Spectral Analysis and SARIMA Model for Forecasting Indian Ocean Dipole (IOD) and Rainfall in West Aceh Regency

Abstract

Indian Ocean Dipole (IOD) in the Indian Ocean is one of the climatic phenomena that affects climate conditions in western Indonesia. West of Aceh Regency is one of the districts in Aceh Province which borders and faces the Indian Ocean directly, so it has a significant impact due to climate events caused by the IOD phenomenon. Analysis for examines the occurrence of climate phenomena is needed to minimize the adverse effects due to the IOD phenomenon. Spectral analysis by calculating the periodogram and the SARIMA model for forecasting historical data. The data used are monthly data on the Indian Ocean IOD index and rainfall in West of Aceh in the period January 2010 to December 2019. The purpose of this study was to determine the periodicity of the IOD index data and rainfall, get a model and obtain the results of forecasting the IOD index and rainfall, and see the relationship of IOD to rainfall in West of Aceh. The results obtained in the spectral analysis are the characteristics of changes in the IOD index tend to increase or decrease in the IOD index every 17 months and the characteristics of changes in rainfall in West of Aceh tend to increase or decrease in rainfall every 6 months. The best model for predicting IOD index data is the SARIMA model (2,1,3)(0,1,1)17. Forecasting for 2020 and 2021 tend to show a downward trend in 2020 and an upward trend in 2021. While the best model for predicting West of Aceh rainfall data is the SARIMA model (2,0.2)(0,1,1)6. Forecasting for 2020 and 2021 tend to experience high rainfall in April and October for each year. The relationship obtained by the IOD index to rainfall in West of Aceh is when the IOD index is in a positive phase, rainfall in the West of Aceh region tends to decrease. Conversely, when the IOD index is in the negative phase, rainfall in the West of Aceh region tends to increase.