Dynamics of Surface Conditions and Hydrological Functioning: The Case of the Ivorian River Basin Aghien Lagoon with the SWAT Model

In the Aghien lagoon hydrosystem, surface conditions are a major factor affecting hydrological processes. Changes in hydrological processes have a significant impact on the availability of water resources. The aim of this study is therefore to simulate the rainfall-discharge relationship in relation to demographic pressure and the dynamics of land use in the catchment area of the Aghien lagoon in southern Côte d'Ivoire. For this purpose, the SWAT model was calibrated and validated using daily time scale flow data at the outlet of the Djibi catchment for the reference year (1987) and gave satisfactory results (NSE ≥ 0.50, R2 ≥ 0.50 and PBIAS ≤ 10). An increase in surface runoff, water supply and evapotranspiration (5.61%), (0.15%) and (0.04%) associated with a decrease in lateral flow (Lat_Q), groundwater flow (Gw_Q), percolation (Perco) and potential evapotranspiration (ETP) (-19.20%), (-6.74%), (-0.15%) and (-0.14), were observed in 2020 compared with the reference year (1987). In a context of climate variability and change, the dynamics of the vegetation cover can provide information about changes in the major hydrological processes such as runoff, infiltration, etc. The increase in runoff and the decrease in infiltration observed can be linked to the dynamics of the plant cover, which has been replaced by crops and bare soil with a higher runoff capacity, thus partly explaining the increase in runoff and the decrease in infiltration.