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California’s ‘lightning siege’ has connections to climate change.

A state fire official described it as a “historic lightning siege” — the nearly 11,000 bolts of lightning that struck California over 72 hours this week and ignited 367 wildfires.

Such a flurry of strikes is unusual in California, where it normally takes a full year to tally up 85,000 or so lightning flashes, said Joseph Dwyer, a physicist and lightning researcher at the University of New Hampshire. That is far fewer than Florida, one of the most lightning-prone states, which averages about 1.2 million flashes a year.

Lightning occurs during storms with strong updrafts. During these storms, charged ice particles in clouds collide, generating an electric field. If the field is strong enough, electricity can arc to the ground as lightning, which can ignite dry vegetation: Nationwide, about 15 percent of wildfires start this way.

Strikes across the United States are expected to increase with climate change, as warmer air carries more water vapor, which provides the fuel for strong updraft conditions. A 2014 study estimated that strikes could increase by about 12 percent per 1.8 degree Fahrenheit (1 degree Celsius) of warming, or by about 50 percent by 2100.

California has been experiencing an intense heat wave this week, and while it is too soon to say precisely how climate change influenced this specific bout of hot weather, “it is likely that there was more lightning because of global warming,” said David M. Romps, a physicist at the University of California, Berkeley, and the lead author of the 2014 study.

“What you could say with certainty is that it was hotter with global warming,” Dr. Romps said. “And certainly the vegetation was drier because of warming. If there were also more lightning strikes, as we would expect, that’s just an additional bump in the direction of more fire.”

Kellen Browning, Nicholas Bogel-Burroughs, Jill Cowan, Henry Fountain and Alan Yuhas contributed reporting.