6 days ago
- Science
- San Francisco Chronicle
Winds behind fierce California wildfires will change, study finds. Here's what it means
Santa Ana winds have driven some of California's most devastating wildfires, including the destructive Palisades and Eaton fires that scorched Los Angeles in January.
A new study reports that these hot, dry winds will become less frequent in the future. But the more rare Santa Ana winds could bring increasing danger, researchers from Princeton University and the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory found. When the winds do arrive, they will be drier than they are today and could pose greater wildfire risk to coastal Southern California, according to the study.
Southern California's Santa Ana winds are close cousins to the Bay Area's Diablo winds, which have also whipped up catastrophic blazes. The winds are a product of cold, dense air hundreds of miles away, in the Great Basin.
Temperature and pressure differences drive air toward California's coast. The air compresses as it barrels down mountain slopes, making it heat up and become drier. The resulting hot, dry winds can spread flames and even propel embers forward, causing blazes to explode in size.
The study used high-resolution computer models to simulate how Santa Ana winds will change in the future. The authors used an extreme emission climate scenario to probe the impacts of human-caused climate change.
They found that, in the future, Santa Ana winds will become less frequent, echoing previous studies. The authors propose that because land warms faster than the ocean, in the future, the temperature gradient that produces offshore winds — driven by cold air inland — will become weaker. Consequently, Santa Ana winds will occur less frequently.
High-resolution models, however, revealed that Santa Ana winds will be drier than they are today, exacerbating wildfire risk. These patterns didn't pop out when the scientists used lower-resolution models.
This could be because Santa Ana winds, as well as Diabo winds, are greatly influenced by small features in the landscape.
'If you have a higher-resolution model that can depict the topography of the region, you will have a more reliable result, ' said Janin Guzman-Morales, a regional climate scientist at San Jose State University, who wasn't part of the new research.
Guzman-Morales led a 2019 study that reported climate change suppressed Santa Ana Winds via changes to atmospheric pressure patterns. The new study makes the earlier findings more robust, Guzman-Morales said.
Alex Hall, a professor of atmospheric and oceanic science at UCLA, agreed that the main contribution of the study is 'highlighting the need for high resolution to simulate the impact of climate change on the Santa Ana wind phenomenon.'
Hall, who also wasn't part of the new research, co-authored a 2011 study that reported a reduced frequency of wintertime Santa Ana winds in the mid-21st century, due to human-caused climate.
The new research relied on one global climate model, produced by the Geophysical Fluid Dynamics Laboratory. Hall said that it will be valuable to analyze additional models, to quantify uncertainty and identify the most likely magnitude of Santa Ana wind weakening.
Another question is how future changes to seasonal precipitation will impact wildfire risk associated with Santa Ana winds, Hall said. While the Los Angeles wildfires in January were driven by offshore winds, a lack of rain in preceding months set the stage for blazes to take off.
Climate change could have similar effects on Diablo winds, given their similarity to Santa Ana winds, Guzman-Morales said. But additional research needs to be done to confirm that.
'There is an absolute need for that research,' Guzman-Morales said.
