Development of Intensity Duration Frequency (IDF) Curves for Rainfall Prediction in Some Selected States in South-West Nigeria

Abstract

Rainfall Intensity-Duration-Frequency (IDF) relationship remains

one of the most widely used tools in hydrology and water resources

engineering, especially for planning, designing and operations of

water resource projects. The target of this study is to develop IDF

curves for the prediction of rainfall intensity in some selected states

in South-West Nigeria.

Forty (40) year’s annual maximum rainfall data ranging from 1974

to 2013 was employed for the study. To ascertain the data quality,

test of homogeneity using residual mass curve and test of hypothesis

was employed. Rainfall depth at selected durations were estimated

using the empirical reduction formula given by Indian

Meteorological Department (IMD) while the mathematical

relationship between rainfall intensity and rainfall durations was

determined using the curve fitting tool in MATLAB. Thereafter,

rainfall intensities for 2minutes, 5 minutes, 10 minutes, 15 minutes,

30 minutes, 60 minutes, 120 minutes, 180 minutes, 240 minute and

320 minutes were estimated coupled with the mean and standard

deviation of the data for different durations. The popular Gumbel

probability distribution model was employed to calculate the rainfall

frequency factor for selected return periods (T= 2, 5, 10, 25, 50 and

100yrs). The rainfall intensity corresponding to a specified return

period was computed using the linear relationship between the

magnitude of a hydrological event XT and the departure

D

XT. To

assess the best fit model that can be employed to predict rainfall

intensity for various return periods at ungauged locations, four

empirical IDF equations, namely; Talbot, Bernard, Kimijima and

Sherman equations were employed. The model with the least

calculated sum of minimized Root Mean Square Error (RMSE) was

acclaimed the best fit empirical model.

Results obtained revealed that the Talbot model was the best fit

model with calculated sum of minimized error of 5.666066E-07 and

6.424229E-07. The model was thereafter employed to predict the

rainfall intensity for different durations at 2, 5, 10, 25, 50 and 100yrs

return periods.