New research published Thursday offers a crop-by-crop, county-by-county picture of how California is drawing down its underground water, KQED reported.
Scientists writing in Water Resources Research found that half of the groundwater depletion between 2008 and 2020 went to three crops: almonds, grapes and walnuts. More than a quarter of all nonrenewable groundwater pumping went to almonds alone. The vast majority of groundwater used for specialty crops such as fruits, nuts, seeds and vegetables — 70% — is water that will not be refilled, the study said.
Lead author Jackie Hanley, a Ph.D. student at the University of Illinois at Urbana-Champaign, compared a sustainable aquifer to a bank account that can be drawn down in lean times and replenished in wet ones. The paper, she told KQED, portrays funds being overspent on almonds, walnuts, pistachios, lettuce, broccoli, peppers, pomegranates and other crops. "We are just spending and spending," Hanley said. "While that's good in the short term to bridge a gap, especially as we adapt to climate change, eventually our habits are going to have to change." Either people change on their own timeline, she said, or the aquifer runs out and makes the decision for them. Her co-author is professor Megan Konar.
A national food hub, and a shrinking account
California produces about 50% of the nation's fruits, vegetables and tree nuts, and about 75% of all the fruits and nuts grown in the country, KQED noted. The Central Valley, particularly Tulare, Fresno, Kings and Kern counties, is a national hotspot for unsustainable groundwater use. Nearly all of the groundwater pumping in the southern Central Valley is estimated to be unsustainable, the researchers said.
The authors did not recommend that consumers simply switch from fresh produce and nuts to less thirsty crops. Hanley said solutions are better left to policymakers than to individual shopping choices. "This can be a hot-button issue, and it can be easy to point fingers," she said. "But what this study really points to is that nothing exists in a vacuum." The researchers crossed satellite-based maps with data from the U.S. Department of Agriculture and the U.S. Geological Survey.
Central Valley growers have been pushed to drill deeper wells, KQED reported, and land has sunk by as much as 11 feet in farming towns because of pumping, permanently reducing storage capacity. For the past 50 years, according to USGS data cited in the story, much more water has been pumped out than has filtered back in. In the short term, groundwater keeps nut trees alive and agricultural jobs in place. In the long term, Hanley said, "We might see California cease to be this specialty [crops] hub eventually."
The 2012-2016 drought helped spur the 2014 Sustainable Groundwater Management Act, signed by then-Gov. Jerry Brown. It aims to make withdrawals sustainable, but the regulations are not intended to be fully enforced until 2040. Paul Ullrich, a UC Davis climate-modeling professor who was not involved in the research, told KQED the law has at least forced local agencies to assess how much water they have and whether current practices are sustainable. He called the new paper a helpful crop-by-crop summary.