Spatiotemporal Analysis of Groundwater Level Fluctuations and Recharge Dynamics in the Sokoto Sedimentary Basin

The Sokoto Sedimentary Basin constitutes the primary aquifer system supporting agricultural irrigation, livestock watering, and domestic supply across north-western Nigeria, yet systematic analysis of groundwater level trends and recharge dynamics under changing climate and abstraction pressures is limited in the published literature. This study conducts a spatiotemporal analysis of groundwater level fluctuations and recharge dynamics in the Sokoto Sedimentary Basin using multi-year groundwater monitoring records, chloride mass balance recharge estimation, and remote sensing drought indices. Groundwater level data from 48 monitoring wells maintained by the Sokoto-Rima River Basin Development Authority for the period 2012 to 2023 were analysed for trend, seasonality, and spatial variability using Mann-Kendall tests and geostatistical interpolation. Chloride concentration profiles in unsaturated zone sediments at 12 sites were used to estimate long-term recharge rates. GRACE satellite gravimetry data were employed to validate monitored trends and extend spatial coverage. Findings reveal declining groundwater level trends at 62 percent of monitored wells, with the most rapid declines exceeding 0.5 metres per year in intensively irrigated sub-areas of the basin. Recharge estimates from chloride mass balance average 18 to 32 millimetres per year across the study sites, which represents 4 to 8 percent of mean annual rainfall, indicating low system resilience to recharge deficit years. The GRACE-derived total water storage anomaly corroborates monitored declining trends. Groundwater management recommendations include abstraction licensing with volume caps, conjunctive use water management planning, and recharge enhancement through water spreading infrastructure on suitable alluvial fans. Keywords: groundwater level trends, Sokoto Basin, recharge estimation, GRACE, water resources management.