New research published in the scientific journal Nature analyzed more than 17,000 watersheds across 11 Western states and tracked wildfire patterns dating back to 1940. Researchers found a significant shift in wildfire activity beginning in the late 20th century, particularly in forested and mountainous areas that generate large amounts of runoff.
The trend was especially pronounced in watersheds that serve large populations. Those supplying water to more than 100,000 people saw the average amount of land burned annually nearly double — from 4.7% to 9.1% — after researchers detected that shift.
“What we were noticing that was alarming, I’d say, [is] that watersheds that were serving over 100,000 people nearly doubled in annual burn area,” said Alicia Kinoshita, a researcher at San Diego State University and one of the study’s authors.
Mountain watersheds stand out
Some of the largest increases occurred in mountainous parts of the Mountain West.
Researchers identified Utah’s Wasatch and Uinta Mountains and the southern Rockies among the Western regions with the most substantial increases in annual burned area. The study also highlighted the Klamath Mountains of California and Oregon.
But the trend wasn’t uniform across the region. The Great Basin, which covers much of Nevada, saw stable or declining trends in annual burned area. Researchers said that could be because the region’s arid landscape has less vegetation available to fuel fires.
The pattern matters because much of the West’s water originates in forested mountain watersheds. Forested lands provide more than half of the region’s water supply and more than half of the surface drinking water used by nearly 83 million people, according to the study.
“After a fire, we usually see increased water quantity and decreased water quality, and that's just because we usually see a removal of the vegetation and things that are kind of holding everything in place,” Kinoshita said.
Those impacts can degrade water quality and create problems for reservoirs, dams and water treatment systems. In some cases, post-fire flooding, sediment and nutrient pollution can affect treatment operations for years.
Aging infrastructure adds to the challenge
The growing wildfire risk is colliding with another challenge: much of the West’s major water infrastructure was built in the mid-20th century, before the changes in wildfire activity documented by the study.
Many of those systems were designed around the assumption that historical hydrologic conditions would remain relatively stable. Today, researchers say aging infrastructure is facing increasing pressure from wildfire, climate change and growing water demand.
Kinoshita said the research could help land and water managers identify places where preventative work may be especially important.
“We’re really hoping [the study] highlights these vulnerabilities and these at-risk areas,” she said. “And for managers, just kind of guiding, like, here are some hot spots that we think are really important, that could be at high risk.”
The study points to approaches such as targeted prescribed burns, restoring streamside vegetation and improving real-time monitoring.
This story was produced by the Mountain West News Bureau, a collaboration between Boise State Public Radio, Wyoming Public Media, Nevada Public Radio, KUNR in Nevada, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio and KJZZ in Arizona as well as NPR, with support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
