Rainfall Probability Density Function (PDF) and nonPDF - IDF Modelling for Uyo City, Nigeria

Suitable rainfallIntensityDurationFrequency
(IDF) models for Uyo City were developed using the
statistical method of leastsquares
for non PDF and optimization solver for PDF models. A total of 20
rainfall models were developed based on 10 years rainfall data. These models are categorically
grouped into three sets. The first set contains 10 rainfall models which represent inverse relationship
between rainfall intensities and duration for specified frequencies called IntensityDuration
Models.
The second set contains 8 rainfall models which represent rainfall intensities and frequencies for
specified duration called IntensityFrequency
Model. The third set has two general models of Log
Pearson Type –3 [LPT3]
and Gumbel Extreme Value Type – 3 (GEVT3)
based on modified
Sherman’s empirical equation of intensity as a function of duration and frequency. The three sets of
models developed in this study recorded high and positive values of coefficient of correlation, an
indication of good curve fitting with values of IntensityDuration
Models ranging from 0.948 to 0.977;
intensity frequency model ranging from 0.641 to 0.938 and the general models from 0.8619 – 0.905.
The graphical comparisons of developed models at frequencies of 5.5 and 11 years confirmed LPT3
to predict highest intensity values at short durations of 50 minutes or less, followed by the Quotient
model (i.e intensityduration
model) and lastly by GEVT3.
For longer durations greater than 50
minutes, the Quotient models gave best performance predictionwise.
These set of models developed
will serve as valuable tools for predicting rainfall events in Uyo City as well as for use in the design of
hydraulic structures, urban drainage and flood control.