A dry winter has turned into a busy summer for firefighters in California's wildlands, and the largest and most intense fires of the year may be yet to come.

According to data provided by the U.S. Forest Service, wildfires had already burned 276,252 acres across the state as of last week, excluding the large Rush fire on the Nevada border.

That fire, which started Aug. 12, had burned 270,684 acres of grass, sagebrush and juniper by Sunday evening.

Last weekend, the Ponderosa fire burning outside Shingletown east of Redding destroyed seven houses. The fire has charred 15,000 acres since it started Saturday morning.

This summer follows several wetter, cooler years with fewer fires. By the middle of August last year, fires had burned only 73,868 acres statewide.

Last week, 8,000 firefighters were battling wildfires in California, including the 47,000- acre Chips fire in Plumas County, the 28,000- acre Reading fire in Lassen Volcanic National Park and the Rush fire east of Susanville.

A similar number of firefighters were on the job this week, too.

"Though we've already seen an increase in fire activity, the busier parts of the year are still ahead of us," said California Department of Forestry and Fire Protection spokesman Daniel Berlant.

Though fall is cooler than summer, the risk of fire is greater because wildland brush and timber continue to dry until major rains begin, usually in November.

"Every week that passes, it just gets drier and drier and drier," Berlant said.

Vegetation across the state already lacks moisture because of drought this winter. Snowpack this winter in the Sierra was 54 percent of normal levels on April 1, according to the state Department of Water Resources.

A National Weather Service precipitation index for the Sierra in the 2011 and 2012 water year was 41.5 inches. The normal level for the index is around 50 inches.

"Knowing what we know about the precipitation patterns this year and the warmth we've had this summer, the amount of fire activity that we've had is to be expected," said Carl Skinner, a fire ecologist at the Forest Service office in Redding.

While the Forest Service sometimes allows fires to burn for the ecological health of the forests it manages, the service issued a memorandum in May stating that it would attack fires more aggressively because of the nationwide drought.

Not only are there more fires statewide in California, but more fires are burning in the northern part of the state. The data from the Forest Service show that the proportion of land burned in Northern California in the first part of the fire season increased from 16 percent of the state's total last year to 78 percent this year. The data include incidents reported by several state and federal agencies.

Several large fires in the north contributed to the shift, including the Chips, Reading and Rush fires, as well as the Mill fire, which burned nearly 30,000 acres in the Mendocino National Forest in July.

Meanwhile, Californians can only wait for autumn rain.

"All we need is one big soaker, a couple of inches in the mountains," said Johnnie Powell, a forecaster in the Sacramento office of the National Weather Service.

"That's hard to get until November, but we'll hope it comes a little early."

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