Spatiotemporal variations in terrestrial water storage: A comparative analysis using gravimetry satellite data and water balance methods over Ethiopia

This study examines spatiotemporal variations in terrestrial water storage (TWS) and drought conditions over Ethiopia using Gravity Recovery and Climate Experiment and its Follow-On mission (GRACE (-FO)) satellite data and the water balance method. The present analyzed monthly GRACE/GRACE-FO Mascon (CSR RL06, release 0602) terrestrial water storage anomalies (TWSA) together with GLDAS over Ethiopia. The GRACE-derived TWS anomalies were compared with the Global Land Data Assimilation System (GLDAS) data to estimate groundwater storage changes. The results reveal substantial spatial variability in water storage across the country. Western Ethiopia showed significant increases in TWS, while eastern regions exhibited notable decreases, indicating potential drought conditions. Comparison of GRACE-based TWSA with a water-balance TWSA (P–ET–R from GLDAS) shows a moderate correlation (r = 0.64, two-sided p < 0.001; n ≈ 240 monthly pairs), with GRACE capturing larger amplitude variability. GRACE-derived groundwater storage and in-situ well observations (2013–2017) exhibit a moderate association (r ≈ 0.5, two-sided p < 0.001; n ≈ 55 months). Agreement between GRACE- and GLDAS-based groundwater storage is also moderate (r = 0.53, p < 0.001; n ≈ 240). Groundwater storage changes derived from GRACE (-FO) were validated using in-situ well measurements, showing a similar overall trend, although GRACE data captured more pronounced short-term fluctuations. The correlation coefficient between GRACE-derived groundwater storage and well data was moderate, suggesting that GRACE accurately reflects regional groundwater fluctuations. Drought conditions were monitored using the Total Storage Deficit Index (TSDI), showing that the western regions of Ethiopia experienced lower drought deficiency while the eastern areas exhibited higher drought severity. These findings have important implications for sustainable water resource management, particularly in drought-prone regions where accurate monitoring of water storage is crucial for mitigating the effects of climate change on agriculture and water security. The study highlights the role of satellite-based data in supporting resilient and sustainable water management strategies.