Atmospheric rivers

The extreme flooding and mudslides across California in recent weeks took many drivers by surprise. Sinkholes swallowed cars, highways became fast-moving rivers of water, entire neighborhoods were evacuated. At least 20 people died in the storms, several of them after becoming trapped in cars in rushing water. As I checked the forecasts on my cellphone weather apps during the weeks of storms in early January 2023, I wondered whether people in the midst of the downpours were using similar technology as they decided whether to leave their homes and determined which routes were safest. Did they feel that it was sufficient? I am a hydrologist who sometimes works in remote areas, so interpreting weather data and forecast uncertainty is always part of my planning. As someone who once nearly drowned while crossing a flooded river where I shouldn’t have, I am also acutely conscious of the extreme human vulnerability stemming from not knowing exactly where and when a flood will st...

California has seen so much rain over the past few weeks that farm fields are inundated and normally dry creeks and drainage ditches have become torrents of water racing toward the ocean. Yet, most of the state remains in drought. All that runoff in the middle of a drought begs the question — why can’t more rainwater be collected and stored for the long, dry spring and summer when it’s needed? As a hydrogeologist at the University of California at Santa Cruz, I’m interested in what can be done to collect runoff from storms like this on a large scale. There are two primary sources of large-scale water storage that could help make a dent in the drought: holding that water behind dams and putting it in the ground. Why isn’t California capturing more runoff now? When California gets storms like the atmospheric rivers that hit in December 2022 and January 2023, water managers around the state probably shake their heads and ask why they can’t hold...

Rivers of muddy water from heavy rainfall raced through city streets as thousands of people evacuated homes downhill from California’s wildfire burn scars amid atmospheric river storms drenching the state in early January 2023. The evacuations at one point included all of Montecito, home to around 8,000 people – and the site of the state’s deadliest mudslide on record exactly five years earlier. Wildfire burn scars are particularly risky because wildfires strip away vegetation and make the soil hydrophobic – meaning it is less able to absorb water. A downpour on these vulnerable landscapes can quickly erode the ground, and fast-moving water can carry the debris, rocks and mud with it. After the 2018 mudslide in Montecito, firefighters checked homes. Twenty-three people died in the disaster. Wally Skalij/Los Angeles Times via Getty Images With more storms expected through mid...

Atmospheric rivers – those long, narrow bands of water vapor in the sky that bring heavy rain and storms to the U.S. West Coast and many other regions – are shifting toward higher latitudes, and that’s changing weather patterns around the world. The shift is worsening droughts in some regions, intensifying flooding in others, and putting water resources that many communities rely on at risk. When atmospheric rivers reach far northward into the Arctic, they can also melt sea ice, affecting the global climate. In a new study published in Science Advances, University of California, Santa Barbara, climate scientist Qinghua Ding and I show that atmospheric rivers have shifted about 6 to 10 degrees toward the two poles over the past four decades. Atmospheric rivers on the move Atmospheric rivers aren’t just a U.S West Coast thing. They form in many parts of the world and provide over half of the mean annual runoff in these regions, including the U.S. Southeas...