Analytical Investigation of the Relationship Between ENSO Phases and Seasonal Rainfall Anomalies Over the Guinea Savanna Zone of Nigeria

The El Nino-Southern Oscillation (ENSO) represents one of the dominant sources of inter-annual climate predictability globally, yet its influence on Nigerian rainfall exhibits important spatial heterogeneity that demands local-scale empirical analysis. This study analytically investigates the statistical relationship between ENSO phases and seasonal rainfall anomalies across Nigeria's Guinea Savanna zone, covering states including Benue, Kogi, Kwara, Niger, and Oyo. Seasonal rainfall anomalies computed from 30-year NiMet records (1993 to 2022) were correlated with ENSO indices including Nino 3.4 SST anomalies, the Multivariate ENSO Index, and the Trans-Nino Index using Pearson and Spearman correlation analysis, composite analysis, and conditional probability assessment. Distinct rainfall responses to La Nina and El Nino events are identified, with La Nina associated with significantly above-normal July to September rainfall over northern Guinea Savanna states, while El Nino corresponds to below-normal rainfall in the same season. Wavelet coherence analysis confirms significant teleconnection energy concentrated in the 2 to 7 year ENSO period band for all stations, with coherence strongest during the boreal summer monsoon peak. A conditional probability framework shows that knowledge of ENSO phase at March provides statistically significant skill in predicting the sign of July to September rainfall anomaly, demonstrating operational seasonal forecast potential. Keywords: ENSO, Guinea Savanna, rainfall anomaly, teleconnection, seasonal forecast.