The rare winter grassland fire that recently blew up along Colorado’s Front Range was rare, but experts say similar wildfires will becme more common as climate change warms the planet, and suburbs grow in fire-prone areas.
“These fires are different from most of the fires we’ve been seeing across the West in the sense that they’re grass fires, and they’re occurring in the winter,” said Jonathan Overpeck, a professor in the University of Michigan School for Environment and Sustainability. “Ultimately, things are going to continue to get worse unless we stop climate change.”
The Colorado wildfire forced 35,000 people from their homes, burning through a pair of heavily populated suburbs between Denver and Boulder. Though the cause is under investigation, experts say it’s clear what allowed it to spread so fast.
“With any snow on the ground, this absolutely would not have happened in the way that it did,” said Keith Musselman, a snow hydrologist in Boulder, Colo. “It was really the grass and the dry landscape that allowed this fire to jump long distances in a short period of time.”
Three ingredients were needed to start this fire — fuels, a warm climate and an ignition source, said Jennifer Balch, a fire scientist with the University of Colorado, Boulder. “And then you add a fourth ingredient, wind, and that’s when it became a disaster.”
Temperatures in Colorado between June and December were the warmest on record, Balch said. The grasses grew thick because they had a wet spring, but then they saw no moisture in recent weeks before the fire.
Colorado Gov. Jared Polis called the fire a “a horrific convergence” of destructive wind gusts that hit the area following the unseasonably dry and warm winter.
“We know that with the climate we face higher risks,” Polis said, “right here in the city and suburbs.”
Balch said Colorado is a dry landscape filled with flammable material for much of the year, “and those chunks of time are getting longer with climate change.”
The lesson learned throughout this event is that the “wildland-urban interface is way bigger than we thought it was,” Balch said.
That means a wider area is under threat of wildfire. That border area — in which structures built by people meet undeveloped wildland prone to fire — always has been the foothills, she said. Firefighters in Boulder consider the interface west of Broadway — a busy road that passes through the center of town. But this fire was sparked east of that line, next to thousands of houses that have sprouted up on the east side of the Rockies since the 1990s, Balch said.
“There were stretches between Denver and Fort Collins that had no development, but now it’s just like one long continuous development track,” Balch said. “And those homes are built with materials that are very flammable — wood siding, asphalt roofing. We need to completely rethink how we’re building homes.”
The other important change is understanding how these fires start in the first place, she said.
“There’s no natural source of ignition at this time of year,” she said. “There’s no lightning. It’s either going to be infrastructure-related, or it’s going to be human-caused.”
Over the past two decades, 97% of wildfires were started by people, according to a study by the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, Boulder. Causes have ranged from accidents at construction sites to a car with a hot tailpipe to tossed cigarettes.
“We need to be thinking about how our daily activities can contribute ignitions or sparks that start wildfires,” Balch said.
Unless people stop climate change by cutting back on fossil fuels, wildfires will threaten communities, Overpeck said.
“There’s little doubt in my mind that the conditions conducive to really bad wildfire, whether it’s grass or forest, are only going to get worse,” he said.
As more people move to areas where wildfires occur, the threat increases.
“We’re building towns and cities and infrastructure,” Overpeck said. “And so it’s just a matter of time before we have whole towns burning down like we had in California and events like this in Colorado.”