The devastating fires that are ravaging Los Angeles They are the latest example of the consequences of climate change. The combination of strong windsthe increase in temperatures due to global warming and drought relentless have served as a catalyst for “one of the most important fires in history,” in the words of Ariel Cohen, a meteorologist at the National Weather Service in Los Angeles.
And scientists warn that this type of extreme phenomena will become increasingly common. According to experts consulted by the Reuters agency, the risk of fires in California is no longer limited exclusively to the summer season, but exists all year round. “Climate change is reconfiguring regimes, patterns characteristic of wildfires in the area,” says Kimberley Simpson from the School of Biosciences at the University of Sheffield.
Los Angeles County, which encompasses a portion of the Southern California (Mojave) Desert, is subject to a hot, dry climate fueled by the well-known Santa Ana windswhich blow regularly across its landscape towards the coast.
These winds, named after the Santa Ana Canyon at the intersection of Orange, Riverside and San Bernardino counties, typically occur in the colder months and consist of strong gusts that blow from the interior of the desert towards the south of the state. They provide a dry and warm air towards the coast, in the opposite direction to the usual humid air that arrives from the Pacific Ocean.
Winds are created due to high pressure about the Great Basinthe vast desert region of the United States that encompasses almost the entire state of Nevada, the western half of Utah and small sectors in Oregon, Idaho and California. This air dries out as it descends and advances. clockwise towards southern California, where you encounter the imposing mountain ranges that separate the desert from the coastal metropolitan areas.
As they pass over mountains and canyons, the winds begin to gain speed and become increasingly dry and warm, drastically reducing humidity, drying out the vegetation that ends up serving as fuel for the flames. In the past, Santa Ana winds have fueled some of California’s worst fires. On this occasion, the gusts have reached 129 kilometers per hour, even reaching 161 kilometers per hour in some mountainous areas.
In addition to the Santa Ana winds, scientists highlight that the current fires are being amplified by what they call a “mountain wave” episode, which occurs when certain temperature conditions occur at the tops of a mountain range and winds that They pass over those mountains. “When those conditions line up perfectly, they behave like a wave in the ocean, when the winds flow over the mountains and then crash over the other side,” explains scientist Paul Schlatter of the National Weather Service in Boulder, Colorado.
A similar ‘mountain wave’ occurred during Colorado’s rapidly advancing Marshall Fire on December 30, 2021, which was fanned by downslope winds with gusts of up to 185 kilometers per hour and leveled thousands of homes and businesses before being extinguished. because of the snowfall the following night. “Any fire under these conditions will quickly get out of control,” adds Schlatter.
This week’s snowstorms over the San Bernardino Mountains, about a two-hour drive from Los Angeles, could be contributing to regional wind dynamics.
To these conditions of strong winds must be added the recent weather conditions in Southern California, which is currently mired in a drought after two winters, in 2022 and 2023, of heavy rains that have caused many trees and shrubs to be now dry due to lack of water and burning more easily.
As climate scientist Daniel Swain explains to ‘The Guardian’, despite the fact that it has rained abundantly in the north of the state, there is a “notable” lack of precipitation in the rest and parts of southern California are experiencing one of their driest periods of the last 150 years.
“Right now, it’s really a question of who has and who doesn’t have rainfall and there’s no real prospect of this changing any time soon,” says Swain. “Even in the long term, it remains possible that this general dipole persists for the rest of the season, although hopefully with less extreme intensity.”
Another factor that is contributing to aggravating the current fires is the increase in average temperatures in California. According to fire management expert Lindon Pronto, from the European Forestry Institute, it has increased by 1 degree Celsius since 1980.
“Finally, there is a cumulative effect in which you see much more extreme fire behavior at different times of the year… whether in December or January,” says Pronto.
Los Angeles’ densely populated urban landscape is another fire catalyst, including flammable material with hanging power lines, wooden telephone poles, and wood-built homes in accordance with seismic codes.
