Reports on two science websites say persistent drought in California may have pushed parts of the Sacramento Valley aquifer into permanent collapse, imperiling the Central Valley’s ability to raise crops. And a quarter of the U.S. food supply is grown in California’s Central Valley.

“Pumping water out of aquifers lowers underground water pressure, which can make the land surface sink in a process called land subsidence,” explains an article in Phys.org. “Moderate sinking can be reversible when water returns because of the elasticity of underground pore spaces. However, intensive pumping can permanently and inelastically compress the sediments that hold water, resulting in a permanent reduction in water storage space.”

Because of the intensity and duration of water pumped out of the Sacramento Valley aquifer in recent years – especially during the area’s extreme drought earlier this decade – that underground storage space is collapsing.

“Satellite observations of land surface deformation reveal that large areas of the Sacramento Valley abruptly transitioned from reversible to irreversible compaction over the 2020–2022 California drought — a transition not anticipated from the groundwater monitoring network alone,” says a July 27 report in Proceedings of the National Academy of Sciences (PNAS), the peer-reviewed journal of the National Academy of Sciences, which was the impetus for the Phys.org article.

“Removing water stored in the pores of an aquifer system stresses its solid matrix since pressurized water helps support the weight of overlying materials,” the PNAS article explains.

“The Central Valley [of which the Sacramento Valley is a key part] has a century-long history of groundwater exploitation to sustain its intensive agriculture economy, which produces roughly a quarter of the United States food supply—primarily from water-intensive crops such as rice, fruits and nuts,” says PNAS. “This dependence is evidenced by the thousands of groundwater wells distributed across the region.”

Phys.org adds, “The [PNAS] study provides evidence that an aquifer can pass a damaging threshold before conventional well records give a clear warning, but satellite data may be able to detect inelastic changes sooner. Incorporating these data can help monitor groundwater stress in water-scarce regions worldwide where ground-based observations are sparse.”

But the PNAS report concludes, "While this compaction will never recover, the recent surge in precipitation in California brings hope that the aquifer system has or will soon transition back to a primarily poroelastic regime in response to decreased groundwater demand and increased recharge."

Maps showing vulnerable areas may be used to target artificial recharge projects and reduce extraction in these zones, limiting inelastic processes. Ultimately, detecting and preventing further permanent compaction can protect roads, canals, levees, wells and flood-prone communities in the region.