Probability Analysis for One Day to Three Consecutive Days of Annual Maximum Rainfall: The Case of Gimbi Town, Oromia Region, Ethiopia

Rainfall data frequency analysis and probability distribution enable future extreme events. Determining the magnitude of an extreme rainfall event for a given probability level is crucial for constructing irrigation and other hydraulic systems. On Earth, rainfall is a rare but significant hydrological characteristic. The analysis was for one to three consecutive days of maximum annual rainfall using a variety of widely used probability distributions. In order to determine the best-fit probability distribution, daily rainfall data for Gimbi Town were taken from 1995 to 2019 and gathered from the Ethiopian Meteorological Institute (EMI). The chi-square (χ²) test was used to measure the goodness of fit between the expected and observed values. The chi-square value of the 1, 2 and 3-day maximum annual daily rainfall was 8.8, 3.8, and 5.4 respectively. Chow method was the best-fit probability distribution for predicting the annual 1 and 2-day maximum rainfall for various return periods and the log-Pearson type-III distribution was the best-fit probability distribution for predicting the annual 3-day maximum rainfall for various return periods. The results of this study would be useful for agricultural scientists, decision-makers, policy planners, and researchers for agricultural development and construction of small soil and water conservation structures, irrigation, and drainage systems in Gimbi Town, Ethiopia.