Unlocking Insight: Past, Present, and Future of Groundwater Storage Change Digital Twins via GRACE and InSAR Integration

Due to the hidden nature of groundwater resources and the geologic complexity of aquifers, an accurate assessment of the groundwater storage change is challenging. Over the last decades, remote sensing technologies have provided novel insights into groundwater dynamics. One example is the Satellite Gravity and Climate Experiment and its Follow-on (GRACE/FO) missions, which are sensitive to water mass changes in regionally sized aquifers. They have brought to light a global phenomenon of water bankruptcy in arid to semi-arid regions with large populations and agricultural activities like the Southwest USA, the Middle East, or northern India. Other essential technologies include those that provide surface deformation measurements and, most importantly, vertical land motion (VLM), caused by changes in water resources. High-resolution VLM maps provided by interferometric synthetic aperture radar (InSAR) acquisitions have helped quantify aquifer mechanics and groundwater dynamics worldwide at management-relevant resolutions. Despite their fine spatial resolution, continuous coverage, and complementary nature, a seamless and physically consistent combination of VLM maps from InSAR with global GRACE TWS change observations has been lacking. This presentation first reviews early advances in GRACE-InSAR combinations and their outcomes. Then, it presents a unifying approach combining GRACE and InSAR observations through a multi-physics joint inversion for quantifying groundwater storage changes (GWS) by considering the underlying physical processes driving each observation. Next, we apply this approach in a case study to estimate GWS for Central Valley California during the 2020-2021 drought. We compare the results to those from other studies. Lastly, we highlight the technological and scientific advances required to expand the approach from drought to non-drought periods and regional to continental or global spatial coverage. Accurate observation of GWS with high spatial resolution will improve our understanding of groundwater recharge processes, for example, by better enabling the integration of the geodetic data products into accurate groundwater hydrological models. This can further support the assessment of climate change's impact on groundwater resources and water management approaches, such as assessing the success of managed aquifer recharge.