Recent Trends and Fluctuations of Annual Rainfall in the Sudano-Sahelian Ecological Zone of Nigeria: Risks and Opportunities

Abstract

This study examines the recent trends and fluctuations in the rainfall regime of the Sudano-Sahelian Ecological Zone of Nigeria in order to discuss the risks and opportunities involve. Rainfall data (1949-2008) for eight meteorological stations were used for this analysis. In order to identify trends, the rainfall series was sub-divided into 30-year overlapping sub-periods (1949-1978, 1959-1988, 1969-1998 and 1979-2008) and the Cramer’s (tk) test was then used to compare the means of the sub-periods with the mean of the whole record period. The results of the test revealed that there was a change towards wetter conditions in the last 30-year period. The student’s t-test, td, was also used to examine the temporal changes in the rainfall series between the two non-overlapping sub-periods (1949-1978 and 1979-2008) and the result shows that Nguru and Katsina were significantly drier than the long-term mean. The 10-year running mean shows that annual rainfall for all the stations were below the long-term mean from the late 1960s to the early 1990s and above-average afterwards. The results of the linear trend lines revealed an increase in rainfall supply over the period of study. Some of the implications of these findings are that models built on the perceived decreasing rainfall, such as drainages, dams, have to be reviewed. On the other hand, farmers would take the advantage of the long growing seasons by the adoption of multiple cropping systems. It is recommended that government policies related to agriculture and water resources development should take into account the risks and opportunities associated with increasing wet conditions in the Sudano-Sahelian Ecological Zone of Nigeria.