Climate change: What role is it playing in the California fires
2025-01-08
Category: news

Climate change has made the vegetation that's driving the LA fires more ready to burn, scientists say.While the flames are being mainly driven by powerful winds, the new study says that rapid swings between wet and dry years are making trees, shrubs and grasses more vulnerable to ignition.This "hydroclimate whiplash" has seen decades of drought in California followed by extremely heavy rainfall for two years but then it flipped again to very dry conditions this autumn and winter.The authors say that climate change has boosted these type of whiplash conditions globally by 31-66% since the middle of the 20th Century.
"This whiplash sequence in California has increased fire risk twofold," said lead author Daniel Swain from UCLA."First, by greatly increasing the growth of flammable grass and brush in the months leading up to fire season, and then by drying it out to exceptionally high levels with the extreme dryness and warmth that followed."The researchers say that with every degree of warming the atmosphere is able to evaporate, absorb and release 7% more water.This "expanding atmospheric sponge" as the scientists term it, not only leads to flooding when things are wetter, but it pulls extra moisture out of the plants and soils when the drier conditions set in.
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Other researchers said the new paper underlined that the fact that the type of whiplash volatility was an important element in driving both floods and fires. "It's clear from the devastation caused by the current wildfires in LA that rapid changes in the volatility of precipitation and evaporation can have a large impact," said Prof Sir Brian Hoskins, Chair of the Grantham Institute for Climate Change at Imperial College London. "It's also interesting to see the paper's findings that climate models likely under-estimate the changes seen so far, but even those models suggest a doubling of the volatility for a global temperature warming of 3C – now looking increasingly likely we'll reach."
The new study adds to the growing body of evidence that a warmer climate has altered the background conditions to the raging wildfires currently burning around Los Angeles.Much of the Western US including California experienced a decades-long drought that ended just two years ago.The resulting wet conditions since then have seen the rapid growth of shrubs, grasses and trees, the perfect fuel for fires.However last summer was very hot and was followed by dry autumn and winter season with almost no rain - downtown Los Angeles has only received 0.16 inches of rain since October, more than four inches below average.Researchers believe that a warming world is increasing the conditions that are conducive to wildland fire, including low relative humidity.These "fire weather" days are increasing in many parts of the world, with climate change making these conditions more severe and the fire season lasting longer in many parts of the world, scientists have shown.In California, the situation has been made worse by the topography with fires burning more intensely and moving more rapidly in steep terrain.This area of California is also dominated by naturally very fire-prone shrub vegetation."While fires are common and natural in this region, California has seen some of the most significant increases in the length and extremity of the fire weather season globally in recent decades, driven largely climate change," said Professor Stefan Doerr, Director of the Centre for Wildfire Research, at Swansea University."That said, it is too early to say to what degree climate change has made these specific fires more extreme. This will need to be evaluated in a more detailed attribution analysis."
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