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High winds, lack of rain and climate change stoking California fires Climate 'whiplash' link to raging LA fires
(about 7 hours later)
High winds and lack of rain are the main factors driving the Southern California fires, but climate change is altering the background conditions, increasing the likelihood of these conflagrations, say experts. Climate change has made the vegetation that's driving the LA fires more ready to burn, scientists say.
Researchers have shown that a warming world increases the number of "fire weather" days, when conditions are more suited to outbreaks of fire. While the flames are being mainly driven by powerful winds, the new study, external says that rapid swings between wet and dry years are making trees, shrubs and grasses more vulnerable to ignition.
California is particularly vulnerable right now because of a lack of rain in recent months, following a very warm summer. 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 powerful Santa Ana winds that naturally occur at this time of year, combined with the dry conditions, can result in fast moving and dangerous fire outbreaks. The authors say that climate change has boosted these type of whiplash conditions globally by 31-66% since the middle of the 20th Century.
Reaching 60-70 mph, these strong, dry winds blow from the interior of Southern California towards the coast and this month has seen the worst high wind event in the area in over a decade. "This whiplash sequence in California has increased fire risk twofold," said lead author Daniel Swain from UCLA.
The winds are drying out the lands, and researchers say that while the strongest winds will occur at the start of this outbreak, the driest vegetation will come at the end, meaning these fires could drag on for quite some time. "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 high wind speeds are also altering the location of the fires. Many outbreaks occur high up on mountains, but these recent fires have rapidly moved down into the valleys and into areas where more people live. 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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"That's where there are more potential ignition sources," said climate researcher Daniel Swain from UCLA in a social media post. 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 also where it's harder to turn off the power pre-emptively than it is in other locations where these public safety power shut offs are more common and are prepped for at a more regular basis. So there's going to be some potential challenges there." "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.
The impact of a changing climate is evident in the bigger picture for the state. "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."
California has experienced a decades-long drought that ended just two years ago. The resulting wet conditions since then have seen the rapid growth of shrubs and trees, the perfect fuel for fires. 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.
However last summer was very hot and was followed by dry autumn and winter season - downtown Los Angeles has only received 0.16 inches of rain since October, more than 4 inches below average. 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.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.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. 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."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.""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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