That was three years ago. The Thomas Fire is no longer the second biggest fire on record. It is also no longer the third largest, or the fourth largest, or the fifth largest. The Thomas Fire is instead now the eighth largest fire in the recorded history of the state. Over the past 12 months, there have been six fires that have burned more acreage than the Thomas Fire, including the currently burning Dixie Fire that is ranked third at about 433,000 acres.
As of writing, that is. By the time you read this, it will have grown. It is only about a third contained. It seems likely to pass the Mendocino Complex Fire’s total acreage, but has a way to go before it passes the largest fire on record: last year’s August Complex Fire, which burned more than a million acres.
There’s not a lot of mystery about the cause. California is once again in the midst of a drought, with every county in the state seeing drought conditions at every point since the end of April. As of writing, about half the state is experiencing the most severe level of drought measured by the U.S. Drought Monitor. Since 2000, the state has regularly experienced drought conditions and, often, that most severe level of dryness.
On the second map, notice the extent of severe drought near the northern boundary with Nevada. That heavily forested area — Plumas, Sierra, Nevada and Placer Counties — is often the site of new fires. The Dixie Fire, for example, is partly located in Plumas County.
Extended periods of drought mean drier air, drier soil and more dead foliage to burn. It means, in other words, excellent conditions for wildfires. And there’s no question that this is in part because of climate change. Climate change models are often too rough to be able to link specific climate effects to the phenomenon, but this sort of extended dryness and drought is specifically what climate models project will happen with increasing frequency. There have been years with bad wildfires in the past, but that there are so many big fires now is clearly in part attributable to the warmer climate.
The California Department of Forestry and Fire Protection (better known as Cal Fire) has publicly available data on wildfires by year, including when the fires are sparked and when they are extinguished. That allows us to create an interactive showing the past eight years of fires, including the recent large ones. (You can click or tap the chart to see information below the graph about the selected period of the identified year.)
Last year was a particularly bad one, burning more than 4.2 million acres — about three-quarters of the area of New Jersey. Nearly 9,300 structures were burned to the ground, and 31 people, three of them firefighters, lost their lives.
2020 was particularly bad, but there’s every reason to think that other bad years are in front of us, given the current trends of warming.