Examining Inter-Annual Variability of Rainfall in Sokoto State Using Long-Term Records

Inter-annual rainfall variability in Nigeria's semi-arid North West zone creates recurring cycles of abundance and deficiency that challenge planning across water, agriculture, and disaster risk management sectors. This study examines inter-annual variability of rainfall in Sokoto State using the long-term instrumental record from Sokoto Airport meteorological station covering 1981 to 2022. Annual and seasonal rainfall totals were subjected to time series analysis including standardized anomaly computation, running mean smoothing, and spectral analysis to identify dominant modes of variability. Teleconnection analysis was performed by correlating Sokoto seasonal rainfall anomalies with global Sea Surface Temperature indices including El Nino Southern Oscillation (ENSO) and the Atlantic Multi-decadal Oscillation (AMO). Results reveal pronounced decadal-scale variability superimposed on higher-frequency inter-annual fluctuations, with a below-normal rainfall epoch persisting through the 1980s and 1990s followed by a partial recovery in the 2000s, consistent with Sahel precipitation trends documented in global literature. ENSO-rainfall correlations are weak but statistically significant in La Nina years, during which Sokoto tends to receive above-average rainfall. The study identifies the AMO positive phase as a stronger predictor of multi-year wet spells. Findings inform the development of probabilistic seasonal forecast tools specific to Sokoto's climate regime. Keywords: inter-annual variability, Sokoto, rainfall, ENSO, Atlantic Multi-decadal Oscillation.