Will massive Western wildfires leave more or less water in rivers?

CAMERON PASS — On a cloudy morning in April, not far from the summit of Cameron Pass, Megan Sears drops a pair of snowshoes onto the shoulder of Highway 14, 60 miles west of Fort Collins 

Sears, a graduate student studying watershed science at Colorado State University, cinches the binding straps tight onto her snow boots. She tucks a scientific instrument that looks something like a giant telescope made of clear plastic under her shoulder and starts walking up a snowy hill into what remains of the forest burned nearly two years ago by the largest wildlife in Colorado history.

In a state where every drop of water matters, Sears and another grad student, Mikaela Richardson, are out collecting data that will help answer an important question that’s gaining more attention from the scientific community: If massive wildfires continue to spread across the West, particularly at higher altitudes where snowpack is more plentiful and critical, what effect will that have on the region’s water supply? “How is this fire and the impact from it changing the hydrologic regime of this area?” Sears says as she treks through the snow. “And what does that mean for, you know, the Poudre River?”

The past two years, beginning around December and continuing through May or June, Sears and other CSU researchers have walked to various points in this burned forest to measure both the snow depth and the amount of water held in the snow. The telescope-looking instrument measures SWE, or snow water equivalent. The device can remove a core sample from the snowpack; Sears and Richardson can then weigh the sample and calculate the water content in the snow. After gathering this data, for comparison, Sears and Richardson will do the same thing in a nearby area spared by the Cameron Peak fire.

Often, post-fire concerns focus on potential challenges with water quality, which can be impacted by sediment and debris more easily running down a barren hillside. But the work Sears and Richardson are doing, sampling snow in the middle of a scorched forest that burned as high as 11,915 feet, aims to get at something else: Will the ecosystem left behind by wildfires translate to more or less water in rivers and streams? 

“I’m really curious,” Sears says, “how this impacts the snowpack.” 

A different view

In August of 2020, when Stephanie Kampf, a professor in the department of ecosystem science and sustainability at Colorado State University, spotted the early plumes of smoke rising out of the Arapaho and Roosevelt National Forests west of Fort Collins, she began to follow the fire with a scientific curiosity. 

Kampft noted a few things in particular. The first was that the fire — the origin of which is still under investigation but is suspected to be human-caused — was burning at a high elevation, places where snowpack builds and persists through the winter. The second thing was that even though the fire was burning high up it appeared to be spreading rapidly, an unusual combination. “It started growing in ways that were surprising,” Kampf said. “It had covered a larger high elevation area than we had seen burn here before.”

Eventually, Kampf, who studies hydrology and how runoff is affected by climate, started to think about how she might exploit this disaster in the name of research. She wrote a proposal to collect data on how the fire could impact “snowpack, streamflow, slope failures, stream channels, and water supply reservoirs,” and received a $50,000 grant from the National Science Foundation to get started. “It seemed that we would be able to address this water supply question,” Kampf said. 

Further west, Kelly Gleason, an assistant professor in the department of environmental science and management at Portland State University, fell in love with this work back in 2010. Gleason loves to ski and burned forests happen to make for pretty good skiing, she said. Gleason was out one day carving turns in a nicely gladed burned area. She found herself thinking about the charred bits of tree branches, twigs and trunk scattered on the snow, when she experienced something of an aha moment. “I realized this is what I want to do,” Gleason said.

The burned woody debris on the snow is one of the critical variables in this research. Those burned bits make the snow darker, which then heats up more quickly when the sun hits the surface. It’s like wearing a black shirt on a sunny day. What’s more, burned forests don’t have the same tree canopy cover as a healthy forest, meaning more light reaches the ground. More sun on a darker surface melts the snow faster. 

Last year, Gleason published a paper in the journal “Water” that examined the long-term, post-fire effects on snowpack based on analysis of 78 SNOTEL sites across the West, including many in Colorado, and in Alaska. (SNOTEL, or snow telemetry sites, are maintained by the National Resources Conservation Service and automatically report snow depth and quality.) The results of the analysis conducted by Gleason and her co-author Emily Smoot found that the snow in these burned areas had less capacity to store water and that snowmelt occurred earlier. 

The impact of the char-darkened snow is counterbalanced somewhat by the fact that less tree cover means more snow accumulates on the ground, but that’s not enough to outweigh the snow warming effect. There’s also more potential for snow to be impacted by wind in a burned forest.

“We were surprised to learn that following fire the amount of stored snowpack is significantly reduced,” Gleason said. “The amount of total snow stored is less and it’s melting earlier.” What’s more, she said, those post-fire effects last for 10 to 15 years. 

Streamflow

There are other variables in this fire-snow-water equation, too. Right after a forest burns, the trees don’t suck up any water. “Once you burn a forest those trees are no longer there so that water that would be consumed by them is now runoff,” Gleason said. “So, often right after a fire occurs, there’s an increase in streamflow. But as the plants regenerate that water will be sucked up — and younger plants use more water than older plants.” 

Park Williams, a hydroclimatologist and associate professor at UCLA, has also recently studied this topic. “Fire degrades water quality,” Williams said, “but I hadn’t seen too much work that I understood about how fire affects streamflow.” A co-author on a January 2022 paper titled “Growing Impact of Wildfire on Western U.S. Water Supply,” Williams said the research found that immediately post-fire, in a forest where at least 20% of the area burned, streamflow increased 20% to 30%. “What’s happening is that after fires streamflow is systematically enhanced across the board,” Williams said. 

That effect, however, doesn’t last forever, he said; once vegetation of any kind grows back the result can be highly variable. “There’s a whole lot more work now to disentangle what all the processes are,” Williams said. But, he said, the great thing about studying the Western U.S. is that there is a lot of good data. For instance, the recent paper Williams worked on utilized flow records from stream gauges. “There are mysteries where these answers are hidden in these data sets,” he said. 

How fires are affecting snowpack and water supply, Portland State’s Gleason said, is a burgeoning scientific field. It’s no wonder in the parched West, where millions of people rely on the water held in the mountains. The key to all this, Gleason said, might actually be timing, not volume. As it is now, the snowpack functions almost like a high-mountain reservoir, storing the moisture and then melting and releasing the water when we need it. 

But what if that timing shifts significantly? “We don’t have the infrastructure to do what the snowpack does for us,” Gleason said. “Scarcity is an issue of timing. Not much may change. Or after a fire you may get more. But if that water is flowing in February and March it is essentially lost to us.”

Gleason hopes her work might eventually translate into some practical uses for water managers, perhaps some kind of tool that would allow people to estimate what percentage of water could be expected at what times based on how much a forest burned how long ago.

“There’s still a lot to discover,” she said. 

Disaster fatigue

Kampf is finalizing a paper based on the first year of data her team collected in the Cameron Peak burned area, which spread across more than 200,000 acres. The early results sound similar to what Gleason described. Last year, at the highest elevations charred by the fire, the snow melted about a week earlier and at slightly lower elevations the snowmelt happened about a month earlier. “That’s a pretty striking difference,” Kampf said.

Then there’s the potential ramifications for streamflow. “It looks like last year it did not result in less water,” Kampf said. “Normally, we’d be concerned that if we have a shorter snow season, and the snow melts earlier, we’d have less water supply. But as the snow was melting it was going straight to the streams, so we got quite a bit of streamflow.” 

The concern, Kampf said, is that the snowpack will remain less plentiful and more susceptible to melting. “It could be that the loss of snowpack in the burned area ends up meaning less streamflow later on,” she said.

Denver Water tracks research in this area. Christina Burri, a watershed scientist at Denver Water, said they share concerns about the potential for big burn scars to accelerate melt and runoff. Burri said research also suggests that trees may struggle to regrow in these areas, which could exacerbate what Burri said is their primary concern: intensified runoff and erosion. It’s also one of the many reasons why, Burri said, Denver Water has invested more than $33 million in a partnership with the U.S. Forest Service, State Forest Service and Natural Resource Conservation Service to try to reduce the risks and impacts of wildfires in water supply areas.

Kampf plans to keep the sampling going in the Cameron Peak area — the work Sears and Richardson were doing on Cameron Pass in April — for another year and also wants to collect similar data in the area burned by the East Troublesome Fire. “It is interesting to see how things change as a scientist, but it’s hard to work on destruction all the time,” Kampf said. “You get disaster fatigue after a while.” 

Still, with significant fires burning so close to home, Kampf said she feels almost pulled toward the work. “It feels like I have to try to understand what’s going on,” she said.