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What are megafires ... and why is it so hard to explain their growth?

The term megafire was first coined in 2005. Now, they're becoming more and more prevalent.
Credit: 9NEWS file photo

KUSA — The intensity and frequency of so-called megafires continues to rise.

This year had been marked by the largest wildfire in California history (the Ranch fire in the Mendocino Complex), and the third largest in Colorado (the Spring Creek fire).

The term megafire was first coined in 2005 by Jerry Williams, the former national director of the U.S. Forest Service Fire and Aviation. A megafire is not strictly defined, but is more of a recognition of the development of more extraordinary wildfires in terms of their size, complexity and resistance to control.

Generally, wildfires that burn nearly 100,000 acres now usually get the tag of megafire.

Climate change, drought, and the overgrowth of fuels are at the top of the list when it comes to blame, but one Colorado scientist found another interesting factor to what might be fanning the flames of these megafires.

An interesting case to study occurred in 2014. The King Fire in California was a 97,000-acre megafire that had an unexpected acceleration four days into the burn.

“It suddenly grew rapidly, 25 kilometers, up to the top of the canyon in 12 hours,” said Project Scientist Janice Coen with the National Center for Atmospheric Research (NCAR).

That sudden growth was not forecast, as there were light winds and no other weather factors expected to contribute to a faster spread. This presented fire commanders at the time -- and later researchers -- with an interesting mystery.

Fortunately, the King fire would hand over some unique clues to help explain the fire’s behavior.

“It was serendipitous that this area had been mapped shortly before the fire,” Coen said.

The U.S. Forest Service had just gathered detailed information about the vegetation in that part of the Sierra Nevadas.

So NCAR and NASA teamed up to quickly gather more measurements, during the fire and right after.

“We captured its shape as it evolved, when it arrived at the canyon, it’s rapid spread up the canyon, and how it stalled at the top,” Coen said.

They had hyper-spectral measurements that shows the amount of radiation coming off the surface of the vegetation in a variety of different wave lengths. They also gathered lidar measurements which scans through the vegetation and gives you a 3-D picture of the trees; all valid before, during, and after the fire.

The NCAR-based CAWFE® modeling system ran a simulation (the acronym stands for Coupled Atmosphere-Wildland Fire Environment). It combines a weather model with fire behavior.

The unique data added to the simulation allowed the researchers to determine the greatest contributor to the King Fire’s sudden growth.

“It was because of a fine-scale circulation within the narrow river canyon first, and also because of winds created by the fire itself,” Coen said. “So the weather directs the fire, in turn, the fire changes the weather.”

That conclusion outweighed the assumption that climate change, severe drought, and overgrown fuels caused the King fire to suddenly explode into another megafire.

“There’s two parts to the fire problem,” Coen said. “Part of it is climate, and the other part is small-scale factors that we’re still working on.”

Coen hopes that her research, which was co-authored by scientists from NASA’s Jet Propulsion Laboratory and the U.S. Forest Service, will be able to improve firefighter safety, and help improve mitigation techniques in valleys, canyons and steep terrain.

The paper “Deconstructing the King Megafire” was published in the Journal: Ecological Applications.

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