Inter-Annual Variability Of Rainfall In Some States Of Southern Nigeria
Egor, A Egor, C Agbor
The study inter-annual variability of rainfall in some states in Southern Nigeria focuses on analyzing the trends and fluctuations in annual rainfall over six states in Southern Nigeria, covering a period of 1972-2012. In order to ascertain the variability's, and to model the annual rainfall for future prediction to enhance policy implementation, the quantitative and descriptive analysis techniques was employed. The rainfall series were analyzed for fluctuations using Standardized Anomaly Index
... (SAI), whereas the trends were examined using Statistical Package for Social Science Software (SPSS 17.0). At 95 percent confidence level, observations in the stations may be signals that the wetter period dominates the drier periods in this study. Each of the series contains two distinct periods when the rainfall anomalies (negative and positive) of a particular type were most significan t. The period where the annual rainfall is above one standard deviation from the mean annual rainfall is considered Wet, and the period below one standard deviation from the mean annual rainfall is considered Dry for each station. The results of the linear trend lines revealed an increase in rainfall supply over the period of study especially of recent. The annual rate of increase in rainfall over the period of investigation 1972-2012 were; 15.21mm/year for Calabar, 2.18mm/year for Port Harcourt, 22.23mm/year for Owerri, 3.25mm/year for Benin City, 5.08mm/year for Enugu, and 16.29mm/year f or Uyo respectively. The variability in amount of annual rainfall revealed that, in 2012 Calabar received the highest amount of rainfall of about 4062.70mm and the least value of 2099.4mm in 1973. In Porthacourt, the highest amount of rainfall occurred in 1993 with a value of 3911.70mm and the least value in 1983 with a value of 1816.4mm. Owerri recorded the highest amount of rainfall of about 3064.0mm in 2011, and the least value occurred in 1986 with a value of 1228.4mm. In 1976, Benin received the highest amount in rainfall of 2435.5mm and the least value of 1190.7mm occurred in 1983. Enugu received 2262.4mm as the highest amount of rainfall in 1997 and the least occurred in 1981 with a value of 913.10mm. From the period of investigation, Uyo received 3172.9mm as the highest amount of rainfall in 2011 and the least value of 1562mm in 1983. The predicted values for the modeled data suggests continues increase in amount of annual rainfall in all the locations. From the cumulative mean deviation graphs, Cal abar and Uyo indicate a tendency towards flood, while the other stations reveal a tendency towards drought.