Meet California's new normal: more lightning, 30% less rain in wildfire season, and double the number of fire-risk days

• Two of California's three largest fires in history are burning right now — part of a group known as the August Lightning Siege of 2020.
• Climate change is linked to larger, more frequent fires because it increases the likelihood of lightning and heatwaves and causes vegetation to dry out.
• Nine of the state's 10 largest fires have happened since 2000.

Once again, California is on fire.

Firefighters are battling hundreds of blazes at once, most of which sparked after nearly 11,000 lightning bolts hit the state over just 72 hours last week. Two of those fires — the LNU Lightning Complex and the SCU Lightning Complex Fires — have become the second and third largest state history, eclipsed only by the Mendocino Complex Fire two years ago.

The group of fires is now known as the August Lightning Siege of 2020, and they've collectively scorched more than 1.5 million acres — an area roughly the size of Delaware. That includes much of Big Basin Redwoods State Park, which was home to towering, old-growth redwoods.

The scale and strength of the fires make them unprecedented, but a growing body of research suggests that giant fires like these will keep happening — largely due to climate change.

As the planet warms, dry conditions, high temperatures, and dry lightning are all becoming more common.

"To cut to the chase: Were the heat wave and the lightning strikes and the dryness of the vegetation affected by global warming? Absolutely yes," David Romps, director of the Berkeley Atmospheric Sciences Center, told MIT Technology Review. "Were they made significantly hotter, more numerous, and drier because of global warming? Yes, likely yes, and yes."

Recent trends show a clear pattern: The state's nine largest wildfires ever — and 13 of the 16 biggest in state history — have all occurred since the year 2000. California's average fire season now lasts 75 days longer than it did in the early 2000s, according to the state's Department of Forestry and Fire Protection.

"We are essentially living in a mega fire era," Jake Hess, a Cal Fire unit chief, said at a recent press conference, according to the LA Times. "We have folks who have been working for Cal Fire for the last five years, and that is all they understand, mega fires, since they started."

Drier conditions year-round make wildfires larger, hotter, and faster

A recent analysis out of Stanford University found that since the 1980s, the average temperature during California's wildfire season has risen by more than 2 degrees Fahrenheit. Overall precipitation in the season, meanwhile, has dropped by 30%. Those conditions have more than doubled the state's number of extreme wildfire risk days in autumn.

This year in particular, California had its driest February since at least 1864. In some parts of the state, including San Francisco, not a single drop of rain fell. January was also fairly dry, and both months were hotter than usual. Snowpack in the Sierras only reached 44% of normal levels.

A 2015 study found that climate change accounted for up to 27% of the extreme drought conditions in the state from 2012 to 2014 and "substantially increased the overall likelihood of extreme California droughts."

Dry conditions in the winter lead to dry foliage in the spring and summer — prime fuel for wildfires. But even without a decrease in rainfall, higher average temperatures cause more water to evaporate from soil, drying out the land.

Extreme heat has become more common

California saw a major heat wave right before the fires began: Cities around the San Francisco Bay Area saw 100-degree temperatures, and parts of Los Angeles stayed at or above 100 for a week. A weather station in Death Valley recorded a temperature of 130 degrees — one of the highest ever on Earth.

Climate change increases the likelihood of extreme heat. The 10 warmest years on record worldwide have all occurred since 1998, according to NOAA.

Even a small amount of warming shifts the range of possible temperatures shifts up, causing numbers that would previously have been extreme to become more common. Think of it like a bell curve: As the curve moves right towards higher numbers, a temperature at the extremely rare end of the curve falls closer to the middle.

"Our recent past is merely a paltry precursor to a much hotter future," Jeff Berardelli, a climate and weather contributor for CBS News, wrote in Yale Climate Connections.

Warming also makes strong, hot fires more common, leading to extraordinary weather phenomena, like fire tornadoes (or firenadoes). Around the time that California's spate of lightning complex fires began, a firenado occurred as part of the Loyalton Fire in Sierra County, which burned nearly 50,000 acres.

This phenomenon, which scientists call a pyrocumulus, happens when fires get so hot and strong that they suck in new oxygen, creating their own weather patterns, including fierce winds.

Rising temperatures increase lightning strikes

Thunderstorms occur when air is warm and humid, as it was during California's heat wave. When a large amount of warm, moist air rises into the atmosphere, it collides with cooler water droplets in clouds, creating a negative electric charge. The earth responds with a positive charge, and electricity runs between the two — that's the phenomenon we know as lightning.

Climate change has also made lightning — and lightning-caused fires — more common and more extreme. A 2014 study found that each degree in planetary warming may increase the number of worldwide lightning strikes by 12%. Fires ignited by lightning, meanwhile, are likely to increase worldwide, according to a 2018 study, as more frequent lightning bolts strike drier grass and forests.

"I'm essentially at a loss for words to describe the scope of the lightning-sparked fire outbreak that has rapidly evolved in northern California – even in the context of the extraordinary fires of recent years," Daniel Swain, a climate scientist at UCLA, wrote in a blog post. "It's truly astonishing."