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Statistical Evaluation of Rainfall Parameters in Ado Ekiti Nigeria

Olatunji Peter Folorunso


Estimation of rainfall for a desired return period is one of the pre-requisites for any design purpose at a particular site, which can be achieved by probabilistic approach. Rainfall is an input for various engineering design such as hydraulic structures, bridges and culverts, canals, storm water sewer and road drainage system. This study is aimed at using the statistical parameters of long-term observed rainfall data to generate monthly rainfall depth and estimate rainfall values at different return periods for hydrological and agricultural planning purposes. The daily rainfall data of 10 years from 1991 to 2000 were collected from the department of meteorological station situated at Ado Ekiti, Ekiti State. In this work, the expected number of observations was 120. However, a sample size of 103 being the months with rainfall amounts was used for the study. Descriptive statistics (mean and standard deviation) were used to analyze the data and the results from analysis showed that rainfall fluctuated in an upward trend through the period of study. Standard Precipitation Index (SPI) and Coefficient of Variability statistical tools were employed to analyze rainfall trends and patterns in Ado Ekiti between 1991 and 2000. The daily rainfall data was subjected to several analyses. The result obtained indicated that there is a downward trend in the rainfall amount received in Ado Ekiti over the last 10 years.

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