This publication was developed with partial support from the US Department of Agriculture under OCE Cooperative Agreement number 58-011-17-004, PPIC does not take or support positions on any ballot measures or on any local, state, or federal legislation, nor does it endorse, support, or oppose any political parties or candidates for public office.
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The San Joaquin Valley—California’s largest agricultural region and an important contributor to the nation’s food supply—is in a time of great change. The valley produces more than half of the state’s agricultural output. Irrigated farming is the region’s main economic driver and predominant water user.
Stress on the valley’s water system is growing. Local water supplies are limited, particularly in the southern half of the region. To irrigate their crops, many farmers use water imported from Northern California through the Sacramento–San Joaquin Delta. But in many places farmers have also relied on groundwater overdraft—pumping groundwater in excess of the rate at which it is replenished.
Worsening droughts, increasing regulations to protect endangered native fishes, and growing demand for Delta imports in Southern California have compounded surface water scarcity. While overdraft has been a challenge for many decades, the pace of groundwater pumping has accelerated, especially during the 2012–16 drought.
Addressing long-term declines in groundwater reserves and adapting to worsening droughts are essential steps toward a more prosperous future. A chronic decline in groundwater levels is making drinking water and irrigation wells go dry, increasing the amount of energy required to pump water, harming ecosystems, and reducing reserves to cope with future droughts. It also causes land to sink, which damages major regional infrastructure, including canals that deliver water across the state.
These problems spurred the enactment in Fall 2014 of the Sustainable Groundwater Management Act (SGMA), which requires local water users to bring groundwater use to sustainable levels by the early 2040s. With the largest groundwater overdraft in the state, the valley is ground zero for implementing this law. SGMA will have a broad impact on valley agriculture in coming years— and will likely entail some permanent idling of farmland.
Balancing Water Supplies and Demands
To close the groundwater deficit, groundwater sustainability agencies (GSAs) in the valley’s overdrafted basins will have to augment their supplies, reduce their demands, or use some combination of these two approaches. A range of options are under consideration, but they are not likely to be equally effective or practical. Our analysis highlights the most promising approaches.
Developing new supplies is limited by a variety of factors, including cost. We find that most valley farmers will not be willing to pay more than $300–$500/acre-feet for new long-term water supplies. The best options:
Capture more local runoff.
Capturing and storing additional water from big storms has the most potential. In particular, recharging groundwater could deliver significant new supplies at a cost farmers can afford. Coordinating management of surface and groundwater storage can help boost overall water storage capacity. Although building the proposed Temperance Flat Reservoir could also help, it appears to cost more than what most farmers would be willing to pay.
Manage the system differently to increase water imports.
Big investments to increase imports have limited potential to help valley agriculture. Most water from California WaterFix and proposed surface storage expansion would go to the Bay Area and Southern California. These options are also relatively expensive for valley farmers. Without federal or state support, expanding Shasta Reservoir—which would principally benefit valley farmers—is also likely to cost too much. Instead of relying on such projects, engaging in more coordinated management of the entire Central Valley network of surface and groundwater reservoirs appears to be a better option. This strategy would significantly increase capacity, yielding nearly half as much new water as building a new reservoir at Temperance Flat, at a much lower cost.
Use urban conservation to support population growth.
New state laws require cities and suburbs to reduce per capita water use. These savings can support population growth— thereby reducing competition with valley agriculture for scarce water supplies. However, farmers should not expect significant additional urban water savings to be available for valley agriculture.
New water supplies available to valley agriculture can address only about one-quarter of the region’s long-term groundwater imbalance. At 1.8 million acre-feet per year, that deficit is substantial. This means that reductions in agricultural water use will have to cover most of the groundwater deficit. The best options:
Reduce agricultural water use.
Switching to crops that use less water and idling cropland are the best ways to reduce water use. In contrast, greater irrigation efficiency (e.g., switching from flood to drip irrigation) generally reduces how much water is applied to the land, but not overall water use. This is because most irrigation water not consumed by plants returns to rivers or recharges aquifers where it can be used again. Investments in irrigation efficiency will remain worthwhile for other reasons—including to protect water quality.
Expand water trading.
By giving farmers more flexibility, water trading can reduce the costs of transitioning to sustainable groundwater use. If farmers have no flexibility to trade water or adapt crop choices, ending overdraft without new supplies requires fallowing 780,000 acres and causes crop revenue losses of about $3.5 billion per year.
If broader, valley-wide surface water trading is an option, farmers in the south would buy some water from the north, where it is more abundant. This would further reduce the need to fallow the most profitable fruit, nut, and vegetable crops. The net result would be much lower crop revenue losses. Overall, the drop in regional GDP and employment would be about a third lower with valley-wide surface water trading than without it.
Land use on the valley floor (2014):
Irrigated farmland: > 5 million acres
Cities and suburbs: > 500,000 acres
Open space and rangelands: > 3 million acres
Managed wetlands: 130,000 acres
Net water use (1988–2017 average):
Total: 16.7 million acre-feet (maf), of which:
Irrigated cropland: 87%
Rangelands and wetlands: 10%
Net overdraft (1988–2017 average): 1.8 maf
Basins subject to SGMA: 15
Groundwater sustainability agencies: > 120