Groundwater gains can’t offset years of loss
For decades, California’s groundwater supplies have plummeted because of too much pumping. In some places, due to the heavy draws, the land above has collapsed, roads and bridges have buckled and communities have run out of water.
But this year, after the historically wet winter, there was at least some reprieve for the state’s overburdened aquifers. Groundwater levels rose or were flat at the vast majority of wells tracked by the state, compared with last year, while groundwater levels dropped significantly at just 9% of the thousands of monitored wells.
The well data, released in a report last week by the California Department of Water Resources, is among the first to show the benefit to groundwater supplies that resulted from the bounty of rain and snow seeping into the earth this year. While a lot of that seepage was natural, some of it was intentionally steered underground in a process known as aquifer recharge.
A full picture of the improvement is yet to come because there’s no realtime, centralized accounting of the vast amounts of water nested in California’s underground. Local water agencies will eventually report much of this information to the state. Also, water on the surface can sometimes take months or even years to percolate into aquifers, meaning an inherent lag in the tally.
The status of groundwater is significant because it accounts for about 40% of the state’s total water supply — and as much as 60% during dry times.
“The amount of water in (many) aquifers is likely more than it was before this winter,” said Steven Springhorn, a supervising engineering geologist at the Department of Water Resources who helped write the new report. “It’s good news but it’s in the context of a lot of years of water depletion.”
Springhorn said any gains this year remain far short of undoing the decades of losses.
Despite the one-year bounce in many places, the multiyear picture is bleak. According to the report, groundwater levels were higher at just 21% of wells this year compared with five years ago while groundwater levels remained lower at more than 30% of wells. The balance of wells reported no significant change between 2018 and 2023.
Compared with 20 years ago, groundwater levels this year were higher at only 11% of wells and lower at 45% of wells.
“It’s really going to require more water years like what happened this past year, and also reductions in pumping (to offset the decline),” Springhorn said.
The most pronounced groundwater problems are in the San Joaquin Valley, California’s farm capital. A preponderance of dry years, including two severe droughts over the past decade that left rivers and reservoirs low, has prompted growers to increasingly lean on groundwater.
Only in 2014 did the state pass regulations on how much groundwater could be pumped, with real limits still years from being enacted, leaving aquifers continuing to bear the brunt of the huge agricultural demand.
Extraction has been greatest, by many measures, in the Tulare Lake region, namely Kern and Kings counties at the southern end of the San Joaquin Valley where fields of almonds, pistachios, grapes and oranges dominate. More than 70% of wells in this region remained lower this year than they were five years ago, according to the state report.
The area is also where California has had the most land subsidence, or the sinking of the earth’s surface, which can happen when aquifers begin to empty. While the amount of subsidence was less across the state this year compared with last year, according to the report, the Tulare Lake region still saw 2,400 square miles of land drop. Even with the reappearance of Tulare Lake, the large, historical body of water that surprisingly filled during the wet winter, aquifers weren’t expected to recover much. The clay floor of the lake bed prevents water from infiltrating.
Conversely, a portion of the western San Joaquin Valley saw ground levels rise this year, owing to the land’s ability to sometimes snap back after subsidence. The uplift, though, was only about an inch or so in most places, far short of how much the land had previously sunk. Parts of the San Joaquin Valley have dropped as much as 30 feet in recent decades.
“The years of subsidence overshadow the rebound that can happen in a wet year like this,” Springhorn said.
California water officials have long been urging water suppliers and communities, mostly in the San Joaquin Valley, to tackle subsidence and groundwater depletion by actively recharging aquifers. This is done primarily by putting land aside for water absorption but sometimes by injecting water directly into the ground through wells.
This year, with all the rain and runoff from snow, state officials reinforced their call for groundwater recharge, easing permitting and providing equipment.
According to early state estimates, about 3.8 million acre-feet of water was actively recharged, roughly the amount that can be held at California’s secondlargest reservoir, Lake Oroville, and enough to supply about 8 million households for a year. About 390,000 acre-feet of the recharge was the result of Gov. Gavin Newsom’s executive orders to expedite permitting, state officials say.
Still, the recent recharge makes only a small dent in the cumulative losses from overpumping, with more than 6 million acre-feet of groundwater lost some years (accounting for both total extraction and seepage).
This year’s net change in total groundwater supplies won’t be known until local agencies begin filing their groundwater reports next spring as required by the 2014 Sustainable Groundwater Management Act.
During the winter, 19 atmospheric rivers made landfall in California, helping drive up precipitation to 141% of average and snow levels to more than twice the norm, according to state data.
“My expectation is that we’ve seen some nice progress (with recharge) since 2017 or 2019, which were also both wet years,” said Ellen Hanak, senior fellow with the Water Policy Center at the Public Policy Institute of California. “(But) I think we’ll be better prepared (for recharge) next time. If this next year is wet, I think we’ll be better prepared.”
California’s groundwater basins can cumulatively hold between 850 million and 1.3 billion acre-feet of water, according to state estimates. This dwarfs the little more than 50 million acre-feet of capacity in the state’s above-ground reservoirs.
Going forward, replenishing groundwater will not only be necessary under the Sustainable Groundwater Management Act, which requires full restoration of overpumped aquifers by 2040, but helpful for communities looking to boost water supplies for use during droughts.
“People are definitely very motivated to recharge more water,” Hanak said.