How will California’s water storage hold up in future dry-wet cycles?

California’s recent storms have brought record amounts of precipitation but have also revived a perennial debate at the state Capitol over water storage and management.

By some estimates, more than 32 trillion gallons of water have fallen on the state since the first storms hit in late December.

On a levee overlooking the swollen Sacramento River last week, a group of Republican state lawmakers criticized their Democratic colleagues and Governor Gavin Newsom for not prioritizing new projects to capture the deluge.

“Overwhelmingly, that’s flowing out to sea and not being captured,” said Assembly Republican Leader James Gallagher, gesturing to the water, which was running high and fast. “Not being set aside and utilized for all the purposes we have in California” including farming and drinking water, he said.

Gallagher and other Republicans called it a “failure of leadership” by Democrats and called for more investments in water storage, both above ground and below.

A large reservoir is planned for the northern Sacramento Valley but has been undergoing a lengthy permitting process. Construction at the Sites project is estimated to begin in 2024 with operations beginning in 2030.

According to the Sites Project Authority, the reservoir could have captured 120,000 acre-feet of water between Jan. 3 and Jan. 15 if it had been operational.

Typically, one acre-foot of water is enough to serve two urban households for one year.

In 2014, voters approved Prop. 1, a $7.5 billion bond for water storage projects including the Sites reservoir.

Newsom has approved $8.6 billion since 2021 on drought mitigation measures, including reservoir expansion and repair, improving water conveyance infrastructure, and streamlining permits for groundwater and new surface storage projects.

“California isn’t waiting to act,” Newsom said in a press release Thursday. “We’re moving aggressively to modernize how we capture and store water to future-proof our state against more extreme cycles of wet and dry.”

The governor has acknowledged the “absurd” length of time it can take to get water projects permitted. In his state budget proposal this month, the governor said he has implemented “strike teams” between agencies to speed permitting for Sites and other Prop. 1 storage projects.

water strategy plan put out by his administration last August set new targets for additional water storage, along with increased water recycling, desalination and conservation.

According to the report, California will lose 10 percent of its water supply over the next 20 years due to a warming climate.

A bill proposed by Assembly member Devon Mathis (R-Visalia) would codify Newsom’s water storage goals: 3.7 million new acre-feet of storage capacity by 2030 and 4 million by 2040.

“The governor set these goals,” Mathis said. “This is just codifying it so we can hold his feet to the fire.”

According to the governor’s office, Prop. 1 projects including Sites would add 2.7 million acre-feet to the state’s water storage capacity – about three times the capacity of Folsom Lake.

The Division of Water Resources is also working to add 135,000 new acre-feet of storage to the San Luis reservoir, which is a critical water resource for farms in the San Joaquin Valley.

While the recent series of atmospheric rivers led to catastrophic flooding in parts of the state and broke some precipitation records, climate scientists say the state’s regular wet and dry cycles will only become more extreme in the future due to a warming climate.


How do reservoirs stack up in storage capacity?


The storms have also boosted levels in the state’s parched reservoirs, though some – including Lakes Shasta and Trinity – are still below their historical average levels.

Jay Lund, Director of the Center for Watershed Sciences at UC Davis, warns building new reservoirs – as some Republican lawmakers are calling for – would be costly and the total additional storage marginal.

“If you built all of the proposed reservoirs that are being talked about, it would add about 10% to [the state’s storage capacity] total and it would add about 1% to the amount of water available,” he said.

Lund said new above ground storage “is not going to be a game changer for floods or droughts in California.”

Rather, he said the state should prioritize delivering more water to existing groundwater basins.

While out of sight, the state’s groundwater tables are vast: at capacity, they could hold between 850 million and 1.3 billion acre-feet of water. That’s compared to the less than 50 million acre-feet of storage at all California’s major reservoirs, according to Stanford’s Woods Institute for the Environment.

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