The San Joaquin Valley is in a time of great change. Decades of groundwater overuse have caused drinking water and irrigation wells to go dry, increased the amount of energy required to pump water, harmed ecosystems, and reduced the reserves available to cope with future droughts. Groundwater overdraft has also caused land to sink, damaging major regional infrastructure, including canals that deliver water across the state.
These problems spurred the enactment of the Sustainable Groundwater Management Act (SGMA), which requires local water users across California to bring groundwater use to sustainable levels by the early 2040s. With California’s largest groundwater deficit, the San Joaquin Valley is ground zero for implementing SGMA.
Although the region will reap many long-term benefits from ending overdraft, the transition to groundwater sustainability will be challenging and costly. The good news is that some approaches can greatly reduce the costs of bringing basins into balance.
The valley faces a groundwater deficit of nearly 2 million acre-feet per year (11% of net annual water use). To close the deficit, local agencies will have to augment their supplies, reduce their demands, or use some combination of these two approaches.
Our new report shows how a portfolio approach—with supply investments that farmers can afford and tools that increase flexibility for managing demand—offers a winning combination. The most promising supply options are to capture and store more local runoff, especially in groundwater basins, and to increase water imports by managing the system differently. On the demand side, increasing water trading—both within and across groundwater basins—can significantly mitigate the impacts of reducing water use, by allowing farmers to maintain the crops that generate the most revenue and jobs.
As the figure below shows, if farmers have no flexibility to trade water or adapt crop choices, ending overdraft without new supplies would require fallowing 780,000 acres—about 15% of the valley’s 5.2 million acres of irrigated cropland. It would also cause crop revenue losses of about $3.5 billion per year—roughly 17% of current crop revenues in the region.
figure - Flexibility Is Key to Managing Farm Water Demand
But if farmers can make flexible crop choices and trade ­water within local groundwater basins, fallowing would decline slightly, and crop revenue losses would fall by nearly half (to $2 billion per year). And with broader, surface water trading across the San Joaquin Valley, farmers in the south would buy some water from the north, where it is more abundant. This also would not change the amount of fallowed acreage by much, but it would further reduce the need to fallow the most profitable fruit, nut, and vegetable crops—lowering revenue losses by nearly two-thirds (to $1.3 billion per year).
Finally, a portfolio approach combining water trading and cost-effective supplies would reduce crop revenue losses by three-quarters (to $0.9 billion per year). The new supplies would also make a large dent in the need for land fallowing, which would fall by nearly one-third (to 535,000 acres).
Using a portfolio approach to achieve groundwater sustainability and avoid economic disruptions in the valley will require coordinated efforts among local, state, and federal agencies. The most pressing priorities are those related to expanding groundwater recharge and water trading, including:

  • Assessing infrastructure needs and modernizing water operations
  • Incentivizing recharge on farmlands
  • Clarifying how much water is available for recharge
  • Developing a healthy local trading culture
  • Facilitating state and federal approvals for trading and banking

Finally, to reap the most benefits from recharge, trading, and other tools, local entities will need to collaborate both within and across basins. Since the valley has more than 120 groundwater sustainability agencies for its 15 groundwater basins, overcoming institutional fragmentation will be key to success.
As originally published in the PPIC Water Blog by  Alvar Escriva-Bou, Ellen Hanak and Josue Medellin-Azuara on March 7, 2019
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