Rainfall Intensity Duration Frequency Optimization Modelling for Akure, South-West, Nigeria

The rainfall Intensity-Duration-Frequency (IDF) relationship is widely used for adequate estimation of
rainfall intensity over a particular catchment. A 25 year daily rainfall data were collected from Nigerian
Meteorological Agency (NIMET) Abuja for Akure station. Twenty five year annual maximum rainfall
amounts with durations of 5, 10, 15, 20, 30, 45, 60, 90, 120, 180, 240, 300 and 420 minutes were
extracted and subjected to frequency analysis using the excel solver software wizard. A total of six (6)
return period specific and one (1) general IDF models were developed for return periods of 2, 5, 10,
25, 50 and 100 years using Gumbel Extreme Value Type-1 and Log Pearson Type -3 distributions.
Anderson Darling goodness of fit test was used to ascertain the best fit probability distribution. The R2
values range from 0.982 to 0.985 for GEVT -1 and 0.978 to 0.989 for Log Pearson type -3 while the
Mean Squared Error from 33.56 to 156.50 for GEVT -1 and 43.01 to 150.63 Log Pearson Type III
distributions respectively. Among the six Geo-Political zones in Nigeria, the South – West of which
Akure is one of the cities is one of the least with IDF model development (16.7%). This is the basis of
IDF model development in Akure to help fill the gap. Is of interest to note that the South – East and
South – South have the highest percentage of IDF developed models (66.7%). The probability
distribution models are recommended for the prediction of rainfall intensities for Akure metropolis.