Wildfires can often be viewed as short-term disasters, but their impacts can linger for years, particularly in the rivers and streams downstream of burned landscapes
A new study led by researchers at the Cooperative Institute for Research in Environmental Sciences (CIRES) reveals that wildfire damage can continue to degrade water quality for nearly a decade after the flames have gone out.
Published in Nature Communications Earth & Environment, the study analysed more than 500 river basins across the Western United States, creating the first large-scale dataset to assess post-wildfire water quality impacts. By examining over 100,000 water samples, researchers found that harmful contaminants, including organic carbon, phosphorus, nitrogen, sediment, and turbidity, can remain elevated for years.
Long-term contamination
Previous studies have typically focused on local or regional effects in the immediate aftermath of wildfires. This new research, however, reveals that water quality degradation can persist for much longer and affect a significantly wider area than previously understood.
The data showed that organic carbon, phosphorus, and turbidity often spike within the first five years following a wildfire. Nitrogen and sediment levels can persist at high levels for up to eight years. This prolonged pollution can make drinking water treatment more difficult and expensive, and it can also harm aquatic ecosystems.
One key factor is the type of landscape that burns. More forested areas were found to experience worse water quality degradation. Fires strip away vegetation and destroy soil structure, making it easier for ash and sediment to wash into rivers and streams during rain. In some cases, the full impact isn’t felt until a major storm arrives, mobilising the leftover contaminants.
Burned vs. unburned basins
To understand these patterns better, the researchers compared water quality data from basins affected by wildfires with those that hadn’t burned. This side-by-side comparison allowed them to isolate the impact of fire from other environmental factors. The findings confirmed that fire-affected watersheds consistently showed more severe and longer-lasting contamination.
The effects varied widely depending on local conditions. Watersheds, where fires occurred near rivers or in areas with loose, erosion-prone soil, tended to suffer more severe water quality impacts. In contrast, some areas exhibited surprisingly little sedimentation, highlighting the interplay of topography, vegetation, and weather patterns in shaping post-fire water quality outcomes.
Implications for water management
This study provides essential information for water managers across the Western U.S., who are increasingly facing the challenge of preparing for and responding to the aftermath of wildfires. As wildfires become more frequent and intense due to climate change, understanding their impact on water quality is crucial for long-term planning.
The researchers hope their findings will support the development of more targeted resilience strategies. By providing concrete, data-driven estimates of the duration and severity of water quality impacts after wildfires, the study fills a significant gap in wildfire planning and recovery efforts.
Working towards resilience
The variability in post-fire impacts makes it difficult to apply a one-size-fits-all solution, but having real numbers helps agencies prioritise resources and plan more effectively. For communities across the West, this research provides a clearer picture of what to expect in the years following a fire, highlighting the importance of investing in water system resilience.
As wildfires continue to reshape landscapes and ecosystems, understanding their hidden and long-term impacts on water quality remains crucial.
