Seasonal and annual rainfall variations over Nigeria

Variations of monthly and annual rainfall over the southern, middle belt and northern regions of Nigeria as well as the country as a whole are examined for a 72–year period (1916–1987). In this way the zonal distribution of the country's rainfall is taken into account. The extent and nature of non‐random changes, such as fluctuations, trend, and persistence, are investigated. The fluctuations were filtered by a Gaussian low‐pass filter and the resulting curves are discussed. Trend analysis showed a tendency towards decreasing annual rainfall totals in all the regions, with rates of decrease being greatest after 1961 in the southern region. All regions experienced the reverse of the trend during the 1931–1960 period. Overall, no significant persistence was evident in all the series. Power spectrum analysis revealed the existence of significant oscillations in the rainfall totals. These have time periods of 2·00–2·82 years in the middle belt and northern regions. 3·00–4·80 years in the middle belt, and 8·009·60 years in all the regions. The implications of these fluctuations, and continued application of the 1931–1960 normal for planning purposes, are pointed out, as well as suggestions for further lines of inquiry.