Raging California fires: Why have the flames spread so quickly?

 

Three separate wildfires are ravaging communities and forests across California, with hundreds of thousands forced to evacuate their homes.

The Camp, Hill and Woolsey fires are expected to continue burning for days. The flames from the Camp Fire in Butte County, California, were spreading at 80 acres per minute Thursday, which is equivalent to burning an entire football field every second, according to UCLA climate scientist Daniel Swain.  

How have the flames spread so quickly in California? USA TODAY breaks it down:

The Santa Ana Winds  

A high pressure system moving over the Great Basin, a watershed that covers parts of Nevada, Idaho, Oregon, Utah and California, is creating “Santa Ana winds,” according to the National Weather Service. The pressure moves winds over California and toward the Pacific Ocean. 

“When you have an easterly flow, especially associated with Santa Anas like we’ve seen in the last day or so, you get a desert air mass that gets shoved westward towards the coast,” Accuweather Meteorologist Brett Rossio said.  

Winds have reached 50 mph in some parts of the state, according to fire officials. This makes it difficult to contain the perimeter of the fire as it spreads in multiple directions, Accuweather reported. The wind gusts are also making it difficult to contain the fire from above with planes or air tankers, Fire Capt. Stan Ziegler told the Los Angeles Times.  

Winds are expected to diminish Saturday as the pressure system weakens, but they will return Sunday as another front moves toward California, according to the NWS.

A “fuel bed” 

Dry conditions are contributing to the spread of the flames as well, according to Butte County CalFire Chief Darren Read. 

“Basically, we haven’t had rain since last May or before that,” Read said in a news conference Thursday. “Everything is a very receptive fuel bed. It’s a rapid rate of spread.”

Rossio said dry climates can be a catalyst for wildfires. “If you don’t have any rainfall to moisten up the soil, moisten up the vegetation, then it creates a more susceptible pattern for fires to occur,” Rossio said. 

But Rossio said the rain California saw prior to May is also contributing to the fires. 

“Over the last few years we actually have had a lot of rain across California, but what that does is create a lot more vegetation for fires.” Rossio said. “It’s a cycle.” 

Drying phenomenon 

The fires are also spreading due to low humidity and high temperatures across California, spurring on flames.   

“When you raise your temperature, you’re also lowering your relative humidity,” Rossio said. “That’s why this is happening. It’s a drying phenomenon.” 

But the Santa Ana winds are making the low humidity even lower, according to Rossio. 

“When you have very low humidity from the desert moving over an area that has vegetation, you’re drying the air mass,” Rossio said. “You’re drying the vegetation out. So any vegetation there becomes kindle for fires to develop.” 

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