Climate change parches Western US, providing fuel for fires

Climate change is making the Western United States drier, which can fuel wildfires like those affecting Los Angeles.

With higher temperatures come parched landscapes full of vegetation that can accelerate and exacerbate blazes. 

“Climate change has a way in which it dries the landscape out faster, keeping the landscape able to ignite and carry fire and that provides less resistance for a fire to spread,” said John Abatzoglou, a climate scientist with the University of California, Merced. 

Abatzoglou added that such “spread” can contribute not only to larger fires, but also to help them in “overcoming some of the barriers and encroaching upon communities.”

As Southern California burns, global warming is literally and figuratively heating up.  

U.S. and European Union scientists announced Friday that 2024 was officially the hottest year on record. And, in a shift, the U.S. carbon emissions that cause climate change did not significantly slow down last year, a new report found this past week. 

How do warmer climates fuel fires?

Warming gives the air “a higher capacity” to hold water, said Jatan Buch, a postdoctoral research scientist at Columbia University who studies wildfires. 

In fact, Noah Diffenbaugh, a professor of Earth system science at Stanford University, said that at higher temperatures, the air “actually demands more water.”

He added that this “draws moisture out of vegetation and soils.”

In other words: The air is thirsty.

Researchers with the University of California, Los Angeles found in a 2021 study that the main driver of this thirst — known as the air’s vapor pressure deficit — was climate change.

Vapor pressure deficit, in turn, is the main cause of wildfire increase in the Western U.S. 

The study found that 32 percent of the deficit or thirst could be explained by natural weather variation, while the other 68 percent was due to man-made warming. 

Another study, from 2020, found that “megadrought” conditions created the second-driest period in the region since the year 800 and were made 46 percent worse by climate change. 

The researchers wrote that climate change pushed “an otherwise moderate drought onto a trajectory comparable to the worst … megadroughts since 800 CE.”

Leading to fire conditions

A dry area is just one factor needed for a major fire like those in California. First, there needs to be an ignition, Buch said. 

“One is the availability of fuel. Second, the fuel needs to be dry enough. And third, these driving factors, like wind — in this case, the Santa Ana winds — that make the fires ... more disruptive.”

“The climate change component comes in the first and second parts,” he said. 

Diffenbaugh also noted that the fire is coming at an unusually dry time, since this is typically the start of the rainy season. 

“Not only is California warming as the globe warms, but California is actually warming most rapidly in the late summer and into the autumn and there's some evidence that the precipitation onset in the autumn is shifting later,” he said. 

This means, he explained, that during a time of year that is typically windy, there’s also going to be more dry vegetation.

“We do have clear evidence that the climate is changing in a way that is increasing the likelihood of severe wildfire weather conditions in this region in this time of year,” he said. 

Kevin Speer, professor and director of the Geophysical Fluid Dynamics Institute at Florida State University, noted that the longer fire season is making extreme fires less predictable. 

“Climate change means that extreme events are harder to predict,” he said. “There's less reliability in our system for predicting disasters than there used to be.”