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A wildfire burning near a home in San Marcos, California on Wednesday.


What’s Behind Early Season Winds Fueling Southern California Wildfires?

It’s not clear if this week’s fires are tied to climate change.

Having the Santa Ana winds howl into San Diego in May, fueling wildfires that this week scorched more than 15 square miles of land and forced thousands to evacuate their homes, is unusual enough.

Typically, the Santa Ana winds—hot, dry gusts that turn small blazes, often cause by humans, into neighborhood-charring infernos—don't arrive in Southern California until September or October. (Pictures: San Diego Wildfires)

But even stranger is that this is the second time this month that the Santa Anas have blown into the Golden State. The first time it happened, at the beginning of the month, the winds helped drive a fire in Rancho Cucamonga to burn more than 2,000 acres.

On Thursday, police in Escondido, north of San Diego, arrested two people they said are suspected of attempting to start a fire, though they are unsure if there's a connection to the raging brushfires.

Meanwhile, the Santa Ana winds subsided Thursday evening, giving way to more normal conditions. And after peaking at over 100 degrees earlier this week, temperatures are expected to drop through the weekend and into early next week, with highs on Monday falling below the normal mid-70s for this time of year.

The National Weather Service on Friday even held out the promise of light rain in some places over the weekend. All this could help firefighters contain the blazes.

But there's still one caveat: Strong winds from the east are expected to switch to milder gusts coming out of the west during the weekend, which could drive fires in a new direction.

As firefighters struggle to contain the wind-fueled blazes, meteorologists and scientists say the fires could signal an especially active fire season for Southern California, fed by the wind, above-normal temperatures and tinder-dry vegetation.

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A NASA picture of large wildfires burning across sections of northern Baja and southern California.

But it's not clear if the fires represent a new normal for expanded fire seasons, which typically start in summer, as it's impossible to tie specific weather and fire events to climate change.

"What we're seeing right now is just a real anomaly," said Norman Miller, an expert in regional climate and hydrology at the University of California, Berkeley. "Whether it's part of natural variability or climate change, we need to have a longer record of occurrences so we can construct a trend and make sense out of it."

Nationwide, western wildfires are expected to grow more severe as climate change continues, according to the recently released National Climate Assessment, a federal report that represents the most comprehensive review of climate impacts in the U.S. in over a decade.

Miller, for his part, has run computer models predicting that climate change could extend the traditionally October to November Santa Ana season, with increasing winds in December and January. But that still wouldn't explain why they've come in May this year.

Santa Ana winds are triggered when high pressure builds in the skies over the Great Basin, in Nevada and Colorado, while low pressure prevails off the Pacific Coast.

That causes the air to rush westward, seeking out the lower pressure zone. It funnels through the mountains near the California coast, bringing winds to the San Diego area that hit 86 miles per hour in a few places this week. The dry desert air forces humidity down into the single digits, and the winds set record temperatures, says Stephen Harrison, a meteorologist at the National Weather Service office in San Diego.

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Flames and smoke fill a valley as the Cocos fire burns Thursday in San Marcos.

Add bushes parched by the California drought and a growing population that triggers more fires, and it's a perfect recipe for catastrophic conflagrations.

As temperatures rise in the future because of climate change, computer models show the region will become more fire prone, said Max Moritz, a researcher at the University of California, Berkeley. That's true even if in the wetter scenario he looked at, because higher temperature trumped the added moisture.

But southern California has always been a tinderbox, he said. The scrubby chaparall that dominate this landscape thrive on fires.

One recent study Moritz participated in found that most of the West has shown a marked increase in forest fires over the last three decades, but it was less clear whether that was true in Southern California specifically.

"We're fire prone almost every year," he said. "It doesn't mean we're not linked to climate change. It's just a more complex set of ecosystems."