Research Feature
Characterization of wildfire impacts: State-of-the-science consensus
Key messages​
Water Treatment Costs Reduced by
per cent

Summary

  1. Wildfire threats to water supplies are recognized and increasing globally. Fires differ in size and intensity, and the severity of impact can vary spatially and temporally, depending on wildfire size, intensity and severity; physical, biological, and chemical attributes of the landscape; and hydroclimatic conditions before and after the fire.
  2. Vegetation is reduced or absent after severe wildfire. In some cases, more precipitation reaches the land surface, soils can become hydrophobic, and there can be reduced infiltration and increased surface runoff, leading to increased erosion. In some areas, intense rainfall can trigger fast-moving debris flows that can strip vegetation, block drainage ways, damage structures, reduce raw/untreated water reservoir storage capacity, and endanger human life. 
  3. When surface water quality is impacted by wildfire, it is typically more variable with increased peak values. In rivers and streams, these changes are typically episodic and observed at higher discharge conditions. Changes in water quality can include increases in turbidity/suspended solids and fine sediment-associated contaminants including metals, organics (e.g., PAHs, dioxins, furans), and nutrients (phosphorus, nitrogen, and micronutrients). Dissolved ammonium and nitrate can also increase. Dissolved organic carbon (DOC) is frequently elevated and more aromatic after wildfire, thereby leading to increased coagulant demand and disinfection by-product formation potential and potentially the associated need for increased removal prior to disinfection. In some areas, releases of phosphorus from sediments to the water column have been observed and have promoted primary productivity, including the proliferation of algae that can produce toxins of human health concern and microorganisms associated with the production of taste and odor compounds.
  4. When fire occurs on the built environment, infrastructure can serve as a secondary source of contaminants via adsorption and desorption processes. These typically persistent organic contaminants can be released to both source (i.e., via runoff) and treated water supplies; for example, VOC/SVOC contamination of isolated water supplies in buried distribution networks. 
  5. Collectively, the potential water quality impacts of wildfire underscore that wildfire may challenge drinking water treatment plants beyond their operational capabilities, possibly resulting in increased costs, service disruptions, or outages. As well, they may further result in the release of contaminants to the distribution system. Thus, water treatment resilience that reflects the collective importance of source water protection, treatment, and distribution barriers should be prioritized.
  6. Wildfire impacts on water quality and treatability can range from none to long lasting and/or severe, and may be immediate or delayed (e.g., years). In some regions they can last for decades or longer. As well, some contaminants can be transported over long downstream distances. Wildfire effects on water quality and treatability are often most evident in the first several years after wildfire. 
  7. Severe wildfire on a relatively small percentage of watershed area (e.g., < 10%) can have a significant impact on untreated/raw water quality and treatability, even at large basin scales and in systems with already deteriorated source water quality.



Publications

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Photo: Working onsite with partner X.

Contributors

List of participants at the Seattle workshop
Charles C. Rhoades, US Government
Uldis Silins, Researcher, University of Alberta
Micheal Stone, Researcher, University of Waterloo
Fernando Rosario, Researcher, Colorado State University
Amanda Hohner, Researcher, Montana State University
T Karanf, Clemson University
Andy Whelton, Purdue University

Mac Gifford, Portland Oregon
Wendy K, Halifax Water
Antoine Rempp, Regional Municipality of Wood Buffalo
Norma Ruecker, The City of Calgary
Todd Schram, SCWA Government

 Amy Labarge, Seattle Utility
Mike Dirks, Water Research Foundation
Kenan Ozekin, Water Research Foundation
Kristen Wilson, The Nature Conservancy
Erin Brooks, University of Idaho