What’s starting all these fires? We are.
Study finds that humans to blame for 95% of blazes since 1910; experts say we can prevent most of them
While weather is driving the severity of California’s wildfires, new research shows that people ignite a lot more fires than nature does.
And we’re starting fires when and where nature normally doesn’t — at times and places where lightning rarely strikes.
But there’s hope: Because we cause them, we can stop them.
“In most of California, if we could stop ignition during extremely high winds and drought and heat spells, like now, that will be an effective approach” to reduce risk, said Jon Keeley, a research scientist with the U.S. Geological Survey’s Western Ecological Research Center in Sequoia National Park, who studied fire patterns since 1910.
These findings come at a time of growing alarm over the state’s 17 major fires burning now. While investigations are still underway, every fire now burning in Califor-
nia may have been caused by humans; no lightning storms were reported.
The Carr fire reportedly was caused when a trailer tire went flat and its rim scraped the asphalt, creating sparks. In Southern California’s Holy fire, a 51-yearold man has been arrested and charged with starting the blaze after a profanityladen text threatening: “Its all gonna burn.” The cause of the Mendocino Complex fire has not yet been determined.
Keeley’s new analysis found that humans caused 95 percent of all wildfires throughout most of the state since 1910. The rest were caused by lightning strikes, mostly in the rural northeastern corner of the state.
In the Bay Area, the portion of human-caused fires ranged from 93 percent in Contra Costa and Santa Clara counties to 98 percent and 100 percent in Alameda and Marin counties, Keeley reports in an upcoming issue of the International Journal of Wildland Fire.
Human-sparked blazes are expanding the fire season, according to Jennifer Balch, director of the Earth Lab at University of Colorado, Boulder, writing in the Proceedings of the National Academy of Sciences. More than three-quarters of lightning fires start in the summer; in contrast, humancaused fires occur throughout the year but especially during the tinder-dry fall, when winds are high.
We’re also starting fires in places that don’t typically see a lot of lightning, such as the Bay Area and central California. And they’re occurring during the most severe fire weather conditions, Balch said. For instance, ignition during Santa Ana or Diablo wind conditions would ordinarily be rare; now, it’s commonplace, she found.
“Human ignitions have expanded the ‘fire niche,’ ” she wrote.
Once started, today’s wildfires are hotter and more destructive than ever.
In the western U.S., regional temperatures have increased by almost 2 degrees Fahrenheit since the 1970s, snowmelt is occurring a month earlier in some places, and the length of fire season has increased by almost three
months, Balch said.
Climate change accounted for more than half of the increase in aridity of western U.S. forests between 1979 and 2015, according to a paper by Cupertino native John Abatzoglou, now an earth scientist at University of Idaho.
Unusual warmth causes vegetation to dry faster — and fire has to do less work to ignite the adjacent vegetation, so it spreads faster, according to Abatzoglou. Warmth also causes an earlier snowmelt in the spring, leading to a drier summer.
Furthermore, there’s been an explosion of development in areas at high risk of fires. We start twice as many wildfires on July 4 as on any other day.
“The patterns are quite striking, with humans starting fires where people live — and also where lightning is very, very rare,” Abatzoglou said. “The story is very different as you move into the Sierra and across much of the more remote western U.S.”
Environmentalists have expressed frustration over Gov. Jerry Brown’s “Wildfire Preparedness and Response” plan to craft policies to respond to increasing wildfire risk. The report blamed climate change but made no direct links to humans.
“There needs to be a shift to reducing the number of fire ignitions up front, rather than simply responding to fire damage — i.e., fastening your seat belt vs. going to the hospital,” said David Kossack of the San Andreas Land Conservancy, a Davenport-based group that protects the forest along the San Mateo coast. Kossack is asking Insurance Commissioner Dave Jones to conduct an audit of fire sources.
“There is nothing ‘natural’ about any of these disasters,” he said.
Human-caused fires also are longer than lightning fires, Balch found. They last 85 days, on average; lightning fires last 45 days.
“When we have lightning events, smoke-jumpers are on them right away. The U.S. Forest Service is pretty aggressive and stops them when they are very, very small. They cut a ring around them, and then let the interior burn out. They might be accompanied by rain,” said Kurt Henke, former chief of the Sacramento Metro Fire Protection District.
“Human-caused fires are closer to populated areas, with houses and lives at risk. We’ll stay on them until they’re completely out. And we’ll ‘mop up,’ digging up stumps, 200 feet out,” said Henke, now a consultant for major fire operations.
We’ve made trouble ever since we got here, yet education and regulations appear to be making a difference, Keeley found. We used to ignite a lot more fires early in the 20th century, when fire prevention was in its infancy and fire response was imperfect. The number of human-caused blazes increased steadily until 1979, then significantly declined with one big exception: power line ignitions. For example, the deadly fires last fall in Sonoma and Napa counties were sparked by downed power lines.
While electric power lines don’t account for many fires, they account for substantial amount of area burned. That’s because they commonly occur during high winds.
Historically, the largest number of fires were caused by equipment, such as gaspowered weed cutters that strike a rock and cause a spark, Keeley said. Ignitions also are triggered by generators, lawn mowers, chainsaws, tractors and off-road vehicles without required spark arrestors.
That is followed by arson, debris burning, kids playing with fire, smoking, vehicles and power lines.
The decline in humansparked blazes can be attributed in part to better neighborhood watch programs, which include patrols during red flag warnings. There are increased penalties for arson. Debris burning is less accepted. Smoking, once a major cause of wildfires, has declined. Children have been taught not to play with fires, and lighters are childproof. Catalytic converters used to trigger fires when cars overheated; modern vehicles have warning lights when they overheat.
But catastrophic fires such as the Carr and Mendocino Complex fires — so early in the fire year — show how much more education and prevention are needed, said Henke.
“Data like this is critical to help us analyze trends,” he said. “It tells us where we need to target.”