The science behind fire danger ratings and regulations

JACKSON, Wyo. — Smoke in the air in early July is a good reminder that wildfires are all around us, and could happen here at any moment. That’s why fire managers at Teton Interagency Fire keep a close eye on conditions and implement fire restrictions when they feel appropriate. But what do the different danger ratings and restrictions actually mean? It’s all about math, said Evan Guzik.

Guzik is the public affairs specialist for Bridger-Teton National Forest and Teton Interagency Fire crewmember. Fire danger is a careful calculation, he said.

“There’s no social component; it’s strictly based on factual data on the ground.”

To determine fire danger — that is, the rankings you see on signs in town and at trailheads that go from “low” to “extreme” — fire crews look at two things: reports from seven Remote Automated Weather Stations (RAWS) scattered in the forest, and fuel moisture. The former gives a snapshot of recent weather: rain, heat, wind, etc. The latter is a little more complicated.

A fuel source is what it sounds like: anything that could burn. But different fuel types have different burn potentials, measured in time it would take moisture to saturate. Grass is going to get pretty wet if it rains,  Guzik explained. That’s considered a “one-hour fuel.” Big logs and downed trees, on the other hand, are going to take more time to dampen. They might be considered “10-hour” fuels, “100-hour” fuels, or even 1,000-hour fuels. In order to measure fuel moisture, the Forest Service collects samples of each fuel size and weighs them when they’re wet, then puts them in an oven to remove all the moisture and weigh them dry, Guzik explained. This happens, on average, every two weeks.

Still following? Great. This is where it gets complicated, but we’ll spare you the math. Basically, Guzik said, fire crews do a bunch of calculations to determine fuel moisture. They use those numbers, combined with weather reports from the RAWS, and come up with one final number: an Energy Release Component (ERC). That’s what they use to determine fire danger.

For context, Guzik explained, the Forest Service carries seasonal charts that map seasonal ERCs with historical averages. This year is already well above the 90th percentile, Guzik said.

“We were climbing pretty steep toward moving above [the summers of] ’87-88 and 2016, which were two really dry years,” Guzik said. “At one point in June, we got up really high compared to historic averages.”

Which is perhaps part of the reason fire officials have implemented Stage 1 fire restrictions already this summer. Fire danger is a “snap shot” of one moment, Guzik said. It’s all numbers. Fire restrictions take into account some more imprecise factors — what the weather might do, how this summer’s numbers compare to historic averages, local and national staffing available to respond to potential local fires. Above all, there’s the human factor.

“We look at things like how many fire starts we’ve had, how many abandoned campfires, visitor use numbers,” Guzik said.

And this summer, human behavior has been sub-par. By the time fire restrictions went into effect at the beginning of July, BTNF had found 80 abandoned campfires. As of July 9 — eight days after restrictions to effect — they had already found 21 more.

It’s easy to think a couple of days of rain make for safer fire conditions. But it’s more complicated than that.

“Stick to the facts,” Guzik said. “We are in fire restrictions right now. You can’t have a campfire outside of developed campgrounds.”

The stakes are too high to disregard fire danger and fire restrictions. Guzik calls it “values at risk.”

“In Teton County, you have million-dollar homes that are values at risk,” he said. “But you also have immaculate and wonderful viewsheds that people are drawn to and hold a really powerful emotional feeling with, and that is a value at risk at well.”

About The Author

Buckrail @ Shannon

Shannon is a Wyoming-raised writer and reporter pursuing a master's in journalism at Boston University. Jackson shaped her into an outdoorswoman, but a love for language and the human condition compels her to write. She believes there's no story too small to tell nor adventure too small to take.

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