Study shows rain-soaking atmospheric rivers are getting bigger, wetter and more frequent

By: Seth Borenstein, The Associated Press Posted: 8:50 AM CDT Wednesday, Mar. 12, 2025

WASHINGTON (AP) — As extreme weather events have hit the world hard in recent years, one meteorology term — atmospheric rivers — has made the leap from scientific circles to common language, particularly in places that have been hit by them.

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Hey there, time traveller!
This article was published 12/03/2025 (578 days ago), so information in it may no longer be current.

That stands to reason.

The heavy rain and wind events most known for dousing California and other parts of the West have been getting bigger, wetter and more frequent in the past 45 years as the world warms, according to a comprehensive study of atmospheric rivers in the current issue of the Journal of Climate.

FILE - Mud and debris is strewn on Fryman Road during an atmospheric river Feb. 5, 2024, in Studio City Calif. (AP Photo/Marcio Jose Sanchez, File)

Atmospheric rivers are long and relatively narrow bands of water vapor. They take water from oceans and flow through the sky dumping rain in prodigious amounts. They have increased in the area they soak by 6 to 9% since 1980, increased in frequency by 2 to 6% and are slightly wetter than before, the study said.

Scientists have long predicted that as climate change from the burning of coal, oil and gas makes the air warmer, it holds more moisture, which means bigger, nastier atmospheric rivers are coming in the future. This week’s study shows that a more moist future is already here.

“This doesn’t mean that it’s necessarily all because of climate change. We didn’t study that, but it does line up, broadly speaking, with some expectations of how (atmospheric rivers) will change in a warming atmosphere,” study lead author Lexi Henny, an atmospheric scientist at the University of North Carolina who did her research while at NASA.

What’s happened already “is still small relative to the changes that we think are going to happen” in a future warmer world, Henny said.

While atmospheric rivers can bring much needed rain to drought-struck places, they are often dangerous when they are strong and last long. Just over a year ago a series of atmospheric rivers caused hundreds of mudslides and killed several people in California. In the 1860s, California had to move its capital out of Sacramento because of an atmospheric river flooding.

These events aren’t just a California thing. They actually happen all over the United States and the world, though sometimes don’t get recognized as atmospheric rivers, Henry said. An atmospheric river in New England in 2023 brought a foot of rain and 50 mph winds. A 2020 atmospheric river dumped 99 inches of snow on Alaska.

The paper not only makes sense, but is rich with new details and data that will help researchers figure out what will happen with these bouts of intense rain and snow in the future, said Christine Shields, a water scientist at the National Center for Atmospheric Research, who wasn’t part of the research.

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