Implications of Trends and Cycles of Rainfall on Agriculture and Water Resource in the Tropical Climate of Nigeria

Abstract

Trends and cycles of rainfall over Nigeria, as well as their implications for water resources and agriculture, have been studied since 1960 on annual, seasonal and monthly bases. Rainfall data of 47 years (1960 – 2006) were obtained for twenty stations over Nigeria for the evaluation of trends using the Mann-Kendall test. Auto correlation spectral analysis was also used to detect cycles of rainfall. The result showed dominant peaks in rainfall return at various rates. For instance, Akure, Benin, Calabar, Maiduguri and Yola stations had decreasing trends of annual rainfall at rates of 1.084, 0.03, 1.80, 0.75, and 0.12 mm/month/yr, respectively with return periods between 1-2 years and 7-10 years. Rainfall trends increased in about 75 % of the locations with return period of dominant peaks varying between 1-2 years and 15 years. Abuja recorded the highest peak of rainfall in the month of October at the rate of 4.7 mm/month/yr with return period of 1-2 years. These results indicate different spatial effects on ecosystem and agriculture. Some of the implications of these trends on agriculture and water resources vary from one station to another, depending on the trends and magnitude of return period of rainfalls. Bauchi and Minna cities are expected to experience serious desertification and complete depletion of underground water due to the effects of no change in trend of rainfall. Meanwhile, agricultural activities are expected to thrive in places like Ibadan, Gusua, Osogbo and others that have moderate increase in trends of rainfall and temperature.