Here’s Why Los Angeles Fires Are Spreading So Fast

Powerful winds combined with record humidity and dry conditions may have contributed to the rapid spread of the fires that have raged since Tuesday in Los Angeles County and have killed five people so far.

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Winds blowing up to 160 km/h first spread the flames at lightning speed to the upscale Pacific Palisades neighborhood, where many celebrities’ villas are located, and where 6,500 hectares were charred and a thousand buildings destroyed.

A day later, flames have now begun to devour the Hollywood Hills, where more than 100,000 residents have been called to evacuate their homes.

Why is it so fast?

This rapid spread of the flames could be explained by the violent winds that rage in Los Angeles County, also called the “Santa Ana” winds.

The current “Santa Ana” winds are a classic of Californian autumns and winters. But this week, they reached an intensity not seen since 2011, according to meteorologists.

These winds are “hot (often scorching), violent and dry,” and blow from the desert, which includes the Great Basin of the western United States, including Nevada and part of Utah, according to a report from the University of California, Los Angeles (UCLA).


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They originate inland and head directly toward the California coast, “moving in the opposite direction to the normal land flow that carries moist Pacific air into the region,” according to The Guardian.

“Santa Ana” winds can blow gusts ranging from 95 km/h to 130 km/h, and sometimes even up to 160 km/h, as seen in Pacific Palisades on Tuesday.

How are these winds formed?

“Santa Ana” winds form during the cool season, from October to March, especially when the desert has a “relatively cold” temperature, according to UCLA.

An area of ​​high pressure is created above the Great Basin, which causes cold air to descend.


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This air is then compressed while descending slopes, resulting in a warming of approximately 10°C per kilometer of descent.

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As temperature increases, relative humidity decreases, which means that the air, initially dry, becomes even drier as it descends toward sea level.


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The UCLA analysis also notes that air accelerates when directed through passes and canyons.

Why do they accelerate fires?

When the “Santa Ana” winds blow, humidity levels drop significantly, causing vegetation to dry out significantly, increasing the risk of fire.

“Fast, hot winds dry out vegetation, increasing the risk of wildfires,” the UCLA report says. Once fires start, winds fan the flames and accelerate their spread. The winds create turbulence and vertical wind shear.”


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Indeed, extreme weather conditions may have worsened the fires in Southern California, according to Pasadena Fire Chief Chad Augustin.

He said wind and fast-moving embers were the main factors that caused the fires in Los Angeles to spread quickly.

“We are seeing fires that spread when it is hot and dry and windy: all of these conditions are present in Southern California right now,” summarizes Kristina Dahl, vice president of the fire organization. scientific research Climate Central.

A real nightmare for firefighters, because California is coming out of two very rainy years which created lush vegetation, due to the El Niño phenomenon, now dried up by an abnormally dry winter.

Temperature also adds an element to the flammable cocktail. It’s around 20 degrees Celsius in the Californian megacity in the middle of the day, a high temperature at the start of winter.

Climate change

Scientists regularly point out that climate change is increasing the frequency of extreme weather events.

“It’s probably climate change that’s affecting everything. I’m sure it contributed to all of this,” Debbie Collins sighs to AFP, in front of her store threatened by flames in Altadena.

– With information from AFP

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