After years of widespread decline, groundwater levels rose significantly across much of California last year, driven by historically wet weather and the state’s increasing efforts to replenish depleted aquifers.
The state’s aquifers received an estimated 8.7 million acre-feet of groundwater during the 2023 water year that ended Sept. 30, nearly twice the total storage capacity of Lake Shasta, according to the latest data compiled by the California Department of Water Resources. .
A large portion of those gains, estimated at 4.1 million acre-feet, are achieved through efforts to replenish aquifers by collecting water from rivers swollen by rainfall and snowmelt and transporting it to areas where the water seeps into the ground. The state says managed groundwater recharge is unprecedented and is nearly double the amount recharged in 2019, the previous wet year.
Still, the increase in underground supplies comes after a long period of significant declines in supplies, largely caused by chronic over-pumping of water in agricultural areas. Those gains only partially offset the estimated 14.3 million acre-feet of groundwater lost during the previous two years of severe drought, when farms relied heavily on wells and aquifer levels plummeted.
“It’s been a good rebound,” said Steven Springhorn, director of engineering geology for the state Department of Water Resources.
“However, we have a severe shortage of groundwater,” Springhorn said. “Overall, the trend has been declining for a long time.”
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The Department of Water Resources released this message semi-annual report Regarding 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, causing flooding and one of the largest snowpacks on record. This year is the eighth wettest statewide in the past half century.
Wet weather and the availability of canal water have led agricultural well owners to reduce groundwater pumping. Floodwater spreads and naturally replenishes groundwater in rivers and wetlands. In some areas, local water agencies direct floodwaters into dedicated recharge basins or farmland, where the water seeps into the ground.
To date, most efforts to manage recharge have occurred in agricultural areas of the San Joaquin Valley, where local agencies have been developing plans to combat overdrafts and invest in infrastructure to move water to recharge facilities.
According to the report, based on available data, 52% of wells have seen water levels rise by more than 5 feet, while 44% have seen little change and only 4% have seen water levels drop by more than 5 feet.
However, over the past five years, water levels have been trending downward in most areas. The report’s authors said this “underscores the fact that one or even several years of heavy rainfall is not enough to replenish the state’s depleted groundwater basins” or make up for a series of severe drought years.
Springhorn noted that researchers have estimated loss The Central Valley has lost approximately 40 million acre-feet of groundwater over the past 20 years.
Since 2000, California has also received Much less precipitation higher than the 20th century average. State water officials call it a “cumulative precipitation deficit” that reflects recurring 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 used to feed dairy cows.
Over the past decade, declining groundwater levels have caused wells to run dry in thousands of homes. But after 1,494 dry wells were reported in the 2022 water year, the total number of dry wells dropped to 669 the following year and continues to decline.
Ground subsidence problems related to declining groundwater have also been significantly alleviated. The area affected by land subsidence is smaller. Between October 2022 and October 2023, an area totaling about 800 square miles, primarily on the west side of the San Joaquin Valley, experienced more than 1.2 inches of measurable “uplift” on the surface.
Springhorn said efforts by local agencies to raise water levels have had positive results.
“These numbers are great. They really reflect a lot of work at the local level,” he said. “But there’s still a lot of work to be done to achieve sustainable development of the groundwater basin.”
In 2023, birds gathered on the high desert waterfront near Lancaster, where the Metropolitan Water District uses water from the state water program to store underground water for Southern California cities.
(Alan J. Schaben/Los Angeles Times)
He noted that California will celebrate the 10th anniversary of the Sustainable Groundwater Management Act this year. The landmark law requires local agencies in many areas to develop groundwater plans and curb overpumping by 2040.
In January, the Department of Water Resources completed a review of local agencies’ groundwater plans.
Regulators last month declared the plans inadequate in six areas of the San Joaquin Valley after state officials announced Vote for one of the regions The Tulare Lake subbasin is on “trial” status after failing to do enough to address chronic overpumping.
Some areas where the state has declared severe overdraft problems, such as the Tule and Kawea watersheds, were also among the areas with the highest aquifer recharges last year.
“The impressive 2023 recharge figures are the result of hard work by local agencies and a dedicated national effort, but we must do more to be ready to collect and store water when wet years arrive,” said the Ministry of Water Resources Sustainable Water Deputy Director of Management.
He said that given the ongoing shortage of groundwater, “we need to continue to streamline processes and invest in water management strategies and infrastructure, such as rainwater harvesting and groundwater recharge.”
The state agency has provided about $121 million to support dozens of local programs aimed at increasing groundwater recharge.
California has also recently Maps most of the state’s aquifers. State officials use helicopters equipped with ground-penetrating electromagnetic imaging systems to scan 1,000 feet underground to map the best areas for aquifer recharge.
This data can now be used to help plan groundwater recharge locations.Officials hope to exploit the channels left by ancient rivers, or what scientists call ancient valley. These areas have coarse-grained sand, gravel, and cobbles that provide highly permeable pathways for groundwater recharge.
“The more we know about these priority pathways or express pathways into the underground, the more we can optimize them” as areas to deliver water when it’s available, Springhorn said. “It allows us to leverage the natural infrastructure that California has to adapt to climate change.”
Experts say replenishing groundwater alone is not enough to address declining aquifers in areas with serious overdraft problems, and that meeting state-mandated goals for the next few years will require significant reductions in water pumping.
Graham Fogg, professor emeritus of hydrogeology at UC Davis, said the past two wet winters have been good for the state’s groundwater conditions and the recharge projects so far are an important start in prioritizing more aquifer recharge.
“This is really just the tip of the iceberg in terms of potential,” Fogg said. “The potential for managing aquifer recharge is very, very high.”
For one thing, there’s plenty of space underground to store water. In the Central Valley alone, the capacity of unused aquifer space drained through pumping could amount to more than three times the state’s total above-ground reservoir capacity, Fogg said.
California is on the cusp of more focused efforts to replenish water reserves, efforts that have long been ignored, he said.
“It’s important that whenever you have a wet winter, you maximize the potential benefits of charging,” he said. “Are we maximizing it? We’re not maximizing what we could be doing.
