Assessment of the Impact of Climate Change on Current and Future Runoff in the Nanija Bolong Watershed (Kaffrine Region, Senegal)

ABSTRACT: Climate change poses a major challenge to water-resource management in West Africa’s Sudano-Sahelian regions. This study assesses projected changes in runoff in Senegal’s Nanija Bolong catchment using ISIMIP3b outputs from two global hydrological models (H08 and Climate, Weather and Atmospheric Modeling (CWATM)) driven by three CMIP6 climate models (GFDL-ESM4, MPI-ESM1-2-HR, and MRI-ESM2-0). The analysis uses 1985–2014 as the historical reference period and 2021–2100 for future projections under SSP1-2.6, SSP3-7.0, and SSP5-8.5. Mann–Kendall, Sen’s slope, and Pettitt tests were applied to the simulated series. The historical analysis shows no statistically significant trend in the simulated runoff series. Future changes differ in magnitude between H08 and CWATM and are not monotonic across scenarios in every time window: relative to 1985–2014, the late-century reductions under SSP3-7.0 are larger than under SSP5-8.5 in the ensemble series. Because a complete, independently documented observed Nanija Bolong discharge series was not available in the material used for this analysis, the study does not claim observational validation of either model. The results should therefore be interpreted as model-based projections and as an assessment of structural and climate-model uncertainty, not as proof that either model reproduces measured discharge accurately. The coarse spatial resolution also limits fine-scale interpretation within this small catchment.