The variability of the onset and end dates of the rainy season in Owerri Imo State, Nigeria.

The paper assessed the onset and end dates of the rainy season in Owerri Imo State, Nigeria using daily rainfall data from 1987 to 2016. The study employed the Hybrid method derived from Walter’s and Anyadike’s methods to determine the dates of the onset and end of the rainy season. The mean dates of the onset are 23rd Feb., 8th April, and 17th March for Walter, Anyadike, and Hybrid methods respectively. The end dates of the rainy season are the 28th, 19th, and 24th of October for Walter, Anyadike’s, and hybrid methods respectively. The area is experiencing early dates of the onset of the rainy season in recent years with later dates of the end of the rainy season. The end dates of the rainy season also significantly impact the rainfall regime in the State. The hybrid method proved better than Walter and Anyadike’s method of prediction in that it attenuated the underestimation associated with Anyadike’s method and the overestimation associated with Walter’s method. Therefore, it should be utilised in the assessment of the onset and end dates of the rainy season in the rainforest ecological zones. The study contributes to the body of knowledge in determining the onset and end dates of the rainy season in Owerri Imo State which is useful to rain-fed agriculture and other hydro-climatic planning.