Time Series Analysis of Rainfall Using Seasonal ARIMA (SARIMA) and Sama Circular Model (SCM): Study from Vadamaradchi, Jaffna, Sri Lanka

The time series analysis was performed with Seasonal Autoregressive Integrated Moving Average (SARIMA) and Sama circular model (SCM) for the rainfall of Ampan, Karaveddi, and Puloly regions of Jaffna to understand the behaviour of rainfall and forecast it with a suitable model. Minitab 17 software was used to run the model with the available monthly data from 2013 to 2019. Time series plots were used for pattern recognition, the independence of the residuals was checked using autocorrelation function (ACF), and Lijung-Box Q statistics (LBQ). The normality of residuals was checked using probability plot. The model with the lowest predicting errors was selected to forecast the future values. The monthly rainfall fluctuates around the mean of 41.6, 71.9, and 35.3 mm for Ampan, Karaveddi, and Puloly respectively. The models SARIMA (0,0,0) (0,1,1)6, SARIMA (1,2,1) (0,1,1)6, and SARIMA (1,1,0) (0,1,1)6 were found as most appropriate for Ampan, Karaveddi, and Puloly respectively and