Study says California's 2023 snowy rescue from megadrought was a freak event. Don't get used to it

Last year's snow deluge in California, which quickly erased a two decade long megadrought, was essentially a once-in-a-lifetime rescue from above, a new study found.

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The study authors coined the term "snow deluge" for one-in-20-year heavy snowfalls, when it's cold and wet enough to maintain a deep snowpack through April 1. But even among these rare snow deluges, last year's stood out as the snowiest, edging out 1922 in snow water equivalent, said study lead author Adrienne Marshall, a hydrologist at the Colorado School of Mines.

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Looking at different scenarios of emissions of heat-trapping gases in the future, she said it would be "increasingly rare" for most people alive now to see snow like this in California in the future. Her team's calculations show that these 1-in-20 year deluges will be 58% smaller by the end of this century compared to recent decades, with even just moderate climate change.

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"California is no stranger to atmospheric rivers, but having so many was pretty bizarre," Serreze said. "Maybe we are moving back to a wetter regime, but even if we are, there is simply not enough water go around anymore. And as the climate warms, the snowpack will keep shrinking, making it harder and harder to manage the water resources."

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"Dams and reservoirs have kind of long been environmentally contentious in California and elsewhere, and we have this massive natural reservoir in the mountains, and that's snowpack," Marshall said. "So when water falls as snow, it sits around in the mountains for often quite a long time and then melts in the late spring and the summer when we need it the most."

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