STATISTICAL MODELING OF MONTHLY RAINFALL AND TEMPERATURE AT SELECTED STATIONS IN FOREST AND SAVANNAH ECOCLIMATIC REGIONS OF NIGERIA

Abstract

The modeling of monthly rainfall and temperature at selected stations in Nigeria was undertaken in the study. Autoregressive Integrated Moving Average (ARIMA) and Seasonal Autoregressive Integrated Moving Average (SARIMA) models were utilized. Seasonal characteristics of rainfall and temperature were analyzed using Minitab, G-stat Statistical software package and Statistical Package for Social Sciences (SPSS) for selected stations in the forest and savannah ecoclimatic regions of Nigeria. Data spanning a period of 30 years (1981-2010) were utilized. The accuracy and trend of time series was analyzed to give the monthly rainfall and temperature prediction for the succeeding year. The results showed that the model fitted into the data well and the stochastic seasonal fluctuation was successfully modeled. Rainfall was minimal in January, February, March and December over the selected stations in Northern, Nigeria but increased progressively in strength and intensity in the months of June, August and September over the selected stations in South west, and June and September over the selected stations in South –south, Nigeria. The highest rainfall intensity of 230mm was recorded in September over Warri and the lowest rainfall intensity of 52mm was recorded in August over Maiduguri. The rainfall intensity recorded over the selected stations in South-south stations was visibly higher than what was recorded over the selected stations in the Northern and the South-west stations. The highest minimum temperature of 250C and highest maximum temperature of 400C were observed in May over Maiduguri and lowest minimum and maximum temperature of 22.40C and 31.80C respectively were observed in March over Warri. The temperature value recorded over the selected stations in the North is reasonably higher than what was recorded over the selected stations in the South-south and the South-west stations. Over the selected stations in Northern, Nigeria, the Peak monthly mean rainfall amount of 91mm was experienced in August and rainfall intensity was very low in January (0.0mm), February (0.0mm), March (0.0mm) and December (0.0mm). Over the selected stations in South-west, Nigeria, the Peak monthly mean rainfall amount of 215mm was experienced in June and September and rainfall intensity was very low in January (0.0mm) and December (0.0mm). Over the selected stations in South-south, Nigeria; the Peak monthly mean rainfall amount of 325mm was experienced on September and rainfall intensity is very low in December (0.0mm). The study concluded that Seasonal Autoregressive Integrated Moving Average (SARIMA) model was a proper method for modeling and predicting the monthly rainfall and temperature.