Improved understanding of the climatic and anthropogenic drivers of groundwater depletion and recovery in California’s Central Valley
The role of climatic and anthropogenic drivers in groundwater storage depletion and recovery in California’s Central Valley has been investigated. Specifically, the dissertation addresses three research questions: (1) How does climate change impact the groundwater storage? (2) Can managed aquifer recharge (MAR) mitigate groundwater overdraft? (3) How much of the drought-caused groundwater overdraft in Central Valley has recovered during the post-drought years and what is the role of climate and water management in the fast versus slow post-drought overdraft recovery? In the first part of the dissertation, integrated hydrologic models have been simulated to predict future groundwater storage changes under multiple climate change scenarios and to evaluate the relative contribution of crop water use and surface water inflow to Central Valley regions. It is shown that climate change will accelerate groundwater depletion in the future and an increase in future crop water use will be the dominant cause of future groundwater decline without mitigation measure. In the second part, the impact of large-scale MAR implementation on groundwater overdraft recovery, flood peak, and low flow have been investigated via numerical experiments. It is shown that MAR has limited capacity to recovery historical groundwater overdraft due to lack of surface water availability in the southern Central Valley (i.e., San Joaquin and Tulare regions). Delivering excess surface water from the delta to the Tulare and San Joaquin region can significantly solve the groundwater overdraft problem. Moreover, MAR can reduce flood peaks, and increase dry season flow. Finally, an ensemble of groundwater storage change estimates has been made using multiple methods and numerical experiments conducted to understand the role of climate and water management to recover drought-caused groundwater overdraft during post-drought years. The result shows that the Central Valley aquifer is not resilient to drought under existing conditions, and it is very challenging to recover drought-caused groundwater overdraft. However, water management measures that restrict groundwater extraction can significantly reduce the groundwater overdraft recovery time.