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What nine atmospheric rivers mean for California


Flooding in San Diego. Image credit: Mike Blake / Reuters.

Disclaimer: This article was written in late January; statistics and conditions may have changed.


From December 27 to January 16, California encountered nine atmospheric rivers, culminating in almost a foot of rainfall (in other words, over 32 trillion gallons of water). California faced widespread flooding leading to at least 20 deaths, mudslides, and power outages. In total, the cost of damages is in the billions—anywhere between $5 billion and $34 billion, depending on who you ask, with L.A. County amounting to $100 million on its own. But what else does this mean for a state that’s been in droughts on and off for the past few decades, with the most recent (and current) drought beginning in 2020?


The short answer is that while California’s drought conditions have improved for the short term, its problems are far from over.


Comparison of California’s drought status before the recent storms. Image credit: NOAA NCEI on Twitter.

The long answer is, predictably, a little more complicated. The presence of atmospheric rivers, or river-like columns in the atmosphere that transport water vapor, in itself is not unusual; California gains up to 50% of its annual precipitation from atmospheric rivers, and they have ended droughts in the Pacific Northwest on many occasions. However, recent storms have been more intense partially due to climate change; studies show that regions throughout the US will experience a trend of more extreme storms, with more precipitation.


The current conditions of California’s major water supply reservoirs. Image Credit: California Data Exchange Center, California Department of Water Resources.

Although this sounds good, at least for California’s water crisis, the recent storms are not enough to eliminate the drought. It has helped; 0% of the state is under extreme or exceptional drought, a dramatic drop from the 41% earlier. Reservoirs, which make up approximately 60% of our total water supply, are also up; Lake Shasta, California’s largest reservoir, is up by 60 feet, and the California Department of Water Resources says it will be able to allocate the most water to municipal and agricultural water agencies since 2019—30% of what’s been requested, which is an improvement from the 5% of the past two years. However, many of California’s main reservoirs are still below the historical average, and the state’s groundwater, which is severely depleted, is much harder to recharge. One problem is that when reservoirs are near capacity, water has to be released to prevent flooding in the case of another storm, and that water usually doesn’t make it to another reservoir. Runoff in populated areas isn’t always collected either due to contamination. So even when more water is available, not all of it is collected.


Graph of water elevation at Shasta Dam. Image Credit: California Data Exchange Center, California Department of Water Resources.

Also, over 90 percent of the state is still in a drought, and it will likely take multiple years of consistent wet weather to reverse that. Unfortunately, periods of wet weather in California are often followed by periods of dry weather, a pattern only expected to get more extreme.


So what does this mean? While this is a step towards getting out of the current drought, don’t expect water restrictions and guidelines to relax. On the other hand, even if the rest of this winter is fairly dry, be prepared for storms of similar or greater magnitude in the upcoming years. The future of extreme weather events that climate scientists have been warning about? It isn’t so far.

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1 Comment


Reda Rountree
Reda Rountree
Feb 23, 2023

Very well-written and informative, and I love the graphs you included!

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