ADDRESSING CRITICAL GAPS IN ASSESSMENT AND PREDICTION OF WILDFIRE IMPACTS ON WATER QUALITY (Invited Presentation)

After wildfires, storms can convey sediment, ash, pollutants, and debris from hillslopes to surface water, leading to immediate and long-term impacts on water quality, reservoir storage, and water treatment costs. Water providers and land managers have a need to effectively plan for, prevent, and mitigate impacts on water supplies, which should be supported through a capacity to accurately assess and predict water-quality impairment during and after wildfire. Critical gaps in our understanding of drivers and processes that determine post-wildfire impacts on water supplies must be resolved and incorporated into models. Relevant drivers of delivery include: precipitation regime (snow or rain; short, high-intensity vs. long, low intensity; drought); watershed characteristics (slope, aspect, geology, vegetation); wildfire parameters (severity, patchiness, size); and land use (historical and current). The sensitivity of receiving waters, and magnitude and duration of water-quality impairment, is a function of residence time, background chemistry, and instream biogeochemical processes. Channel geomorphic processes can alter surface-water/groundwater interactions and potentially water quality. For example, wildfire in the Colorado Front Range can shift the timing of water, sediment, and nutrient yield from the snow-dominated season to rainfall-dominated season, and the intersection of wildfire and legacy mine waste can result in increased transport of metals to surface water. The importance of various drivers will vary across hydro-ecoregions. Thus, a regional, comprehensive framework for incorporating post-fire drivers of water quality is needed. Efforts by the USGS Water Resources Mission Area are focused on improving our understanding of post-wildfire water-quality drivers and processes across different hydro-ecoregions. These results will be integrated with geospatial data to advance modeling and prediction of post-fire water quality. Given that the size and severity of wildfires in the western U.S. are increasing, it is imperative that we enable society to develop capacity to predict and mitigate wildfire effects on our water resources.