EKSPERIMENTASI PRAKIRAAN DEBIT ALIRAN (INFLOW) DENGAN MODEL ARIMA DAN KEMUNGKINAN PENERAPANNYA SEBAGAI METODE ALTERNATIF UNTUK EVALUASI MODIFIKASI CUACA (Kasus : Inflow Waduk Saguling)
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Abstract
ARIMA. Tujuan penelitian ini adalah melakukan kajian penggunaan model ARIMA untuk memprakiraan inflow bulanan dan kemungkinan penerapannya untuk evaluasi Modifikasi Cuaca. Data inflow bulanan waduk Saguling periode 1986 – 1996 digunakan untuk identifikasi dan estimasi parameter/koefisien model, sedangkan data tahun 1997-2000 digunakan untuk pengujian hasil model. Dari hasil kajian diketahui bahwa data time series tidak stasioner dan menunjukkan adanya pola musiman dengan panjang musim 12 bulan. Untuk mencapai data time series yang stasioner pertama kali dilakukan transformasi data asli ke nilai logaritmik, kemudian dilanjutkan dengan pembedaan pertama tidak musiman dan musiman (d=1) dan (D=1) . Perhitungan koefisien model dilakukan dengan menggunakan paket software STATISTICA/w.5.0 dengan hasil sebagai berikut: (p=0.5722);(q = 0.9565); (Ps = 0.0944) dan (Qs = 0.8105). Hasil pembandingan antara keluaran model dengan data aktual memberikan hasil baik. Hal ini berarti model ARIMA (1,1,1)(1,1,1)12 layak untuk memprakirakan inflow bulanan Waduk Saguling.
Box and Jenskins (1976) have developed time series model used in forecasting, namely
ARIMA. The aim of this research is to study the use of ARIMA model to forecast monthly
inflow and the possibility of its application for Weather Modification evaluation Monthly inflow data from Saguling dam during 1986 - 1996 has been used to identity and estimate parameter or coefficient of model and data 1997 - 2000 was used for fitting test model. Result of study is known that pattern of time series data is non-stationery and there is seasonal pattern with period 12 month. In order to reach stationery data, firstly we transform the original data to logarithmic value. And from logarithmic value series data we did next transformation to non-seasonal and seasonal differencing order one (d=1) and (D=1). Coefficients model are calculated by using STATISTICA/w.5.0 and the coefficients value are : (p=0.5722);(q = 0.9565); (Ps = 0.0944) and (Qs = 0.8105) Comparing forecast model and actual data it gives goods result. Therefore the model ARIMA (1,1,1)(1,1,1) is appropriate to forecast the monthly inflow of Saguling dam.
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