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Another California Heat Wave Will Bake Forests Already Primed to Burn

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Extreme heat danger signage stands as visitors walk along sand dunes at sunset inside Death Valley National Park in June 17, 2021 in Inyo County, California. (Patrick T. Fallon/AFP via Getty Images)

May Gray, June Gloom, No-Sky July … whatever you call it, the marine layer and California’s coastal summer weather patterns are insulating the Bay Area from yet another punishing summer heat wave descending on the Central Valley.

While inland areas will broil this weekend, the forecast for cities around the bay is warm, but not uncomfortable.

Meteorologists are still sizing up the projections, and say the heat isn’t likely to break all-time records like the heatwave that cooked the Pacific Northwest last month.

Carbon pollution is trapping heat and warming the planet, causing more frequent and severe heat waves, even as companies and governments continue to emit planet warming gases with little abatement.

A pre-print study released Wednesday by an international group of climate researchers found that the Pacific Northwest heat wave would’ve been “virtually impossible without human-caused climate change.”


The World Weather Attribution group produced the rapid-turnaround modeling of the extreme weather event. The researchers predict similar heat waves will be increasingly common in a warming world, although the conclusions have not yet been scrutinized through a peer review process.

Hidden away in coastal fog, residents of the inner Bay Area could almost forget that June saw daily temperature records crushed all across the state. For the Sierra and other interior regions of California, it was the hottest June in more than a century of record keeping, according to climate scientists.

The baking continues. The National Weather Service issued a heat warning for the Bay Area region which lasts until Sunday, July 11. Residents of the far eastern parts of the region — Antioch, Brentwood, Napa and Livermore — face triple-digit temperatures, hotter nights and homes that likely won’t cool off in the evening, all of which compound to create health dangers.

The good news for the Bay Area is that the marine layer will function as natural air conditioning for the coast, as it usually does this time of year. The bad news is that statewide, forests are extremely dry and vulnerable to wildfire. Scorching temps will likely only create more heightened risk of a big fire.

Heat Could Bring a ‘Significant Health Risk’

The incoming weather event — a couple days of heat brought on by a high pressure system moving in from the southeast — is fairly normal, said Jan Null, meteorologist with Golden Gate Weather Services, but cautioned that high temperatures can be dangerous.

“When we start seeing temperatures in the upper 90s and past 100, there is a significant health risk in people overexerting themselves, especially when they’re not acclimated to it,” he said.

If you live west of the East Bay Hills, or wear shorts when it’s 60 degrees out, that’s you, likely to be poorly acclimated to heat.

The heatwave won’t extend to the coast “because there just isn’t enough offshore flow to overcome the strong marine influence this time of year and to fully suppress the marine layer,” wrote Daniel Swain, a climate scientist at UCLA’s Institute of the Environment and Sustainability, on his blog, WeatherWest. Most of the state’s population lives in places where cool ocean air provides some relief from summer heat, like the Bay Area, Los Angeles and San Diego metro regions.

“This is a pattern we’ve seen occur somewhat frequently in recent years, with searing heat inland yet quite mild conditions where the marine influence hangs on, and which also makes for a rather strange reality,” he wrote.

Later in the season, when high pressure and hot air push toward the coast, effectively turning off the coast’s natural AC, the extreme temperatures will likely push out to the Pacific.

Hot Temperatures Intensify Already Bone Dry Conditions

This particular heat wave will bake an abnormally dry landscape, priming it further to burn. Much of the Bay Area is in an exceptional drought, the highest category on the U.S. Drought Monitor.

Scott Stephens, a forestry professor at UC Berkeley is seeing evidence of that first hand in the Plumas County town of Quincy, where he’s teaching a summer field course for undergraduates.

He said after several weeks of temperatures above 90 degrees, plants there are “already showing signs that look like August: leaves starting to shrivel, shutting shut down because moisture is being depleted by the heat.”

“The hot temperatures plus the combination of two years of below average precipitation this year is really worrisome because that lower moisture is going to make fire behavior more extreme, spread rates more extreme,” he said.

It’s typical for plants and trees to dry out in the summer in California’s Mediterranean climate, but not typically this fast, Stephens said. During the state’s last major drought, which lasted from 2012 to 2016, more than 120 million trees in the Sierra Nevada succumbed to bark beetles infestation and drought.

Those stands of dead trees and dry timber fueled blazes like the Creek Fire, which ignited near Shaver Lake last September and burned for nearly four months, consuming an area larger than the city of Los Angeles, almost 600 square miles of forest.

Stephens notes that the northern tier of the Sierra has not yet experienced a similar tree die off during this drought, although he’s seeing an increase in bark beetle activity.

“If we put two more years of drought and warm conditions on this part of California, I’m afraid we might see the same kind of disaster,” he said.

Stephens blames decades of fire suppression and poor forest management for the larger fires in recent years, making parched land more vulnerable to extreme fire behavior. These policy failures are compounded by rising average summer temperatures.

“You put climate change on top of [years of fire suppression] and it makes it worse,” he said. “We’ve got warmer periods, lower fuel moistures, snow melting earlier. All of this is contributing to what fire is doing,” he said.

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