Climate Change is bringing warmer and wetter storms, reducing our snowpack and increasing the need for more storage. At the same time, extended droughts have contributed to the over-pumping of our groundwater basins, leaving ample storage space for new water supplies, provided we can get the water to them. How is California managing its water storage dilemma?
At the April meeting of the Southern California Water Dialog, Jeff Mount with the PPIC, Tim Godwin with DWR, and Aaron Fukuda with the Tulare Irrigation District and Mid-Kaweah Groundwater Sustainability Agency discussed water storage in California, both surface and groundwater, and how groundwater recharge is a critical tool for long-term sustainability.
WATER STORAGE IN CALIFORNIA
Dr. Jeff Mount, a senior fellow at the PPIC Water Policy Center, began the presentations by discussing California’s water storage.
California wouldn’t exist without surface storage; the state’s 1500 dams and reservoirs are the backbone of the water supply grid. California reservoirs have a total capacity of approximately 40 million acre-feet – about one year’s supply. Most are 50-75 years old.
Surface storage presents benefits and challenges, especially for large multi-purpose reservoirs like Shasta and Oroville. These dams serve various functions, including water supply, hydropower generation, recreation, maintaining downstream ecosystems, ensuring water quality, and managing floods. However, these objectives often compete with one another, complicating management.
“Five of those six objectives want a full reservoir,” said Dr. Mount. “One wants an empty reservoir, and the tension between those always drives issues, particularly on the large, multi-purpose reservoirs.”
Besides the reservoirs, 30% of California’s water supply is stored in the snowpack. The graphic on the left by Mike Dettinger shows the total amount in reservoirs plus the amount of water held in the snowpack, which illustrates how vital snowpack is to storage. Snowpack is the state’s largest surface reservoir – although the warmer temperatures associated with the changing climate alter and reduce the snowpack.
Groundwater is an essential component of the state’s water supply; in a typical year statewide, roughly 30 to 35% of the water supply comes from groundwater, and during droughts, it is 65%, even as much as 70% in significant droughts.
“Groundwater is our drought reserve,” said Dr. Mount. “Unfortunately, we haven’t treated it like that. We’ve treated it like our regular water supply. So we’ve been in chronic overdraft for almost the last century. The average overdraft in the San Joaquin Valley is as much as 2 million acre-feet per year. That is pretty significant.”
In 2014, California passed the Sustainable Groundwater Management Act with the goal of achieving sustainable groundwater management by 2040 for the critically overdrafted basins and 2042 for other basins.
“This is a painful process,” Dr. Mount said. “This is the most transformative legislation in the history of water since the modern water rights system was established in 1913. It is transformative but sets us up for a long-term sustainable future in water management. It’s just going to be really painful because it involves a lot of demand management and a big emphasis on improving groundwater recharge. Both are absolutely necessary.”
Demand management most often means taking land out of production. The PPIC has estimated that if not managed well, about 900,000 acres of land will have to go out of production in the San Joaquin Valley, with the loss of more than 50,000 jobs and a 2.3% decline in the rural counties’ GDP. He noted that’s a significant economic, social, and environmental issue.
Cities and farms rely on California’s elaborate conveyance system to move water hundreds of miles from the Delta, the Colorado River, and the Owens Valley.
“This long distance transport is because we decided to put our people and most of our crops in places where it doesn’t rain, so we have to move water at great distances in California,” said Dr. Mount. “So you can’t lose sight of the fact that that infrastructure is essential to basically making this work.”
The age of large dam construction projects is over, he said. While some reservoirs, such as Sites, are being considered, it’s not anything like the dam construction that occurred in the mid to late-20th century. All the good spots have been taken; the rest are too expensive. When constructed, the Prop 1 storage projects, a mix of reservoirs and groundwater projects, would only increase storage capacity by 7% at best.
However, groundwater storage offers immense potential for increasing California’s water capacity. Depleted aquifers in the San Joaquin Valley alone hold over 100 million acre-feet of available space—more than two and a half times the total capacity of the state’s surface storage infrastructure.
“If we do a much better job of wet year management to get us through the dry years, it really will help,” said Dr. Mount. “It will not solve the groundwater overdraft problem that we have now; that’s got to come with demand management as well as investments in improvements in conveyance, but we really do have this opportunity to substantially improve how we store water in the ground. It is much less expensive and certainly easier to permit than building new surface reservoirs. You don’t lose it to evaporation. There are always benefits associated with groundwater recharge that we think we at PPIC feel very strongly is a place we need to put a lot of effort into.”
GROUNDWATER RECHARGE IN THE CENTRAL VALLEY COULD AFFECT WATER DELIVERIES TO SoCAL
Dr. Mount cautioned that filling available groundwater storage could potentially affect State Water Project deliveries because the water would come from the Delta, the hub of the state’s water supply system and one of the most intractable management problems in California.
“Putting water in groundwater recharge reduces the amount of water that flows into the Delta, which has the potential to impact the amount of water that can be exported to Southern California from the Delta,” said Dr. Mount. “So there’s some trade-offs there that we have to worry about.”
Pumping from the Delta is complex, governed by rules and regulations that determine when water can be exported and how much, and water used for recharge in the San Joaquin Valley would affect that.
To illustrate the issue, Dr. Mount presented data from 2023, a very wet year. From the north, the Sacramento River flows into the Delta and out to the San Francisco Bay. The dark blue shows what was required for Delta outflow, the rust color is in-Delta use and exports, and the yellow is the wates potentially available for groundwater recharge in the Sacramento Basin – about 11 MAF, per the PPIC calculations. “That’s 11 times the amount of water that you would hope in a good year to get out of the Delta, so that suggests the potential recharge is huge,” said Dr. Mount.
“The problem is that’s not where the empty aquifers are that we want to fill. Rather, it’s on the San Joaquin side,” he said, noting that in the same year, only 3.4 MAF was potentially available on the San Joaquin River.
“This is where the shortage is so strong and such a big issue,” he said. “It’s our most productive agriculture region, so the demands there are very, very high.”
The problem is that potentially available water starts creating trade-offs. He explained that two categories of water flow into the Delta. One is water that we lack the capacity to capture; nothing can be done upstream or downstream as the reservoirs are full.
However, if folks upstream start taking a lot of water off the San Joaquin River, it can impact the amount that gets exported out through the State Water Project to Southern California. So that’s why we call this trade-off water. And a lot of negotiation has to take place over this.”
“The folks who regulate this are struggling with how to figure out who can take how much and when. So that trade-off water is actually a big, big deal and a major policy issue.”
IMPLICATIONS FOR POLICY AND PRACTICE
Dr. Mount said that the balance between who takes how much water upstream and how much water downstream after water rights have been met must be worked out. Some upstream diverters might appeal to “Area of Origin” laws to make the case that they should have priority over export. “That’s a really big issue that has to be worked out in policy discussions. Nothing that can happen overnight.”
“We estimate roughly, you could have, easily, without impact to anybody, have put 600,000 acre-feet of water into storage upstream of the Delta on the San Joaquin, both in 2017 and 2023, very wet years, probably more than that.”
So if there is a relationship between the exporters and the upstream users, in wet years when exporters run out of places to put their water, it can be put into groundwater. “This is why we’re really encouraging recharge partnerships between the exporters you rely on in Southern California and the upstream diverters.”
TIM GODWIN: Expanding recharge through sustainable groundwater management
Tim Godwin, Supervising Engineering Geologist at DWR, then discussed how DWR is working to expand groundwater recharge.
California’s water system was designed for a hydrology that has fundamentally changed. As the graphic below shows, historic patterns of floods and droughts have shifted dramatically. Intense droughts are now more frequent, punctuated by very wet periods that are becoming even wetter and arriving more rapidly. Warmer temperatures carry more moisture into the mountains, but instead of falling as snow, it increasingly comes down as rain. This, combined with the rising temperatures, reduces the snowpack’s ability to last into the warmer months. What was once a steady and manageable runoff has now become an unpredictable and less reliable water supply.
These changes present multiple challenges: Growing agricultural, urban, and industrial water demands, coupled with changing hydrology marked by reduced snowpack, early melts, and extreme weather, are straining water resources. Limited surface water storage, designed for persistent snowpack and flood control, prioritizes purging dangerous flows, disrupting natural recharge. Expanding groundwater storage faces challenges like water quality, infrastructure needs, usage rights, and equity. Groundwater management must address overdraft, subsidence impacts, well dewatering, and water quality issues.
To address these challenges, Governor Newsom has put forward the Water Resiliency Portfolio and the Climate Adaptation Strategy, which highlight the need to look at the state’s water resources holistically and bring all management strategies to the table as potential actions. The Water Supply Strategy set a target of an additional 500,000 acre-feet of groundwater recharge, but Mr. Godwin said we can do a lot more, and we need to do a lot more.
“We need to expand this concept and learn how to capture our flood flows when they’re there and distribute them safely across the landscape, where they can infiltrate into our groundwater basins,” he said. “That can be a highly engineered process through injection wells, but the easiest is infiltration galleries or concepts like Flood MAR where we take large flood waters and distribute them over agricultural or open lands and allow them to percolate naturally into the system.”
HOW THE STATE IS WORKING TO INCREASE GROUNDWATER RECHARGE
The Water Supply Strategy sets a target of 4 million acre-feet of new groundwater and surface storage by 2040 as the state works to shift the management strategy from reliance on a persistent snowpack that lasts well into the season to a strategy that capitalizes on the water when it is available and where it is available.
To achieve the goal of adding 4 million acre-feet of new groundwater and surface storage, California has implemented several actions. During the wet 2022-23 winter, the Governor issued executive orders to accelerate groundwater recharge on open and working lands by amending Water Code 1242.1. This modification allowed water to be diverted during locally determined imminent flood threats. By channeling excess water into irrigation ditches and spreading it across open lands, flood pressures were reduced, and surplus water was stored in the groundwater system. Additional executive orders suspended CEQA requirements for local groundwater recharge projects and introduced other streamlining measures.
The state is also investing significantly in groundwater management. The Department of Water Resources (DWR) has allocated over $500 million to Groundwater Sustainability Agencies (GSAs) for plan development and recharge projects. Further funding is coming through Proposition 4, the climate change bond, which supports groundwater initiatives, and the Multibenefit Land Repurposing Program to assist regions in retiring farmland to meet sustainability targets. Additionally, the State Water Board has established an expedited process for groundwater recharge permits, offering temporary and standard water rights to facilitate these critical efforts.
HOW MUCH HAS BEEN CAPTURED?
Water Code Section 1242.1 allows for capturing the flood flows when there is no water right, and the flows are well in excess of any claimed water rights.
In 2023, over 400,000 acre feet were diverted to 90,000 acres and into storage. Significant surplus water was moving through the State Water Project and Central Valley Project. However, in 2024, no water was diverted during flood conditions, and in 2025, only 500 acre-feet was captured. Mr. Godwin attributed the low numbers to folks being unprepared, so DWR has been working with GSAs to provide technical and regulatory guidance for using flood waters for groundwater recharge.
In 2025, the State Water Project captured an additional 16,000 acre-feet through the storm flex provisions included in the State Water Project’s 2024 federal and state Endangered Species Act permits, which allow for additional water supply diversion when certain ecological conditions are met during storms.
“However, had the Delta Conveyance Project been in place during Water Year 2025, we would have been able to move an additional 700,000 acre feet out of the Delta into storage and into our groundwater basins,” said Mr. Godwin. “Because we don’t have that piece of infrastructure, that’s the dichotomy between the Sacramento River and the San Joaquin River systems. The Sacramento was flooding and high flows and lots of water, but we couldn’t capture it because of the water quality and ecosystem rules around the pumping plant adjacent to the San Joaquin River. So it’s very important for added flexibility through improved conveyance structures like the Delta Conveyance Project. These are opportunities where we can capture more water when it’s available and where it’s available.”
Lastly, Mr. Godwin emphasized the critical need to address land subsidence in the Central Valley, as it compromises conveyance systems and reduces the capacity to move water effectively. He stressed the importance of establishing clear regulations for long-term groundwater banking to mitigate subsidence while also ensuring resilience against prolonged droughts.
AARON FUKUDA: Recharge – Above, Below, and Beyond
Aaron Fukuda is the general manager of the Tulare Irrigation District and interim general manager of the Mid-Kaweah Groundwater Sustainability (MKGSA) agency. In his District, SGMA compliance is all about recharge, he said.
The Tulare Irrigation District, established in 1889, serves approximately 65,000 irrigated acres. The District comprises roughly 200 small farms, averaging 300 acres each, with numerous dairies relocated from Southern California. The primary crops include walnuts, almonds, pistachios, corn, wheat, and alfalfa.
Three hundred miles of earthen canals deliver surface water across the District. These canals play a crucial role in the recharge system by allowing surface water to percolate into the groundwater. Additionally, the District manages around 1,300 acres of recharge basins, actively utilized during the winter months.
On average, the District’s surface water supply totals about 150,000 acre-feet annually, derived from pre-1914 water rights on the Kaweah River and 30,000 acre-feet from the Central Valley Project. Wet-year supplies include 141,000 acre-feet of Class 2 water; however, even in the best years, only about 50% of this Class 2 allocation has been delivered.
THE ROAD TO SGMA COMPLIANCE
The District’s first groundwater sustainability plan in 2020 focused on building projects first and then demand management second. “We’re going to lead with projects,” said Mr. Fukuda. “We’re going to build more of them, and then whatever we can’t fix with projects that small amount we hoped we would eliminate through demand management or allocation.”
That plan was submitted to DWR and ultimately rejected; however, even before the determination from DWR came down, they had already acknowledged the plan would not work.
So the plan now is demand management; the GSA is leading with allocations and cutbacks and then projects – meaning, if we add more projects, there’s less demand management needed. “This was not popular at all,” Mr. Fukuda said.
In 2022, the District introduced a groundwater allocation and cap designed to manage resources more effectively. Water users are divided into two categories: those with access to surface water and those relying exclusively on groundwater. The groundwater accounting system, available to growers online, tracks the native yield or the shared groundwater supply as well as the surface water recharged into the system that is available for future extraction. To enforce the cap, the penalties for exceeding allocations are strict. Growers who exceed their limit face a fine of $500 per acre-foot, the maximum permitted under SGMA, and any overage is deducted from their allocation for the following year.
“Our program is predicated on the assumption that you only get to take out what you put in,” he said. “If you’re not putting anything into the groundwater system, all you get is the native yield, which is a very small amount – about 10 inches per acre of groundwater.”
Initially, the system faced resistance, but in December 2022, when a series of atmospheric rivers arrived, farmers were encouraged to open their turnouts with the incentive that doing so would lead to an increase in their allocations.
“Within 24 hours, we had basically doubled our sinking capacity in the fields with a phone call and an email,” said Mr. Fukuda.
They filled up the entire canal system, all of the recharge basins, and flooded fields. “It was the highest diversion rate we’ve ever had in our record,” he said. “We diverted about 200,000 acre feet to the fields. Groundwater levels rebounded tremendously during that period, some as high as 30 to 40 feet.”
DEVELOPING THE RECHARGE GAME PLAN
The GSA has utilized Airborne Electromagnetic Surveys (AEM), a technology used to map subsurface characteristics, to gain a deeper understanding of the lithography of the subbasin using SkyTEM at the subbasin level and TowTEM at the field level.
The data collected serves multiple purposes, including confirming subsurface conditions, enhancing the efficiency of on-farm recharge programs, increasing the sinking capacity of existing recharge basins, providing valuable textural input for groundwater models, and assisting in selecting locations for new groundwater monitoring wells.
PLAN FOR THE FUTURE
Tulare Irrigation District’s plan for the future includes continuing to use existing recharge basins and develop multibenefit projects to aid disadvantaged communities and/or habitat restoration, continuing to develop and enhance the on-farm recharge, and implementing small-scale banking to replace groundwater in areas experiencing subsidence.
Going forward, partnerships will be key. “Our most exciting project is in partnership with the Water Blueprint and Southern California,” said Mr. Fukuda. “It is a large regional groundwater banking operation in the west area of our subbasin, where we have a huge holding capacity, and we’ll set up retired farm ground into large recovery systems where we can put the water in the ground and recover it. … We have supplies in the San Luis reservoir that we can’t get over to our east side, so we would trade that water to Southern California in dry years and bank the water on the west side. And we think it’s a fantastic opportunity for us to partner with other folks, including Southern California, on a large regional banking project.”
“None of this gets done without the support and the partnerships that we have. Largely the support comes from the growers and the landowners. They’re the ones that are doing this. I’m just the one telling the story. The partnerships with DWR, the State Board, PPIC, Sustainable Conservation, and others are leading the way in helping us understand what we’re doing, what we need to avoid, and what we need to pay attention to. This is a statewide effort, and I’m happy to be a part of it.”
Question: Why doesn’t the state limit what farmers can plant?
During the Q&A, the question was asked, given the tight water supplies, why doesn’t the state limit the amount of certain crops, like almonds, that farmers can plant? Here’s how the panelists answered.
Tim Godwin, Department of Water Resources, said: “The policies of the state and the laws we have dictate that land use decisions are made at the county level, and the counties have the authority to evaluate how they want to lay out land use practices. So, there is the pathway, but most haven’t. Most have allowed the agricultural communities to figure out what the best commodities are with the growing conditions and the water resources there.
Jeff Mount, Public Policy Institute of California, said, “We’ve spent a great deal of time looking at what the future of the San Joaquin River and South San Joaquin basin looks like, and I would be remiss if I did not channel my inner economist here, who says it’s the farmers who do the best job of working this out. Sometimes, they make mistakes; it’s a risk-based industry. When almonds were fetching such a tremendous return as the commodity prices were high, we probably over-planted those. But that happens in agriculture all the time, and it self-corrects.”
“But in this case, we now have this added burden of trying to come to balance with the use of water. And we have argued repeatedly that really smart choices here during how you retire some lands, and water markets, definitely. With an organized transition, you can really reduce the economic impact in the valley. And that’s why we keep saying that the people who work that out best of the farmers, but it must be at the county level. There’s got to be a tremendous amount of coordination at the county level to get that to work.”
Aaron Fukuda, Tulare Irrigation District, said, “We were the last state to implement a groundwater. So, prior to that, you could buy a piece of ground and put what you wanted on it. And you’re right. The county could have had some regulations on cropping, but we don’t operate that way.
“There were large companies that were coming in, and if you’re a large corporation, you have a big portfolio of investments. You’re buying ground for $1,000 an acre and getting a grant from the state to put in a drip system because that was the big deal – let’s efficiently create agriculture. … So corporate America came into California like you couldn’t imagine. They bought up that white area (undistricted or groundwater-dependent areas). It was cheap ground. They could get a grant for a drip system. They could put in an almond orchard; if they lost money for the first three years while the crops were coming up, they just wrote that off against other things. It’s just a write off at that point; then they get in the money. So the only people that will survive California agriculture is corporate farming.
“Our small growers, if you go to them right now, they’re done. They’re out of here. Our small growers are either consolidating or selling out to bigger corporations. So we have a concern. The opposite is giving some tools and flexibility. My goal in our subbasin is to give our growers as many tools in their toolbox as they can and let them go to work. Because if you can imagine, if you run an 80-acre plot of trees, that’s 1000s of individual biological units, you have to take care of. I’m not doing that. I can’t even do my vegetable garden. So, so long answer, sorry, but I’m passionate about it.”
