How Santa Ana Winds Intensify California’s Wildfires

Hurricane-force Santa Ana winds roared down the mountains near Los Angeles on January 7, 2025, driving wildfires into multiple neighborhoods and creating a harrowing spectacle.

By January 9, thousands of homes and buildings, including multiple schools, had been destroyed, and at least five lives were lost. Authorities called for the evacuation of over 180,000 residents at the peak of the fires. The powerful winds left firefighters with limited options to contain the flames.

Jon Keeley Explains the Factors Driving Extreme Winds and Their Wildfire Hazard in Southern California

Jon Keeley, a research ecologist with the U.S. Geological Survey and an adjunct professor at UCLA, sheds light on the factors driving these extreme winds in Southern California and why they pose such a significant wildfire hazard.

Santa Ana winds are strong, dry gusts that descend from the mountains toward Southern California’s coastline. The area typically experiences around 10 of these wind events annually, mainly between fall and January.

In dry conditions like the current ones, these winds pose a significant wildfire risk.

Santa Ana winds are strong, dry gusts that descend from the mountains toward Southern California’s coastline. The area typically experiences around 10 of these wind events annually, mainly between fall and January.

In dry conditions like the current ones, these winds pose a significant wildfire risk.

As the winds descend from the peaks of the San Gabriel Mountains, they grow hotter and drier due to the physics of air masses.

By the time they reached Altadena, where the Eaton Fire ignited on Jan. 7, their relative humidity often dropped to less than 5%, effectively leaving no moisture in the air.

Canyons Channel Winds, Amplifying Their Intensity

Canyons further amplify the winds by channeling them. Having lived in Altadena, I experienced days during Santa Ana events where the wind was absent at home but ferociously strong just a few blocks away.

Typically, these dry winds blow at speeds of 30 to 40 mph, but they can be much stronger. In early January 2025, gusts were reported to exceed 80 mph.

Usually, by this time of year, Southern California receives enough rainfall to keep vegetation damp and less prone to ignition. A study from a few years ago highlighted that autumn rainfall significantly lowers the likelihood of fires driven by Santa Ana winds.

This year, however, the region has experienced exceptionally dry conditions, with minimal rainfall in recent months. Combined with the intense winds, this creates an ideal scenario for severe wildfires.

The Challenge of Extinguishing Fires Fueled by Santa Ana Winds

Under these conditions, extinguishing a fire is extremely difficult. Firefighters in the region will say that when a fire is driven by Santa Ana winds, their strategy is to evacuate people in advance of the fire’s path and focus on controlling the edges. However, with winds this strong, there is little chance of containing the fire until the wind calms down.

Other states have experienced similar fires fueled by intense downslope winds. In November 2016, the Chimney Tops 2 Fire in Tennessee was spread by strong winds, igniting homes in Gatlinburg, resulting in 14 fatalities and the destruction of over 2,500 homes.

Similarly, in December 2021, powerful winds in Boulder County, Colorado, contributed to the spread of the Marshall Fire, causing the loss of around 1,000 homes.

While Santa Ana wind events are not a new phenomenon, they are occurring more frequently during this time of year.

A recent study by my colleagues and me analyzed 71 years of Santa Ana wind data, starting in 1948. We found that overall wind activity remains similar, but the timing of these events is shifting, with fewer occurring in September and more in December and January.

Though it’s tempting to link this shift to global warming, due to well-documented climate change trends, there is currently no strong evidence to support this.

California is experiencing more destructive fires than in the past. This increase is driven not only by changes in climate and wind patterns but also by population growth.

Expansion of Power Lines Increases Fire Risk as Population Grows in Wildland Areas

As more people move into and near wildland areas, the expansion of the power grid has also increased, creating more opportunities for fires to ignite. In extreme weather conditions, power lines are at greater risk of falling or being struck by tree branches, potentially sparking fires.

The area affected by fires caused by power lines has expanded significantly and is now the primary source of ignition for destructive fires in Southern California.

The Eaton Fire, which has consumed many homes, is situated at the upper perimeter of the San Gabriel Basin, at the base of the San Gabriel Mountains. Fifty years ago, fewer people lived in this area. Back then, some parts of the basin were surrounded by citrus orchards, which helped contain fires, preventing them from reaching homes.

Today, there is no natural buffer between homes and wildland. The ignition point of the Eaton Fire appears to have been near or within one of those residential areas.

Homes, often built with dry materials, catch fire easily in dry conditions, allowing fires to spread quickly through neighborhoods and posing a significant risk of destruction.

Read the original article: Science Alert

Read more: Weather Whiplash Driving LA’s Wildfire Could Lead to Record-Breaking Costs