Frequency Analysis of Rainfall in Abuja Using Probability Distributions

Precipitation patterns in Abuja, Nigeria exhibit a concerning trend characterized by a gradual and persistent decline accompanied by a rise in the intensity of individual rainfall events, leading to double-edged sword situations like intensified floods. This decline is likely attributable to the combined effects of climate change and climate variability. This change necessitates a thorough characterization. This research investigated the applicability of three probability distributions (Normal, Log-Pearson Type III, and Gumbel Type I) for modelling extreme rainfall events in Abuja, Nigeria. The study was focused on determining the best-fit distribution method and trend of changing rainfall in Abuja, Nigeria. Daily annual rainfall data of 20 years (2003-2023) was obtained from the Nigerian Meteorological Agency (NIMET). The models were rigorously analysed using formulae specific to each distribution and their performances were compared using Microsoft Excel. The key objectives of the research were to calculate the design rainfall depth (<i>X</i>_T) for return period T = 2, 5, 10, 50, 100 and 1000 years and to compare the performances of the three distribution methods so as to determine the best fit which then, can be used to characterize the alarmingly changing rainfall pattern of Abuja. The study compared the performance of the three probability distributions (Normal, Log-Pearson Type III, and Gumbel Type I) at Guinea Savannah, ID-65125 Abuja rainfall gauging station and found that the Gumbel Type I distribution consistently generated the highest estimates for extreme rainfall events in Abuja, suggesting that the Gumbel Type I distribution is the most suitable model for predicting extreme rainfall in Abuja. The design rainfall values generated, ranging from 74 mm to 238 mm for return periods of 2 to 1000 years, can inform the design of flood control measures and resilient infrastructure, ultimately contributing to enhanced disaster preparedness and sustainable urban development in Abuja.