{"id":13185,"date":"2025-01-23T11:03:00","date_gmt":"2025-01-23T16:03:00","guid":{"rendered":"https:\/\/cnr.ncsu.edu\/news\/?p=13185"},"modified":"2025-10-28T22:17:58","modified_gmt":"2025-10-29T02:17:58","slug":"how-do-wildfires-impact-water-quality","status":"publish","type":"post","link":"https:\/\/cnr.ncsu.edu\/news\/2025\/01\/how-do-wildfires-impact-water-quality\/","title":{"rendered":"How Do Wildfires Impact Water Quality?"},"content":{"rendered":"\n\n\n\n\n

The Cache la Poudre River usually runs cold and clear as it flows more than 120 miles from the Rocky Mountains to the South Platte River. But in July 2012, the river\u2019s water suddenly turned pitch black. Heavy rain had filled the river with soot, ash and debris from a wildfire that burned thousands of acres of nearby forested land a month before. As a result of the pollution, cities downstream of the Poudre, including Fort Collins and Greeley, had to close their intakes on the river and use alternative sources for drinking water.<\/p>\n\n\n\n

Eight years later, the city of Fort Collins was facing a potential water shortage<\/a> after once again closing its intakes on the Poudre River \u2013 in part due to poor water quality caused by the Cameron Peak Fire. The fire, which is the largest in state history, has scorched more than 130,000 acres across northern Colorado since igniting in August and continues to burn along the river in the Rocky Mountains National Park.<\/p>\n\n\n\n

As climate change spawns hotter and drier conditions across North America and around the world, scientists are warning that intense and repeated wildfires could affect the quantity and quality of water available. Research shows that wildfires are getting bigger and more destructive as climate change intensifies drought conditions and creates large areas of dry fuels (leaves and other combustible materials) that are more likely to ignite and carry fire.<\/p>\n\n\n\n

High-intensity wildfires can increase the susceptibility of watersheds to runoff and erosion and can have detrimental impacts on water supplies, including increased treatment costs, need for alternative supplies and diminished reservoir capacity. These impacts can last anywhere from months to years after a wildfire has been contained.<\/p>\n\n\n\n

Much of the precipitation that falls within a forest is intercepted by the tree canopy and forest floor. But high-intensity wildfires can remove vegetation and reduce the ability of soils to take up water, according to Ge Sun<\/a>, a hydrologist with the U.S. Forest Service and professor in the Department of Forestry and Environmental Resources. <\/p>\n\n\n\n

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The 2013 Rim Fire in California consumed much of the forest canopy, resulting in tree mortality, exposure of soil to erosion and increased water runoff. Photo courtesy of USDA Forest Service<\/figcaption><\/figure>\n\n\n\n

Sun, whose areas of expertise include forest hydrology and global change, said these changes to the forest floor can ultimately lead to an increase in runoff that can transport vast quantities of ash, nutrients, sediments, heavy metals and toxins into streams, rivers and downstream reservoirs used for drinking water supplies.<\/p>\n\n\n\n

“When trees are killed due to fire, forests lose their capacity of evapotranspiration, the sum of intercepting rain water and transpiring water into the atmosphere,” Sun said. “Consequently, there will be more water flowing to the rivers once you have big storms after fire. When water flow increases and accelerates, bank erosion can occur.”<\/p>\n\n\n\n

The contamination from wildfires can have serious impacts on water quality and availability. A 2018 study<\/a> co-authored by Sun in Nature Communications <\/em>found that wildfires can change the amount of water that comes from upstream forests and the seasonal timing of water flows. Such changes could potentially cause water shortages for some communities as less water might be available during periods of high demand.<\/p>\n\n\n\n

High-intensity wildfires can also impact the health of aquatic life and humans by releasing mercury from soil and plants into waterways, where it can travel downstream and contaminate watersheds and accumulate in fish, according to Sun. Federal health agencies warn that people who consume fish containing high levels of mercury, especially pregnant women and young children, can experience brain and nervous system damage.<\/p>\n\n\n\n

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Wildfires can destroy grasses, shrubs and other vegetation. This can lead to increased runoff of ash, sediment and other pollutants into nearby waterways. Photo by FedBul via iStock<\/figcaption><\/figure>\n\n\n\n

In addition to posing a public health threat, increased sediment loads in reservoirs can create a financial burden for utilities and taxpayers by causing increased processing costs and requirements for water treatment plants.<\/p>\n\n\n\n

A large and severe wildfire can increase drinking water production costs by $10 million to $100 million. After the 2002 Hayman fire in Colorado, for example, Denver Water had to spend more than $10 million to remove sediment from its Cheesman and Strontia Springs reservoirs.<\/p>\n\n\n\n

With the duration and extent of wildfires continuing to worsen, public utilities and policy makers face a considerable challenge in preventing added strain to existing water resources as the impact on water quality and supply depends on multiple factors<\/a>, including the extent and intensity of the wildfire, post-wildfire precipitation, watershed topography and local ecology.<\/p>\n\n\n\n

Resource managers can employ forest restoration and management strategies to protect reservoirs and other drinking water sources, according to Sun. These strategies \u2013 which include prescribed burning, thinning of trees and shrubs, planting native trees and reducing the area of impervious surfaces \u2013 can “increase forest health and resilience and may increase water availability to people,” he said.<\/p>\n\n\n\n

Sun and other researchers are actively studying how prescribed burning as a forest management tool affects water quality, such as the mobility of mercury and other chemical concerns. <\/p>\n\n\n

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