Modeled effects of rice field idling on groundwater systems in the Sacramento Valley, CA

Rice farmers occupy a potentially important intersection between economics and hydrology in Northern California. While drought makes water an increasingly precious commodity across California, the monetary worth of water is not uniform across different localities. As a result, circumstances have given many Sacramento Valley rice farmers an unconventional economic option: sell their water to users elsewhere, in lieu of using it themselves. While local and state regulations are limiting, or potentially will limit the option of substituting the sold water with pumped groundwater, the effects of idling fields instead may still be of consequence to local aquifers. Because the sold water is surface water that would normally help recharge local aquifers when applied to a field, it is reasonable to suspect that transferring that water elsewhere would adversely affect local aquifers since that recharge would also cease. To better understand any spatial and temporal effects of this practice, this study performed numerical experiments using the United States Geological Survey’s Central Valley Hydrologic Model. CVHM is capable of modeling the entire Central Valley, which encompasses the Sacramento Valley, and of representing rice field idling on a large scale. These experiments were executed using historical data to contrast recently typical amounts of rice field idling with varying degrees of hypothetical, increased idling. In doing so, this study aims to characterize the nature and potential magnitude of idling rice fields on groundwater storage and hydraulic heads in the Sacramento Valley. The results of these numerical experiments were compared the results of an unaltered baseline model scenario, and were quantified relative to this baseline. While the results of such experimentation and analysis were likely more “proof of concept” than “precise prediction,” they may provide a basis for future study, and perhaps policy decisions.