There Are "Rivers in the Sky" Happening in California RIght Now
If you've tuned into a weather report over the last six months, you've likely heard of the "atmospheric rivers" bombarding the West Coast, particularly California. The meteorological phenomenon refers to long, narrow streams of water vapor in the atmosphere—truly akin to rivers in the sky. They can run for thousands of miles, though they're typically only 300 miles wide, and sometimes even narrower. And they're very wet, carrying seven to 15 times more water than the Mississippi River, leading to exceptional rainfall and snowfall beneath their path.
Atmospheric rivers occur all over the world, transporting moisture from the tropical regions of the planet elsewhere. In the case of the West Coast, an atmospheric river called the Pineapple Express draws moisture from Hawaii, runs across the Pacific Ocean, then dumps the water onto the continental U.S. in the form of rain or snow when the river runs over land—this most commonly happens during the winter. Atmospheric rivers, including the Pineapple Express, aren't necessarily constant, and their specific paths and the amount of moisture they hold vary.
But what is constant is that there are anywhere from four to 12 atmospheric rivers occurring around the world at any given time.
According to the Department of Energy, an average of 24 atmospheric rivers hit the West Coast each winter between 1979 and 2019, providing some 50% of the region's water supply. While most are weak and provide gentle rain showers or snowfall, intense atmospheric rivers can cause catastrophic flooding and mudslides—particularly in wildfire-scarred areas of the West Coast.
And that's what the West Coast has experienced this year. Atmospheric rivers are rated on a scale that measures the amount of moisture they hold, from a "weak" Category 1 to an "exceptional" Category 5. Several of the atmospheric rivers that have hit California this year have been rated Category 5, resulting in the state experiencing extraordinary amounts of rainfall some "400-600% above average values," per the National Oceanographic and Atmospheric Administration (NOAA). Unfortunately, the storms associated with this season's atmospheric rivers have led to 35 deaths.
If there's any silver lining to atmospheric rivers, however, it's the fact that they can help reduce drought. The United States Geological Survey found that between 1950 and 2010, atmospheric rivers ended between 60% and 74% of the droughts in the Pacific Northwest during that 60-year period. This winter, California's drought has been cut by half, according to NOAA.
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