The Carr Fire doubled in size twice in just several days. What kind of conditions can make this happen?
There are lots of drivers. Fuels like timber and grass, drought to dry them to the point of combustion, and high temperatures that help flames spread quickly are usually involved.
The Tubbs Fire, which burned into Santa Rosa in 2017, was counterintuitively set up by a break in California’s drought during the previous winter. That pulse of moisture allowed a burst of what firefighters call “one-hour fuels”—grasses and other fine vegetation that grow fast, but can be dried to the point of burning in an hour when drought conditions return.
California’s drought has also killed more than 100 million trees, which can stoke more intense fire behavior. Dead needles on coniferous trees killed by drought can act like fine fuels, spreading fire rapidly through the crowns of the dead trees and igniting heavy timber below them.
What does it mean when reports say a fire is 10 percent or 20 percent controlled? Can that erode if a fire spreads in unexpected ways?
In the United States we fight wildfires more often with dirt than with water. Containment usually describes the percentage of the blaze surrounded by a fire line—a perimeter around the fire that’s been dug down to mineral soil, leaving no fuel to carry the fire across the line. Fire lines can join together other barriers, such as paved highways and rivers, to corral the blaze.
But strong breezes behind a wildfire can launch fire brands a mile or more to ignite timber, grasses or even communities on the other side of the containment line. So a sudden wind change can push a blaze across a fire line that otherwise would have held it back.
Three firefighters have died on the job in California in the past several days. Do you think this work is becoming more dangerous in a warming world?
Climate change is definitely magnifying some of the hazards that firefighters face, but rapid development in the West is probably a bigger factor. The U.S. Forest Service estimates that more than one-third of all U.S. homes are in the wildland-urban interface—the area where development abuts flammable open space, and houses are at risk of burning in a wildfire.
Out of necessity, the nation is prioritizing fighting wildfires close to communities and infrastructure. So firefighters who once only had to worry about the hazards of fires burning through forests now also have to contend with threats like power lines and fuel tanks. When I recertified my wildland firefighting credentials a few years ago, the test included questions about what to do if I found a meth lab or an illegal chemical dump while fighting a forest fire.
Human nature is also a factor. It’s much easier to step back from a fire that’s behaving unpredictably if it’s just going to burn a stand of trees than if it might destroy homes or take lives. Protecting communities can push wildland firefighters to take more risks.