Rainfall trends and variability over Onitsha urban area in Anambra State, Nigeria: urban planning and policy implications

Abstract

This paper examined the variations of monthly and annual rainfall over Onitsha urban Anambra state for a 44 - year period (1974-2017). The purpose was to determine the frequency, variations, durations and intensity of rainfall events over Onitsha urban and, finally to examine the planning and other implications of the changing rainfall pattern in the study area. The climatic data used in the analysis were obtained from Nigerian Metrological Agency (NIMET) from 1974-2017. The linear regression statistics was applied to determine the linear trend of rainfall over the period; while Microsoft excel package was used to plot the frequency, variations and durations of rainfall events in Onitsha urban. The inverse distance weighted method was used to calculate the intensity of rainfall in Onitsha urban over the study period using 5mins interval of 0.08333hrs. The results of the study show that the month of September has the highest rainfall distribution in Onitsha and that the durations of rainfall increased in recent years (2008-2017) and the intensity as well across the catchment. The significant planning and policy implications of a changing rainfall pattern in a rapidly urbanizing area were outlined especially the issues which the SDG 6 and 11 seeks to address, providing a tangible link between an empirical research and practices in an urban environment plagued by frequent floods, landslides and associated runoff related natural disasters.