Source water protection and wildfire threats: A simplified vulnerability assessment framework for drinking water intakes

Post-wildfire contamination poses a serious threat to drinking water in forested watersheds, with implications for long-term resilience of drinking water treatment plants. Infrastructure such as pumping equipment and transportation piping systems can also be exposed to wildfire-related impacts. Wildfires significantly alter water quality by increasing sediment loads, dissolved organic carbon, nutrients, and heavy metals. Fire suppression efforts further introduce contaminants, such as per- and polyfluoroalkyl substances, which persist in the environment and pose long-term risks to drinking water safety. This study presents a broadly applicable framework to assess the vulnerability of drinking water intake to the post-wildfire runoff and erosion response. It is designed for use across diverse geographic and environmental contexts, draws on readily available data, incorporates key post-wildfire runoff and erosion parameters, and accounts for climate change to address future contamination threats to water supplies. The framework calculates a vulnerability index incorporating information about forest cover, runoff potential, fire regime under climate change, and rainfall under climate change. The index is further refined accounting for drinking water intake exposure. Its design enables prioritization of sub-watersheds despite data availability while remaining adaptable to more refined datasets when available. The results indicate that forest cover and runoff potential are the dominant variables influencing final index scores, while rainfall projections under climate change amplify post-wildfire water contamination. Although wildfire threats driven by climate change continue to increase, drinking water managers often fail to integrate potential climate-driven hazards to surface water supply into their long-term adaptation strategies. Ensuring drinking water treatment plant resilience will require both adaptable assessment tools and scalable protection planning. In response, this framework supports informed decision-making to enforce targeted land use regulations, and develop emergency response strategies. These measures help mitigate post-wildfire impacts on drinking water intakes and support infrastructure adaptation accordingly.