By Kendra Pierre-Louis and John Schwartz August 22, 2020

Again, California is aflame.

More than 400,000 acres have been burned in Northern and Central California, with many of the fires set off by nearly 11,000 lightning strikes. High temperatures and strong winds have made the situation even worse.

Evacuation orders in Santa Cruz County covered 48,000 people, including the campus of the University of California, Santa Cruz, and those being evacuated must weigh the risks of seeking refuge in evacuation shelters in the midst of the coronavirus pandemic. People living far beyond the burn zone are struggling with the smoke, and beloved sites like Big Basin Redwoods State Park have been badly damaged.

What is it about California that makes wildfires so catastrophic? There are four key ingredients.

The first is California’s climate.

“Fire, in some ways, is a very simple thing,” said Park Williams, a bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory. “As long as stuff is dry enough and there’s a spark, then that stuff will burn.”

California, like much of the West, gets most of its moisture in the fall and winter. Its vegetation then spends much of the summer slowly drying out because of a lack of rainfall and warmer temperatures. That vegetation then serves as kindling for fires.

But while California’s climate has always been fire prone, the link between climate change and bigger fires is inextricable. “Behind the scenes of all of this, you’ve got temperatures that are about two to three degrees Fahrenheit warmer now than they would’ve been without global warming,” Dr. Williams said. That dries out vegetation even more, making it more likely to burn.