The Santa Ana winds have returned to California, a signal to the state’s residents that the wildfire season has begun in earnest.

The winds are created by high pressure over Nevada’s Great Basin as cool weather starts to arrive in the Fall. Low pressure systems in warmer California pull them along, and as they flow through the Sierra Nevadas and other ranges, twisting their way through narrow passes and canyons, they heat up, lose moisture and gain speed.

Once they hit California, their low humidity and high heat can quickly turn the bushy chaparral into an explosive fuel source. It’s part of the reason that California accounted for 92% of all insured wildfire losses in the U.S. from 2008 to 2018, according to insurer Munich Re. Colorado was second with 3%.

“The high winds cause the fires to spread incredibly rapidly,” according to Mark Bove, a natural catastrophe solutions manager at Munich Re. In some cases, he said, they have burned at the equivalent of “one football field per minute,” driven by the wind.

They also “cause more severe types of fire behavior,” Bove said, spurring “fire tornadoes or whirls” where the blazes move speedily from the ground to the tree tops.

Read more