After years of widespread decline, groundwater levels rose significantly across much of California last year, spurred by historic wet weather and the state’s growing efforts to replenish depleted aquifers.
The state’s aquifers gained approximately 8.7 million acre-feet of groundwater, nearly double the total storage capacity of Lake Shasta, during the completed 2023 water year on Sept. 30, according to newly compiled data from the California Department of Water Resources.
Much of the gains, estimated at 4.1 million acre-feet, are the result of efforts to capture water from rivers swollen by rains and melting snow and send it to areas where water seeps into the ground to recharge aquifers. The state said the amount of managed groundwater that was replenished was unprecedented and was nearly double the amount of water replenished in 2019, the previous wet year.
Yet increases in groundwater reserves follow much larger long-term declines, driven largely by chronic overpumping in agricultural areas. The gains only partially offset losses estimated at 14.3 million acre-feet of groundwater during the previous two years of severe drought, when farms relied heavily on wells and aquifer levels rose. were collapsing.
“It was a good rebound,” said Steven Springhorn, supervising engineering geologist with the state Department of Water Resources.
“However, we face a significant groundwater deficit,” Springhorn said. “Overall, the trend has been downward for a long time.”
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The Ministry of Water Resources published the information in its semestrial report on groundwater conditions. The report does not include data for late 2023 and early 2024, which will be assessed in the next update later this year.
In early 2023, a series of powerful storms ended three years of extreme drought, triggering flooding and leaving one of the largest snowfall accumulations on record. The year ranked as the eighth wettest year in the state over the past half-century.
Wet weather and the availability of water delivered in canals led agricultural well owners to pump less groundwater. Floodwaters spread and naturally replenished groundwater along rivers and wetlands. In some areas, local water agencies directed floodwaters to dedicated recharge basins or agricultural fields, where the water seeped into the ground.
Most of the recharge efforts managed so far have taken place in agricultural areas of the San Joaquin Valley, where local agencies have worked on plans to combat overdraft and have invested in the region’s transportation infrastructure. water to recharge the installations.
According to the report, water levels increased more than 5 feet in 52% of wells with available data, while there was little change in 44% of wells, and only 4% of wells decreased. over 5 feet.
However, over the past five years, most areas have experienced a declining trend in water levels. The report’s authors say this “underscores the fact that a single year, or even a few years, of heavy rainfall is not enough to refill the state’s depleted groundwater basins,” nor to make up for a series of extremely dry years.
Springhorn pointed out that researchers have estimated losses groundwater in the Central Valley to about 40 million acre-feet over the past two decades.
Since 2000, California has also received much less precipitation than the 20th century average. State water officials call it the “accumulated precipitation deficit,” reflecting repeated droughts and the worsening effects of climate change.
Central Valley farms have long relied on a mix of river water and groundwater to produce crops such as almonds, pistachios, grapes and hay to feed dairy cows.
Declining groundwater levels have left thousands of families with dry wells over the past decade. But after 1,494 dry wells were reported in the 2022 water year, the total dropped to 669 dry wells the following year and continued to decline.
The problem of land subsidence, linked to the reduction of groundwater, has also been significantly reduced. Land subsidence has affected smaller areas. Between October 2022 and October 2023, areas totaling about 800 square miles – largely on the west side of the San Joaquin Valley – experienced a measurable “lift” of the ground surface of more than 1.2 inches.
Springhorn said efforts by local agencies to boost groundwater have had a positive effect.
“These numbers are fantastic. And they really reflect a huge amount of work at the local level,” he said. “But there is still much to be done to achieve the sustainability of our groundwater basins. »
The birds gather in 2023 at the High Desert Water Bank near Lancaster, where the Metropolitan Water District uses water from the State Water Project to store groundwater for Southern California cities.
(Allen J. Schaben / Los Angeles Times)
He noted that California will mark the 10th anniversary of the Sustainable Groundwater Management Act this year. This landmark law requires local agencies in many regions to develop groundwater plans and reduce excessive pumping by 2040.
In January, the Department of Water Resources completed a review of local agencies’ groundwater plans.
State officials declared the plans inadequate in six areas of the San Joaquin Valley, and last month regulators voted to place one of these regions — the Tulare Lake sub-basin — in “probationary” status for not having adopted sufficient measures to combat chronic excessive pumping.
Some of the areas where the state has declared serious overdraft problems, like the Tule and Kaweah sub-basins, are also among the regions that have replenished their aquifers the most in the last year.
“The impressive recharge numbers in 2023 are the result of hard work by local agencies combined with dedicated efforts from the state, but we must do more to be ready to capture and store water when the wet years arrive,” said Paul Gosselin, the Department of Water Resources’ Deputy Director for Sustainable Water Management.
He said that in light of the persistent groundwater deficit, “we must continue to streamline processes and invest in water management strategies and infrastructure, such as rainwater harvesting and water recharge.” underground”.
The state agency provided about $121 million to support dozens of local projects aimed at increasing groundwater replenishment.
California also recently mapped large portions of the state’s aquifers. Using a helicopter equipped with a ground-penetrating electromagnetic imaging system, state officials scanned up to 1,000 feet underground to map optimal areas for recharging aquifers.
Data is now accessible to help plan groundwater recharge locations. Authorities hope to take advantage of channels left by ancient rivers, or what scientists call paleovalleys. These areas contain coarse-grained sand, gravel, and cobbles that provide highly permeable pathways for replenishing groundwater.
“The more we understand where these preferential routes, or expressways, to the subsurface are, the better they can be optimized” as areas to send water when it is available, Springhorn said. “It allows us to use this natural infrastructure that we have in California to adapt to climate change.”
Experts say groundwater replenishment alone will not be enough to solve the problem of declining aquifers in areas facing serious overdraft problems, and that to achieve state-mandated goals in the coming years , it will also be necessary to reduce pumping considerably.
The past two wet winters have been good for the state’s groundwater, and the recharge projects so far represent an important start toward increasing priority on aquifer replenishment, said Graham Fogg, professor emeritus of hydrogeology. at UC Davis.
“This is literally just the tip of the iceberg in terms of potential,” Fogg said. “There is much, much, much more potential for managed aquifer recharge. »
For one, there is plenty of space underground to store water. In the Central Valley alone, unused aquifer space where water has been pumped away could hold more than three times the total capacity of the state’s overhead reservoirs, Fogg said.
He said California is poised to make a more dedicated effort to replenish water supplies that have long been largely out of sight and out of mind.
“It’s important that whenever you experience these wet winters, you maximize the potential benefits of charging,” he said. “Have we maximized it? We failed to maximize what could have been done.
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