The mountain snowpack provides as much as a third of California's water supply by accumulating snow during our wet winters and releasing it slowly when we need it during our dry springs and summers. Warmer temperatures will cause what snow we do get to melt faster and earlier, making it more difficult to store and use. …Climate change is also expected to result in more variable weather patterns throughout California. More variability can lead to longer and more severe droughts.

-   California Department of Water Resources

 If you want to save water for dry years, it’s groundwater.

-   Dr. Jay Lund, director of the UC Davis Center for Watershed Sciences

 In California, average water use is roughly 50% environmental, 40% agricultural and 10% urban, although the percentage of water use by sector varies dramatically across regions and between wet and dry years.

-  Jeffrey Mount and Ellen Hanak, Water Use in California

Improving groundwater management will go a long way to counter the effects of climate changes on agriculture in California, as well as other regions threatened by periodic severe drought. Some methods currently being used:

Percolation ponds (or basins):  large open water ponds  that store rainwater with the main aim of infiltrating the water to aquifers. They may be dry between rainy seasons.

Artificial recharge (AR): increase the natural replenishment or percolation of surface waters into the groundwater aquifers

Aquifer storage and recovery (ASR): re-injection of potable water back into an aquifer for to store water for later recovery and use

Intentional Flooding: flooding agricultural fields with winter rainwater so the water will percolate down to the aquifer.

AR and ASR use injection wells in areas where surface infiltration is impractical. Federal and state agencies regulate injection wells to minimize intrusion of toxic substances and salt water into freshwater aquifers. Although the regulatory management is an ongoing challenge, the rules and technology keep evolving, and injections wells are increasingly popular: the number of wells in the US has more than quadrupled since 1999. 

Intentional flooding is being used to capture and store water when crops are dormant – providing a kind of water savings account to be tapped for the long dry season in California and other western states. Research is ongoing but so far results are promising. Scientists have tested the flooding treatment on grapes, pistachio and alfalfa and found it did increase groundwater levels while leaving the crops unharmed under certain conditions. Researchers continue to look into potential effects on soil and crop health and to identify methods and conditions for optimal benefit.

Intentional flooding could also be used to absorb premature or excessive snowpack melt, minimize unintentional flooding and make use of river water that otherwise would have flowed out to the ocean. There is hope yet.