234-3 Did the Historic Wet Water Year of 2023 Recharge Central Valley’s Deep Confined Aquifers?

Session: Advance Ground Surface Modeling for Hydrological and Environmental Applications

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California’s Central Valley, a major agricultural hub, depends heavily on groundwater from confined aquifers for irrigation, leading to long-term aquifer storage loss and widespread land subsidence. In 2023, the region experienced an exceptionally wet water year with statewide precipitation exceeding 140% of average and the Sierra Nevada receiving record snowfall up to ~300% of normal, driven by nearly 30 atmospheric rivers. The intense winter downpours flooded parts of the Central Valley and significantly increased reservoir levels, temporarily reducing the region’s reliance on groundwater for irrigation. Furthermore, the record snowpack likely contributed to sustained surface water availability through snowmelt, further increasing the potential for aquifer recharge. However, it remains unclear whether this extreme hydrologic event recharged the Valley’s highly stressed and depleted deep confined aquifers. To address this, we quantified groundwater storage (GWS) changes during the 2023 water year (September 2022 – August 2023) using Gravity Recovery and Climate Experiment and its follow-on mission (GRACE/FO) derived terrestrial water storage (TWS), conventional groundwater-level-based storage modeling, and novel one-dimensional poroelastic modeling constrained by Interferometric Synthetic Aperture Radar (InSAR)-derived surface deformation. GRACE/FO based estimation indicate a regional GWS increase of 19.4 ± 4.1 km³. Well based storage estimates, suggest recharge of 21.41 ± 6.71 km³ in unconfined aquifers and 3.09–12.3 km³ in confined aquifers. For the first time, we apply 1D-poroelastic modeling during the post-drought period to independently quantify GWS change in deep aquifers. We generated a seamless, high-resolution (~75m) spatio-temporal vertical land motion (VLM) dataset using 88 Sentinel-1A/B C-band SAR images acquired from 14 overlapping ascending orbit frames, yielding a vertical deformation rates between 10.4 cm/yr and -29.3 cm/yr. By modeling delayed compaction, using head levels from the preceding drought and aquifer properties, and removing its contribution from total deformation, we estimate a recharge of 1.11–4.45 km³ in confined aquifers. Our findings reveal limited recharge in deep confined aquifers with most recharge occurring in shallow aquifers. Although the 2023 water year contributed to recharge in deep aquifers, it cannot offset the long-term depletion caused by decades of sustained overdraft. Our study advances the understanding of deep aquifer response to transient hydrologic extremes and demonstrates the utility of spaceborne techniques for improved recharge quantification in the Central Valley.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9170

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