Abstract

The trends of rainfall have a great impact on the hydrologic cycle and therefore affect both the quality and quantity of water resources. There is therefore the need to examine the trend of rainfall in Sudano- Sahelian Ecological Zone of Nigeria comprising Kebbi, Sokoto, Kano, Jigawa, Yobe, Katsina and Borno States. The study examined the trend in rainfall patterns over a period of fifty years i.e. 1960-2009 so as to know the effect of rainfall variability in the occurrence of drought and flood in the zone. The study makes use of rainfall data, which were collected from the Nigeria Meteorological Agency, Oshodi, Lagos. The Standardized Anomaly Index was used to test for fluctuations in rainfall while the Spearman Rank Statistics was used to look for the trend in rainfall. The study revealed that there was a downward trend in rainfall amounts in the 1970s and 1980s which was responsible for the drought episodes of 1972/73 and 1980 and an upward trend in the amount of rainfall between 1990 and 2009 which accounts for the flood episodes in Northern Nigeria. There is a general increase of 5% in annual rainfall over the entire fifty years under study in the zone due to an observable 5.4% increase in mean rain-days and 4% increase in the rains that fall as heavy rain, which was found to be responsible for the increase in runoff, ground water recharge and the frequent flood episodes in the zone. Based on this study, it can therefore be concluded that the Sudano-Sahelian Ecological Zone of Nigeria has been experiencing an increase in the annual rainfall with little recession in 1970s and 1980s, the rainfall has been very high and this has significant consequences on water resources in the zone with the zone becoming prone to flood events, erosion and sedimentation which may have adverse effect on both quantity and quality of water available for human consumption. The study therefore recommends that a study of the interactions between the ecosystems due to the distortion in the hydrology of the zone should be carried out among others.

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