GEORGETOWN, California – Waves of fire swept through the Sierra Nevada forest, raising smoke and leaving charred vegetation behind, all under the watchful eye of a heavy drone. Instruments along the perimeter collected samples of the scorched particles that spewed into the air.
Prescribed burns, a centuries-old practice that clears forests of small trees, bushes, and other matter that can fuel fires, are receiving a 21st-century update.
As climate change dries up the earth and increases the risk of forest fires, scientists are starting to use cutting-edge technologies and computer models to make low-intensity controlled burns safer, more effective and less harmful to neighboring communities.
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“The fire has civilized us, but we still don’t fully understand it,” said Tirtha Banerjee of the University of California, Irvine, as she watched a tall pile of dead branches go up in flames.
As useful as the burns prescribed for forest maintenance may be, they are difficult to perform – expensive, labor-intensive, and dependent on narrowing windows of favorable weather. And even well-planned burns can prove disastrous, like when a fire started by the United States Forest Service this spring was transformed by gusts of wind into the largest fire ever recorded in New Mexico.
Scientists think we can do better. Several teams recently met at the Blodgett Forest Research Station northeast of Sacramento, California, an area filled with towering Ponderosa pines, Douglas fir and frankincense cedar. A planned burn in Blodgett was a valuable opportunity to gather data in the field, and researchers packed loads of equipment including GoPro cameras, drone-mounted sensors to map the terrain in minute detail, a sonic anemometer to measure wind, and an assortment of machines that collected particles suspended in the air.
While researchers have long implemented advanced techniques to examine fire behavior, fewer have examined specific questions about prescribed fires, such as whether debris needs to be removed early with chainsaws and bulldozers, said Robert York, a forest ecologist at the University. of California, Berkeley.
Preventive thinning could allow more wind to pass during a burn, producing warmer flames and making it more difficult to control the blaze. But it could also help the burn consume more leftover fodder, creating a more durable buffer against fires.
“For the prescribed fire, I think it’s really all out there to explore,” Banerjee said.
When Prometheus stole fire from the gods and gave it to humans, he probably did not imagine how difficult it would be to handle it on a planet heated by the burning of fossil fuels.
Global warming has brought more of the extremely hot and dry conditions that can turn fires into deadly disasters. Fierce flames like last year’s Dixie Fire, which burned nearly 1,563 square miles of Northern California, weren’t part of the picture for scientists half a century ago when the Forest Service and other agencies first developed their models. mathematicians to predict how fires will spread.
Scientists were “simply caught off guard at how fast things are changing,” said James T. Randerson, an earth scientist at the University of California, Irvine.
The Forest Service has acknowledged that its methods are failing to keep pace with global warming. The agency’s investigation into this spring’s ill-fated New Mexico burn found that, even though it was properly planned, the resulting fire proved more dangerous and faster than expected.
To help teach land managers how to burn in increasingly unstable landscapes, J. Kevin Hiers, a fire scientist with the US 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 game-like training system that would be “a Minecraft-like experience to burn bosses,” as Hiers calls it.
Better fire modeling is important, but so is turning that knowledge into easy-to-use tools for firefighters, he said. “We should be able to represent, in a training environment, what fire should or could do in a very sophisticated way, long before we light a match.”
For scientists who traveled to Blodgett Forest, the first two days on the site were spent installing equipment and carefully observing the landscape before it engulfed in flames, which would be impossible if they tried to study a fire.
Banerjee and his team of graduate students and postdoctoral researchers repeatedly flew their drone over the area, mapping it with lidar, a technology for capturing detailed three-dimensional images; a thermal imaging camera; and a multispectral camera, which told them how dry the brush was. By comparing images from before, during and after the fire, Banerjee’s team was able to pinpoint exactly how the fire had transformed the forest floor.
In the evening, Banerjee’s team burned small piles of dead wood and shot GoPro videos of the flickering flames and embers rising into the air. The footage would help the team study how embers travel, which could reveal how the fires spread out of control.
In another patch of the forest, Randerson and Audrey Odwuor, a PhD student in Irvine, put pine twigs and needles in ziplock bags, as if they were gathering evidence from a crime scene. They planned to burn the material in their laboratory to analyze the chemical composition of the resulting emissions. They had also brought tools to Blodgett to collect smoke samples. One day, Odwuor said, such methods could help gauge how effectively a prescribed fire burned the fuels it was supposed to get rid of.
York, who works most of the year in Blodgett, led the researchers to an area of the forest that he said hadn’t burned in three years. Burning now would help keep the plot in a healthy and natural state, even if all the planning, coordination, and effort needed was far from natural.
The morning of the burn was sunny and warm. The researchers donned fireproof T-shirts and helmets, and York, as the boss of the burn, led the group to a rise. He lowered the drip torch and a thin jet of fuel dripped out and caught the flame on the torch wick. A thread of fire sprouted from the brown, dead soil. The burn had started.
York and a small experienced crew walked perpendicular to the forest slope, using their torches to draw lines of fire that burned uphill. The landscape was quickly transformed. The tall trees cast veiled and dramatic shadows on the whitish-gray smoke screens. A thick haze scattered the sunlight, flooding the forest with a deep orange glow. The crackle of the burning bushes mingled with the faint mechanical wail of the drone above.
For a while the flames had a mild, almost delicate quality; the vegetation was too wet to burn fiercely. But as the day got warmer, the fires began to blacken the hillsides at a rapid pace. Scientists watched the scene cautiously as their machines collected data.
By late afternoon, York and his team had burned about 13 acres and sat down to catch their breath. His face was slick with sweat and dirt. The forest burned all around him.
Randerson took a moment to admire the brutal firepower they were studying – a natural, but also unnatural, way to safeguard the earth. “The older I get”, he said, “the more I appreciate how much science is like an art”.
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