In recent years, wildfires on the West Coast have become larger and more damaging. A combination of almost a century of fire suppression and hotter and drier conditions has created a tinderbox ready to ignite, destroying homes and polluting the air over large areas.

New research led by the 天美影视传媒 and the University of California, Santa Barbara, looks at the longer-term future of wildfires under scenarios of increased temperature and drought, using a model that focuses on the eastern California forests of the Sierra Nevada. The , published July 26 in the journal Ecosphere, finds that there will be an initial roughly decade-long burst of wildfire activity, followed by recurring fires of decreasing area.

鈥淭hat first burst of wildfire is consistent with what we鈥檙e seeing right now in the West. The buildup of fuels, in conjunction with the increasingly hot and dry conditions, leads to these very large, catastrophic fire events,鈥� said lead author , assistant professor at the 天美影视传媒 Tacoma. 鈥淏ut our simulations show that if you allow fire to continue in an area, then the fire could become self-limiting, where each subsequent fire is smaller than the previous one.鈥�

How climate change, tree growth and wildfires will interact over coming decades is only beginning to be explored, Kennedy said, through experiments and simulations. Existing models of vegetation often assume wildfires will strike at set intervals, like every 10 years, or based on past patterns of wildfire risk for that ecosystem. But those previous patterns may not be the best guide to the future.

鈥淭he big question is: What鈥檚 going to happen with climate change? The relationships that we鈥檝e seen between climate and wildfire over the past 30 years, is that going to continue? Or is there going to be a feedback? Because if we keep burning up these fuels, and with extreme drought that limits new growth, there will eventually be less fuel for wildfires,鈥� Kennedy said.

The new study used a model that includes those feedbacks among climate, vegetation growth, water flows and wildfire risk to simulate the Big Creek watershed outside Fresno, California, near the site of the September 2020 . Climate models suggest that here, as in other parts of the West, conditions will likely continue to get hotter and drier.

Results of the 60-year simulations show that under increased drought and rising temperatures, the large wildfires will continue for about a decade, followed by recurring wildfires that occur in warm and dry conditions, but are smaller over time. Even without wildfire the trees in the forest declined in number and size over time because they were less productive and more stressed in the hot and dry conditions. These findings would likely apply to other forests that experience drought, said Kennedy, who鈥檚 now using the model on other regions.

What happens with wildfires over the longer term matters now for planning. Current understanding is that communities will have to coexist with wildfire rather than exclude it entirely, Kennedy said. A combination of prescribed burns and forest thinning will likely be the future of managing forests as they contend with both wildfires and climate change.

鈥淲ith such high density in the forest, the trees are pulling a lot of water out of the soil,鈥� Kennedy said. 鈥淭here is growing evidence that you can relieve drought stress and make more drought-resilient forests if you thin the forests, which should also help with, for example, reducing the impact of that initial pulse of wildfire.鈥�

After thinning out smaller trees, managers could then do controlled burns to remove kindling and smaller material on the forest floor. But knowing how to manage forests in this way requires understanding how local weather conditions, plant growth and wildfire risk will play out in future decades.

鈥淚t鈥檚 important to include climate change so we have an idea of the range of variability of potential outcomes in the future,鈥� Kennedy said. 鈥淔or example, how often do you need to repeat the fuels treatment? Is that going to be different under climate change?鈥�

Kennedy was also a co-author of another that uses the same model to tease apart how much climate change and fire suppression increase wildfire risk in different parts of Idaho.

鈥淥ur 鈥榥ew normal鈥� is not static,鈥� said , a professor at UC Santa Barbara who is a co-author on both studies and developed the RHESSys-FIRE model that was used in the research. 鈥淣ot only is our climate continuing to change, but vegetation 鈥� the fuel of fire 鈥� is responding to changing conditions. Our work helps understand what these trajectories of fire, forest productivity and growth may look like.鈥�

This research was funded by the National Science Foundation and the U.S. Forest Service. Other co-authors are Ryan Bart at the University of California, Merced, and Janet Choate at UC Santa Barbara.

For more information, contact Kennedy at mkenn@uw.edu or Tague at ctague@bren.ucsb.edu. 聽

NSF grant: EAR-1520847, USFS

The 2014 Carlton Complex wildfire in north central Washington was the largest contiguous fire in state history. In just a single day, flames spread over 160,000 acres of forest and rangeland and ultimately burned more than 250,000 acres in the midst of a particularly hot, dry summer.

The wildfire, driven by strong winds and explosive growth, was unprecedented in how it burned the landscape, destroying more than 300 homes in Washington’s Methow Valley. But “megafires” like the Carlton Complex are becoming more common in western U.S. forests as the climate warms and forests are crowded with trees after years of fire exclusion.

In the first major study following the devastating Carlton Complex fire, researchers from the 天美影视传媒 and U.S. Forest Service found that previous tree thinning and prescribed burns helped forests survive the fire. The , published Feb. 22 in the journal Ecological Applications, shows that even in extreme wildfires, reducing built-up fuels such as small trees and shrubs pays off.

“Our study suggests that the fuel treatments were worth the investment, yielding a more desirable post-fire outcome than if they hadn鈥檛 been implemented,” said lead author , a research scientist at the UW School of Environmental and Forest Sciences. “There are a lot of benefits to creating more resilient landscapes, and this study suggests that even in the worst-case scenario wildfires, it can be worth it.”

On July 17, 2014, sustained winds of 35 mph raced through the Methow Valley, blasting oxygen into several fires that had started earlier that week. Before long, the fires joined and spread. A column of smoke stretched 30,000 feet high, dropping embers and igniting dry grasses, trees and other fuels on the ground over thousands of acres.

Propelled by the fast-moving column of smoke and wind, the flames traveled all the way to the Columbia River.

“It was the kind of fire that even experts who have studied them for decades had not seen before,” said Prichard, who lives in the Methow Valley. “It was a devastating fire for our community. I truly thought people would be killed by that fire, and it still feels miraculous that everyone survived.”

In the aftermath, Prichard and collaborators wondered if actions such as controlled burns and thinning were helpful in the case of a megafire like the Carlton Complex. State and federal agencies sink ample resources into these efforts to increase the resiliency of forests to wildfires by removing small- and medium-sized trees, leaving larger, mature trees that are more likely to survive future drought and wildfires.

After a forest is thinned, prescribed burning is used to reduce leftover woody debris on logging sites or across landscapes that have built up downed trees, pine needles, grasses and shrubs.

The Carlton Complex fire burned across hundreds of sites that were previously thinned or burned, offering a testbed for the researchers to analyze whether the work helped reduce fire impacts in those areas during the megafire. The researchers used satellite images of burn severity to examine how past fuel treatments performed in the context of this extreme wildfire event.

They found that even during the first explosive days of the Carlton Complex, areas that were thinned and prescribed burned had more trees survive than areas that didn’t receive those fuel treatments.

“Some of the treatments measurably reduced fire impacts even under very hot, dry and windy conditions,” said co-author , a research scientist at U.S. Forest Service Wenatchee Forestry Sciences Lab. “Our results suggest that as we increase our ‘restoration footprint’ 鈥� the proportion of forest area treated to reduce fuels 鈥� forests may become increasingly resilient to wildfires under a broad range of conditions.”

They also found that thinning and burning on slopes that were protected from prevailing winds was more effective in reducing the wildfire’s impacts on the landscape than similar treatments in areas directly exposed to the wind. Because winds often move through the Methow Valley in a predictable pattern, fire managers could thin and burn strategically in areas where these activities would be most effective.

Those efforts helped mature, naturally fire-resistant ponderosa pines survive. These mature trees, in turn, will provide seeds that produce younger trees across the landscape.

While this study focused on the Carlton Complex fire, its results have broader implications for forests around the world that are prone to wildfires. This work adds to the growing library of studies showing how thinning trees and controlled burns can reduce the severity of the next fire on the landscape.

“I鈥檓 hopeful our study will encourage policymakers as well as managers to invest in restoration,” Prichard said. “It’s our best hope for protecting our streams, rivers and landscapes from catastrophic fires.”

Other co-authors are , assistant professor at UW Tacoma, and , research scientist at U.S. Forest Service Wenatchee Forestry Sciences Lab.

This research was funded by the U.S. Forest Service’s Western Wildland Environmental Threat Assessment Center, the Joint Fire Science Program and the National Fire Plan.

For more information, contact Prichard at sprich@uw.edu and Peterson at dave.peterson@usda.gov.

It’s hard to find a place in the U.S. that isn’t impacted by wildfires and smoke.

Dry landscapes, warmer temperatures and more development near forested areas all contribute to massive wildfires across North America each year. Smoke and haze from these fires can travel hundreds of miles from their source, affecting the health and wellbeing of communities across the U.S.

Given these impacts, scientists rely on models that try to predict the severity of wildfires and smoke. The amount of living and dead vegetation on a landscape, known as fuels, is a key part of the equation when modeling wildfire and smoke behavior. But in many areas, fuel estimates are imprecise, leading to unreliable smoke and fire forecasts 鈥� potentially endangering communities.

Researchers from the 天美影视传媒 and Michigan Technological University have created the first comprehensive database of all the wildfire fuels that have been measured across North America. Called the , the tool incorporates the best available measurements of vegetation in specific locations, and allows fire managers to see where information about fuels is missing altogether.

Ultimately, it can help scientists make more informed decisions about fire and smoke situations.

“Where there are fuels and fire, there’s smoke,” said lead author , a research scientist at the UW School of Environmental and Forest Sciences. “This database is informing more realistic predictions of smoke that allow for the fact that we might not have dialed in the fuels perfectly.”

The new database is described in a published Dec. 4 in the Journal of Geophysical Research 鈥� Biogeosciences.

There are many types of vegetation that burn during wildfires, including live and dead trees, freshly fallen leaves and needles, shrubs, grasses, moss 鈥� and even decomposing logs and soil. The database, which includes a map view, shows a breakdown of each type of wildfire fuel and its amount in various locations across the U.S. It provides, for example, a quick way to see that dead trees are more densely packed along the West Coast, while decomposing materials, called “duff,” are more prevalent along the East Coast and upper Midwest.

The amount of vegetation in a particular area can vary drastically by season and natural events like windstorms that blow down trees, or wildfires that burn up fuels on the ground. As a result, the researchers found that it takes a wide range of observations to encompass the natural variability that is common within vegetation on a landscape.

Their dataset incorporates all of the existing information about fuels across the country 鈥� drawn from other datasets and published studies 鈥� and also factors in the potential range of variability for each vegetation type in different locations.

“Setting a static map of fuels is not going to be an accurate depiction of what the vegetation will be like in that location forever,” said co-author , an assistant professor at UW Tacoma. “It was important to us to find ways to communicate that fuels on the landscape are variable and have uncertainty.”

The researchers hope that smoke modelers and fire managers use this data to analyze the range of wildfire fuels in their location, and use it to make better predictions about smoke emissions and fire severity. All of the data is accessible and downloadable from their website.

Managers also could use this data when deciding where and when to do a prescribed burn, which is important for reducing fire hazard in dense forests. More accurate fuels information will help determine if smoke and other pollutants will be too high or within a safe range for surrounding communities during a burn.

The team also hopes to add more data as other researchers continue to take measurements of the fuels in their areas. Data on live and dead trees is robust because of satellite imagery, Prichard explained, but data on fuels that must be measured by hand, such as leaves, needles and small branches, are largely missing. Fuels all burn differently 鈥� some smolder while others ignite quickly 鈥� which can also impact the accuracy of smoke and fire predictions.

“One of the things we didn’t anticipate is that the database would also let us know what still needs to be done,” Prichard said. “The big surprise for all of us is how little data we have on non-forest vegetation such as grasslands and shrublands. That data gap is big and worth closing over time.”

Other co-authors are Anne Andreu and Paige Eagle, research scientists at the UW School of Environmental and Forest Sciences, and Nancy French and Michael Billmire of Michigan Technological University.

This research was funded by the Joint Fire Science Program and the U.S. Forest Service Pacific Northwest Research Station.

For more information, contact Prichard at sprich@uw.edu and Kennedy at mkenn@uw.edu.