Recent years have brought unusually large and damaging wildfires to the Pacific Northwest – from the in 2014 that was the largest in Washington’s history, to the in Oregon, to the 2018 Maple Fire, when normally sodden rainforests on the Olympic Peninsula were ablaze. Many people have wondered what this means for our region’s future.

A 91Ě˝»¨ , published this winter in Fire Ecology, takes a big-picture look at what climate change could mean for wildfires in the Northwest, considering Washington, Oregon, Idaho and western Montana.

“We can’t predict the exact location of wildfires, because we don’t know where ignitions will occur. But based on historical and contemporary fire records, we know some forests are much more likely to burn frequently, and models can help us determine where climate change will likely increase the frequency of fire,” said lead author , a research scientist at the 91Ě˝»¨School of Environmental and Forest Sciences and with the U.S. Forest Service.

The review was done in response to a survey of stakeholder needs by the , a UW-hosted federal–university partnership. State, federal and tribal resource managers wanted more information on the available science about fire and climate change.

“We’re on the cusp of some big changes. We expect that droughts will become more common, and the interaction of climate and fire could look very different by the mid-21st century,” said , professor at the 91Ě˝»¨School of Environmental and Forest Sciences. “Starting the process of adapting to those changes now will give us a better chance of protecting forest resources in the future.”

The greatest increased risk was found for low-elevation ponderosa pine forests, of the type found at lower elevations on the east side of the Cascade Range in Washington, Oregon, Montana and Idaho. This ecosystem has the highest fire risk today and also has the highest increase in risk due to climate change. The authors predict with high confidence that wildfires in this region will become larger and more frequent.

“We can’t attribute single fire events to climate change. But the trends in large fire events that have been occurring in the region are consistent with expected trends in a warming climate,” said co-author , assistant professor at the 91Ě˝»¨School of Environmental and Forest Sciences. His 91Ě˝»¨ studies forests and fires in the Pacific Northwest and Northern Rockies.

The authors also summarize how other Northwest ecosystems might experience the combined threats of drought, warmer temperatures and insect outbreaks. Moist, coniferous forests — found on the Olympic Peninsula, in Western Washington and in Northern Idaho — will likely burn more often, but fires won’t be significantly larger than they were historically. Fires in subalpine, high-elevation forests, found in mountainous terrain, will similarly become more frequent but only slightly larger or more severe.

After describing the threats, the authors evaluate potential strategies to prepare. Land managers could remove dry organic material, or fuels, and maintain forest densities at lower levels to reduce the severity of fires, since the severity of wildfire is more controllable than the frequency or total area burned. Thinning would also help the remaining trees to withstand drought. Planting genetically diverse seedlings could also help with regeneration after fires — an important step for long-term survival of forests.

Rural landowners can also play a role, the authors write.

“Individual landowners can reduce hazardous fuels, promote species that can survive fire and drought, and increase diversity of species and structures across the landscape,” Peterson said.

Historically the Northwest has had lower risk of wildfire than other states, such as California, but that may be changing.

“In general, the climate in the Northwest is cooler and wetter than in most low-elevation areas of California,” Halofsky said. But the Northwest summers are dry and warm. “Climate change will accentuate dry summers, and Northwest climate will become more similar to current-day California climate, leading to more and bigger fires.”

The study was funded by the U.S. Department of the Interior through its UW-hosted Northwest Climate Adaptation Science Center. Additional funding came from the U.S. Forest Service through its and .

For more information, contact Halofsky at jhalo@uw.edu, Harvey at bjharvey@uw.edu or Peterson at wild@uw.edu.

The first volume of the fourth assessment, released in 2017, looked at the physical science underlying the report. , a research scientist at the 91Ě˝»¨Joint Institute for the Study of Atmosphere and Ocean, was an author on chapter two, “,” that provides an overview and update of the first volume. The rest of the second volume, released Nov. 23, focuses on impacts, risks and adaptation across the United States.

, a 91Ě˝»¨professor of both global health and environmental and occupational health sciences, was a lead author of the chapter on . This chapter looked at human health effects from exposure to heatwaves, floods, droughts and other extreme events; infectious diseases; changes in our food and water; and mental health and well-being. The chapter also assessed the health co-benefits of various mitigation policies that address climate change.

Previous versions of the climate assessments considered various impacts, such as from extreme weather events or for public health, separately, Ebi told . The new report, she said, includes regional chapters that consider the interconnected and often compounding risks within the Northwest and other regions.

Two researchers at the School of Environmental and Forest Sciences contributed to the new assessment’s chapter on . Professor was one of two coordinating lead authors, and research scientist was a technical contributor. The chapter looked at how extreme weather, including droughts, will make wildfires more frequent and intense nationally and in specific regions of the U.S. It also describes how climate change will affect other ecological disturbances, such as insects. The authors find that many options exist to reduce the largely negative effects of climate change, and list how federal agencies and other entities are already implementing adaptation measures across the United States.

The national assessment includes 10 chapters that focus on impacts, risks and adaptation in specific regions. The ‘s former deputy director, Joe Casola, was an author on the . (Amy Snover, director of the Climate Impacts Group, was a lead author in 2014 of the ). The new report emphasizes many of the same impacts on water, coasts, forests and agriculture in the Northwest. The Northwest region has warmed almost 2.0 degrees Fahrenheit since 1900, with a portion of the warming directly linked to human-caused climate change. The authors use 2015, a year characterized by record-breaking warm and dry conditions, to explore how climate change will be experienced in the Northwest region. This chapter, and the larger national assessment, emphasizes how climate change will disproportionately affect poor and disadvantaged people and Indigenous communities.

, an assistant professor of environmental and forest sciences and of civil and environmental engineering, contributed to the second , also released Nov. 23, for the first time in conjunction with the national climate assessment. This report each decade summarizes carbon-cycle science, or how increasing atmospheric carbon dioxide from burning fossil fuels moves through the Earth system across North America. Butman was the lead author of the chapter focused on and a contributing author to the second chapter on of rising atmospheric carbon dioxide. , an assistant professor at 91Ě˝»¨Bothell, contributed to the carbon cycle report’s chapter on .

, a research scientist in the Polar Science Center at the 91Ě˝»¨Applied Physics Laboratory, was a contributor to the Fourth National Climate Assessment’s regional chapter focused on . Former 91Ě˝»¨research scientist , now a faculty member at the University of Connecticut, was an author on the climate assessment’s chapter on .

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For more information, contact Ebi at krisebi@uw.edu, Peterson at wild@uw.edu, Heidi Roop at the Climate Impacts Group at hroop@uw.edu and Butman at dbutman@uw.edu.

As wildfires burn across the western U.S., forest biologist and 91Ě˝»¨ professor David Peterson explains which natural materials burn hotter and faster during a wildfire, what homeowners can do to protect their properties and how climate change is impacting the fire season.

Researchers expect two to three times more area burned each year in the western U.S. than has occurred historically in the region. That’s 15 or 20 million acres burning each year across the West.

Additionally, climate change likely will have an “enormous” impact on wildfire in the coming century, Peterson said. First, as the temperature gets warmer, the western regions will experience a longer fire season. Second, warmer temperatures will produce more extreme weather. That means higher temperature periods and more drought periods — both critical times during which large wildfires occur.

“As more and more people move into the wildland-urban interface, we have more opportunities for homes to burn and more opportunities for economic damage,” Peterson said. “Even in fairly remote areas now, it’s hard to find an area, outside of wilderness, where at least somebody doesn’t live or have a structure. So that’s a real challenge.”

Peterson said that about 95 percent of the area that’s burned each year in the western U.S. is caused by 2 percent of the fires. That means the fires that occur during very extreme weather with high fuels and long periods of very dry, windy weather are the ones that cause most of the effects in forest ecosystems and other ecosystems.

“Once a fire becomes very large, and the energy release is extremely high, those fires become extremely difficult to put out,” he said.

Peterson worked for years at the U.S. Forest Service’s Pacific Northwest Research Station, providing information and developing tools to help fire managers across the country.

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For more information, contact Peterson at wild@uw.edu or 360-422-5735. See a of UW-affiliated wildfire and forest ecology experts.

The book brings together years of conversation about what resource managers are seeing – and doing – on the ground. While Halofsky and Peterson wrote the introduction, other chapters were written by scientists and resource managers who are members of the , a group of 35 organizations that the two 91Ě˝»¨environmental scientists co-lead.

Q: Where exactly are the Northern Rocky Mountains?

JH: We focused on the northern region of the U.S. Forest Service in the Rockies. Our area includes northern Idaho, all of Montana and North Dakota, a small portion of South Dakota, and all of the Greater Yellowstone Ecosystem (including part of Wyoming).

Q: How is this book different from other climate change reports?

JH: This book is a deeper dive into the Northern Rockies region, and federal forest lands and grasslands in particular. The book also focuses on the specific needs of the Forest Service and National Park Service, which manage millions of acres of land in this area. It puts it in the context of their management practices, and what they may be able to do about climate change.

Q: What new threats will this region face?

JH: Some of the biggest threats are lower snowpack, which affects a number of different areas. Obviously skiing and winter recreation are affected, but water supply is another big impact. Lower snowpack and less precipitation falling as snow means that the water runs off earlier in the season, and then you have lower streamflow in the summer. That affects water availability for cities and people, for agriculture, and for fish and other aquatic organisms. When we have lower streamflow and lower moisture levels, we also see more wildfires.

Q: What are people doing, or what could they do, to prepare for these changes?

JH: A lot of the “what do we do about it?” is promoting healthy ecosystems. The idea is that a healthier ecosystem will be better able to respond to these changes. We can make sure that the streams are healthy, and that impacts from roads, livestock grazing, and other stressors are minimized.

Restoring the functionality of streams and floodplains is very important. Reintroducing the beavers can also be helpful, because they build dams that slow the water flow, retain cool water in the mountain streams and augment summer flows.

Q: What about forest fires? Is there any way to prevent that risk from increasing?

JH: For forests, it’s about reducing existing stressors. Fire suppression has really affected forest conditions — the forests are denser than they were historically. Doing things like thinning treatments, where you reduce the density of the forest, can help reduce fire risk and help trees respond to drought because they’re not competing with other trees. Reducing high fuels on the forest floor, with prescribed fire or other methods, is also important.

These actions are not necessarily going to decrease the number of fires, but thinning and other treatments can reduce the severity of the fire. So the fire won’t burn as hot, or damage the soil as much.

Q: What about the forest fires this summer that caused evacuations and smoky conditions as far west as Seattle? Were those fires related to climate change?

JH: It is difficult to say how much of a role climate change has played in recent wildfire activity. However, climatic conditions are a major driver for how much area is burned. Over the past century, wildfires in the mountainous areas of the West have seen larger areas burned during periods of low precipitation, higher temperatures and drought conditions. Climate change will bring higher temperatures and more severe droughts in fire-prone regions of the U.S., and that is projected to lead to larger areas burned.

Q: What do you hope this book will achieve?

JH: We hope that it increases awareness of climate change and its effects on natural resources, and also can give people some hope that there are things that can be done on the ground, and things that are already being done, that can help reduce the negative effects of climate change.

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For more information, contact Halofsky at jhalo@uw.edu.