Djigbo Félicien BADOU^{1, 2,}, Audrey Merveille ADANGO², Chaim Vivien DOTO³

This study assesses the relationship between extreme precipitations and reservoir sedimentation dynamics in the Beninese portion of the Niger River Basin. Historical daily rainfall data (1980-2020) and future climate projections (2021-2049) from the WRF regional climate model under the RCP 4.5 scenario were analyzed to assess trends in extreme rainfall using the Modified Mann-Kendall test and the Theil-Sen slope estimator. The impacts of changing heavy rainfall patterns on runoff and sediment yield were simulated using the Soil and Water Assessment Tool (SWAT), applied to the Sota catchment. The findings reveal mixed heavy rainfall trends across the study area, with a significant decrease projected under the RCP 4.5 scenario for several stations. The SWAT model showed satisfactory performance for streamflow simulation (NSE = 0.70 during calibration; 0.66 during validation). The historical mean sediment yield was estimated at 18.6 ton ha⁻¹yr⁻¹, exceeding commonly accepted sustainability thresholds. Spatial analysis revealed persistent sedimentation hotspots in the southwestern part of the catchment. Future simulations indicate an increase in runoff but a decline in sediment yield to 12.8 ton ha⁻¹ yr⁻¹ by 2049. This counterintuitive trend is attributed to a projected shift toward less erosive rainfall regimes coupled with temperature-driven changes in soil surface processes. While providing valuable insights into climate-sediment interactions, these projections are subject to uncertainties from the lack of measured sediment data, the use of a single climate scenario, and the assumption of static land use. Overall, the study highlights the sensitivity of reservoir sedimentation to changes in extreme rainfall and provides a scientific basis for improving sediment management strategies in small dams under future climate change.

heavy rainfall trends, sediment yield, small dams, WRF-GFDL model, hydrological Modeling, Sota catchment