Monthly rainfall data for 16 stations in Nigeria were collected for the period . From this, the annual, the wet season, the onset, the peak, and the retreat rainfall data were derived. The patterns of fluctuations of rainfall were analysed therefrom. The series were first examined for trends and then for periodic fluctuations. Trend analysis revealed that a majority of the series exhibit negative trends, and in some cases the trends were significant. For all the series analysed, there is the general tendency towards increasing aridity. Spectral analysis indicates prominent periods of between 2-and 8-year cycles. Other periodicities observed include 1 6 , 18-, and 21-year cycles.

The study assessed changes in the rainfall regime in Nigeria between 1961 and 2004 in terms of (a) absolute seasonality-the length of dry and wet season; (b) relative seasonality-rainfall contrast during the year; (c) number of rainfall maxima and minima; and (d) timing of rainfall maxima and minima. Trends in the mean monthly surface locations of the Inter-tropical Discontinuity (ITD) were also examined as a prominent factor of the rainfall regime. Changes in the regime were examined over four time slices: