Last year’s wet winter gave California Central Valley groundwater levels a major boost

California’s groundwater reservoirs got a major boost during last year’s record wet season, offering a glimmer of hope for the depleted underground aquifer’s that remain in a long-term deficit.

The 2023 water year, which was marked by above average rainfall and a concerted effort to recharge reservoirs, led to the addition of at least 4.1 million acre-feet of water underground, according to data released by the California Department of Water Resources.

That’s more than what Lake Oroville, the state’s second largest reservoir can hold — which is now 100% full. An acre-foot is the amount of water it takes to cover an acre with 1 foot of water and is generally enough to supply two California households for a year.

“California is invested in preparing for weather extremes by maximizing the wet years to store as much water as possible in preparation for the dry years,” said Paul Gosselin, DWR deputy director of sustainable water management. “The impressive recharge numbers in 2023 are the result of hard work by the local agencies combined with dedicated efforts from the state.”

Much of that recharge took place in the San Joaquin Valley, where aquifers have been heavily taxed by pumping for agriculture. Glen and Colusa counties north of Sacramento saw major groundwater gains, as did Ventura and Santa Clara counties.

This groundwater boost was driven in part by deliberate efforts to recharge the state’s vast underground reservoirs, which accounts for about 40% of California’s total water supply and is relied on more heavily during periods of drought.

Most recharge is done by allowing water to pool on a piece of land, sometimes in specific recharge basins, and then slowly soak into the ground. Reduced groundwater pumping and enhanced conservation measures also played a role in stashing supplies underground.

Recharge boosted by local water agencies

This latest groundwater data comes from water agencies, which were required to file reports with the state last month, and captures the last “water year” from Oct. 1 to Sept. 30.

The data is a product of the state’s Sustainable Groundwater Management Act, passed in 2014 as the state’s first effort to regulate groundwater. It requires local water agencies to manage their aquifers sustainable levels by 2040.

Local and regional water agencies such as the Westlands Water District, one of the state’s largest irrigation agencies that serves Fresno and Kings counties, last year bolstered new programs that encourage groundwater recharge.

Westlands spokesperson Elizabeth Jonasson said the agency recharged record amounts of water, nearly 162,000 acre-feet during the 2023 water year and around 200,000 acre-feet since then. She credited the programs’ success to the widespread availability of surface water.

The district received 100% of its requested water supplies from federal reservoirs in 2023, but so far will receive 40% this year.

“Groundwater recharge is hugely important because it allows us to capitalize on wet years and save it for dry years,” she said. “This past year showed us how much our growers are willing to step up and invest their own resources to capture as much water as possible for the sustainability of the aquifer.”

California’s groundwater deficit remains

After decades of over-pumping to irrigate California’s agricultural heartland, the state’s groundwater reserves remain in a long-term deficit. In some parts, so much water has been pumped from the ground that wells have run dry and the land has sank.

While no one knows the exact amount of water that can be stored within California’s 515 groundwater basins, DWR estimates the total storage capacity at somewhere between 850 million and 1.3 billion acre-feet.

Between 2022 and 2023, according to the new data, the nearly 100 groundwater basins and sub-basins tracked by the state logged 8.7 million acre-feet of total additional water. During the previous three years, however, those basins experienced losses of almost twice that amount, the data show.

Experts like Dr. Pablo Ortiz-Partida, water and climate researcher at the Union of Concerned Scientists, are celebrating the good news of increased recharged but keeping it in context within the bigger problem that will take many more years to solve.

“There’s an increase based on 2023 numbers, but this isn’t a 2023 problem. This is a problem that’s been increasing for over 100 years now,” he said, pointing to the need for land transition away from agriculture.

A report by the Public Policy Institute of California calculated that at least 500,000 acres of irrigated agriculture will need to be retired to achieve groundwater sustainability.

“We need to be investing more money into strategies that will make this transition equitable,” said Ortiz-Partida, “for farmers and landowners but also farm workers. There will be potential impacts, but the question is how do we turn those into opportunities?”