The Sacramento Valley Aquifer System: Irreversible Land Subsidence Via Aquifer Compaction Deformation Due to Overuse and Drought, According to Study

      California and much of the U.S. West have been under a drought for many years. The years 2020-2022 were the worst drought years. During those two years, as new research shows, the Sacramento Valley aquifer system was compacted and deformed due to land subsidence. The study measured ground deformation and groundwater levels during the period 2016-2022. Along with the drought, continued high groundwater withdrawals contributed to the subsidence. When groundwater is extracted, the pressure in the aquifer drops, making land subsidence more likely. While some land subsidence is reversible, or elastic, the study confirms that in this case, the subsidence is irreversible, or inelastic. 

     The Sacramento Valley, along with the San Joaquin Valley to the south make up California’s Central Valley, which is responsible for about 25% of U.S. food production.

     The study concludes that the Sacramento Valley aquifer system’s capacity has been permanently reduced as the land subsidence was accompanied by compaction deformation of the aquifer.

"All available measurements suggest that the accelerated subsidence starting in 2021 primarily results from inelastic compaction due to groundwater extraction," the researchers write in their paper.

"On average, the ground surface does not rebound to its pre-2021 state even as groundwater levels recover with seasonal recharge at the end of 2021, indicative of irreversible deformation."

     The result is a permanent loss of storage capacity in the aquifer. Satellites equipped with navigation systems and radar instruments measured ground deformation down to the millimeter level. These are known as Interferometric synthetic-aperture radar, or InSAR. During the period 2016-2020, the data showed that ground subsidence was elastic and returned to its previous level after sufficient recharge. The subsidence during those years was in the range of about 2 centimeters per year, but during 2020-2022, that increased to as much as 50 centimeters per year, 25 times as much. The paper's significance and abstract are shown below, followed by the acceleration in subsidence, a map of the inSAR and groundwater data stations, and historical groundwater level changes.

     The researchers also noted that the methods they used could be used worldwide to monitor groundwater withdrawal-induced land subsidence.

"By imaging this sharp transition at the regional scale, our analysis demonstrates the potential of space-based monitoring for early detection of groundwater overdraft and the resulting loss of aquifer storage capacity worldwide," write the researchers.

     Science Alert explains:

“They estimate that the loss of water storage space per year jumped up to 0.2 cubic kilometers (about 7 billion cubic feet) from 2021, around a five-fold increase compared to the previous years.”

“That's the equivalent of around 30 percent of the annual water consumption of Los Angeles being lost in terms of capacity: a shrunken aquifer that's not going to be able to store as much water going forward.”

     Importantly, they note that analyzing the network of 2500 groundwater wells did not yet reveal the aquifer changes that the satellite data did, emphasizing the importance of satellite-based land subsidence measurements.

"Real-time monitoring of surface displacements through satellite geodesy, which provide an integrated measure of internal deformation over the entire sedimentary column, could have enabled early detection of this sharp transition and potentially reduced storage loss through timely remedial actions," write the researchers.

"Developing such capability is especially critical in regions where in situ monitoring is unviable but groundwater resources increasingly vital."

     According to the paper, there may have been a shift in the aquifer, which, like many aquifers, has lots of heterogeneity, from withdrawal mainly from coarse-grained, highly permeable rocks to withdrawal from the finer-grained portions of the aquifer.

“…the groundwater dataset is likely skewed toward pressure variations occurring in the coarser-grained, high-permeability aquifer units and the outer edges of fine-grained formations. The in-phase poroelastic response during this period thus suggests that deformation predominantly occurs within these units. In this context, the abrupt acceleration of subsidence in 2021 may indicate a transition from water being primarily drawn from the coarse-grained layers and the edges of adjacent units to significant extraction from the deeper portions of fine-grained units due to higher vertical head gradients associated with increased extraction and decreased recharge during drought periods.”

     The paper’s conclusions are given below and stress the need for more conservative groundwater management strategies in the future.

References:

 

California's drought has now caused irreversible damage to a crucial aquifer. David Nield. Science Alert. August 4, 2026. California's drought has now caused irreversible damage to a crucial aquifer

Central Valley (California). Wikipedia. Central Valley (California) - Wikipedia

Abrupt transition to irreversible damage in the overdrafted Sacramento Valley aquifer system. Stacy Larochelle, Kristel Chanard, Manon Dalaison, Jérôme Fortin, Romain Jolivet, Laurent Longuevergne, Luce Fleitout, Donald F. Argus, Louis-Marie Gauer, and Jean-Philippe Avouac. PNAS. Vol. 123. No. 31. July 27, 2026. Abrupt transition to irreversible damage in the overdrafted Sacramento Valley aquifer system | PNAS