TITLE:
Climate Change and Surface Water Availability in West Africa: A Case Study of the Diaguiri River Basin
AUTHORS:
Ibrahima Thiaw
KEYWORDS:
CORDEX-Africa, Climate Change, Diaguiri River Basin, Hydrological Modeling, Surface Water Availability
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.13 No.9,
September
25,
2025
ABSTRACT: This study evaluates the projected impacts of climate change on surface water availability in the Diaguiri River Basin, a sub-catchment of the Gambia River in West Africa, using the conceptual rainfall-runoff model GR4J. The model was calibrated (1981-1992) and validated (1998-2004) with daily hydroclimatic observations, and forced with bias-corrected outputs from five CORDEX-Africa CMIP5 Regional Climate Models (GFDL-ESM2M, HadGEM2-ES, IPSL-CM5A-LR, MIROC5, and NorESM1-M) under RCP4.5 and RCP8.5 scenarios. Model performance was satisfactory across multiple metrics (NSE = 0.66 - 0.71; KGE = 0.71 - 0.83; logNSE = 0.54 - 0.77). Future simulations reveal a non-linear precipitation-runoff response, with ensemble mean annual discharge increasing by +24.3%, +20.0%, and +30.7% under RCP4.5 for the near-term (2021-2040), mid-century (2041-2070), and late-century (2071-2100), respectively, driven by moderate increases in precipitation anomalies (+6.72%, +5.79%, and +12.16%). Under RCP8.5, streamflow anomalies are more erratic—+45.3%, +35.0%, and +26.5% across the same time slices—despite a declining precipitation signal (+13.68%, +10.19%, and +5.32%), reflecting amplified hydrological sensitivity and non-stationarity. Monthly hydrographs indicate earlier onset of runoff, intensified wet-season flows, and increased intra-annual variability, particularly under RCP8.5, which exhibits elevated skewness and kurtosis, signaling a higher frequency of hydrological extremes. The Diaguiri Basin’s strong rainfall-runoff coupling, compounded by scenario- and model-dependent uncertainties, underscores the vulnerability of West African headwater catchments to climate-induced hydroclimatic shifts. The results highlight the urgent need to integrate ensemble-based projections and seasonal regime alterations into adaptive water resource planning and flood risk management frameworks under non-stationary climate conditions.