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New evidence shows rising temperatures accelerating frequency and intensity of Northern California wildfires

As they toil to extinguish the last of the LNU Lightning Complex fires burning across the North Bay, firefighters tasked with that Herculean labor also must contend with another adversary: the excessive heat warning issued by the National Weather Service.

Asked why it was going to be so hot over the holiday weekend, meteorologist Drew Peterson spoke of a “600-decameter high-pressure ridge” squatting over Northern California.

Think of that high-pressure system, Peterson said, “as a 20,000-foot-high mountain of hot, dry air sitting over us.”

“We’ve had them in the past,” he said of the Denali-sized dome bringing furnace-like conditions to inland areas this weekend. “But the frequency with which we’re seeing new, record temperatures is unusually high. And it’s a direct result of warming across the planet.”

We know by now that climate change has extended California’s fire season, which begins earlier and ends later, if it ends at all. What’s becoming clearer, according to climate scientists, meteorologists and fire experts, is that even modest increases in temperature have dramatically ratcheted up wildfire risk.

The ingredients required for a catastrophic wildfire “are lining up more frequently,” said John Abatzoglou, assistant professor of fire science at UC Merced. Longer fire seasons combined with parched fuels are resulting in more extreme fire danger days, or as Abatzaglou put it, “many more spins on the roulette wheel.”

Rising temperatures, drier fuels

While many Northern Californians speak of wildfires, evacuations and degraded air quality as “the new normal,” Daniel Swain doesn’t find that expression useful. It suggests a stability that does not exist.

“We have not arrived at some ’new normal,’” said Swain, a climate scientist at UCLA and author of the influential Weather West blog.

“The reality is we’re not in some new, stable-but-warmer state. We just continue to move progressively in the same direction,” he said.

That direction is hotter and drier. California has warmed 1.7 degrees Celsius over the last 125 years — though some parts of the state have heated up much more than others — with most of that temperature increase occurring over the last three or four decades, Swain said. “That doesn’t sound like a lot, but it is a lot.”

“I think a lot of folks underestimated what this would actually mean on the ground” in terms of fire risk. “We’re seeing some pretty major impacts already.”

During an interview Wednesday, Swain pointed out the second-, third- and seventh-largest fires in California history were burning at that moment.

He was referring to the SCU Lightning Complex, the LNU Lightning Complex and August Complex fires, respectively. (The latter blaze, roughly 45 miles northeast of Ukiah, had charred 298,629 acres in the Mendocino National Forest as of Friday, and moved up to No. 4).

While no one thought climate change would decrease fire risk, Swain said, he and his peers didn’t realize that “even very incremental changes in the atmosphere can really amplify what’s going on.”

“You may have heard of the Clausius-Clapeyron relationship.” he said to a reporter, hopefully.

The reporter had not.

“It’s an exponential function that describes moisture as a function of temperature.”

For every one-degree increase (Celsius) in temperature, he explained, the amount of water vapor that could be in the air increases by 7% — “like compounding interest.”

What does that have to do with wildfire risk?

As the amount of water vapor that could be in the air goes up, the amount that is actually in the air can’t keep up. That gap creates a vacuum that sucks moisture out of trees and plants. It makes them drier, more parched, more flammable.

It resulted, during those infamous August lightning storms, in an exceptionally high ignition rate: between 4% and 6% of each strike resulting in a fire, Swain estimated, due to the dryness of the vegetation.

The fires spawned by that lightning moved with a speed that surprised Swain.

“We’ve seen some of these crazy fires in the past, moving very fast, taking out neighborhoods and killing people,” he said. “But almost all of those have been wind-driven events” — conflagrations abetted by offshore winds coming from the east and north.

The blazes that blackened over a million acres in Northern California over the past three weeks did so without help from the kinds of offshore winds that accelerated the 2017 fires and the Kincade fire last year.

The winds whipping these latest blazes were generated, in large part, by the fires themselves. “That’s part of the story,” Swain said, “when you have drier fuel that burns hotter, more intensely.“

If it’s not flood, it’s fire’

After 16 days in a hotel, Herman Hernandez Sr. returned Friday to his family’s ranch at the south end of Sweetwater Springs Road, near Guerneville. Like plenty of others around there, he’s an old hand at evacuating. In 1986, the place flooded with 2 feet of water; in 1995 it was a foot and a half.

“If it’s not flood, it’s fire,” said Hernandez, whose property made it through the Walbridge fire just fine. Others, a few miles north, were not as lucky. Which raises the question: how could this area, a magnet for rainfall in the winter months — it includes Venado, often the wettest spot in Sonoma County — go up like so much kindling?

True, it’s one of the wettest parts of the state, but it was coming off one of its driest winters on record.

As Swain pointed out, some very destructive infernos, such as the Tubbs fire in 2017, have followed very wet winters.

“What we’re seeing,” he said, “is how much temperature is dominating now. In wet years, you get a lot of growth, and it all dries out to an extreme level. In dry years, there’s isn’t as much growth, but it dries out even more.”

Either way, it’s highly combustible.

Before moving back home, Hernandez figured he’d keep some possessions in boxes on the dining room floor, rather than unpack everything. After all, he said, “We’ve got at least three more months of fire season.”

Gone forever’

When lightning ignited large swaths of the Bay Area, Bernie Krause and his wife, Katherine, prepared their “go bags,” cat carriers and the few belongings they’d accumulated since the Nuns fire in 2017 burned their previous home to the ground.

Last month while studying maps, the 81-year-old Krause said, “we saw firewalls to the north, south, east and west.” As the LNU Lightning Complex spread around them, they decided to stay put in the stone house they’re renting in a valley just north of Sonoma.

“We figured we’d have a better shot right where we were.”

Some measure climate change in rising temperatures and acres burned. Krause has experienced it most profoundly with his ears. As one of the world’s preeminent soundscape ecologists, he’s devoted the past half century to recording the sounds of nature. His archive of field recordings features more than 15,000 species.

Many of those habitats, and some of those creatures, are no more. “Whole biomes, marine and terrestrial,” he wrote in an email, “once vibrant and dynamic with a biophonic density and diversity, are gone forever, silent and inactive.”

Between that loss, and the trauma of losing their home three years ago, “a sense of despair and anguish runs pretty deep for us,” said Krause, who has an easy grin and lively, if dry, sense of humor. So it’s surprising to learn that he often wakes up in the night screaming — still traumatized by the Nuns fire.

Krause fights the darkness by working to “get the message out there,” to remind people that much still remains “of the world’s stunning beauty.”

He is buoyed by the generation coming up behind him, what he hopes is “a whole group of Greta Thunbergs.”

That said, he admitted, “hope, itself ain’t gonna do much.”

Good fire, bad fire

Until carbon dioxide emissions are curbed enough to slow the rate of climate change, other tools are available in the fight against catastrophic wildfires.

“Using ‘good fire’ is really important,” said Michael Jones, a forestry adviser for Lake, Mendocino and Sonoma counties.

He's talking about prescribed burns to clear out fuels that accumulated over a century of fire suppression, the legacy of a Smokey the Bear and a misguided approach, said Jones, “that we could control nature; that we have the ability to manage the landscape however we want.

“We’re seeing now how that turned out for us,” he said.

In addition to creating defensible space and hardening homes, especially those in wildland urban interfaces, Jones would coax people toward a new relationship with fire.

“Yeah, it’s sad to lose a thousand-year-old redwood,” he said. “But fire is really important for clearing out the understory and creating the conditions where redwoods can regenerate.”

“We’re not gonna stop fires,” Jones said. “We have to get to the point where we understand the difference between good fire and a bad fire.”

You can reach Staff Writer Austin Murphy at 707-521-5214 or austin.murphy@pressdemocrat.com or on Twitter @ausmurph88.

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