Fire season is becoming longer and more intense worldwide, a reality which Americans were painfully reminded of this week, when a spate of wildfires sparked Sunday night and Monday morning turned vast swaths of northern California into an apocalyptic hellscape. As of 8am Pacific time today, the so-called North Bay fires had torched 170,000 acres of land, destroying more than 2,000 structures and claiming at least 17 lives.
Many of the largest fires, including the now-28,000 acre Tubbs fire raging across Napa County, are still completely out of control.
The reason that any one wildfire gets big and bad can vary widely, although in California as in many parts of the country, the vast majority of these blazes are started by people. Urban sprawl, and more humans living at the wildland-urban interface, means more opportunity for fires to be set accidentally—the spark can be something as small as a cigarette butt. More sinisterly, as we saw in the South last year, fires can be set on purpose.
Once a fire is started—by people, lightning, or downed power lines—it needs the right conditions to grow and spread. Large, fast-moving fires thrive in hot, dry, windy environments with plenty of fuel. Unfortunately, northern California had all of those ingredients this week.
Following years of drought, an exceptionally wet, rainy winter caused a rapid burst of vegetation growth this spring. Much of that new growth has spent a long, hot summer drying out into fuel that would light up at the first spark.
What caused those first sparks to ignite on Sunday night and Monday morning is unknown. But we do know what caused them to spread: a dome of high pressure air centered over the Rockies that drove hot, dry gusts—so-called “diablo winds”—toward the coast. “Historic” winds of up to 75 mph late Sunday and early Monday enabled the fires to consume entire neighborhoods in a matter of hours.
The encouraging news for Northern California is that those winds have eased up since Monday, and the atmosphere has cooled off a bit. The bad news, according to Weather Underground meteorologist Bob Henson, is that gusts in the 45 to 55 mph range are expected again in the North Bay area starting this afternoon. “With fires ongoing and the fuels still tinder-dry, any strong wind would not be good news,” Henson told Earther.
While today’s gusts are not expected to be as bad as those on Monday, they could still be strong enough to topple power lines, thus running the risk of igniting new fires.
“Unfortunately, there may be yet another round of dangerous fire weather on Friday/Saturday, this time with somewhat warmer temperatures and higher gusts than Wednesday,” Henson added. A fire weather watch is also in effect for LA-area mountains Thursday night through Saturday.
Weather aside, it’s hard to have a conversation about this week’s pyrotechnic devastation without acknowledging climate change, which exacerbates many of the conditions fueling fire in California and elsewhere.
The West has warmed nearly 2°F in recent decades, causing wildfire season to stretch out longer and encompass more land. A study published last year in the Proceedings of the National Academies of Sciences concluded that climate change has doubled the area affected by fire season out West over the past 30 years, and that fifty percent of the increase in Western fire activity since 1979 can be directly attributed to climate change. The rest of the increased fire activity is attributable to a mix of factors, including natural climate variability and the Forest Service’s history of fire suppression, which has caused too much fuel to build up on landscapes.
Other phenomena linked to climate change, including the spread of bark beetles that have devastated millions of acres of pine forest, could be reshaping the fire regime out West as well. Some researchers have even suggested that this year’s exceptionally wet, rainy, growth-inducing winter was a preview of what’s what’s to come in a warmer future.
Clearly, fire season is changing dramatically, and it’ll continue to change as the Earth warms and urban development proceeds apace. Tragedies like this week’s California fires remind us it’s more important than ever that we treat our wildlands with care and manage them responsibly. It’d also be responsible to start getting the carbon in our atmosphere under control.