Abstract:
Trends and cycles of rainfall and temperature in Nigeria since 1960 were studied on annual, seasonal and monthly bases and implications for water resources and agriculture were discussed. Data used for this study were collected from the Nigerian Meteorological Service, Oshodi Lagos. Rainfall and temperature data were available between 1960 and 2006 (47 years) for twenty stations in Nigeria. Mann-Kendall test was used to evaluate trends while Auto correlation spectral analysis was used to detect cycles, respectively.
The result showed that dominant peaks in rainfall and temperature return at various rates. For instance, Abeokuta, Akure, Enugu, Iseyin and Maiduguri stations were decreasing in trends of annual temperature at the rate of 0.080 °c /mo/yr, 0.040 °C/mo/yr, 0.030 °C/mo/yr, 0.110 °C/mo/yr and 0.120 °C/mm/yr respectively with return periods between 1-2 years and 7-10 years. Akure, Benin, Calabar, Maiduguri and Vola stations were decreasing in trends of annual rainfall at rate of 1.084 mm/mo/yr, 0.03 mm/mo/yr, 1.80 mm/mo/yr, 0.75 mmlmo/yr, and 0.12 mmlmo/yr respectively with return periods between 1-2 years and 7-10 years. However, annual temperature showed increasing trends in 15 out of 20 stations studied. The return period ranged between 1-2years to 13 15 years. Similarly, rainfall trends increased in about 75 % of the locations with return period of dominant peaks varying between 1-2years and 15years.
Abuja station recorded the highest peak in rainfall trends in the month of October at the rate of 4.7 mm/mo/yr with return period of 1-2years while Benin station recorded the highest peak in trends of temperature in the month of September at the rate of 3.390 °C/mo/yr with return period of 1-2years.
This result indicates different spatial effects on ecosystem and agriculture. Some of the implications of this trend on agriculture and water resources vary from one station to another, depending on the trends and magnitude of return period of both rainfall and temperature. For instance, Bauchi and Minna cities are expected to experience serious desertification and high level of depletion of underground water due to the continuous monotonic increase in trend of annual temperature and zero change in trend of rainfall. Agricultural activities are expected to thrive in stations like Ibadan, Gusau, Osogbo and others that have moderate increase in trends of rainfall and temperature
