Numerical Model for Lake Chad Basin Groundwater. Results from simulation of water resources under different climatic and abstraction conditions

 

The Lake Chad Basin (LCB), a critical hydrological system in Sub-Saharan Africa, supports over 40 million people across several countries. Characterized by arid and semi-arid climate, the basin’s water resources are under constant threat from declining precipitation and decreasing natural recharge, over pumping, and transboundary management complexities. The main land uses in the basin are the native vegetation and irrigated areas (together with wetland areas). A 3D ‘quasi steady-state’ regional groundwater flow model of the Chad Formation, based on MODFLOW code, to evaluate quantitative recharge and transboundary water fluxes within the basin, to quantitatively develop abstraction scenarios and further impacts on groundwater, lake and connected rivers was developed. Also, long-term sustainability, under different climatic conditions and water abstraction was simulated.

The basic assumption adopted is that the hydrological conditions during the considered model baseline period (2008-2011) are representative of system functioning. To estimate the natural recharge and for the proposed ‘dry scenario’, the strategy adopted for the simulation was to apply a scaling factor of -10% to the baseline recharge data sets obtained from Modflow run. To meet future demand resulting from population growth, water abstraction increases by 10%  in  the areas where abstraction currently occurs (baseline).

Obtained simulation for the Quaternary aquifer indicates that the impact of reducing recharge by 10% is much more important for aquifer than increasing water abstractions, an expected output for a large-scale model as the one developed. For specific areas of the basin and model run at greater scale, outputs reveal a different behaviour as limited by contour conditions.