It's not your imagination. You're hearing the term "atmospheric river," which was not a thing on weather reports a couple decades ago, much more often each year in part because these weather events are happening more often.
Meteorologists have used other terms for the same phenomenon over time — tropical plume, Pineapple Express — and atmospheric rivers like the kind California sees most winters now have been around forever. (Read our primer on atmospheric rivers here.)
A series of atmospheric river storms is blamed for the Great Flood of 1862, which caused massive damage and livestock deaths and flooded much of the Central Valley and Sacramento — leading to the capital having to be moved temporarily to San Francisco that year.
And though this is referred to as a 200-year or 1,000-year flood event — as in, it only happens once in a thousand years — it had happened before, according to Native American storytellers who told of an inland sea that could form in the Sacramento area when the rains came.
Still, atmospheric rivers are something the globe is having to adjust to on a more frequent basis, with California and the West Coast being just one place that is prone to seeing them. A new study in the Journal of Climate finds that atmospheric rivers have been growing bigger and wetter, in addition to coming more frequently, over the last 45 years likely due to climate change.
Since 1980, these types of storms have seen a 2% to 6% uptick, the study finds, and the average area that they soak has increased as much as 9%.
Lexi Henny, an atmospheric scientist at the University of North Carolina and the lead author of the study, tells the Associated Press that while the study did not look at causes, like climate change, the findings do "line up, broadly speaking, with some expectations of how [atmospheric rivers] will change in a warming atmosphere." And, Henny adds, this increase in atmospheric river activity "is still small relative to the changes that we think are going to happen" due to climate change.
The study begins by noting that the term "atmospheric river" only came into being in the 1990s, and more recently has become commonplace in the news media, with some news organizations even creating their own rating systems, like for hurricanes, categorizing coming storms on a 1 to 5 scale.
"Because of the sheer amount of extreme precipitation produced by ARs, changes in their characteristics will be crucial in determining changes in the overall extreme precipitation profile across the extratropics," the study says.
One example of strengthening ARs from just the past couple of years was the reappearance of Tulare Lake in early 2023, an inland lake in the Central Valley that once had ferries crossing it, but which dried up in the late 19th Century. It reformed following a series of intense AR storms which also spurred mudslides and other flood events across the state.
Climate scientist Daniel Swain and a colleague also published a paper in 2022 suggesting that megaflood events like the 1862 flood are likely to become more common in California's future.
Top image: In an aerial view, a car is left stranded in widespread flooding as a series of atmospheric river storms melts record amounts of snow in the Sierra Nevada Mountains on March 23, 2023 near Corcoran, California. The region is site of the once-massive Tulare Lake, which was the largest freshwater lake in the western United States, before farming diverted its waters and the area was developed for agriculture. As levees become unable to hold back the floods, speculation is rising that the lake will reappear. (Photo by David McNew/Getty Images)
