By Kurtis Alexander
March 13, 2024
Climate change is driving up the thirst of crops significantly in California’s San Joaquin Valley, new research shows, adding to the critical water challenges faced by one of the world’s leading agricultural regions.
The total water demand of orchards, vineyards and row crops in the area is up 4.4% over the past decade compared with the prior 30 years because of hotter, drier conditions,and it’s likely to continue growing, according to a federally funded study published this week. In 2021, the water demand of crops was up an astonishing 12.3%, the study shows.
While the warming atmosphere has long been known to dry out plants and soil, the new research identifies the impact specific to the San Joaquin Valley. The resulting estimates of increased crop water demand come on top of the region’s well documented decrease in water supply, which is the result of less snow in the mountains and deeper droughts, also largely the product of the warming climate.
“We know that there’s been a water (supply) issue,” said Joshua H. Viers, professor at the School of Engineering at UC Merced and co-author of the new study. “This is the other side of the issue where we’re thinking about the additional water required by the agricultural system.”
The authors of the study describe the increased water demand of crops as an “invisible water surcharge” that’s forcing farmers in the San Joaquin Valley to lean more heavily on overdrafted groundwater supplies and limited imports from mountain reservoirs. They say it’s putting stress on the sustainability of the global fruit and nut supply and shouldn’t be ignored.
“This increased water demand needs to go into the balance sheet of the water accounting folks,” said Josué Medellín-Azuara, also a professor at UC Merced’s School of Engineering and co-author of the study.
Put in real terms, the crops in the region demanded about 582,000 more acre-feet of water annually between 2012 and 2023 than they did in the previous three decades, the authors say. This yearly increase is close to twice the amount of water that San Francisco’s Hetch Hetchy Reservoir in Yosemite National Park can hold.
Because rates of evapotranspiration, or water loss, have risen so significantly with the warming climate, the high water demand of crops remains even in very wet conditions, including the record-setting 2023 water year, according to the study.
“We’ve seen a lot of these years that have not been dry from a precipitation standpoint but they have had high water evaporative demand,” said John Abatzoglou, a professor of climatology at UC Merced and co-author of the study.
The research was published Wednesday in the scientific journal PLOS Water. Financial support came from the U.S. Department of Agriculture, National Institute of Food and Agriculture and the Agriculture and Food Research Initiative.
The authors arrived at their conclusions by using climate data and crop coefficients, which help model evapotranspiration, to estimate crop water demand for major crops over 40 years. Their approach isolates the climate change effects from other changes over the time period, such as how farmland is managed and what crops are grown.
The San Joaquin Valley, which stretches from just south of Sacramento to the Bakersfield area, is home to seven of the state’s top 10 agricultural counties. It accounts for most of California’s more than $50 billion of annual crop production.
The region provides at least a third of the nation’s fruits and nuts. Its top crops are almonds, pistachios, wine grapes, citrus and cotton.
Cannon Michael, president and CEO of Bowles Farming Co., which grows a range of crops near Los Banos in Merced County, said the increasing water demand of crops has been largely intuitive within the farming community.
The past decade has seen two multiyear droughts as well as record-high temperatures.
Like other growers, Michael has addressed the elevated crop water demand by saving water in other places when he can, such as using more drip irrigation. He’s also planting crops that use less water, such as carrots, garlic and onions.
Some growers have eliminated low-value crops like alfalfa altogether, to redirect water to more lucrative investments.
“We just kind of shifted our thinking and maximized the value of every single acre,” Michael said.
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