One of the best places to see how dramatically big storms this winter have changed California's water picture is three hours north of the Bay Area, in the foothills east of Sacramento Valley.
There, Lake Oroville, the second-largest reservoir in California and a key component of the state's water system, has undergone a breathtaking transformation. Sixteen months ago, the reservoir was so parched from severe drought that it was just 22% full. For the first time since it opened in 1967, its power plant had shut down because there wasn't enough water to spin the turbines and generate electricity.
Now Oroville reservoir is 65% full. Since its lowest point on Sept. 30, 2021, the massive lake's level has risen 182 feet, boosted by nine atmospheric river storms in January.
How much water is that?
The lake has increased by 1.5 million acre-feet since its low point 16 months ago, adding enough water for the annual needs of 7.5 million people. During the week that began Jan. 9, the raging storms that soaked California sent 360,000 acre feet into Oroville — the equivalent of dumping in all of San Francisco's main water supply, Hetch Hetchy Reservoir in Yosemite National Park.
Oroville is now at its highest level since May, 2020, a few months after the drought began. The expanding water level there and in other reservoirs means cities, farms and wildlife will have more water this summer.
"This is a fantastic way to be starting our winter," said Karla Nemeth, director of the state Department of Water Resources, on Wednesday during a visit to survey the biggest Sierra snowpack in nearly 30 years near Lake Tahoe.
But Nemeth and other water leaders say the state was in a deep hole after three years of severe drought, and still will need more storms in February and March to fill its biggest reservoirs, like Oroville, and end the drought. Last year, a wet December gave way to a very dry January, February and March, bursting hopes the drought was ending then.
"Does our big January actually bust the drought in California? It's too soon to tell," Nemeth said, adding "I don't want to be the downer here. But I do want to make sure that everyone understands that we need to exercise caution."
Built in the 1960s by former Gov. Edmund "Pat" Brown, Jerry Brown's father, Oroville reservoir holds 3.5 million acre feet when full — enough water for about 18 million people a year. The massive reservoir in Butte County captures water from the Feather River watershed. Its dam is the tallest in the United States. At 770 feet tall, it towers more than 200 feet higher than the Washington Monument.
Shasta Lake, near Redding, is the only reservoir larger in California.
Oroville's spillway, an enormous concrete chute as wide as 15 lanes of freeway, famously collapsed during massive storms in 2017. A $1 billion construction project rebuilt it and upgraded the dam.
Over the past 20 years, Oroville has filled to the top seven times: 2003, 2005, 2006, 2011, 2012, 2017 and 2019.
It is currently holding 2.3 million acre feet of water. By comparison, the largest reservoir in Santa Clara County, Anderson, near Morgan Hill, holds about 90,000 acre feet when full.
To fill completely to the top, Oroville's water level would have to rise another 90 feet. When the massive Sierra snowpack, which Thursday was 206% of its historical average, begins to melt in the months to come, it is sure to continue increasing storage levels at Oroville and other major reservoirs, experts say.
Exactly by how much won't be known until the next two or three months of weather play out.
"Even if it melts a bunch between now and April 1, we are going to have a pretty good snow pack by April 1," said Jay Lund, a professor of civil and environmental engineering at UC Davis. "That's really good news compared to some of the drought years of the past."
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