Firefighters battle flames in Santa Paula, California, on Monday.

Gene Blevins / Reuters

Ferocious, fast-moving wildfires have caused unprecedented destruction this year in California, and experts say they’re only going to get more deadly and strike communities more often.

As of Friday, six major fires were tearing across wide swaths of Southern California, burning hundreds of square miles, destroying entire neighborhoods, and forcing hundreds of thousands of people to flee. The outbreak comes at the tail end of an explosive autumn that left at least 44 people dead in wildfires that ravaged California's famed wine country, making 2017 far and away the single deadliest year for wildfires in the state's history.

The record-breaking fire season follows a trend in which fires have become bigger and more destructive in recent years. Of the 10 largest fires in California history, all but three occurred within the last 15 years. Of the 10 most destructive fires, all but two happened since 2003, and the two previous fires took place in the 1990s.

This week's fires have been singeing their way into the record books as well. As of Friday, Ventura County's Thomas Fire had burned 132,000 acres, making it the largest wildfire during the month of December in California history.

Experts who spoke with BuzzFeed News say a host of factors contributed to the devastating fire season. And more alarmingly still, none of those things are going away. Here's what's going on:

Santa Ana winds combined with a bone-dry fall to create perfect brush fire conditions

Santa Anas are the hot, dry winds that blow from the mountains and arid deserts east of the coastal cities in Southern California. Daniel Swain, a climate scientist at UCLA, told BuzzFeed News they form when a strong, high-pressure system forms over California's inland deserts. In recent days, the Santa Anas have come sweeping over Southern California, leading to unprecedented "extreme" fire conditions.

Emanuel Vasquez passes a burning home in Ventura, California, Tuesday.

Noah Berger / AP

Making matters worse this year, the Santa Anas arrived during an abnormally dry start to the wet season, leaving soil moisture low and fuels like grass and brush bone dry.

"Southern California has been completely shut out," Swain said. "There has been no precipitation at all, which at this point isn’t completely unprecedented, but it’s starting to get there."

That lack of rain is due to a strong, high-pressure "ridge" over the West Coast that has diverted fall moisture elsewhere.

This is the second time hot, dry winds have led to explosive conditions in California. The deadly fires earlier this fall — which burned in Sonoma, Napa, and Lake counties — were driven by Diablo winds, the Northern California equivalent of the Santa Anas, according to Yufang Jin, who studies fire and ecosystems at University of California, Davis.

An aerial view of properties destroyed by the Tubbs Fire in Santa Rosa, California, as seen on Oct. 11.

Stephen Lam / Reuters

Research suggests that hot and dry wind events in California — like the Santa Anas and the Diablos — are getting more severe with time.

"The intensity of those events is getting stronger," she told BuzzFeed News. "If you look at relative humidity and wind speed, the intensity of those events, there’s a trend."

Climate change is probably making things worse

Jin said it isn't entirely clear why the Santa Anas are getting more intense, though the "overriding warming temperature may be an important factor." Warming temperatures have consistently extended the fire season, she said, leading to large wildfires during what used to be the off-season.

Last year was the hottest on record globally for the third year in a row. And since 2000, the annual global temperature record has been broken five times, according to the National Oceanic and Atmospheric Administration (NOAA).

As of November, this year was on track to be the third warmest year on record.

Smoke rises behind a leveled apartment complex in Ventura on Tuesday.

Noah Berger / AP

The extent of the relationship between climate change and California's wildfire problems is complex and includes many still unanswered questions. But experts said the climate was getting warmer, which makes fires worse by drying out fuel and, over the longer term, exacerbating drought — the most recent one of which lasted five years.

"Things are changing around here," said Lynne Tolmachoff, a spokeswoman for Cal Fire, the agency that fights California's wildland blazes. "The earth is just changing."

Research led by Swain suggests a trend of more high-pressure ridges over the West Coast, which is what drove away the rain and primed California to burn this fall.

A wildfire burns just northwest of Fillmore, California, Thursday.

Amanda Lee Myers / AP

Population growth in fire-prone areas is turning blazes into deadly infernos

More people moving into areas prone to brush fires also isn't helping. Multiple experts who spoke with BuzzFeed News pointed to the Handley Fire, which in 1964 hit California's Sonoma County. The blaze burned more than 52,000 acres and leveled more than 100 homes. But it was a far cry from this year's deadly wine country fires, which, according to Cal Fire, killed 44 and reduced thousands of homes to rubble.

The difference, Tolmachoff said, was the number of people who lived in the region.

"In 1964, the Hanley Fire had almost the same footprint, but the biggest difference is there weren’t nearly as many homes in the way," she said. "The amount of people in California has increased, and so the growth into wild lands has increased."

In 1960, California's population was only 15 million people. But 2016, it was nearly 40 million. Many of those new Californians live in what is — or once was — a space known as the wildland-urban interface, where a city's outer edges meet wilderness areas, many of which are prone to wildfires.

Volker Radeloff, who studies the wildland-urban interface at the University of Wisconsin, said building into areas with a high likelihood of brush fire is a pattern that has been seen "all over California" and other parts of the US.

In California, lawmakers have enacted regulations to help make at-risk communities safer, including requiring homeowners to clear brush around their homes and banning the use certain highly flammable building materials. But Volker said those regulations can only do so much because fire-igniting cinders can fly up to a mile and a half through the air.

He also said that the type of buildings in the interface can make matters even worse. Low-density track homes, for example, have "more flammable vegetation between the houses," exacerbating the fires that do reach them. And contemporary living practices — households with fewer people, a proliferation of vacation homes, etc. — means there are more structures per person in California than ever before. Many of those structures are standing in places that are likely to burn.

"The prospects are, I’m afraid, a little grim," Radeloff added. "I don’t see any big change in the trend. Right now, we see that the number of houses in what we call the wildland-urban interface, it’s risen a lot."

A person bicycles as a section of the Thomas Fire burns in La Conchita, California, Thursday.

Mario Tama / Getty Images

The other experts who spoke with BuzzFeed News had similar outlooks, including Jin, who said communities abutting wildlands need to think about planning for brush fires because they cannot be avoided and "one trend is we are seeing is more extremes."

Tolmachoff also characterized fire as "just part of the landscape" that will increasingly come into conflict with California's growing population.

"We’re going to have the fires no matter what," she said. "And then you add all the other problems to it, the potential for it to get worse is definitely there."

LINK: This Is How California Officials Alerted Millions Of People As Wildfires Approached Homes

LINK: 2016 Was The Hottest Year On Record, And Scientists Are Sounding The Alarm

LINK: California's Drought Emergency Is Finally Over, But Its Impact May Last Forever

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