Section 7 of SB762 directs Oregon State University (OSU) to work with the Oregon Department of Forestry (ODF) to complete a statewide map of social vulnerability. The social vulnerability data is publicly available on the Oregon Wildfire Risk Explorer, which serves as an interactive educational tool for Oregonians. A more detailed version of the methods and raw data for mapping social vulnerability can be accessed at OSU Scholar’s archive.
Figure 1 The OSU team generated three data products to support state agencies with implementation of various sections of SB762: (1) WUI map; (2) wildfire risk map; and (3) social vulnerability map. One way in which the social vulnerability map will be used with the other two products is to determine how community assistance resources are allocated based on risk and need.
Vulnerability to wildfire is a function of the physical exposure to wildfire (wildfire risk), as well as the social, economic, and demographic characteristics that influence the ability of individuals or communities to prepare for, respond to, and recover from hazards (social vulnerability) (Cutter et al. 2003). Social vulnerability is often assessed using a Social Vulnerability Index (SVI), a tool that approximates social vulnerability for a given place by combining multiple indicators (i.e. poverty rate, access to transportation, and unemployment, among others) into a single score that indicates how likely it is that one place is more socially vulnerable as compared to others across the state. For the map layer identifying socially vulnerable communities required under SB 762, we use an SVI to map social vulnerability for all of Oregon that shows which communities may need more support before, during, or after a wildfire, and for state agencies to use as they implement aspects of Senate Bill 762.
To meet the needs of Senate Bill 762 we followed the methodologies of the Centers for Disease Control Social Vulnerability Index (CDC SVI) (Centers for Disease Control Social Vulnerability Index 2018 Documentation, 2022). The CDC SVI uses up to 15 indicators to calculate four vulnerability themes and an overall social vulnerability score (Table 1). For our map layer, all data for the indicators come from the US Census American Community Survey (ACS) 5-year estimates from 2016-2020.
Figure 2. Components of community vulnerability to wildfire.
Table 1. Indicators and themes that comprise the overall social vulnerability score.
Social vulnerability can be measured and mapped at many different spatial scales, from neighborhoods to nations, depending on how the data is to be used (Figure 3). For SB762, our goal was to produce a map that supports statewide decision-making, but we recognized that it might also be used by individuals and communities with more local concerns. To support planning across a range of different scales (“geographies”), we calculate and mapped the SVI by US Census block groups. Block groups are areas delineated by the US Census Bureau that contain between 600 and 3,000 people. There are 2,970 block groups in Oregon. Block groups are not all the same size. In densely populated areas they are quite small, while in rural and remote parts of Oregon a single block group could include half the county (Figure 3).
The Oregon Wildfire Risk Explorer shows SVI data for block groups across Oregon because they are the smallest unit for which most social and economic data are available, allowing for the most detailed picture of social vulnerability. However, we also curated and provided SVI datasets for tracts and county subdivisions using the 2016-2020 American Community Survey. These datasets are available to download from Scholars Archive.
Figure 3. The relationship between US Census Bureau geographies. Red boxes outline levels of geography for which OSU provides SVI data (adapted from Rossiter, 2014).
Social vulnerability indices provide a relative measure of social vulnerability. In other words, we calculated SVI values for each block group in Oregon and then compared and ranked each block group relative to all the other block groups. We calculated four social vulnerability themes and overall social vulnerability using up to 15 indicators in Table 1 as follows:
Step 1. Calculate SVI Indicators at Block Group Level
To assess social vulnerability for a given block group, first we calculated each of the 15 individual indicators listed in Table 1using data from the 2016-2020 ACS.
Step 2. Rank Each Indicator Across All the Block Groups
Then, we took a percent rank for each indicator and block group. The percent rank tells us how any one block group compares to all others for that individual indicator. For example, when we take the percentile rank for the indicator “population in poverty” the block with the highest percentage of population in poverty will be given a score of 1, and the block group with the lowest population in poverty will be given a score of 0. The value of 1 indicates that it is the 100th percentile or that it has a higher level of poverty than 100% of the block groups in the state. The block groups with the highest scores (those closer to 1) represent the most vulnerable communities for each indicator.
Step 3. Calculate Theme Scores for Each Block Group
To calculate the themes, we summed up the percent ranks from Step 2 for all indicators in each theme (Table 1). For instance, to calculate the theme score for the Minority Status and Language theme (part C in Figure X), we summed the indicator scores for Minority Population and Limited English Language within each block group. Again, we calculated a percent rank for each block group relative to all the other block groups in each theme. A score closer to 100% represents higher relative vulnerability and those closer to 0% represent lower relative vulnerability.
Figure 4. Overall social vulnerability for each block group in Lane County (A) is the sum of cumulative indicator scores for each of the four themes (B – E). Block groups around Eugene, the most developed part of Lane county are much smaller than block groups in less populated parts of the county.
Step 4. Calculate Overall Relative SVI Scores for Each Block Group
To get the overall relative vulnerability score, we summed up the percent rank of the individual themes from Step 3 and take a final percent rank of each block group relative to all other block groups (Figure 3). We multiplied overall scores by 100 to yield a percentage and to make interpretation of the final score more intuitive. A score closer to 100% represents higher relative vulnerability and those closer to 0% represent lower relative vulnerability.
Figure 5. Final statewide map of relative social vulnerability for all block groups in Oregon
The SVI map layer on the Oregon Wildfire Risk Explorer divides all block groups in Oregon into one of four equal categories from lowest to highest relative vulnerability. There are no objective thresholds that determine whether or not a community is socially vulnerable. Instead, the SVI is best for showing the relative social vulnerability, or how social vulnerability in one part of Oregon compares to the rest of Oregon.
It is also important to acknowledge that social vulnerability is a complex topic that covers many elements of people’s lives and livelihoods. In creating a metric to capture this concept, we are limited to the available data, which is an estimate of actual community characteristics. Vulnerability varies over space and over time. We cannot be sure that in an area mapped as low vulnerability, all households are well equipped to prevent, respond to, or recover from wildfire. Likewise, we cannot be sure that an area mapped as high vulnerability will still be highly vulnerable in six months, a year, or five years from now. We recommend that this tool be used in conjunction with other information whenever possible to inform decisions about how to allocate resources, especially if granting resources to individuals and households.
It is widely understood that not all communities are equally equipped to respond to or recover from wildfire. Senate Bill 762 directs agencies responsible for implementing aspects of the bill to consider this when allocating resources for fire prevention, response, and recovery. For instance, section 8a directs the State Fire Marshal’s office and local governments to prioritize support for the creation of defensible space for “members of socially and economically vulnerable communities, persons with limited proficiency in English and persons of lower income.”
The intent of this mapping tool is to assist agencies with achieving the equity goals outlined in SB762. Based on the language in SB762 and conversations with our partner agencies, we anticipate that agencies will use this information, along with other assessments of community vulnerability to prioritize funding for hazardous fuels reduction and defensible space projects, to tailor outreach and education programs to meet the needs of communities (e.g. offering bilingual communications in areas where high proportions of the population have limited English proficiency). We advise members of the public to contact agencies directly for details on how the social vulnerability map will be used.
The social vulnerability map is not limited to agency use. Organizations and community groups may utilize the social vulnerability map to understand the social and economic conditions that may contribute to community vulnerability to wildfire, to apply for grants, and to inform their community wildfire protection plans (CWPPs).
- Centers for Disease Control Social Vulnerability Index 2018 Documentation. (2022).
- Cutter, S. L., Boruff, B. J., & Shirley, W. L. (2003). Social Vulnerability to Environmental Hazards. Social Science Quarterly, 84(2), 242–261.
- The community indicators handbook: measuring progress toward healthy and sustainable communities. (1997). [Redefining Progress].
- Rossiter, K. (2014, July 31). Understanding Geographic Relationships: Counties, Places, Tracts and More US Census Bureau.
How can I tell which communities are socially vulnerable? How do I locate these places on the map?
The SVI layer shows us how all communities rank relative to others in the state based on the components of social vulnerability described above. There are no specific thresholds for what constitutes a vulnerability community. The CDC SVI flags areas that are in the top 10 percent as highly vulnerable. Map users may wish to designate a different threshold for what constitutes a vulnerable community that is more suited to the question of interest.
How should I use this map layer?
This map layer can be used to understand what social vulnerability looks like across the state of Oregon. Organizations and community groups can include information on their community’s level social vulnerability for grants, planning, and awareness.
Where does the data for SB762 SVI come from?
The data for the SVI layer comes from the American Community Survey (ACS), a survey administered annually by the US Census to measure the changing social, economic, and demographic characteristics of the U.S. population (i.e. education, housing, health insurance, jobs etc). In areas of low population, data is combined over several years to produce a more reliable estimate of the population characteristics sampled; annual data is not available. We use the 5-year average data from 2016-2020 which samples about 1 in 12 households through mail, internet, telephone, and in-person surveys. Get more information on the ACS methods.
How reliable is the data?
The American Community Survey provides estimated statistics using a sample of the US population. Because the ACS does not sample every person, there is a margin of error associated with each estimate that tells us about the amount of error in the results of the survey. In general, larger sample sizes (e.g., more people surveyed) produced more reliable estimates; typically, the smaller the level of geography, the smaller the sample, and the larger the sampling error. There is a trade-off between reliability and the size of the geographic units used to calculate SVI. We compared reliability between block groups, census tracts, and county subdivisions to the stated purpose and goal of the map layers dictated by SB762 in order to determine which level of geography to display. Full reliability information can be found in ScholarsArchive.
How is the OSU SVI layer related to other SVI or related mapping tools being developed across the state?
In addition to OSU’s SVI work under SB762, other organizations and institutions are developing tools to measure social, economic, and environmental inequities across the state. For example, the Department of Environmental Quality (DEQ) is directed by House Bill 4077 to develop an Environmental Justice Mapping Tool by 2025 to evaluate how communities are being affected by health disparities and environmental hazards. Additionally, Portland State University’s Population Research Center (PRC) is working with the Department of Administrative Services to integrate census data points that have been used in a variety of equity indicator projects around the country into the state’s geospatial framework. Contact the PRC directly to learn more about this project.
Given the deadlines set forth in SB762 for a social vulnerability map deliverable by June 30th, 2022, OSU moved forward to develop a SVI map layer independent of other tools and projects underway. However, OSU is connected with the agencies working on these tools and will continue to share information and look for areas to collaborate into the future.
What are the limitations of the Social Vulnerability Index layer?
Social vulnerability is a complex topic that covers many elements of people’s lives and livelihoods. In creating a metric to capture this concept, we are limited to data that are, at best, proxies for elements we believe to be significantly related to vulnerability. For instance, the social vulnerability index layer is based on Census data which is consistent, well-known and available, but may not always correspond to political or cultural definitions of a given community.
In addition, when vulnerability is assessed across any unit of geography – i.e. Census block groups – it gives the impression that vulnerability characteristics are the same across the entire area. In fact, vulnerability can vary dramatically from one household or one neighborhood to another within a block group or any other geography. Likewise, vulnerability is not static through time and can change from one year to the next, or even from one season to another.
We recommend that this tool be used in conjunction with other information whenever possible to inform decisions about how to allocate resources, especially if granting resources to individuals and households.
What if I don’t agree with the Social Vulnerability Index value assigned in my area?
There are many reasons why the SVI reported for your area may not match your expectations. As discussed above, the SVI for a given area does not necessarily apply to all households or individuals within the area. The unit of geography used may also differ from your definition of your neighborhood or community, which can lead to unexpected results. SVI is also dynamic, and the gathering, processing, and releasing of census American Community Survey (ACS) data takes time. We are reporting an SVI based on data gathered between 2016 and 2020, which was the most recent ACS data release (March 2022).
Will the Social Vulnerability Index value change over time?
SVI is dynamic, changing with changing populations, economic contexts, and other factors. The Census ACS data is released annually for a rolling five-year window of data gathering. SVI can be updated annually; the language of SB 762 directs the Statewide Wildfire Risk Map, of which the SVI layer is a component, to be updated within 12 months of updates to the most current wildfire risk assessment.
How is the Social Vulnerability Index incorporated into the wildfire risk assessment (or other government programs)?
Language in SB 762 directs agencies responsible for implementing elements of the bill to prioritize socially and economically vulnerable communities. You can contact agencies responsible for implementation directly to learn more about how the SVI layer is used to inform their work.
Where can I find the SB 762 SVI map layer?
You can find the SVI map layer on the Oregon Wildfire Risk Explorer. All information related to the social vulnerability map layer will be archived at OSU Scholars Archive including data files at other levels of geography and accompanying technical documentation: Download the dataset from OSU Scholars Archive.