Bone-Dry Nights Make California Fires Spread Faster Than Ever

(Bloomberg) -- A wildfire spreading at breakneck speed through hills in Northern California is a grim reminder that an unprecedented drought gripping the U.S. West is putting blazes on steroids.

It’s so dry that these parched areas aren’t getting the moisture relief that nighttime usually delivers, adding fuel to blazes like the Caldor fire east of Sacramento. Arid conditions helped expand that blaze eightfold in just a few hours overnight to nearly 54,000 acres (22,000 hectares) after scorching the town of Grizzly Flats, destroying homes and threatening lives.

“The fire is burning and it’s surrounded by more gasoline -- except that it’s just more dry vegetation,” Tom Di Liberto, a meteorologist with the National Oceanic and Atmospheric Administration, said Wednesday in an interview. “It can spread really fast just because there’s so much fuel around it.”

Climate change and a warming planet means that more and more of the world has been struck by drought and wildfires, with effects ranging from swings in crop prices to drops in air quality to injuries and deaths. A wildfire burning near the French Riviera killed two people this week and injured at least 27, while at least five people have been killed this month by wildfires in southern Italy and a blaze outside Athens is forcing villages to evacuate.

In the U.S., fire season is running ahead of schedule this year because of a drought that covers more than 95% of 11 western states, according to the U.S. Drought Monitor. California is completely gripped by drought as are the neighboring states of Nevada, Utah, Idaho and Oregon.

California’s arid conditions are robbing the environment of a chance to rebuild humidity overnight, according to Isaac Sanchez, a battalion chief of communication for California Department of Forestry and Fire Prevention, commonly called Cal Fire.

“We are seeing sustained temperatures and low humidity and we are seeing significant fire growth at night,” Sanchez said, adding that in normal conditions there can be a recovery period when moisture in the air rises overnight, but when the landscape and atmosphere is parched there’s no drop in a fire’s intensity even after the sun sets.

Scorched Lands

California has seen 1.3 million acres burn this year, up from 860,500 acres that burned during the same period last year.

“The extreme fire behavior we’re seeing is not like what we’ve seen in the past,” Chris Carlton, forest supervisor for Plumas National Forest, said earlier this month in a briefing.

Year upon year of drought also has a cumulative effect as increasingly parched soil soaks up any rainfall or snow-pack runoff the following year. That lowers the level in lakes and reservoirs, including those where firefighting planes pick up water to dump on flames.

“Obviously there’s a connection between drought and wildfires,” NOAA’s Liberto said, noting that droughts bring drier ground that lead to higher temperatures. “It’s not a wildfire season anymore, it’s a wildfire year.”

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