Geodetic Insights into Water Resources and Drought Dynamics in the Western United States

Developing a comprehensive understanding of global water resources – and their responses to extreme events and variations in climate – requires integrating diverse modeling and observational approaches across disciplines, with geodesy playing an increasingly integral role. Geodetic measurements and models, including those tracking solid Earth deformation caused by mass redistribution in the hydrosphere, provide key insights into water-cycle processes and systems. This study focuses on Global Navigation Satellite System (GNSS) data from the western United States to examine recurring cycles of severe drought and rapid recovery over the past two decades. Interdisciplinary evidence from hydrology, meteorology, and geodesy suggests that these cycles are strongly associated with variability in the frequency and intensity of seasonal atmospheric rivers (ARs). During Water Year 2023, GNSS data revealed record-breaking water-storage gains in California’s Sierra Nevada mountains and Sacramento-San Joaquin-Tulare (SST) river basins, driven largely by an exceptional series of powerful ARs. In the six-month period between October 2022 and March 2023, water-storage gains in these regions surpassed those of any prior year in the analysis, which began in 2006, with an estimated 80% of the gains delivered by ARs. By early spring 2023, we infer that approximately half of the water-storage gains had infiltrated the subsurface, providing a critical water resource for downstream communities through processes such as mountain block recharge. Our analysis further shows that hydrological drought and recovery, based on GNSS estimates of total water-storage changes, respond more slowly to precipitation patterns than meteorological drought and recovery, highlighting the insulation of subsurface pools from surface fluxes. We find that years with heavy precipitation can help to sustain storage levels into subsequent years with less precipitation. Moreover, as geodetic observational accuracy improves, a deeper understanding of the assumptions, limitations, and opportunities inherent in our models is necessary. To assess the precision of GNSS-informed water-storage estimates, we compare results derived from independent GNSS position estimates and inversion techniques. Additionally, we provide updates on recent progress in developing community-available modeling tools and investigating the effects of 3-D heterogeneities in Earth structure on deformation responses to surface mass loading.