Central Valley is sinking

California's Central Valley is sinking at a record-breaking pace, new study shows

By Tessa McLean

Parts of California’s Central Valley have been sinking for years, but a new Stanford study quantifies just how much the ground has given way in the past two decades. 

In the San Joaquin Valley, the vast swath of land responsible for much of the state’s agricultural production, the study showed that the ground receded nearly 1 inch per year from 2006 to 2022. The new investigation fills in a gap in the data, allowing researchers to look at the full extent of the “subsidence” — the technical term for the ground sinking — in the area and study how to potentially solve the problem in the future. 

“I am optimistic that we can do something about subsidence,” Rosemary Knight, study author and professor of geophysics at Stanford, told the Stanford Report. “My group and others have been studying this problem for some time, and this study is a key piece in figuring out how to sustainably address it.” 

Knight told the Stanford Report that she believes they can mitigate the issue by restoring the groundwater through “flood-managed aquifer recharge,” a flooding technique used to refill aquifers using excess diverted precipitation and snowmelt. Based on the team’s research, there should be enough water on a yearly basis to prevent additional sinking. 

Sagging ground isn’t a new phenomenon in California. Groundwater pumping became a regular practice starting in the 1920s, causing dried-out pores and crevices under the land’s surface to collapse when emptied. In the 1970s, the state built new aqueducts that slowed down subsidence, until 2006 brought about a new phase of groundwater pumping after a series of droughts and other land use changes.

Knight and co-author author Matthew Lees filled a gap in the data formed from 2011 to 2015 using technology called interferometric synthetic aperture radar (InSAR) to measure elevation changes in the land, which then is beamed up to satellites that analyze the fluctuations. Previous reporting from the U.S. Geological Survey called the subsidence in the valley before 1999 “one of the single largest alterations of the land surface attributed to humankind.” 

Some areas of the more than 4,000 square miles affected sank as high as 30 feet and, without groundwater pumping regulations in place, aquifers collapsed and infrastructure buckled. Today, the issue can threaten the development of the state’s proposed high-speed rail system, exacerbate flood risks and result in the requirement of multimillion dollar repair projects.