Atmospheric rivers

Wild weather has been roiling North America for the past few months, thanks in part to a strong El Niño that sent temperatures surging in 2023. The climate phenomenon fed atmospheric rivers drenching the West Coast and contributed to summer’s extreme heat in the South and Midwest and fall’s wet storms across the East. That strong El Niño is now starting to weaken and will likely be gone by late spring 2024. So, what does that mean for the months ahead – and for the 2024 hurricane season? What is El Niño? Let’s start with a quick look at what an El Niño is. El Niño and its opposite, La Niña, are climate patterns that influence weather around the world. El Niño tends to raise global temperatures, as we saw in 2023, while La Niña events tend to be slightly cooler. The two result in global temperatures fluctuating above and below the warming trend set by climate change. El Niño starts as warm water builds up a...

Millions of Californians were under flood alerts as a powerful atmospheric river brought heavy rain to the West Coast in early February 2024. Los Angeles saw one of its wettest days on record with over 4 inches of rain on Feb. 4. Other communities were hit by more than 12 inches of rain and reported widespread flooding. Debris and mudslides shut down sections of highways and roads into Malibu. It was the latest in a series of atmospheric rivers to bring extreme rainfall to the West Coast. While these storms are dreaded for the damage they can cause, they are also essential to the region’s water supply, particularly in California, as Qian Cao, a hydrologist at the University of California, San Diego, explains. What are atmospheric rivers? An atmospheric river is a narrow corridor or filament of concentrated water vapor transported in the atmosphere. It’s like a river in the sky that can be 1,000 miles long. On average, atmospheric rivers have about twice the regul...

To get a sense of the enormous amount of water atmospheric rivers dumped on the Western U.S. this year and the magnitude of the flood risk ahead, take a look at California’s Central Valley, where about a quarter of the nation’s food is grown. This region was once home to the largest freshwater lake west of the Rockies. But the rivers that fed Tulare Lake were dammed and diverted long ago, leaving it nearly dry by 1920. Farmers have been growing food on the fertile lake bed for decades. This year, however, Tulare Lake is remerging. Runoff and snowmelt from the Sierra Nevada have overwhelmed waterways and flooded farms and orchards. After similar storms in 1983, the lake covered more than 100 square miles, and scientists say this year’s precipitation is looking a lot like 1983. Communities there and across the West are preparing for flooding and mudslide disasters as record snow begins to melt. Tulare Lake, long dry, begi...

Another round of powerful atmospheric rivers is hitting California, following storms in January and February 2023 that dumped record amounts of snow. This time, the storms are warmer, and they are triggering flood warnings as they bring rain higher into the mountains – on top of the snowpack. Professor Keith Musselman, who studies water and climate change at the University of Colorado’s Institute of Arctic and Alpine Research, explained the complex risks rain on snow creates and how they might change in a warming climate. What happens when rain falls on snowpack? For much of the United States, storms with heavy rainfall can coincide with seasonal snow cover. When that happens, the resulting runoff of water can be much greater than what is produced from rain or snowmelt alone. The combination has resulted in some of the nation’s most destructive and costly floods, including the 1996 Midwest floods and the 2017 flood that damaged California’s Oroville Dam....

Atmospheric rivers, those long, powerful streams of moisture in the sky, are becoming more frequent in the Arctic, and they’re helping to drive dramatic shrinking of the Arctic’s sea ice cover. While less ice might have some benefits – it would allow more shipping in winter and access to minerals – sea ice loss also contributes to global warming and to extreme storms that cause economic damage well beyond the Arctic. I’m an atmospheric scientist. In a new study of the Barents-Kara Seas and the neighboring central Arctic, published Feb. 6, 2023, in Nature Climate Change, my colleagues and I found that these storms reached this region more often and were responsible for over a third of the region’s early winter sea ice decline since 1979. More frequent atmospheric rivers By early winter, the temperature in most of the Arctic is well below freezing and the days are mostly dark. Sea ice should be growing and spreading over a wider area. Yet the...