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Northern California is facing catastrophic wildfires more typically seen in the south. Experts aren't sure why

Block after block of tidy housing tracts reduced to heaps of ash. Death counts in the double digits. Homeowners numbly poking through the ruins of domestic life.

California has seen this before.

But the harrowing images of loss and destruction usually come out of the south.

“These kinds of fires and the losses are very uncharacteristic of that part of the world,” University of California fire specialist Max Moritz said of the firestorm that ignited in Northern California last week, killing dozens of people and torching thousands of homes.

“It has all the signatures of a massive, Southern California Santa Ana wind event,” he said.

Driven by hot, dry winds blowing a sustained 50 mph, the Tubbs fire — one of the most destructive of the wine country blazes — chewed across a small mountain range in a few hours on the night of Oct. 8 and roared into northeastern Santa Rosa.

Local officials estimate the city of 177,000 lost nearly 3,000 homes, or roughly 5% of its housing stock. Even big-box stores and a Hilton hotel next to Highway 101 went up in flames.

“It hit the city like a bull’s-eye,” said Scott Stephens, a UC Berkeley professor of fire science. “[That] is probably the place that surprises us the most — it burned so many houses in the urban area.”

Hot, dry winds from the interior are not uncommon in Northern California. The Bay Area’s version of the Santa Ana winds are called Diablo winds, the kind that drove the 1991 Tunnel fire in the Oakland hills, leaving 25 dead and leveling 2,900 buildings.

But in the grim record of the state’s worst wildfires, that was an outlier.

Until last week, 13 of the 20 most destructive — and 16 of the 20 deadliest — wildfires in modern state history occurred in Southern California.

Two years ago, the Valley fire in Lake, Napa and Sonoma counties made the list when it claimed four lives and destroyed 1,955 structures.

“It seems like every summer now we’re seeing some big, horrific event like this. Why?” Moritz said.

“How much of this is climate change? Was some of this left over from five years of drought?” he said. “How much of this is because we’ve built increasing numbers of homes and communities in relatively fire-prone landscapes?”

The last is unquestionably a factor.

In September 1964, the wind-driven Hanley fire and several smaller blazes tore across much of the same landscape as the Tubbs. The fires blackened some 83,000 acres and reached the edge of Santa Rosa.

“This is the craziest fire I’ve ever seen,” the Guerneville fire chief at the time told the San Francisco Chronicle in 1964. “The wind just hangs back, then fire comes in a rush with the wind, and you’re dead.”

But no lives were lost in 1964. A few hundred buildings burned.

Santa Rosa was then roughly one-fifth of its current size, and Sonoma County had a third of its current population.

There was, quite simply, far less to incinerate.

A century of suppressing the natural fire cycle also could be playing a role in fiercer wine country fires.

Before the region was widely settled, Humboldt State associate forestry professor Jeffrey Kane said, mild fires were the norm. But without regular grass fires, woodlands have grown denser — with more oaks and even pine and Douglas fir trees.

“If you looked at historical photos, you’d see it was much more open,” Kane said.

More trees means “there’s much more fuel available. So what was a lower-intensity grass fire is now a much higher-intensity fire,” Kane said. “It can send more embers and cause more spot fires.”

And typical Northern California wildfires die down at night as temperatures drop and humidity levels rise, Stephens said. The Tubbs fire, he said, did not act that way.

“I had a friend and colleague in Santa Rosa who measured relative humidity at 10% early Monday morning. The temperature was in the 70s and the winds 50 mph.”

Stephens said he has noticed the same conditions at other Northern California blazes in recent years.

“In Southern California, there is no [letup] at night when you have the Santa Anas,” he said. “The winds are dry and hot. That seems to be happening more here… People have asked, is it climate change? And to be honest, I cannot say.”

Kane predicted that with global warming, “our ability to suppress these kinds of fires — even up here in the northern part of California — is going to be more challenging.

“If there’s an imaginary line of what climatically separates Northern and Southern California,” he said, “it’s probably getting pushed farther north.”

bettina.boxall@latimes.com

Twitter: @boxall

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