Spatio-temporal groundwater storage trends in the Woleka sub-basin, Ethiopia: A comparative assessment of GRACE-CSR mascon and GLDAS-2.2 DA CLSM datasets with in situ validation

ABSTRACT

Graphical abstract illustrating the overall workflow of the study, from data collection and processing to analysis, output generation, and interpretation of the results.

The Gravitational Recovery and Climate Experiment (GRACE) satellite datasets are useful to measure groundwater storage (GWS) variations in the absence of direct observations. The temporal and spatial variability of GWS in the study area was assessed using the GRACE CSR Mascon solutions and GLDAS 2.2 DA CLSM datasets. The modified Mann–Kendall trend test was utilized to analyze the trends. The GRACE-GWSA was calculated using GLDAS terrestrial water storage (TWS) components, which included surface moisture, root zone water storage, and canopy water storage. Monthly groundwater level data from 18 wells were collected over a year (March 2024–February 2025) to validate GRACE-GWSA and GLDAS-GWSA with R2 and Nash–Sutcliffe efficiency (NSE) metrics. Validation using 1 year of in situ measurements indicates reasonable agreement, though longer-term observational records would strengthen confidence in trend assessments. GRACE-GWSA achieved higher NSE and R2 values. The study found substantial increases in GRACE TWS (16.08 cm) and GLDAS TWS (11.44 cm), with GWSA increases of 13.71 and 8.91 cm, respectively, at P < 0.001, over a 21-year study period (2003–2024). These findings underscore the need for enhanced watershed management and conservation initiatives to safeguard groundwater supplies in the region.