SGMA – A look into California Groundwater Supply
SGMA and the new rules for groundwater.
Last Updated July 16, 2026
For most of California’s history, groundwater was the one water supply nobody measured and nobody capped. The Sustainable Groundwater Management Act changed that. It is the law now bringing the state’s most heavily pumped basins back into balance, and it reshapes the cost, reliability, and footprint of what California grows. Almonds sit squarely in its path.
Part of California Water 101
What SGMA Is
One backstop, closed.
California farms on two water supplies. Surface water arrives through rivers, reservoirs, and canals, and it rises and falls with the weather. Groundwater sits in aquifers beneath the valley floor, and for generations it was the reserve growers leaned on whenever surface deliveries were cut.
The trouble was that no one was counting. Across most of the state, a landowner could pump as much as a well would produce, with no permit and no ceiling. In dry decades that caught up with basins from the Sacramento Valley in the north, down through the San Joaquin Valley, out along the central coast, and into Southern California. Wells ran dry, water quality slipped, and in places the ground itself sank by feet.
SGMA, signed in 2014, is California’s first statewide law to manage groundwater, and it makes California one of the last western states to do so. It reaches every high and medium priority basin in the state, 94 in all, and together they hold the great majority of the groundwater California pumps. It does not hand control to Sacramento. It puts the job on local agencies, on the principle that the people closest to a basin are best placed to fix it. SGMA sets the destination and the deadline. How each basin gets there is a local decision.
The Bar It Sets
Six ways a basin breaks.
SGMA does not set one number for every basin. It defines sustainability by what a basin has to avoid. Pumping is out of balance when it causes any of six “undesirable results.” Local plans exist to keep all six from crossing into significant and lasting harm.
Each of the six is described below.
-
01
Falling water levels
A steadily dropping water table, so wells must reach deeper and pumping costs climb.
- 02
Lost storage
Aquifers emptied faster than they refill lose capacity that can take decades to rebuild.
- 03
Land subsidence
As water is drawn out, the ground compacts and sinks, buckling canals, roads, and wells.
- 04
Degraded water quality
Overpumping can pull in salts and contaminants, fouling water that communities and farms rely on.
- 05
Seawater intrusion
Along the coast, heavy pumping lets ocean water move inland into freshwater aquifers.
- 06
Surface water depletion
Where aquifers and rivers are connected, pumping can draw down streams and the habitat they support.
Fig.01 · Land subsidence near Mendota, San Joaquin Valley.
Signs on the pole mark the ground surface in 1925, 1955, and 1977. The land fell close to 30 feet over that span as groundwater was pumped from the aquifer. Dr. Joseph Poland, who documented the subsidence, stands at the 1977 level. Source: U.S. Geological Survey.
When wells pump from the deep aquifer below the Corcoran Clay, the pressure that holds the clay open drops and the clay compacts, so the ground above settles. Unlike an ordinary drop in the water table, this loss of elevation and storage is permanent. Source: U.S. Geological Survey data; infographic by the Bay Area News Group.
How It Works
Local agencies, a plan, and a clock.
SGMA runs on three moving parts. Local agencies organize, they write a plan, and then a twenty-year clock starts. The state sets the guardrails and steps in only if a basin cannot deliver.
Agencies form. In the higher-priority basins, local water districts, counties, and cities had to organize into Groundwater Sustainability Agencies, or GSAs. A GSA can be a single district or a coalition that shares a basin.
Plans get written. Each GSA had to file a Groundwater Sustainability Plan, or GSP. The plan measures how much water the basin holds, how much is leaving, and exactly how the agency will close the gap, by adding supply, pumping less, or both.
The clock runs. Once a plan is in place, the basin has twenty years to reach balance.
The state backstops. The Department of Water Resources reviews each plan and can send it back if it falls short. If a basin cannot produce a workable plan or stalls on carrying it out, the State Water Resources Control Board can place it on probation and regulate pumping directly. That is the outcome local agencies work to avoid.
- 2014
SGMA becomes law
A three-bill package caps groundwater pumping for the first time in state history.
- 2017
Local agencies form
GSAs organize across the high and medium priority basins to take on management.
- 2020
Plans come due
The critically overdrafted basins, most of them in the San Joaquin Valley, file their first plans. The other high and medium priority basins follow in 2022.
- 2024
The state steps in
For the first time, the State Water Board places a basin, the Tulare Lake subbasin, on probation after its plan was found inadequate.
- 2040
Balance required
The 21 critically overdrafted basins must reach sustainability by 2040. The rest of the covered basins have until 2042.
Where things stand in 2026: most covered basins now have plans the state has accepted, several San Joaquin Valley basins have been sent back for revisions, and a handful of the most stressed basins are under State Water Board review or on probation. The planning phase is largely finished. Implementation, including the first real pumping limits, has begun.
The Local Toolkit
How basins actually cut back.
Every basin reaches balance with its own mix of tools. For growers, these are the parts of SGMA that show up in day-to-day operations.
Pumping allocations
Many GSAs give each acre a yearly groundwater budget. Pump within it and there is no charge. Go over and the cost rises steeply.
Metering and reporting
Wells are increasingly metered and growers report what they pump. Probationary basins require flow meters and regular reports to the state.
Pumping fees
Fees tied to volume fund the basin’s work, from buying surface water to recharging aquifers, and put a real price on every acre-foot.
Groundwater trading
Where allocations exist, growers can buy and sell them. Water moves toward higher-value crops while those who pump less are paid for it.
Recharge
In wet years, agencies spread floodwater on fields and basins to refill aquifers, sometimes crediting growers toward future pumping.
Land repurposing
Where the math does not work, land shifts out of irrigated production, to solar, habitat, low-water crops, or fallow ground.
In a wet year, growers and districts flood a basin so water soaks down and refills the aquifer, banking supply for the dry years. Here the recharge basin sits beside dormant almond orchards. Source: Central California Irrigation District.
For Growers
Less water, and a smaller footprint.
SGMA reaches farmers across California, not one corner of it. Wherever you farm over one of the state’s 94 covered basins, the same rule applies. The basin has to reach balance, and pumping has to fit inside it. What changes from place to place is how sharp the cut is and which problem shows up first.
Sacramento Valley
More surface water and milder overdraft than the south, but pumping is still capped, with dry wells and sinking land to watch in the drier subbasins.
San Joaquin Valley
The largest imbalance in the state and the deepest cuts. Most of the critically overdrafted basins sit here, which is why the biggest acreage numbers come from this region.
Central Coast
Salinas, Pajaro, Cuyama, and Paso Robles all pump more than returns, and on the coast that pulls seawater inland. Several of these basins are critically overdrafted.
Southern California
Many basins here have been actively managed and metered for decades. SGMA brings the remaining high and medium priority basins under the same standard.
Sinking runs deepest in two areas, near Chowchilla and El Nido in the north and around Corcoran, Tulare, and Pixley in the south. This is the same region facing the sharpest pumping cuts under SGMA. Shading shows total subsidence in millimeters. Source: U.S. Geological Survey.
The sharpest adjustment is in the San Joaquin Valley
This is where SGMA bites hardest and where the numbers are clearest. The valley has been pumping far more groundwater than nature returns, and that has to stop. Independent estimates from the Public Policy Institute of California put the shortfall at close to twenty percent of the valley’s farm water supply by 2040, once SGMA, a warming climate, and river protections are all counted.
Water that is not there cannot irrigate a crop. Even in an optimistic case, where growers and agencies add new supply and recharge aggressively, at least 500,000 acres of valley farmland, roughly one acre in ten, is expected to leave full irrigated production by 2040. Without new water, that number could approach 900,000 acres.
As the land around this well sank, the rigid casing stayed in place and was left projecting above the ground. The exposed lower section shows roughly how far the surface has dropped. Photographed in the western San Joaquin Valley. Source: Central California Irrigation District.
Why almonds feel it first
Almonds grow across the Central Valley, from Sacramento Valley orchards in the north to the heart of the San Joaquin, so much of the crop sits over covered basins. And a tree cannot be idled the way a field can. A row of tomatoes can be fallowed for a season and replanted later, but trees need water every year or they die, so their demand is fixed. In one modeling scenario without water trading, perennial crops like almonds make up about two-thirds of the fallowed acres, and orchard removal crews have reported they cannot keep up with demand in the hardest-hit basins.
It is not felt evenly
None of this is the end of California agriculture, and no two operations face it the same way. A grower’s exposure depends on the basin, the depth to water, and how much surface supply and storage back up the well. The operations best positioned are the ones managing water deliberately: holding senior surface rights, banking water in wet years, trading within their basin, and matching new plantings to a realistic long-term supply.
Annual land subsidence measured near Sack Dam, in the Red Top area of the western San Joaquin Valley. After peaking at about half a foot in 2016, the rate fell to roughly two inches a year once growers cut deep-aquifer pumping and recharged the shallow aquifer with imported and flood water. Source: San Joaquin River Exchange Contractors Water Authority, from U.S. Bureau of Reclamation monitoring.
Groundwater is the part of California’s water story that used to stay out of sight. SGMA is bringing it into the open, one basin at a time. We will keep tracking it, and keep buyers and growers current as the rules take hold.