The relentless storms that hit California from Dec. 27 to Jan. 16 caused extreme flooding and extensive damage in most of the state, killing at least 22 people. A series of storms hit back to back, soaking the state in the midst of California’s driest three-year period on record.
“If anybody doubts that climate is changing, then they must have been asleep for the last couple of years,” President Joe Biden said in California on Jan. 19, after witnessing the destruction left behind by the storms.
He later added: “For example, places that were ravaged by past wildfires are now at a higher risk of landslides. Extreme weather caused by climate change means stronger and more frequent storms, more intense droughts, longer wildfire seasons — all of which threaten communities across California.”
There is a good scientific basis to think that storms, including the type that struck California, are generally becoming more extreme due to climate change. But climate scientists told us it’s too soon to know whether climate change had a role in this particular event, and if so, to what degree.
“We are not entirely sure,” Julie Kalansky, a climate scientist at the Scripps Institution of Oceanography at the University of California, San Diego, told us in an interview. “It’s an active area of research.”
Daniel Swain, a climate scientist at the University of California, Los Angeles, told us all extreme weather events are the result of multiple complex and interrelated processes happening across time and space. Therefore, climate change is not “the singular cause” of the storms. But did it affect the storms’ intensity?
“Here, the answer is probably yes, climate change thus far has likely increased both the intensity and likelihood of seeing such an intense period of precipitation in California,” he wrote in an email. “But then the question becomes: to what degree?”
Here is what we know so far.
What kind of storms hit California?
California was hit by a series of nine atmospheric rivers, which the National Oceanic and Atmospheric Administration describes as “naturally occurring air currents” that can create extreme rainstorms and flooding. The atmospheric rivers were accompanied by a bomb cyclone, a mid-latitude storm or weather system that rapidly intensifies.
Atmospheric rivers are long and narrow corridors in the lower atmosphere that transport water vapor from the tropics to the poles — “like rivers in the sky,” as NOAA explains. When these columns of vapor move inland from oceans and over mountains, the water vapor cools and creates heavy precipitation in the form of snow or rain. Their contribution to the water supply is crucial: A few of them provide, on average, 30% to 50% of the U.S. West Coast’s annual precipitation.
Satellite image taken January 4, 2023, at 1:20 p.m. of an atmospheric …