Comparative analysis of rainfall IDF equation types for predicting rainfall intensity in southern Nigeria

Abstract

This paper compared the differences and similarities in the rainfall intensities predicted by four standard IDF equations for return periods between 5 and 40 years and for storm durations between 15 and 30 minutes. The empirical models employed for comparison on the development of standard IDF equations using historic data for Benin, Calabar, Port Harcourt, Onitsha and Warri meteorological stations, all in Southern Nigeria were available in literature. The strength and weakness of the different models were assessed using the mean ± standard deviation as range between intensities estimated for 5 and 40 years, and percent relative error between the observed and predicted rainfall intensities as performance criteria. The results obtained showed that there were significant differences in the rainfall intensities as predicted by the equation types. However, the IDF types-1 and 2 equations displayed lower range values in intensities for all returned periods. Types-1 and 2 equations predicted the lowest relative error of less than or equal to 6% in all stations considered. Because IDF studies are associated with hydrologic extremes, both types-1 and 2 equations are therefore recommended for hydrologic design of flood control structures. The study has advanced the understanding of the equations and further insight in their utility as hydrologic design tools.

Keywords: Rainfall, IDF models, Intensity-Duration-Frequency, Equation types, Southern Nigeria