How do Wildfires — And Efforts to Abate Them — Affect the Nation’s Water Supplies?

One consequence of wildfire is the increased probability of flash floods. Photo by John A. Moody, courtesy of USGS.
One consequence of wildfire is the increased probability of flash floods. Photo by John A. Moody, courtesy of USGS.

More than 180 million people across the United States rely on forest watersheds to store, filter, and deliver the water that flows from their taps. Unfortunately, in many parts of the country, these watershed functions face an increasing risk of severe wildfire.

Prescribed burning is one treatment that can reduce forest fuels and wildfire’s threats to municipal areas, but how does fire—planned or not—impact water quantity across the landscape? Can forest thinning, which causes forests to take up less water, reduce fire risk and also increase water supplies? U.S. Forest Service researchers are beginning a first-of-its-kind study to explore these questions.

Most previous research on this topic has taken place at a relatively small scale, so little is known about the effects of wildfire and fuel treatment strategies on water flow and yield over regional areas. “This is significant because there is an immediate need to identify high priority watersheds and to optimize limited resources for managing them based on the effectiveness of prescribed fuel treatment options,” says Ge Sun, a research hydrologist with the Eastern Forest Environmental Threat Assessment Center and principal investigator of the study, which is being funded by the Joint Fire Science Program. “Our study will extend the Forest Service’s research capacity and understanding of fire-water relationships to a much larger scale compared to traditional research methods.”

Over the course of the three-year study, researchers will use computer models, including the Water Supply Stress Index, to simulate and quantify water supply changes in response to wildfire and fuel treatments across 88,000 U.S. watersheds. “We hypothesize that water yield increases with fire severity and that streamflow is most sensitive to fire disturbances in regions where rates of precipitation and potential forest water use are similar,” says Sun. Researchers will test this idea by analyzing historic streamflow and wildfire data collected in multiple forested watersheds in the southern and western United States.

The study’s findings could have important implications for local forest management decisions that ultimately affect water quantity as well as quality. Researchers plan to share results throughout the study period and will engage forest managers in training workshops to support sustainable, science-based management practices that ensure water supplies can meet demand. More than 180 million people are counting on it.

 For more information, email Ge Sun at gesun@fs.fed.us.

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