Thanks To A Wet Winter In 2023, California's Groundwater Levels Went Up Statewide For The First Time In 4 Years

The water levels in California's underground aquifers bounced back during a wet winter in 2023, marking the first time since 2019 that the state's groundwater resources have increased overall.

A new report from the state Department of Water Resources has found that Water Year 2023 was a boon for the state overall, when nearly every part of California saw above-average precipitation levels. (Water years, like financial years, don't start in January: Water Year 2023 lasted from Oct. 1, 2022 to Sept. 30, 2023.)

4.1 million acre-feet — slightly less than the volume of the Shasta Lake reservoir — were replenished due to managed groundwater recharge programs, which intentionally put storm runoff and recycled water back into wells. The overall increase in groundwater storage was 8.7 million acre-feet.

The report's findings are welcome news for California, which built up a groundwater deficit as the state has experienced a series of droughts over the last two decades.

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"Groundwater basins are really our water savings account," said Steven Springhorn, supervising engineering geologist with the California Department of Water Resources. "It's our drought buffer."

This trend could continue statewide if 2024 is another above-average year of rainfall — and it's likely Southern California will make it out ahead. According to the report, precipitation levels from October 2023 to March 2024 were roughly average, though Southern California saw about 135% more rain than average.

While there have been visible signs in the last few years that the state's water supply is doing better — snow-topped mountains and relatively full reservoirs, for instance — Springhorn said that the replenishing of aquifers is even more significant.

"Groundwater basins hold much more water in storage than all of our surface water reservoirs combined, or even our snowpack," Springhorn said.

According to the report, about 52% of wells statewide saw an increase in water levels, with about 45% remaining stable and just 4% seeing a decrease.

This trend remained true even in some of the state's most water-starved regions. Aquifers in the vicinity of Tulare Lake — which reappeared after the 2023 storms — saw a considerable increase in water levels of about 68%. Still, about three-fifths of groundwater basins in the area had below-normal levels in October 2023. The state only recently took action last month against the over-reliance on groundwater in that farming region, imposing fees with the aim of stopping the large-scale pumping of groundwater for agriculture.

In a normal year, about 40% of the water Californians use comes from underground aquifers. In a dry year, that number can rise to 60%, according to Springhorn. Nearly 85% of state residents use groundwater for at least a part of their water supply.

The Department of Water Resources estimates it will take about five years of above-average rainfall in order to replenish the state's groundwater supply to where it was two decades ago — though drought years could potentially set the state back, as they have in the past.

"One wet year is a good thing, but there's still more work to be done to make sure all of our groundwater basins are being used sustainably," Springhorn said.

That sustainability will become even more crucial as climate change makes California's weather even more unpredictable in years to come.

"Groundwater basins really have a huge opportunity as a climate adaptation strategy to utilize them in a sustainable way, more so than has been done in the past," Springhorn said. "A swing from intense dry to intense or extreme wet conditions is what California is expecting and planning for going forward under climate change."