Stochastic Analysis of Rainfall Events in Ilorin, Nigeria

Abstract

This paper reports on a stochastic analysis of rainfall events in Ilorin, Nigeria. Rainfall, the most common form of precipitation in most parts of the world, is a principal component of the hydrologic cycle. Rainfed agricultural practices dominate agricultural activities in Ilorin, which could be enhanced by accurate predictions of rainfall attributes. Since rainfall exhibits natural variability, its analysis in a stochastic framework provides a more realistic premise.
Five probability distribution namely the normal, lognormal, logPearson typeIII exponential and extreme value type I distributions – were used in this study because of their desirable properties. The analysis was based on 41 years of daily and monthly rainfall data (1955-1995) for Ilorin, with peak values computed for each year.Weibull plotting positions and the number of rainy days were also determined. September had the highest number of rainy days, followed by June. Rains are least expected in Ilorin in January and December. The maximum daily rainfall has a mean depth of 85mm and a standard deviation of 28mm while the corresponding values for the maximum monthly rainfall are 275mm and 56mm. The logPearson type III distribution best suited the maximum daily rainfall data while the normal distribution best described the maximum monthly rainfall for Ilorin.


JARD Vol. 1 2001: pp. 39-50