High-resolution terrestrial water storage from GNSS vertical deformation using a remove–restore hydrological loading framework: Application to Chile

Changes in terrestrial water storage (TWS) induce measurable elastic deformation of the Earth’s surface, known as hydrological loading. GNSS observations quantify these surface deformations and, despite being point measurements, they contain the full spectrum of the hydrological loading. Likewise, GRACE and GRACE-FO satellite missions support the monitoring of these hydrological loads, but their coarse spatial resolution (i.e., long-wavelength components) limits the characterization of short-wavelength and localized hydrological processes. Given these two different yet complementary geodetic remote sensing technologies, recent efforts have been made to combine them for recovering high-resolution TWS fields.

Building on these recent efforts, we adopted a remove-restore framework, a widely used technique in regional gravity field modeling, to invert TWS variations from GNSS-derived vertical displacements. In this framework, GRACE-based hydrological loading is first synthesized into vertical deformation up to degree and order 60, and then removed from GNSS observations, isolating residual displacements dominated by sub-GRACE-scale hydrological signals (i.e., short-wavelength components). These residuals are then inverted using a modified elastic Green’s functions to recover residual high-resolution TWS anomalies, which are subsequently restored with the long-wavelength GRACE signal to obtain high-resolution TWS anomaly fields. We applied the method to Chile, a region characterized by strong hydro-climatic gradients and significant tectonic activity, which served as a challenging testbed for the inversion of hydrological loading into high-resolution TWS.

Our results showed that the remove–restore approach enhances both the spatial detail and amplitude of TWS variations compared to GRACE alone, while preserving consistency with large-scale mass changes. Comparisons with land surface and hydrological model outputs indicated improved representation of regional and local hydrological variability. Overall, this exercise demonstrates the potential of integrating GNSS and GRACE/GRACE-FO through a remove-restore strategy to reconcile complementary geodetic observations and better resolve multi-scale water storage dynamics.