Pumping extra groundwater has gotten many California farmers through this drought, and if managed well, it can help the state weather future dry periods. Groundwater is our most important drought reserve, but overuse is a serious problem in some regions. We talked to Thomas Harter—a groundwater expert at UC Davis and a member of the PPIC Water Policy Center’s research network—about managing groundwater for the long term.
PPIC: What are some of the biggest challenges for California’s groundwater management?
Thomas Harter: Farmers are facing a lot of change. They have to address new laws on groundwater use and water quality. The agricultural community uses by far the most groundwater but has never been asked to actively manage and protect it. It’s a fundamentally new world, and it will take time for the industry to adjust.
The first step for farmers is to understand their groundwater resources. They’ll need to learn what drives their basin’s "water budget.” The state’s new groundwater law requires locals to form groundwater sustainability agencies and develop sustainability plans, and it will be important for farmers and rural communities to actively engage in that process. Locals have a lot of information and ideas that regulators in Sacramento may never come up with, so working on this issue together is key.
In areas with significant overuse, the first challenge will be to increase local recharge of groundwater. To the degree that regions can’t balance their groundwater budgets through recharge or by using more surface water, the toughest challenge will be to reduce groundwater use while minimizing the economic effects.
In Northern California, the most challenging piece is understanding how pumping affects groundwater flowing to rivers and streams. That’s a challenge for state and local agencies, consultants and scientists alike.
PPIC: What is the link between improving groundwater quality and quantity?
TH: Farmlands make up the largest landscape overlying our groundwater basins. Finding creative ways to use that landscape to put clean water underground—while also reducing groundwater pollution—are what we should focus on.
Farmers hold the key to maintaining water quality through their management practices. Excess fertilizers and pesticides can leach into groundwater. Pollution can be reduced through practices such as being very water efficient with crops that require lots of chemicals or, alternatively, by replacing fertilizer-hungry crops with crops that fix their own nitrogen or use little.
PPIC: What are some approaches to help us get to groundwater sustainability?
TH: Setting back levees allows some of the floodplain to act as a recharge area. Levee setbacks on the Cosumnes River raised the water table in just one storm last winter. Another option is to recharge groundwater during times when there is excess runoff. In parts of the Central Valley we’re looking at what crops can take flooding to increase recharge. Vineyards and alfalfa are promising candidates because they use very little fertilizer and pesticides. We’re also considering setting aside dedicated recharge basins. For example, farmers might be paid to fallow land short-term to allow groundwater recharge. We’re just beginning to find out how some of these solutions will work, what changes to infrastructure we’ll need to implement them, which are economically and agronomically feasible, and under what conditions they can be done.
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