New research from scientists at Stanford University shows that the San Joaquin Valley is sinking faster than ever due to excessive groundwater pumping.
Even though aquifers are plummeting and the ground is sinking, the situation is never static. Since the historic wet year of 2023, some localities have seen significant rebounds in groundwater levels, though not enough to permanently change the trajectory, experts warn.
Researchers brought together separate existing subsidence datasets from 2006 to 2022 to paint a more reliable picture of conditions in the valley.
“If you don’t accurately know what’s going on with the subsidence, then you won’t effectively be able to deal with it to fix the problem,” said Matthew Lees, lead author of the study.
One of the biggest challenges with the research was a lack of data from 2011 to 2015. To overcome that gap in data, they used subsidence measurements taken at GPS points throughout the valley during those years and then estimated subsidence based on the gathered data, said Lees.
The study showed that, on average, the valley has been sinking about an inch per year since 2006.
If nearly all available water each year was put into recharge, it would halt subsidence, said Lees. That is obviously not a realistic scenario, he added.
“You’ve got to be strategic with the recharge,” said Lees. “Strategic means focus on the areas where subsidence is causing the greatest harm, the greatest impact, and focus on getting your recharge water down to the deeper parts of the aquifer system where the subsidence is originating.”
Lees said farmers and groundwater sustainability agencies have already been doing incredible work prioritizing and expanding recharge.
The study didn’t cover 2023 as research concluded prior to the start of that historic year. The scientific process leading to publication is slow going, said Lees.
Some areas saw drastic changes after 2023.
Rosedale-Rio Bravo Water Storage District in Kern County saw aquifer levels skyrocket. In some areas it rose by 40 feet and up to 120 feet in others, according to Dan Bartel, engineer-manager of the district.
“Our subsidence in our area is generally elastic, meaning it goes down a little bit in a dry year and comes back a little bit when we recharge,” said Bartel.
Some water tables in the Rosedale area are still rising but most have flattened off, he said.
Over the past year, ground levels uplifted about 0.1 feet, putting the surface back to 2015 levels, said Bartel. Rosedale-Rio was able to recharge more than 362,000 acre feet of water in 2023.
Researchers are focusing on better understanding where water goes once it’s recharged, said Lees. Using airborne electromagnetic methods is an important part of that methodology, he added.
“I think that direction is being closely followed,” said Lees. “There’s some really promising work there to make a difference in this space.”
