The explosive growth of a massive wildfire in northern California's drought-parched Sierra Nevada Mountains this week has stunned firefighters, defying all predictions about how quickly it would grow.

The racehorse pace of the fire, which tripled in size between Wednesday and Thursday as it extended itself by more than ten miles, is likely to be discussed in the firefighting world for years to come.

The King fire, as it's known, has forced the evacuation of 3,000 people and threatens 12,000 homes east of Placerville, about halfway between Sacramento and Lake Tahoe. It grew to more than 73,000 acres on Thursday, when the El Dorado County district attorney announced the filing of charges against 37-year-old Wayne Allen Huntsman for allegedly starting the blaze.

Windy weather; steep, treacherous terrain; and overgrown forests are all partly to blame for fanning the inferno. But California's record-setting drought is making matters much worse, fire experts say, turning normally green bushes and trees into tinder. (Related: "California Drought Spurs Groundwater Drilling Boom in Central Valley.")

The drought has acted like a testosterone-booster for California wildfires by stretching out the dry season, sucking the last drops of water from a summer landscape that's relatively dry even in a year with normal precipitation. Northern California has been under a special alert for extreme fire behavior since June, thanks in part to extremely low moisture levels in plants and dead branches and logs littering the forest floor.

The landscape dried out much earlier than normal this year, prompting the fire season—and the special alerts—to kick off sooner. "It's unprecedented [that] we've had one up for June, July, August, and most of September," says Larry Hood, a U.S. Forest Service fire behavior specialist who has tracked and forecasted California wildfires for more than a decade, referring to the special alerts. "That's kind of crazy."

Effects of Climate Change?

Periodic droughts have always been part of California's climate cycle, but climate change could be making them more common.

It's not clear whether global warming will translate into more or less precipitation in California, said Malcolm North, a forest ecologist at University of California, Davis and with the Forest Service's Pacific Southwest Research Station.

But there's concern that droughts could grow more frequent and intense, one of the key findings of the sweeping National Climate Assessment released earlier this year by the Obama administration, which specifically cited the danger of more severe droughts and more intense wildfires in the West and Southwest.

The King fire is the most threatening of nine large fires now burning in California, making it the country's wildfire epicenter, according to the National Interagency Fire Center. On Wednesday, Governor Jerry Brown declared a state of emergency for counties hit by the King fire and the Boles fire, which destroyed 150 buildings Monday in the northern California town of Weed.

Much of the Golden State has proved relatively lucky so far this year, with the number of acres burned hovering close to the average for the years since 2000, at 446,573 acres. But fire season lasts into October in California, and the King fire means luck has run out for some.

"Our number just came up," said Bill Stewart, co-director of the Center for Forestry at the University of California, Berkeley, which runs a 4,200-acre research forest in the area.

Bone-Dry Forests

On recent visits to the forest, Stewart had seen clear signs the drought was taking a toll. Leaves on the buckeye trees were shriveled, the gleam of pine needles had dulled, the normally moist layer of detritus covering the forest floor was desiccated, and dust seemed to cover everything. "I've never seen the forest so dry," he said.

He is waiting to see if decades of meticulously studied trees there would be reduced to ashes. The King fire was less than a mile from their site on Thursday. The staff had two hours to evacuate some 15 buildings on Tuesday, grabbing computers, critical files, and maps before fleeing.

The effects of drought in these California forests aren't always immediately clear. The small branches and twigs that typically burn first in a wildfire are bone dry. But they're always dry by this time of year, said the Forest Service's Hood.

But the prolonged lack of water shows in plants like manzanita, oak, and small evergreens. In a typical year, those plants might dry out to the point that the water in the leaves is about 45 percent of the leaves' total weight.

This year, those moisture levels have fallen close to one-third of the leaves' weight near the King fire, making them catch fire more quickly. The dry low-lying plants give fire a boost into the forest canopy, turning drought-stricken trees into towering torches that throw embers as much as half a mile.

The King fire has proved so unpredictable that Hood has begun questioning whether the models he relies on are still accurate in extreme drought conditions. On Wednesday, his computer system came up with a worst-case scenario looking ahead seven days. A day later, the fire had already hit that limit.