California fires driven by record heat
Unusually dry fuel makes blazes spread dangerously fast
REDDING, Calif. — The northern Sacramento Valley was well on its way to recording the hottest July on record when the Carr fire swept into town last Thursday.
It was 113 degrees, and months of above-average temperatures had left the land bone-dry and ready to explode. Within a few hours, hundreds of structures were lost and six people killed.
The Carr Fire has burned more than 880 homes and killed six people in and around Redding. The blaze has also destroyed another 348 outbuildings and damaged 165 homes. It is now the seventh-most destructive wildfire in California history, fire officials said.
The destruction adds to California’s worst wildfire year on record — dozens dead since October, with more than 10,000 structures lost from San Diego to Redding.
A new blaze erupted Tuesday and drove through a rural area near Covelo, which is about 180 miles north of San Francisco. Gusty winds quickly drove it through about a square mile of brush, forest and grasslands near Mendocino National Forest, Mendocino County Undersheriff Matthew Kendall said.
Two older fires straddling Mendocino and Lake counties had burned 10 homes along 116 square miles of rural land by Tuesday.
There are many reasons for the grim totals, but experts say one common denominator connects the disastrous fires: California is facing extreme heat, the likes of which it has never seen in the modern historical record.
“The temperatures have just been almost inexorably warmer all the time,” said University of California, Los Angeles climate scientist Daniel Swain, and fires “burn more intensely if the fuels are extremely dry.”
In the past, there has been some reluctance among scientists to cite climate change as a major factor in California’s worsening wildfires. Human-caused ignitions and homes being built ever closer to forests have played a large role. But the connection between rising temperatures in California and tinder-dry vegetation is becoming impossible to ignore, according to experts who study climate and wildfires.
“The regional temperatures in the western U.S. have increased by 2 degrees since the 1970s,” said Jennifer Balch, director of Earth Lab at the University of Colorado, Boulder. “You’re seeing the effect of climate change.”
Neil Lareau, assistant professor of atmospheric sciences at the University of Nevada, Reno, said unusual warmth is now routine, and that heat “leads to drying things out quicker.”
Vegetation can have various degrees of dryness — a wet log in the woods could smolder before puttering out, while tinder-dry chaparral on a 110-degree day could explode when ignited, Swain said.
“What that means is the fire has to do less work to ignite the vegetation right next to it. And it can spread faster, and it releases energy more quickly,” Lareau said.
Swain said California is seeing more fires spreading much faster than what was customary. “It’s just that much easier for fires to escape initial control,” he said. According to Swain, an ominous warning sign before each of the major fires of the last year — including last fall’s catastrophic Santa Rosa blaze — was alerts about record or near-record dryness in the vegetation.
The effect of temperature — and how dry the vegetation is — can matter more than how much rain or snow fell the previous winter.
Northern California saw its wettest winter on record in 2016-17, followed by its warmest summer and the devastating Santa Rosa fire in the fall.