Spatiotemporal Data Acquisition and Validation Pipeline for Groundwater Storage based on Satellite Gravimetry and Hydrological Models

Groundwater resources are an essential source of freshwater, but groundwater observation is difficult because of the sparse spatial density and high costs of direct measurements. Satellite gravimetry and land surface models are promising tools for the joint studies of large-scale groundwater storage (GWS) change. This study presents a spatiotemporal data acquisition and validation framework for the estimation of groundwater storage change using the GRACE/GRACE-FO satellite dataset and the GLDAS hydrologic models. Two methods are examined for the estimation of groundwater storage change by combining the satellite and hydrologic models in a complementary way. The first method involves the residual technique, where the GRACEderived TWS anomalies are merged with the corresponding components of the GLDAS-NOAH hydrologic model, excluding the groundwater parts. The second method involves the physically consistent estimation of groundwater storage using the direct output of the GLDAS-CLSM hydrologic models. The developed framework allows the automated download, merging, and analysis of multi-source NetCDF datasets for any geographic region and time span. The application of the developed framework is done at a weekly time interval for the period of 2003 to 2025 to test the accuracy of the methods applied for the monitoring of groundwater storage change with a case study focused on the Cape Town metropolitan area in South Africa. Results highlight substantial differences in temporal continuity and uncertainty between the two approaches, with GLDAS-CLSM providing continuous and more interpretable groundwater storage estimates. The proposed pipeline establishes a robust methodological foundation for long-term groundwater monitoring and future predictive modeling.