“It is the season of suicide and divorce and prickly dread, wherever the wind blows,” the great Los Angeles chronicler Joan Didion once wrote of the Santa Ana winds. It also happens to be the season of wildfires. The winds “bedeviled” efforts to fight the deadly Woolsey fire in 2018 and created “dangerous conditions” when they whipped the nearly 20,000-acre Mountain fire in Ventura County this past fall. And they were blowing, too, when a spark of unknown origin ignited the now 23,000 acres of wildfire burning through the suburbs of Los Angeles.
Though steeped in mystery and superstition (writers call them the “devil winds”), the Santa Ana winds are common in Los Angeles during this time of year. (Scientists call them simply “offshore winds.”) The phenomenon is caused by winter’s cold, dry air becoming lodged in the bowl of the Great Basin, where it forms a high-pressure area. That clockwise-moving air wants to escape, and it does so by rushing down and south through the mountain passes to the low-pressure area on the coast: Los Angeles.
The wind can pick up a lot of speed — on Wednesday morning, gusts topped 100 miles per hour in the San Gabriel Mountains. It can also become drier and warmer — by as much as 50 degrees Fahrenheit — as it rushes through the passes toward the coast, which is what gives the Santa Anas their signature warmth, which so many find disquieting.
What makes the Santa Ana winds happening now unique?
For one thing, the current Santa Anas are on the upper end of the spectrum for velocity, which is part of why they have such a significant impact — and cause firefighters so much trouble. For another, there is a “rare placement of upper-level jet stream winds” giving the system a more northerly flow as opposed to the usual north-easterly orientation, Scott Capps, an atmospheric scientist and the head of Atmospheric Data Solutions, a forecasting firm, told me in an email. As a result, “many areas that are typically not impacted by Santa Ana winds were impacted.”
Does climate change affect the Santa Anas?
“Logically, it makes sense that climate change will impact the frequency and characteristics of [the Santa Anas],” Capps told me. However, “due to the complexity of the environment, we cannot blame one single factor for any extreme weather event.” The more obvious connection between the L.A. fires and climate change is the lack of precipitation during what is supposed to be the region’s wet season; some parts of southern California have received just 10% of their normal rainfall since October, making the area ripe for a fire.
Scientists used to think that inland warming would reduce the cold weather-related high pressure in the Great Basin and weaken the Santa Anas. While it does appear that so-called “cold” Santa Anas — caused by air in the Great Basin that is so cold initially that it’s still chilly when it reaches L.A., and which account for about a third of all Santa Anas — are becoming less frequent, the more traditional “warm” winds that are associated with wildfires don’t actually seem to bear out this hypothesis. Instead, they “are spread uniformly over the seven decades of record,” the authors of a 2021 study wrote.
If climate change is doing anything to warm or accelerate Santa Anas, the data would appear to suggest“an increasing potential of warmer and drier [Santa Ana winds] to dry out coastal vegetation and, particularly in anomalously dry winters, enhance the coastal wildfire season even into spring,” the authors went on.
While it’s far too soon to link the California disaster to climate change, the study’s authors now seem prescient: dry vegetation and an unusually dry winter both go far in explaining why this week’s fires are so destructive.
