Los Angeles fires have scorched largest urban area in California in at least 40 years

Experts say several factors could lead to wildfires reaching cities more often. Urban areas continue to sprawl into wildland. Climate change is raising global temperatures that lead to more severe weather, including droughts, especially in the western United States.

"If these conditions get worse or more frequent in the future, it wouldn't be surprising, in my opinion, if there were more events that threaten densely populated places," said Franz Schug, a researcher studying the boundaries between the wildland and urban areas at the University of Wisconsin-Madison.

The Eaton and Palisades fires' rampage through Los Angeles has killed at least 27 people, destroyed more than 12,000 structures and put more than 80,000 under evacuation orders. The fires are likely to be among the most destructive in California history, according to the state agency CalFire.

The Woolsey Fire eventually grew to about twice the current size of the Eaton and Palisades fires but most of the area it burned was uninhabitated.

Silvis, and AP, defined urban areas as those that are "high density," where the land has at least 3 housing units for every acre, calculated with U.S. Census data.

The Great Chicago Fire of 1871 burned about 3.3 square miles of the downtown area of the city, according to the Chicago Architecture Center. San Francisco's Great Fire of 1906 destroyed 4 square miles of the city, according to the Museum of the City of San Francisco.

Besides burning the most urban area, the Eaton and Palisades fires are the largest ever for California in January. Alexandra Syphard, a senior research scientist at the Conservation Biology Institute, said their timing and path through the city "may have no precedent in history."

Authorities haven't determined a cause for the major blazes in California. But experts have noted the extreme weather that created more favorable conditions: heavy rains that drove vegetation growth, then extreme drought that turned much of that vegetation into good fire fuel. Scientists say such extreme weather events are a hallmark of climate change.

Then there's the human element.

Across California, about 1.4 million homes were built in areas where residential areas and vegetation intermingle between 1990 and 2020, a 40% increase, the Silvis Lab found.

Fires that begin close to populated areas are often caused by people, and their proximity to people means they are usually extinguished sooner. As David Helmers, a data scientist and geographer at the Silvis Lab, put it, "Humans tend to ignite fires, but they also fight fires."

But that wasn't the case with the Eaton and Palisades fires, which were whipped by fierce Santa Ana winds to overwhelm fire crews.

The 2017 Tubbs Fire in northern California's wine country came under similar high winds. That blaze, sparked by a residential electrical system, tore through suburban areas of Santa Rosa, killing 22 people and destroying more than 5,600 homes, businesses and other structures. Overnight, the rubble of the Coffey Park neighborhood became a symbol for how quickly a wildfire can reach a populated area.

Some 53 years prior, another fire — the Hanly Fire — burned through almost the exact same area. Winds helped it spread with furious speed. But with little development at the time, nobody died and only 100 homes were lost.