Seasonal Variability of Rainfall and its Decadal Anomaly over Nigeria: Possible Role of Solar and Geomagnetic Activities

This study investigates seasonal variations of rainfall and its decadal anomaly over Nigeria and the possible role of solar and geomagnetic activities. Sunspot number and geomagnetic aa index were used as solar indices. Monthly mean rainfall data from Nigeria Meteorological Agency was used in this study. Bivariate and power spectral density analyses were employed in analyzing the data. Rainfall anomaly was calculated using the mean of the base period, 1981 – 2010. Seasonally, rainfall varies from the coastal areas to the hinterland from January to December during rainy and dry seasons. On the decadal rainfall anomaly, positive anomalies increases steadily towards the coastal regions; indicating an increase in rainfall characteristic, whereas negative anomalies increases towards the northern regions; depicting decrease in rainfall characteristic. This was confirmed from the Mann-Kendall trend test. These variations are evidence of climate change. Correlation analysis revealed that the correlation of rainfall with sunspot and aa index were statistically insignificant. The spectral analysis revealed signatures of solar and geomagnetic activities on the rainfall spectrum. We therefore infer that, in addition to anthropogenic activities, solar and geomagnetic activities might play important role in the observed climate change in Nigeria; since rainfall is used as climate change indicator.