Understanding Niger Delta Rainfall Variability and Trend Using Parametric and Non-parametric Statistics

This study investigates the variability and long-term trends of annual rainfall in the Niger Delta region of Nigeria over a 41-year period (1981‒2021). Annual rainfall data from five key meteorological stations—Benin, Calabar, Port Harcourt (PH), Uyo, and Warri—were analyzed using both parametric (Linear Regression) and non-parametric (Mann-Kendall and Sen’s Slope Estimator) statistical techniques. Descriptive statistics revealed high mean annual rainfall across the region, with Uyo exhibiting the highest variability (CV of 28.71%). The Mann-Kendall test indicated a statistically significant increasing trend in annual rainfall only at the Calabar station (Z = 1.988, p < 0.05), with a magnitude of 12.52 mm/year as estimated by Sen’s Slope. Benin showed a strong increasing tendency (Z = 1.898, p > 0.05) with a magnitude of 7.56 mm/year, just below the significance threshold. The remaining stations (Port Harcourt, Uyo, and Warri) showed no statistically significant trend. The Rainfall Anomaly Index (RAI) for the region highlighted periods of severe wet and dry years, with the most pronounced positive anomalies occurring in the early 2000s and the most severe negative anomalies in the late 1980s. These findings are crucial for water resource management, agricultural planning, and flood mitigation strategies in the vulnerable coastal environment of the Niger Delta.