A series of wildfires erupted in Southern California on Wednesday, fueled by a combination of strong Santa Ana winds and parched vegetation, creating favorable conditions for devastating fires that resulted in homes being destroyed and thousands being forced to evacuate.

In Pacific Palisades, just west of downtown Los Angeles, a blaze has burned nearly 3,000 acres. Another fire ignited in Eaton Canyon, located in the San Gabriel Mountains, approximately 28 miles inland. Meanwhile, a smaller fire in the Sylmar suburb of the San Fernando Valley affected around 500 acres.

Cal Fire is currently investigating the origins of these three fires. The National Weather Service had already issued a top-level alert for extreme fire hazards in the area prior to the start of the fires.

All three affected regions share a common characteristic: they are situated at the edges of mountainous areas, which climate scientists believe may be more susceptible to wildfires compared to other regions in Los Angeles County.

Santa Ana Winds

The intense Santa Ana winds, which carry dry air from further inland towards the coast, play a crucial role in intensifying the wildfires. As high-pressure systems move from east to west over the Santa Ana Mountains, the wind compresses and heats as it descends.

Janice Coen, a project scientist at the National Center for Atmospheric Research in Boulder, Colorado, mentioned that these winds dry out vegetation along the mountain ridges and can spread embers over great distances, enabling fires to expand quickly.

The Santa Monica Mountains, encompassing the Pacific Palisades, and the San Gabriel Mountains, which border the Eaton Canyon and Sylmar fires, are densely packed with vegetation that becomes particularly flammable during the current dry season in Southern California. This ground cover fosters conditions that facilitate rapid fire spread.

Mountainous Geography

The steep terrains, canyons, and valleys characterized by the Santa Monica and San Gabriel Mountains further escalate fire risks.

As heat rises from a fire located on mountain slopes, it can pre-heat the vegetation situated above it, hastening the fire’s ascent, explained Jennifer Marlon, a senior research scientist at Yale University. Canyons and valleys may also serve as channels for the Santa Ana winds, which further expedite wildfire propagation in these mountainous locales.

Conversely, regions closer to the coast, such as some areas in Santa Monica, tend to retain more moisture, which can mitigate fire hazards, according to Coen. Certain valleys and ridges throughout Los Angeles might act as natural barriers that can slow down or halt the spread of fires.

Urban Development

Many desirable neighborhoods within the Greater Los Angeles area are located along the edges of these mountain ranges. Pacific Palisades is often depicted by real estate agents as sophisticated and understated. In November, the typical home price in Altadena reached $1.3 million, according to Realtor.com.

However, expanding development in these regions has also heightened wildfire risks, according to Coen.

Experts refer to these areas as wildland-urban interfaces—zones where human settlements intersect with natural ecosystems. Approximately 25% of California’s population resides in these risky regions.

“Structures and infrastructure can catch fire, creating embers that feed a cycle of intensified heat release and ember dissemination,” Coen noted.

Urbanized areas of Los Angeles County, which have less vegetation and include fire-resistant building materials, are likely to offer greater protection against fires than neighborhoods that are adjacent to natural landscapes.