From the AGU
February 4, 2021
A dry California riverbed in 2009. New research has shown that the start of California’s annual rainy season has been postponed from November to December, adding nearly a month to the state’s increasingly devastating wildfire season. Image credit: NOAA.
WASHINGTON – The start of California’s annual rainy season has been postponed from November to December, adding nearly a month to the state’s increasingly devastating forest fire season, according to new research. The study can’t confirm that the shift is related to climate change, but the results agree with climate models that predict drier fall months for California in a warming climate, the authors say.
Forest fires in California can happen anytime, but fires typically burn from May to October when the state is in the dry season. The start of the rainy season, historically in November, ends with the forest fire season, as the plants get too damp to burn.
The rainy season in California has started increasingly over the past few decades, and climatologists have predicted that it will get shorter as the climate warms. In the new study, the researchers analyzed precipitation and weather data in California over the past six decades. The results show that the official start of the California rainy season is 27 days later than the 1960s, and the rain that falls is concentrated in the months of January and February.
“We have shown that it won’t happen in the future, it is already happening,” said Jelena Luković, climate researcher at Belgrade University in Serbia and lead author of the new study. “The onset of the rainy season has been increasingly delayed since the 1960s, and as a result, the rainfall season in California has become shorter and sharper.”
The new study in AGU’s journal Geophysical Research Letters, which publishes meaningful, short-format reports with immediate implications for all earth and space sciences, is the first to quantify how much later the rainy season begins.
The results suggest that California’s wildfire season, which has worsened due to man-made climate change, will be even longer in the years to come, and Californians can expect more fires to flare up in November. 2020 was California’s worst wildfire season in history. Nearly 10,000 fires burned more than 4.2 million acres of land.
An extended dry season means there is more overlap between the forest fire season and the influx of Santa Ana winds that bring hot, dry weather to California in the fall. These winds can ignite the flames of forest fires and increase the risk of fires spiraling out of control in the late season.
The full press release can be found here.
Paper here.
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