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, begins to reemerge in March 2023 as flood water spreads across farm fields.
NASA Earth Observatory
We asked Chad Hecht, a meteorologist with the Center for Western Weather and Water Extremes at the University of California San Diego’s Scripps Institution of Oceanography, how 2023’s storms compare to past extremes and what to expect in the future.
How extreme were this year’s atmospheric rivers?
California averages about 44 atmospheric rivers a year, but typically, only about six of them are strong storms that contribute most of the annual precipitation total and cause the kind of flooding we’ve seen this year.
This year, in a three-week window from about Dec. 27, 2022, to Jan. 17, 2023, we saw nine atmospheric rivers make landfall, five of them categorized as strong or greater magnitude. That’s how active it’s been, and that was only the beginning.
Where atmospheric rivers hit during the first half of the 2023 water year, which started Oct. 1. The arrows show where the storms were strongest, but their impact reached far wider.
Center For Western Weather and Water Extremes, Scripps Institution of Oceanography
In all, the state experienced 31 atmospheric rivers through the end of March: one extreme, six strong, 13 moderate and 11 weak. And other storms in between gave the Southern Sierra one of its wettest Marches on record.
These storms don’t just affect California. Their precipitation has pushed the snow-water equivalent levels well above average across much of the West, including in Oregon, Nevada, Utah, Idaho and the mountains of western Colorado, Arizona and New Mexico.
Snow water equivalent is a measure of the water in snowpack. Many basins across the West were well over 200% of average in 2023.
NRCS/USDA
In terms of records, the big numbers this year were in California’s Southern Sierra Nevada. The region has had 11 moderate atmospheric rivers – double the average of 5.5…
