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Colorado is fighting its largest wildfire in history. Other massive blazes are close behind.

Three of the four largest fires in Colorado history have ignited since July.

Calwood Fire Burns Near Jamestown
The CalWood Fire is now the largest wildfire in the history of Boulder County in Colorado. The largest wildfire in state history, the Cameron Peak Fire, is also continuing to gain ground.
Matthew Jonas/Boulder Daily Camera/Getty Images
Umair Irfan is a correspondent at Vox writing about climate change, Covid-19, and energy policy. Irfan is also a regular contributor to the radio program Science Friday. Prior to Vox, he was a reporter for ClimateWire at E&E News.

Snowfall over the weekend gave firefighters in Colorado some some desperately needed relief as they worked to contain the two largest blazes in state history burning just ten miles apart. The cold snowy weather helped limit the growth of the infernos, but it also prevented fire crews from making progress in containing them.

The Cameron Peak Fire near Rocky Mountain National Park is now the largest wildfire in Colorado history, at almost 208,000 acres in size. The fire was 64 percent contained as of Monday morning.

It’s followed closely by the East Troublesome Fire to its southwest, which has now burned more than 192,000 acres and was 10 percent contained as of Monday. The blaze stunned forecasters last week when, over a period of 24 hours, it grew six times in size to more than 125,000 acres. The fire is burning at an elevation of 9,000 feet and across both sides of the continental divide. forced Rocky Mountain National Park to close. It’s now the second-largest fire in Colorado history.

The previous record-holder before Cameron Peak was the 137,000-acre Pine Gulch Fire near Grand Junction, Colorado. That fire also ignited this year and was declared 100 percent contained in September. It only held on to its record as Colorado’s largest wildfire for seven weeks. Three of the four largest wildfires in state history have ignited just since July.

Smaller blazes this year have set records too. The CalWood Fire became the largest wildfire in the history of Boulder County after igniting earlier this month. The fire burned 10,000 acres and was 76 percent contained by Monday.

Beyond the threat from the flames, these various wildfires have sent dangerous, smoky air into cities like Denver and Fort Collins, triggering air quality alerts off and on for months. The smoke from Colorado’s wildfires has even reached Europe.

Together, the recent blazes in Colorado add up to an unusually long, late, and severe wildfire season, and it’s not likely to let up anytime soon. “The current fire season, it’s definitely a crazy one,” said Chad Hoffman, an associate professor of fire science at Colorado State University. “We still have dry, windy conditions pushing these fires.”

Some unique weather conditions this year set the stage for Colorado’s blazes, but the threat from wildfires is growing across the state due to human development and climate change.

What’s fueling Colorado’s fires this year

It’s an increasingly familiar story. Like the epic wildfires this year across California, Oregon, and Washington, the wildfires in Colorado arose amid a year of extreme heat and dryness.

Heat waves baked the state this summer and persisted into the fall. The high temperatures increased the evaporation of moisture from vegetation, leaving plants dry and ready to burn. There was also less rainfall. Over the past month, precipitation was less than 10 percent of what is typical.

“By the end of September, nearly 100% of the state was experiencing some level of drought, up from 51% since the beginning of the calendar year,” according to the Colorado Climate Center’s Monthly State of the Climate report. The state is on track to have its second-driest year on record.

That aridity has left almost every type of vegetation in the state primed to burn, as was evident in the Cameron Peak Fire. “It burned all the way from fir forest, ponderosa pine, mixed conifer. It’s burned through some grasslands and shrublands as well,” Hoffman said. “It’s burned through areas that have previously burned, like during the Bobcat Fire. It’s burned through bark-beetle-affected areas. So a really big mix of fuels that this fire has burned through over the last 60 days.”

It’s also uncommon to see fires this late in the year in Colorado. Typically, winter precipitation starts to set in and cap fire seasons in the autumn.

This fits within the trend of fire seasons in Colorado getting longer. Wildfires are a natural part of the landscape in the state, as they are in places farther west. Many woodlands have evolved to deal with and benefit from periodic fires.

However, humans have been making fire risks worse. That’s in part due to climate change, which is changing weather patterns and driving some of the aridity in Colorado’s forests.

“Our 2020 wildfire season is showing us that climate change is here and now in Colorado,” said Jennifer Balch, director of the Earth Lab and an associate professor of geography at the University of Colorado Boulder, in an email. “Warming is setting the stage for a lot of burning across an extended fire season.”

In particular, there has been a growth in late-season fires in Colorado. The area burned by October fires over the past decade has tripled compared to the area burned between 1980 and 2000. “We do see fall fire events in Colorado, related to fast, downslope winds. But to see multiple events start this late, in the middle of October, is very rare,” Balch said.

It’s also a function of more people living in high-risk areas. “The growing population in Colorado means we have more people in the woods, which leads potentially to more ignitions,” Hoffman said. The vast majority of wildfires in the United States have human causes, though in Colorado about half of fires in the state are ignited by lightning strikes.

The growing fire risk is also a consequence of more than a century of suppression of natural wildfires. By putting out blazes, vegetation in the state has accumulated, so during periods of extreme dryness, there is much more fuel to burn than there would be had more fires been allowed to proceed.

There are now efforts to reintroduce fire to the landscape, but vast swaths of the state need fuel reduction treatments, and the window for safely conducting measures like prescribed burns is shrinking as the climate warms.

“We love our beautiful mountain landscapes to live and to recreate,” Balch said. “But these beautiful landscapes are also flammable, and more flammable with climate change. We need proactive solutions that manage our fuels in places where it matters most for ecosystems and people.”