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What is 'fuel moisture' and why is it important for firefighting?

Taylor Zarifis plucks live leaves off of sagebrush to demonstrate how to collect samples to measure fuel moisture levels.
Madelyn Beck
Mountain West News Bureau
Taylor Zarifis plucks live leaves off of sagebrush to demonstrate how to collect samples to measure fuel moisture levels.

On a recent 99-degree afternoon, Taylor Zarifis was plucking leaves off of a tall sagebrush in front of a Bureau of Land Management building in Boise.

“We’re only collecting the live leaves,” she explained.

Zarifis is a wildfire fuels technician, and she’s collecting this brush to demonstrate how to calculate something called “fuel moisture,” which refers to how much water is in live plants.

“So any of this dead stuff, we’ll avoid. And then also, if you have bugs or any fungus or anything on the leaves, we’ll avoid picking off of those, too,” she said.

Zarifis and others at the Boise office visit sites around southern Idaho every few weeks to collect parts of plants like sagebrush and juniper. Many other BLM offices collect this kind of data, too, sampling different shrubs or trees in their own area. But that’s only the first phase of getting a fuel moisture reading.

From there, those plant samples get the moisture baked out of them. In some places, that requires an oven and some math. But in Boise, it means taking the plants to an office about the size of a large closet, which has two machines that heat up the plants and calculate moisture percentages automatically.

That reading is critical.

It tells forecasters and firefighters how easily a wildfire might start, or how quickly it could spread. Extremely dry brush can mean easy-starting, fast-moving fires, especially when paired with winds and lightning.

Fuel moisture levels.png
Courtesy of Taylor Zarifis
Boise District BLM
Sagebrush, juniper, and forage kochia live fuel moisture results for the Boise District BLM from samples collected on 8/31-9/1. "Due to consistent high temperatures over the last two weeks, we are seeing a significant drop in fuel moisture at most sites. We now have most of our sagebrush sites in the advanced fire behavior category and one in the extreme category. Most sites are near the average values for this time of year, and a couple are nearing record lows. Forage kochia at our Simco site has reached dormancy for the season, so values were not calculated."

Nolin Page is another fuels technician in Boise who used to work as a firefighter. He says fuel moisture numbers are important for planning.

“For just a basic firefighter, it's not so much of something I can change, but I can anticipate it. But for management, (that) is where the real change is, because (the data helps them) address their funding needs, resource needs, allocate people where they need,” he said.

Forecasters at the National Interagency Fire Center even use fuel moisture to help create a monthly analysis of where wildfire dangers may crop up.

Nick Nauslar is a predictive services meteorologist there, and he explains that the heat wave in the West has been drying up plants even more.

Heat waves “kind of prime the pump a little bit – dry out the fuels, cure the fuels and make them available to burn," he said. "And then we start worrying about, ‘Are we going to get a critical fire weather event?’”

Critical events include lightning storms and high winds.

And to make wildfire predictions, forecasters can look at average plant moistures from the last few decades and how fires behaved in those conditions.

But the only reason we have all this fuel moisture data is thanks to a project started in Nevada about 40 years ago. It was called the Great Basin Live Fuel Moisture Project.

“We're going back to 1980, ‘82ish, right around there,” said Sandy Gregory, who worked on the project from the beginning with its founders Greg Zschaechner and Marcus Schmidt.

“And what we did is we developed, or they developed, an applied science project based off of plant biology,” she said.

This machine in Boise tests fuel moisture levels in plants like the sagebrush (above).
Madelyn Beck
Mountain West News Bureau
This machine in Boise tests fuel moisture levels in plants like the sagebrush (above).

She says they started just trying to figure out the best way to get accurate moisture levels from live plants.

And then people started to realize how important it could be. Offices in other states even started sending their brush to Nevada to get moisture levels.

The program grew from a shed in Carson City, to a shed in Reno and eventually to a lab, where it was a bit easier to work through hundreds of plant samples.

“I mean, gosh, at one point in time we had somewhere around 100 canisters, and some of them would have nine different samples,” she said.

More funding came into wildland firefighting efforts, too, so field offices could purchase their own ovens to check fuel moisture levels, and share them over what was then a new technology: the internet.

The project even provided standards for measuring different kinds of brush, and how to store it. Without those metrics and standardization — now going back a few decades in many places — it would be much harder to forecast wildfire dangers. Especially as climate change and drought alter the Western landscape.

Boise District BLM

Chris Chronmell is a BLM fire management specialist with the fuels program in Boise. Over the years, he says, communication about fuel moisture levels and dangers has gotten a lot better between government agencies.

They’ve even worked with transportation departments to make sure brush is cleared or managed in a way that reduces fires where cars and trucks are driving.

And if we didn’t have the decades of standardized data we have now, he says some of our fire danger tools might not be so accurate.

“You’ve seen the Smokey Bear signs out there that say ‘low fire danger’, ‘high fire danger.’ And you know, I think it was typically, in the past, more of a gut (feeling) or what kind of activity we were actually having,” he said.

He says while some may have used data before it was standardized, others likely didn’t, depending instead on their own experience.

Wildfire threats have increased as the Western heat wave continues to dry out fuels. On September 6, the National Interagency Fire Center increased its fire preparedness level to 4 out of 5 – only the second time the organization has increased to a Level 4 in the month of September – as large fires increased competition for wildland firefighting resources.

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Boise State Public Radio in Idaho, KUNR in Nevada, the O'Connor Center for the Rocky Mountain West in Montana, KUNC in Colorado, KUNM in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.

Madelyn Beck was Boise State Public Radio's regional reporter with the Mountain West News Bureau.

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