The influence of the recent California drought on water table levels in the Sacramento Valley
University of California, Davis
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Rice (Oryza sativa) covers more area worldwide than any other crop and irrigated rice accounts for over 75% of all rice production. Rice is unique from other agronomic crops in that it is typically cultivated under flooded conditions, which may allow for both groundwater withdrawal for irrigation and groundwater recharge from deep percolation. Despite the importance of irrigation to rice production and the fact that many important rice growing areas rely on groundwater for irrigation, the relationship between groundwater and rice systems is poorly characterized. Rice production in California, which accounts for approximately 25% of all U.S. production, typically relies on surface water for irrigation. While the water table is usually at or near the surface throughout much of California’s principal rice growing region, this area experienced declining groundwater levels during the recent drought along with the rest of the state. Anecdotal evidence has revealed that rice field water budgets changed significantly during the drought, with increased water input requirements per land area, likely due to dropping groundwater levels (and thus more deep percolation) and less rice acreage under flooded cultivation (and thus more lateral seepage). Here we characterize the changes in groundwater levels in the Sacramento Valley (the state’s principal rice growing region) during the drought. Our subsequent research will analyze the relationship between groundwater levels during the drought and landscape-level water management associated with rice cultivation, including water inputs to rice fields and the land area flooded for rice cultivation or winter fallow. The goal of this work is to understand the reciprocal interaction between groundwater levels and water input requirements to rice fields, under both normal and drought conditions, in order to inform policy and management decisions associated with California rice production.