Application of Vector Auto Regression Model for Rainfall-River Discharge Analysis

Abstract

River discharge quantity is highly depended on rainfall and initial condition of river discharge; hence, the river discharge has auto-correlation relationships. This study used Vector Auto Regression (VAR) model for analysing the relationship between rainfall and river discharge variables. VAR model was selected by considering the nature of the relationship between rainfall and river discharge as well as the types of rainfall and discharge data, which are in form of time series data. This research was conducted by using daily rainfall and river discharge data obtained from three weirs, namely Sojomerto and Juwero, in Kendal Regency and Glapan in Demak Regency, Central Java Province. Result of the causality tests shows significant relationship of both variables, those on the influence of rainfall to river discharge as well as the influence of river discharge to rainfall variables. The significance relationships of river discharge to rainfall indicate that the rainfall in this area has moved downstream. In addition, the form of VAR model could explain the variety of the relationships ranging between 6.4% -70.1%. These analyses could be improved by using rainfall and river discharge time series data measured in shorter time interval but in longer period. Keywords: rainfall, river discharge, VAR AbstrakBesar kecilnya debit sungai sangat tergantung pada hujan dan kondisi awal dari debit itu sendiri, sehingga terdapat hubungan auto-correlation. Sementara itu, proses pengalihragaman dari hujan menjadi debit aliran pada sungai membutuhkan waktu (lag) antara terjadinya hujan dan kenaikan debit sungai. Penelitian ini menggunakan model Vector Auto Regression (VAR) untuk menganalisis hubungan antara curah hujan dan debit. Model VAR dipilih dengan mempertimbangkan bentuk hubungan antara kedua variabel dan tipe data hujan maupun debit yang keduanya merupakan data deret waktu (time series). Data curah hujan dan data debit harian diperoleh dari tiga bendung yaitu Bendung Sojomerto, Bendung Juwero di Kabupaten Kendal dan Bendung Glapan di Kabupaten Demak, Provinsi Jawa Tengah. Hasil uji kausalitas menunjukkan hubungan yang signifikan baik antara pengaruh variabel curah hujan terhadap debit maupun pengaruh debit terhadap curah hujan. Hubungan kausalitas yang signifikan antara debit terhadap curah hujan mengindikasikan bahwa karakteristik hujan di wilayah ini bergeser dari hulu ke hilir. Model VAR yang terbentuk dapat menjelaskan keragaman hubungan antara kedua variabel antara 6,4% -70,1%. Hasil penelitian menunjukkan bahwa model statistik berpeluang digunakan dalam peramalan hubungan hujan dan debit sungai. Analisis ini dapat dipertajam dengan menggunakan data deret waktu pada interval waktu yang lebih rapat dan periode yang lebih panjang.Kata Kunci: hujan, debit sungai, VAR.

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