Climate change has made the grasses and shrubs fueling the Los Angeles fires more vulnerable to burning, scientists say.

The region’s rapid cycling between dry and wet conditions in recent years has resulted in a huge amount of tinder-dry vegetation ready to ignite.

After decades of drought in California, there were two years of extremely heavy rainfall in 2022 and 2023, which then led to very dry conditions again in the fall and winter of 2024.

Scientists say in a new study that climate change has increased what they call “whiplash” by 31-66% worldwide since the mid-20th century.

The wildfires have spread across parts of the Los Angeles area, claiming at least five lives, burning hundreds of buildings and prompting evacuation orders for more than 179,000 people.

“This whiplash sequence in California doubled the risk of fire,” said lead author Daniel Swain of UCLA.

“First, by greatly increasing the growth of flammable grass and brush in the months leading up to fire season, and then by exceptionally drying out, resulting in extreme dryness and warmth.”

The researchers say that for every degree of warming, the atmosphere can evaporate, absorb and release 7% more water.

This “expanding atmospheric sponge,” as scientists call it, not only causes flooding in wetter conditions, but also deprives plants and soil of additional moisture when drier conditions occur.

Other researchers said the new paper underscores the fact that the type of whiplash volatility is an important factor in causing floods and fires.

“It is clear from the devastation caused by the current wildfires in Los Angeles that rapid changes in the volatility of precipitation and evaporation can have large impacts,” said Prof. Sir Brian Hoskins, chair of the Grantham Institute for Climate Change at Imperial College London.

“It is also interesting to see the paper’s findings that climate models are likely to underestimate the changes we have seen so far, but even these models suggest a doubling of volatility for 3°C of global temperature warming – which is now becoming increasingly likely reach them.”

The new study adds to the growing body of evidence that a warmer climate has changed the background conditions for the raging wildfires currently burning around Los Angeles.

Much of the western United States, including California, experienced a decade-long drought that ended just two years ago.

The resulting wet conditions have since led to rapid growth of shrubs, grasses and trees, providing the perfect fuel for fires.

However, last summer was very hot and was followed by a dry fall and winter season with almost no rain – downtown Los Angeles has received just 0.16 inches of rain since October, more than ten inches below average.

Researchers believe a warming world is increasing conditions conducive to wildfires, including low relative humidity.

These “fire weather” days are increasing in many parts of the world as climate change worsens these conditions and the fire season lasts longer in many parts of the world, scientists have shown.

In California, the situation was made worse by topography, with fires burning more heavily and spreading faster in steep terrain.

This area of ​​California also has naturally very fire-prone shrub vegetation.

“While fires occur frequently and naturally in this region, California has experienced some of the most significant extensions and endpoints of the fire weather season in the world in recent decades, largely due to climate change,” said Professor Stefan Doerr, director of the Center for Wildfire Research at Swansea University.

“However, it is still too early to say to what extent climate change has made these specific fires more extreme. This needs to be assessed in a more detailed attribution analysis.”