Characterizing Community Drinking Water Systems Exposed to Wildfire in the Western U.S.
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Rising temperatures and prolonged droughts contribute to longer wildfire seasons as well as larger and more severe wildfires (Hohner et al. 2019). This increase in wildfire hazard has led to growing concern over the environmental and health impacts of wildfires. Pennino et al. (2022) found that wildfires are associated with increased drinking water contaminant levels, which can last multiple years post-wildfire. We advance the wildfire and water security literature by analyzing the association between exposure to upstream wildfire events and community water system characteristics across the Western US. Our objective is to develop a more complete understanding of the relationship between wildfire and community drinking water security.
The empirical analysis uses data from the EPA’s Safe Drinking Water Information System (SDWIS) to identify nearly 12,000 community water systems (CWSs) that provide drinking water to communities in eleven states across the Western US. The population served by the CWSs in our sample cover more than 90% of the total population in the Western US. Although most CWSs are relatively small and rely on groundwater sources, we find that most people in the Western US receive their water from larger CWSs that rely on surface water sources, and thus may be particularly vulnerable to wildfire impacts on source water quality.
We use facility-level CWS intake information provided by the U.S. EPA’s Drinking Water Mapping Application. Then, we use spatial data on wildfire events from 1984 to 2022 from the Monitoring Trends in Burn Severity (MTBS) program to map upstream fires and calculate the percentage of area burned upstream from CWS intake locations. Approximately 63% of all CWSs in our data overall were exposed to wildfire between 1984 and 2022, with approximately 70% of CWSs that rely on surface water sources being exposed to wildfire.
To characterize the populations impacted by upstream wildfire events, we use novel CWS service area boundaries from the Environmental Policy Innovation Center and SimpleLab to assess the demographic information of the populations served by each CWS. Similar to Sanchez et al. (2023), who use the Social Vulnerability Index (SVI) to examine the extent to which socially vulnerable groups experience water shortages, we use the SVI to characterize the vulnerability characteristics of populations exposed to wildfire events in upstream watersheds.
Our results reveal that exposure to wildfire in upstream watersheds is positively correlated with the overall SVI measure, meaning that community drinking water systems serving socially vulnerable populations have been disproportionally impacted. The difference in vulnerability is most pronounced among indicators related to socioeconomic status, such as the percentage of population below 150% of the poverty level, the percentage of population without a high school diploma, and indicators related to racial and ethnic minority status. On average, CWSs that experienced a wildfire during the study period have almost 4% more people with income less than 150% of the poverty level, 3% more people without a high school diploma, and have a 7.7 percentage point higher proportion of the population that are racial and ethnic minorities compared to CWSs that have not experienced a wildfire. These differences are statistically significant in each case. We are actively working to evaluate heterogeneity in wildfire impacts over time and to incorporate different measures of wildfire scale and severity.