New research shows that, far from a short-lived pulse, fire-driven pollutants linger in Western U.S. watersheds much longer than scientists once thought.
The study, published today in Nature Communications Earth & Environment, marks the first large-scale assessment of post-wildfire water quality across more than 500 river basins. By analyzing over 100,000 water samples from burned and unburned sites, the researchers painted a continental picture of how organic carbon, phosphorus, nitrogen, sediment, and turbidity respond after fires.
“We were attempting to look at notable trends in post-wildfire water quality across the entire U.S. West, to help inform water management strategies in preparing for wildfire effects,” said Carli Brucker, lead author and former CU Boulder and Western Water Assessment PhD student.
The team found that organic carbon, phosphorus, and turbidity spike significantly in the first one to five years following a fire. Nitrogen and sediment proved even more persistent.
“It can take two years, up to eight years, for the effect to be fully felt,” Livneh said.
Here, Livneh refers to CIRES Fellow and Western Water Assessment Director Ben Livneh, whose modeling revealed that some contaminants peak only when subsequent storms mobilize ash and eroded soils.
Fire-driven impacts also varied widely by location. Basins with denser forests or fires closer to streams suffered the worst degradation, while differences in soil type, vegetation, and rainfall patterns meant that no two watersheds responded in exactly the same way. “There’s a huge amount of variability in sedimentation rates,” Brucker said. “Some streams are completely clear of sediment after wildfires, and some have 2000 times the amount of sediment.”
Despite this variability, the study offers water managers concrete timelines and contaminant thresholds to guide future planning. By comparing burned basins to unburned controls year by year, the researchers provided a robust framework for anticipating long-term water quality challenges.
The findings underscore the need for proactive strategies that extend well beyond the initial fire season. Armed with these new numbers, water managers across the Western U.S. can now prioritize monitoring, treatment upgrades, and watershed restoration efforts to build resilience against the lingering legacy of wildfires.
The study has been published in Communications Earth & Environment.
