Analysis of Rainfall Intensity for Southern Nigeria
Abstract
The estimation of rainfall intensity is commonly required for the design of hydraulic and
water resources engineering control structures. Considering notable changes in rainfall trends
as a result of global and regional changing of climate and weather in recent times, the need for
intense study of rainfall and accurate estimation of rainfall intensity duration frequency (IDF)
curves cannot be over emphasized. In this paper, rainfall Intensity-Duration-Frequency (IDF)
studies were undertaken for Southern Nigeria using annual extreme rainfall series available for
10 cities. A Microsoft Excel model was developed to conduct frequency analysis using the
Extreme-Value Type 1 (Gumbel) Distribution. IDF relationships and curves for 1, 2, 5, 10, 25, 50
and 100 yrs return periods were then generated for Ondo, Ibadan, Warri, Benin, Oshogbo, Ikeja,
Port-Harcourt, Umudike, Calabar and Enugu. The results were compared for a storm of 10 yr
return period with a time duration of 9 minutes. It was observed that Port-Harcourt had the
highest rainfall intensity (207.40mmhr-1.), followed by Enugu (164.53 mmhr-1.) and then Ikeja
(114.65mmhr-1.). The computer model developed in this study will be of immense help to
engineers in developing a database for the continuous (or long term) analysis of rainfall in
Nigeria and generation of IDF curves for the design of hydraulic and water resources
engineering control structures, few of which were done in this work
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