Analytical Study of Groundwater Recharge Rates and Aquifer Sustainability in the Chad Basin, North East Nigeria

Sustainable groundwater extraction from the Chad Basin aquifer system in North East Nigeria is threatened by increasing abstraction demand and declining recharge rates linked to reduced Lake Chad surface water extent and changing rainfall patterns. This study analytically assesses groundwater recharge rates and aquifer sustainability in the Nigerian sector of the Chad Basin. A multi-method recharge estimation methodology was adopted, applying the water table fluctuation method, chloride mass balance, and Richards equation unsaturated zone modelling to data from 25 groundwater monitoring wells in Borno and Yobe States. Long-term groundwater level trends were analysed using Mann-Kendall trend tests. Aquifer water budgets were constructed integrating recharge estimates, abstraction records, and natural discharge estimates. Climate downscaling from CMIP6 models provided future recharge projections. Results indicate current annual recharge rates of 15 to 40 mm per year in unconfined aquifer zones and 3 to 8 mm per year in semi-confined systems. Groundwater levels show statistically significant declining trends in 68 percent of monitored wells. Current abstraction for agriculture and domestic use exceeds recharge estimates in 40 percent of the study area. Under a moderate climate scenario, recharge is projected to decline by 18 to 32 percent by 2050. The study contributes original recharge estimates for the Nigerian Chad Basin sector and recommends strict groundwater abstraction licensing aligned with recharge capacity.

Keywords: groundwater recharge, Chad Basin, aquifer sustainability, Borno State, North East Nigeria