Prescribed burning updated for 21st century
Scientists use tech to improve effects of controlled blazes
GEORGETOWN, Calif. — Waves of fire swept through the Sierra Nevada forest, churning up smoke and leaving charred vegetation behind — all under the watchful eye of a heavy-duty drone. Instruments around the perimeter snatched up samples of the singed particles spewing into the air.
Prescribed burns, an age-old practice that rids forests of the small trees, brush and other matter that can fuel wildfires, are getting a 21st-century upgrade.
With climate change parching the land and increasing wildfire hazards, scientists are beginning to use cutting-edge technology and computer modeling to make controlled, low-intensity burns safer, more effective and less disruptive to nearby communities.
“Fire has made us civilized, but we still don’t understand it fully,” said Tirtha Banerjee of the University of California, Irvine.
As useful as prescribed burns can be for maintaining forests, they are tough to carry out — costly, labor-intensive, contingent on narrowing windows of favorable weather. And even well-planned burns can turn disastrous, as when a fire started by the U.S. Forest Service this spring was transformed by gusting winds into New Mexico’s largest wildfire on record.
Scientists think we can do better. Several teams recently converged at Blodgett Forest Research Station northeast of Sacramento, California, an area thick with towering Ponderosa pine, Douglas fir and incense cedar. A planned burn at Blodgett was a precious opportunity to collect data in the field, and the researchers
packed carloads of gear, including Gopro cameras, drone-mounted sensors for mapping the terrain in minute detail, a sonic anemometer for measuring wind and an assortment of machines that collected airborne particles.
While researchers have long deployed advanced techniques to examine wildfire behavior, fewer have looked at questions specific to prescribed fires, like whether debris should be cleared with chainsaws and bulldozers in advance, said Robert York, a forest ecologist with the University of California, Berkeley.
Thinning preemptively could allow more wind to whip through during a burn, producing hotter flames and making the blaze harder to control. But it might also help the burn consume more of the remaining fodder, creating a longer-lasting buffer against wildfire.
“For prescribed fire, I
think it’s really all out there to be explored,” Banerjee said.
Global warming has brought more of the extremely hot and dry conditions that can turn wildfires into deadly catastrophes, which weren’t part of the picture for scientists a half-century ago, when the Forest Service and other agencies first developed their mathematical models for predicting how wildfires spread.
Scientists have been “just completely caught off guard about how fast things are changing,” said James Randerson, an earth scientist at the University of California, Irvine.
The Forest Service has acknowledged that its methods are failing to keep up as the planet warms. The agency’s investigation into this spring’s ill-fated burn in New Mexico found that even though it had been properly planned, the resulting
fire proved more dangerous and fast moving than anticipated.
To help teach land managers how to burn in increasingly volatile landscapes, J. Kevin Hiers, a fire scientist with the U.S. Geological Survey and Tall Timbers Research Station in Tallahassee, Florida, has spent years working with other researchers on the fire equivalent of a flight simulator — a video-gamelike training system that would be “a Minecraft-type experience for burn bosses,” as Hiers calls it.
Better fire modeling is important, but so is baking that knowledge into easy-touse tools for burn crews, he said. “We should be able to represent, in a training environment, what fire should or might do in a very sophisticated way, long before we strike a match.”
For the scientists who had traveled to Blodgett Forest, their first two days at the site
were spent setting up equipment and carefully surveying the landscape before it was engulfed in flames — something that would be impossible had they been trying to study a wildfire.
Banerjee and his team of graduate students and postdoctoral researchers flew their drone repeatedly over the area, mapping it with lidar, a technology for capturing detailed three-dimensional images; a thermal camera; and a multispectral camera, which told them how dry the brush was. By comparing images from before, during and after the burn, Banerjee’s team could pinpoint exactly how the fire had transformed the forest floor.
In the evenings, Banerjee’s team burned small piles of dead wood and shot Gopro videos of the flickering flames and the embers being lofted into the air. The footage would help the team study how embers travel, which might reveal how fires spread out of control.
In another patch of forest, Randerson and Audrey Odwuor, a doctoral candidate at Irvine, placed twigs and pine needles into zip-lock bags, as if collecting evidence from a crime scene. They planned to burn the material back at their lab to analyze the chemical composition of the resulting emissions. They had also brought instruments to Blodgett to collect smoke samples. Someday, Odwuor said, such methods could help evaluate how effectively a prescribed fire had burned through the fuels it was supposed to get rid of.
The morning of the burn was sunny and hot. The researchers put on flameresistant shirts and hard hats, and York, as the burn boss, led the group to an area of high ground. He lowered his drip torch, and a thin stream of fuel dribbled out and caught the flame on the torch’s wick. A wisp of fire sprouted from the dead brown ground. The burn had begun.
York and a small, experienced crew walked perpendicular to the slope of the forest, using their torches to draw lines of flame that burned uphill. The landscape was quickly transformed. Dense haze scattered the sunlight, bathing the forest in a deep orange glow. The crackling of burning bushes mingled with the low mechanical whine from the drone above.
For a while, the flames had a meek, almost dainty quality; the vegetation was too damp to burn very fiercely. But as the day warmed, fires began blackening the hillsides at a rapid clip. The scientists took in the scene cautiously as their machines gathered data.
By late afternoon, York and his team had burned about 13 acres, and he sat down for a breather. His face was slick with sweat and grime. The forest smoldered all around him.