Social Vulnerability Index was first advanced by Susan Cutter and her colleagues at University of South Carolina, who constructed a county-level index in 2003. The CDC picked up on this idea to develop a similar index at the more granular Census tract level, released in 2011.
[2] The CDC releases two different versions of the SVI: one that is scaled based on nationwide values, another that limits its comparisons to within a state. We are using the SVI specifically scaled for Georgia.
[3] Following the lead of how the CDC presents these data in their mapping tool, the vulnerability groups presented in these maps represent quartiles, i.e., dividing counties (and tracts) into four equal-sized groups.
[4] The following five indicators comprise the Socioeconomic Status theme: % population with incomes below 150% of the poverty line; % unemployed; % housing cost-burdened households earning less than $75k; % population without HS diploma; % population without health insurance.
[5] Just a reminder that correlations range between 0 and 1 in absolute value. A correlation of -1 represents a perfect negative relationship, a value of 1 denotes a perfect positive relationship, and a value of zero means there is no relationship.
[6] Five indicators make up the Housing Type theme: % of housing in structures with 10 or more units; % mobile homes; % crowded housing units (more than 1 person per room); % of households with no vehicle available; and % of population living in group quarters (e.g., dormitories, nursing homes, prisons, etc.).
[7] The Household Characteristics theme includes the following five indicators: % population 65 and older; % population 17 and younger; % disabled civilians; % single-parent households; and % with limited English proficiency.
[8] The Racial & Ethnic Minority Status theme is measured via the percentile percentage minority (i.e., everything except for non-Hispanic White).
[9] To paraphrase Anna Karenina, every vulnerable population is vulnerable in its own way.