Over the past century, groundwater levels in California’s San Joaquin Valley have dropped more than 30 meters in some areas due to excessive groundwater extraction used to irrigate agricultural lands and feed a growing population. Between 2012 and 2016 California experienced the worst drought in its recorded history, further exacerbating this groundwater depletion. Due to lack of groundwater regulation, exact quantities of extracted groundwater in California are unknown and hard to quantify. We use a synthesis approach, combining modeling results from the integrated hydrologic model ParFlow-CLM with remote sensing data from NASA’s Gravity Recover and Climate Experiment (GRACE) to evaluate the impacts of water management activities on water storage in a highly managed agricultural system during drought. Using ParFlow-CLM with multiple groundwater extraction and irrigation simulations compared to total water storage anomaly (TWSA) estimates from GRACE data, we can constrain water table declines and begin to untangle the complicated impacts of individual water management activities on groundwater depletion. Additionally, using this approach we can evaluate how these water management activities changed throughout the drought to adapt to water shortages. Results from this study show that total groundwater extraction and irrigation volumes were the most critical simulation parameters for estimating annual total water storage changes. Temporal variability in groundwater extraction rates and irrigation were significantly less importance for estimating annual variations but were critical for evaluating seasonal variations in total water storage. Additionally, results showed that the simulated initial groundwater table configuration did not have a significant impact on total water storage changes within the model domain either annually or seasonally.
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