For residents and firefighters, the shift in weather on Wednesday was a welcome reprieve, if a temporary one; hot, dry weather will return Friday. (The heavy rain in Los Angeles on Tuesday passed too far to the south to help with the blazes.)

Two people in Calaveras County were confirmed killed in the Butte Fire, and one in Lake County in the Valley Fire. Four firefighters suffered burns fighting the Valley Fire. Here are answers to some questions about the developments:

Q. How much damage has there been so far from these fires?

A. In the past few days, more than 1,000 buildings were destroyed, officials estimate, though the real number will not be known for a while and will almost certainly be higher. Fire officials have confirmed at least 585 homes and hundreds of other structures have been destroyed by the Valley Fire, and there are areas they have not yet been able to survey. The Butte Fire has destroyed at least 252 homes and 188 other structures. About 13,000 people were evacuated; most of them stayed with friends and family, but about 2,700 went to evacuation centers. For areas that were not burned but were threatened, some evacuation orders were lifted on Tuesday and Wednesday, allowing thousands of people to return home..

Q. So just how bad are the fires?

A. Around 700,000 acres have burned this year in California, compared with about 500,000 in a typical year, and the fire season is nowhere near over. Right now, 15,000 people are deployed to fight wildfires across the state. But what has officials on edge is less the total acreage than how readily new fires start, and how quickly — and unpredictably — they grow. “We’ve had fires in California since the beginning of time,” said Mark Ghilarducci, director of the governor’s Office of Emergency Services, “but what we’re seeing now that’s different is the extreme rapid spread of the fires, and the extreme volatility.”

Q. Why is it this bad?

A. Two reasons: drought and heat. Vegetation in California, from the mesquite scrub in the desert to the tall pines in the Sierra Nevada, is as dry as kindling after a yearslong drought, the worst in the state’s recorded history. So fire catches more easily, spreads faster and carries farther on the wind.

The state’s major reservoirs hold less than half the water they typically contain at this time of year, many wells have run dry, and underground aquifers are so depleted that in some places, the ground has been sinking as much as two inches per month.