Wildfires threaten water quality for up to eight years after they burn
A study of 100,000 water samples from 500 river basins found elevated levels of contaminants persist for years after a fire
University of Colorado at Boulder
Years after wildfires burn forests and watersheds, the contaminants left behind continue to poison rivers and streams across the Western U.S. — much longer than scientists estimated.
A new study, published today in Nature Communications Earth & Environment, analyzed water quality in more than 500 watersheds across the Western U.S., and is the first large-scale assessment of post-wildfire quality.
The research was led by scientists from the Cooperative Institute for Research in Environmental Science (CIRES) at the University of Colorado Boulder.
“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 results showed contaminants like organic carbon, phosphorus, nitrogen, and sediment can degrade water quality for up to eight years after a fire. Water managers can use this data to help them plan for the future and respond appropriately when wildfires strike.
CIRES Fellow and Western Water Assessment Director Ben Livneh was the principal investigator and co-author of the study. Much of his research focuses on hydrology, or water supply, on a continental scale. When he realized he could use the same approach to understand large-scale trends in water quality, he was excited to test the method.
“There’s been a lot of work, for example, in the National Climate Assessment and the International Panel on Climate Change talking about changes in global water supply,” said Livneh, associate professor in the Department of Civil, Environmental and Architectural Engineering. “But those assessments point to this gap in water quality assessments in a continental scale context, whereas people like me in physical hydrology have been thinking about the continental scale challenges for a while.”
Researchers have long known that fire ash and soil destruction contribute to degraded water quality. Yet, past research has largely been limited to state and municipal studies — cities and towns test water quality in local streams and rivers following large fires.
For the new study, the team analyzed more than 100,000 water samples from 500 sites: half from burned river basins and half from unburned. They measured levels of organic carbon, nitrogen, phosphorus, and sediment as well as turbidity, or cloudiness, of each sample.
To understand wildfire-driven impacts, the team built data-driven models to measure how much contaminants changed in each basin before and after wildfires. In the final step, they compiled data to find the average across the burned basins for each pre- and post-wildfire year, and then compared those to the unburned basins.
The results showed watersheds take longer to recover after wildfires than previous studies found. Organic carbon, phosphorus, and turbidity are significantly elevated in the first one to five years post-fire. Nitrogen and sediment show significant increases up to eight years post-fire. Fire-driven impacts were worse in more forested areas.
“It can take two years, up to eight years, for the effect to be fully felt,” Livneh said. “Sometimes it can be a delayed effect, meaning, it's not all happening right away, or sometimes you need a big enough storm that will mobilize enough of the leftover contaminants.”
Each watershed in the study felt the impacts differently. This is likely tied to where the fire struck — a fire closer to the river would be worse than an upstream fire. Different soils, vegetation, and weather also change the impact in each watershed, making it difficult to plan for the future.
“There's a huge amount of variability in sedimentation rates,” said Brucker, who now works as a consultant. “Some streams are completely clear of sediment after wildfires, and some have 2000 times the amount of sediment.”
Despite variability across river basins, the study provides concrete numbers that give insight to water managers across the Western U.S. Researchers hope the results provide better direction on informing future planning efforts for increasing wildfire resilience.
“I'm hoping that providing concrete numbers is very impactful to water managers,” Brucker said. “You can’t fund resilience improvements on general concerns alone. Water managers need real numbers for planning, and that’s what we’re providing,” Brucker said.
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Journal
Communications Earth & Environment
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
Wildfires drive multi-year water quality degradation over the Western U.S.
Article Publication Date
23-Jun-2025
Repeated exposure to wildfires can incrementally increase heart failure risk
Study shows both the intensity of smoke and how often it happens matter for heart health
American College of Cardiology
Long-term exposure to wildfire smoke may increase the risk of heart failure (HF), especially in older adults, women and vulnerable populations, according to a study published today in JACC, the flagship journal of the American College of Cardiology. In this first national, population-based study to examine how prolonged wildfire smoke exposure impacts HF risk, compared to other types of air pollution, researchers found that as the level of air pollution from wildfire smoke increased over a two-year period, the risk of developing heart failure also increased.
PM2.5 is a type of air pollution that consists of very small, inhalable particles that are 2.5 micrometers or less in diameter. It can come from different sources, including vehicle emissions, industrial activities, burning fossil fuels, construction and wildfires. Wildfire smoke pollution is an increasing global health concern as environmental changes drive more frequent and intense fires. The PM2.5 in the smoke can penetrate deep into the lungs and even enter the bloodstream, posing serious health risks.
“Over time, the average smoke pollution someone breathes in can increase very slightly — but that slight increase matters a lot for heart health, especially for vulnerable populations,” said Hua Hao, PhD, Research Scientist at the Rollins School of Public Health at Emory University and lead author of the study. “Even a small individual risk translates into a large public health impact.”
In addition to overall wildfire smoke PM2.5 levels across the United States, researchers looked at how frequently people were exposed to it. They counted how many days in a year the wildfire smoke pollution was higher than certain levels — 1 or 2.5 micrograms per cubic meter.
Among a study cohort of all Medicare beneficiaries enrolled in the Fee-For-Service program from 2007 to 2018, researchers found that each time the level of PM2.5 in wildfire smoke increased by just 1 microgram per cubic meter over a two-year period, their risk of heart failure went up by 1.4%. They estimate that this level of smoke exposure could be linked to over 20,000 additional heart failure cases each year in the U.S. among older adults.
“We also found that the association between smoke PM2.5 and HF was stronger in women, Medicaid eligible individuals and those living in lower income areas, indicating higher susceptibility,” Hao said.
Compared to the same increase in air pollution from non-smoke sources, the increase in heart failure risk rose only 0.5%. Researchers said this means there’s a potential greater relative toxicity of wildfire smoke per unit of measure compared to other types of air pollution.
“By century's end, under a high greenhouse gas emission scenario, we expect 74% of the globe to experience substantial increases in the length of wildfire season and the frequency of wildfire events,” said Joan A. Casey, PhD, Associate Professor of epidemiology at the University of Washington’s Department of Environmental and Occupational Health Sciences and an author of the accompanying editorial comment. “This is already the case in the United States, where wildfire smoke days, once rare, now happen several times per year.”
“This study highlights a growing and underappreciated threat to heart health,” said Harlan M. Krumholz, MD, SM, Harold H. Hines Jr. Professor at Yale School of Medicine and Editor-in-Chief of JACC. “As wildfire smoke becomes more frequent and intense, we are learning that even small, long-term exposures can raise the risk of heart failure, especially among the most vulnerable. These findings elevate the urgency of protecting communities through both environmental policy and health care preparedness.”
Study limitations include potential measurement errors of predicted smoke PM2.5 concentrations, potential outcome misclassifications due to the reliance on Medicare claims data, and potential unmeasured confounding due to the inability to fully control for individual-level heart failure risk factors, such as lifestyle habits or family history. Geographical confounding may have also been a limitation.
For an embargoed copy of the study “Long-term Wildfire Smoke Exposure and Increased Risk of Heart Failure in Older Adults” publishing in JACC, contact JACC Media Relations Manager Olivia Walther at owalther@acc.org.
The American College of Cardiology (ACC) is a global leader dedicated to transforming cardiovascular care and improving heart health for all. For more than 75 years, the ACC has empowered a community of over 60,000 cardiovascular professionals across more than 140 countries with cutting-edge education and advocacy, rigorous professional credentials, and trusted clinical guidance. From its world-class JACC Journals and NCDR registries to its Accreditation Services, global network of Chapters and Sections, and CardioSmart patient initiatives, the College is committed to creating a world where science, knowledge and innovation optimize patient care and outcomes. Learn more at www.ACC.org or connect on social media at @ACCinTouch.
The ACC’s JACC Journals rank among the top cardiovascular journals in the world for scientific impact. The flagship journal, the Journal of the American College of Cardiology (JACC) — and specialty journals consisting of JACC: Advances, JACC: Asia, JACC: Basic to Translational Science, JACC: CardioOncology, JACC: Cardiovascular Imaging, JACC: Cardiovascular Interventions, JACC: Case Reports, JACC: Clinical Electrophysiology and JACC: Heart Failure — pride themselves on publishing the top peer-reviewed research on all aspects of cardiovascular disease. Learn more at JACC.org.
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Journal
Journal of the American College of Cardiology
Article Title
Long-term Wildfire Smoke Exposure and Increased Risk of Heart Failure in Older Adults
Article Publication Date
23-Jun-2025
