Author: Laurel Hamers / Source: Science News
Wildfires are not known for their restraint. They’ll jump rivers, spew whirling dervishes of flames and double in size overnight.
Take the Carr Fire — one of California’s most destructive — sparked in mid-July when the rim of a flat tire met pavement. As the blaze grew, it jumped across the Sacramento River and sparked a flaming whirlwind that trapped and killed a firefighter near Redding. By the time it was fully contained on August 30, it had burned 930 square kilometers, destroyed more than 1,000 buildings, and killed seven people.
“Once these fires are spreading fast enough and intensely enough, you can’t stop them,” says Ruddy Mell, a combustion engineer with the U.S. Forest Service based in Seattle.
Federal and state agencies that manage wildfires use mathematical equations — fire models — to predict how blazes will spread and decide how to commit firefighting resources or whether an evacuation is needed. But the models can’t always predict when a fire will suddenly veer in a new direction or grow exponentially.
Now, scientists are developing more nuanced fire models with increasingly detailed satellite data and better understanding of how fires can create their own weather and fan their own flames. These finer-scale models take hours or days to run on a computer, so they aren’t likely to replace more quick-and-dirty field models for responding in the heat of the moment. But they can help scientists figure out what’s driving a wildfire’s behavior — and learn how to better protect communities from fires.
Fire it up
The Carr Fire created a fire tornado on July 26. An analysis suggests the unique phenomenon started when fast winds swept down the slope of nearby mountains (1), bottomed out and broke like a wave (2). That created turbulent, swirling air at the base of the hills (3). Meanwhile, air warmed by the fire became less dense and rose (4). As the flames met with turbulent air (5), the fire and hot air began swirling and rising together in a whirling column of flames (6).
In 2018, wildfires are on track to cause at least as much damage in the United States as in 2017, when they burned a bigger area than in almost any year since consistent data collection began in 1983, according to the National Interagency Fire Center in Boise, Idaho. As of September 5, fires had torched almost 30,000 square kilometers nationwide, an area larger than Massachusetts. In the past few years, these wildfires have cast an especially thick veil of particulate pollution over the western United States (SN: 7/18/18, p. 9), where almost 100 large fires are currently burning.
While wildfires sparked naturally by lightning strikes are a healthy part of many ecosystems, humans have inadvertently made such fires worse. Years of forest management policies that suppress natural fires have made the ones that do bubble up even more ferocious, since there’s so much fuel on the ground. Plus, people start 84 percent of all wildfires, accidentally or on purpose, researchers reported in the Proceedings of the National Academy of Sciences in March 2017. Our influence has made fire season three times as long as it would be naturally, the study suggests.
Climate change is likely to intensify the problem. Much of the western United States will probably see an increase in the area of land burned over the next 30 years, according to a December 2017 study in PLOS One that analyzed temperature, snowpack and wildfire data. And in the future, cyclic climate fluctuations such as El Niño will exert a stronger influence on heat waves and wildfires, making such natural disasters more severe, researchers suggested in August in Geophysical Research Letters.
Capturing fire behavior through mathematical equations, though, is almost as hard as stopping the burn. Wildfires are influenced by a complex set of variables. What kind of plants cover the ground? Is the terrain flat or hilly? How fast is the wind blowing? What’s the temperature?
Fire managers take these variables into account, but their prediction models are designed for emergency scenarios where a fast response is key. The rough field equations don’t capture the finer details — the way fires interact with the atmosphere, for instance, creating their own winds that can blow flames and spit embers in unexpected directions.
Of course, gathering data about the way fires interact with the atmosphere poses some logistical challenges. “It’s pretty much impossible to set up instruments right next to a high intensity wildfire,” says Warren Heilman, a…
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