Land in California’s San Joaquin Valley has been sinking at record-breaking rates over the past two decades due to excessive groundwater pumping.
A new study, published in Communications Earth and Environment, reveals that this problem, called “subsidence,” is worsening water supply challenges and causing expensive damage to infrastructure.
How Fast Is the Land Sinking?
The study shows that between 2006 and 2022, land in the valley sank at an average rate of nearly one inch per year.
Some areas experienced even faster sinking. While subsidence in the valley has been known for years, the total amount of land sinking and the long-term impacts had not been fully measured before this research.
The lack of data between 2011 and 2015, when satellite radar coverage was limited, left gaps in understanding.
Researchers at Stanford University used a technique called InSAR, which uses radar signals from satellites to detect changes in ground elevation, combined with GPS data to fill in the missing information.
Why is this happening?
Subsidence occurs when too much groundwater is pumped from aquifers—underground layers of sand, gravel, and clay that hold water. Removing water from these aquifers causes the sediments to compact, permanently lowering the ground level in some cases. This not only causes the land to sink but also reduces the aquifers’ ability to store water in the future.
The San Joaquin Valley, one of the most agriculturally productive areas in the world, has a long history of groundwater pumping. From 1925 to 1970, aggressive pumping caused more than 4,000 square miles of land to sink by over a foot, with some areas dropping up to 30 feet. Efforts to reduce groundwater use in the 1970s temporarily slowed the problem, but droughts, reduced water deliveries, and increased pumping in the 2000s caused the subsidence to worsen again.
What Are the Consequences?
Subsidence is causing major problems:
- Damage to canals and aqueducts, like the Friant-Kern Canal and the California Aqueduct, has led to multimillion-dollar repair bills.
- Farmers are spending money to re-level their land for irrigation.
- Local wells and water systems are being damaged, making it harder for small communities to access water.
It may also worsen flooding, as subsidence alters the landscape and changes how water flows during storms.
Can it be fixed?
Researchers estimate that about 220 billion gallons of water need to be added to the region’s aquifers every year to prevent further sinking. This can be done through natural recharge or engineered solutions.
One promising method is flood-managed aquifer recharge (flood-MAR). This involves redirecting excess water from heavy rains and snowmelt to areas where it can soak into the ground and refill aquifers. However, this approach needs to focus on areas where subsidence is causing the most harm, such as locations near aqueducts or small communities relying on local wells.
“We need a big-picture approach to find sustainable solutions,” said Rosemary Knight, the study’s lead researcher. With careful water management, the hope is to stop the sinking and protect California’s vital water infrastructure.
Source: Stanford University.
