Comparative Analysis of Effective Onset Rainfall and Intra-Seasonal Variability over Minna and Sokoto, Nigeria

Abstract

This paper analysed and compared the effective onset rainfall and its intra-seasonal variability in Minna and Sokoto using daily rainfall data from the archives of Nigerian Meteorological Agency (NIMET)for the period of 35 years (1981-2015).The onset date of rain, trends and intra-seasonal variability were determined using a drought monitoring and early warning (EW) methodology based on an intra-seasonal rainfall monitoring index (IRMI). The uncertainty in the onset date from one season to another were also determined by subtracting the succeeding onset date from the previous. The results demonstrate distinction in the effective onset date over the two stations as the onset date were earlier in Minna. The pattern in the onset date were similar as the earliest (1997) and late (1987) onset year were the same indicating interconnectivity in the rainfall regime across the two stations.The effective onset date showed a downward trend implying tendencies toward early onset date at the two stations.The intra-seasona rainfall analysis showed an increased frequency of intense and distribution of rainfall in years with earl onset rainfall at the two stations. As the beginning of seasonal rainfall in the two stations are basicall different,this should signal a need for specific cropping type in each stations.