Rainfall variability: implication for flood occurrence in Ibadan and Ikeja, south-west Nigeria

Abstract Rainfall in Nigeria varies in distribution and amount at temporal and spatial scales. One of the risks associated with rainfall variability is flood. Flood is a natural phenomenon that causes havoc to lives, properties, economic, cultural heritage and environment in a flood-prone region. Literature has revealed that the major determinant of this natural phenomenon is rainfall. Reoccurrence of floods in some parts of southwest (SW) Nigeria has demanded investigation into the distribution of rainfall for proper monitoring of its increment. Rainfall distribution data covering Ikeja and Ibadan from year 2005 to 2011 were obtained from the Nigerian Meteorological Agency, Nigeria. The obtained data were used to compute monthly and annual average rainfall occurrences in the two locations using a semi-automated technique. Basic statistics were performed on the data to know the trend in the rainfall pattern, which could be used for flood prediction and management in the study area. The maximum annual rainfall recorded in Ikeja during the period of investigation ranged from 327.6 to 476.9 mm, while that of Ibadan ranged from 234.1 to 373.4 mm. The driest years in Ibadan and Ikeja were 2007 and 2009, while the wettest years in the two locations were 2008, respectively. The correlation between the monthly variations in each year across the two locations showed positive correlation, which are significant at 1% level. The trend of rainfall occurrence in SW Nigeria revealed that for every dry year, there is always subsequent wet year, which could generate flood. Proper data acquisition, management and analysis of rainfall data would assist to mitigate the occurrence of flood disaster in our environment, which is directed towards actualizing sustainable cities and communities.