Rainfall Variability and Change over Nigeria: Mechanisms, Observed Trends, Extremes, Future Projections, and Socioeconomic Implications

Nigeria's rainfall is controlled by the West African Monsoon (WAM), but its variability reflects interactions among monsoon migration, oceanic forcing, land-atmosphere feedbacks, synoptic disturbances, and organised convection. This review synthesises evidence on the mechanisms, observed variability, hydroclimatic extremes, future projections, and socioeconomic implications of rainfall variability and change across Nigeria. The literature consistently shows a strong south-north rainfall gradient, a transition from bimodal rainfall in the humid south to unimodal rainfall in the savanna and Sahel, and major modulation by the Intertropical Discontinuity (ITD), African Easterly Waves (AEWs), the African Easterly Jet (AEJ), the Tropical Easterly Jet (TEJ), Mesoscale Convective Systems (MCSs), and sea-surface temperature anomalies. Observed changes do not support a single national narrative of wetting or drying. Instead, rainfall risk is being reorganised: twentieth-century drought strongly affected northern Nigeria, partial rainfall recovery has occurred in parts of the Sudan-Sahel, and intense rainfall has become increasingly important for flood risk. Climate models agree more strongly on warming and increased potential for heavy precipitation than on the direction and magnitude of future changes in mean rainfall, especially in the central transition zone. Major gaps remain in sub-daily observations, MCS dynamics, station coverage, attribution of extremes, and integration of climate projections with agricultural, hydrological, health, and disaster-risk models. The review argues that future research should move from descriptive trend detection toward process-based, impact-oriented, and decision-centred climate services that connect rainfall mechanisms, hazards, vulnerability, and adaptation options.