An investigation of the characteristics of the onset and cessation of the rains in Nigeria

Summary Rainfall and potential evapotranspiration (PE) data spanning 35 years (1959–1993) were analysed to determine the onset and cessation of the rains for 4 selected stations in each of the 4 major selected zones of Nigeria. The characteristics of onset and cessation of the rains have been categorised as normal, early and late. The pattern of occurrence of each category varies among the ecological zones. For instance, the occurrence of normal onset of the rains is highest at locations in the Forest and Guinea Savanna Zones. In the Sudan Savanna area, however, the occurrence of normal onset of the rains is equal with that of late occurrence. It was, however, found that the occurrence of normal cessation of the rains is higher than early or late cessation at locations in all the zones. Furthermore, the occurrence of each category of the cessation of the rains is more consistent than that of the onset. The influence of the Inter-Tropical Discontinuity (ITD) on the latter observation have been noted. Further analysis of the characteristics of the onset and cessation of the rains showed that occurrence of short-falls in the duration of the rainfalls for normal agricultural activaties is peculiar to all the zones. However, such shortfalls are lower in the Forest Zone than in the Savanna regions, indicating that the reliability of the duration of the rainfalls for normal agricultural activities decreases northwards from the forest to the Sudan Savanna region. The implications of the observations for farm operations have been stressed.With 10 Figures