A multi-source approach to groundwater storage and recharge assessment in the Volta Basin

Assessing groundwater storage changes is important in semiarid regions such as the Volta Basin in sub-Saharan Africa but can be challenging due to data scarcity. This study presents a multi-source approach combining NASA's Gravity Recovery and Climate Experiment (GRACE) mission data, Climate Hazards group Infrared Precipitation with Stations (CHIRPS) precipitation data, the new Global Land Data Assimilation System (GLDAS) v2.2 CLSM groundwater storage anomaly dataset, traditional non-groundwater terrestrial water storage components from GLDAS v2.1, and Copernicus satellite data for surface water dynamics to analyze groundwater storage changes and recharge rates in the Volta Basin. Our study reveals: (1) A small change in groundwater storage from 2002 to 2012, followed by a significant increase from 2012 to 2022; (2) A total groundwater increase of approximately 30 cubic kilometers or about 10 cm of liquid water equivalent over the entire study period; (3) Water storage in the basin is dominated by fluctuations in Lake Volta, which accounts for ∼50 % of terrestrial water storage; (4) Groundwater recharge rates estimated using the Water Table Fluctuation Method on GRACE- and GLDAS-derived data, aligned with values from monitoring wells and previous studies; (5) The GLDAS v2.2 dataset exhibits similar seasonal trends with periodic peaks and troughs, yet the amplitude of anomalies from GLDAS are larger compared to the GRACE dataset; and (6) Groundwater recharge shows a weak correlation with extreme precipitation events, suggesting more water percolates rather than evaporates during such events. However, other factors, including land use changes and agricultural practices, may also impact groundwater storage and recharge.