Snowpack

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...

An avalanche swept up skiers at Lake Tahoe’s largest ski resort on Jan. 10, 2024, as a 150-foot-wide sheet of snow slid down a mountain slope into a pile 10 feet deep. One person died in the avalanche and three others were rescued, according to the Placer County, California, Sheriff’s Office. The slide happened in steep terrain near the KT-22 chairlift, which had just opened for the season that morning. A second unplanned avalanche hit the same ski resort the next day, but no one was injured. Avalanche deaths are rare inbounds at ski resorts like Palisades Tahoe, but the risk rises in the backcountry – 30 backcountry avalanche deaths were reported in the U.S. during the 2022-2023 season. Nathalie Vriend, a skier and physicist at the University of Colorado Boulder who studies avalanches, explains what happens in an avalanche and techniques for surviving one. What causes avalanches? The behavior of an avalanche depends on the structure of the snowpack, but that...

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...

After three years of extreme drought, the Western U.S. is finally getting a break. Mountain ranges are covered in deep snow, and water reservoirs in many areas are filling up following a series of atmospheric rivers that brought record rain and snowfall to large parts of the region. Many people are looking at the snow and water levels and asking: Is the drought finally over? There is a lot of nuance to the answer. Where you are in the West and how you define “drought” make a difference. As a drought and water researcher at the Desert Research Institute’s Western Regional Climate Center, here’s what I’m seeing. How fast each region recovers will vary The winter of 2023 has made a big dent in improving the drought and potentially eliminating the water shortage problems of the last few summers. I say “potentially” because in many areas, a lot of the impacts of drought tend to show up in summer, once the winter rain and snow stop and the...

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....