VERIFIKASI PREDIKSI CURAH HUJAN ENSEMBLE MENGGUNAKAN METODE ROC

Elza Surmaini, Tri Wahyu Hadi

Abstract


Prediksi musim dibutuhkan untuk merencanakan waktu tanam adalah 1-2 musim ke depan. Informasi jumlah curah hujan dan deret hari kering merupakan parameter yang diperlukan dalam perencanaan pertanian. Penelitian bertujuan untuk menguji kemampuan model prediksi curah hujan musim ensemble, menentukan peluang optimal pengambilan keputusan, dan menentukan akurasi prediksi berdasarkan peluang optimal. Verifikasi model dilakukan untuk musim kemarau (MK) I (Februari-Mei) dan MK 2 (Mei-Agustus) pada daerah dengan pola hujan monsunal (Kabupaten Indramayu) dan MK 1 (Mei-Agustus) untuk pola hujan lokal (Kabupaten Bone). Keluaran prediksi musim dari Climate Forecast System (CFS) v2 digunakan untuk men-downscale jumlah curah hujan (CH) dan deret hari kering ≥15 hari (DHK15) di wilayah penelitian. Downscaling menggunakan metode Constructed Analogue dengan prediktor angin pada paras 850 hPa pada lima wilayah monsun. Metode yang digunakan untuk mengevaluasi keandalan prediksi probabilistik adalah Relative Operating Characteristics. Peluang optimal berdasarkan cut point ditentukan menggunakan Youden Indeks, dan akurasi prediksi pada peluang optimal ditentukan dengan metode Proportion of Correct. Hasil penelitian menunjukkan bahwa pengambilan keputusan menggunakan peluang optimal berdasarkan cut point untuk pengambilan keputusan dapat meningkatkan keandalan prediksi jumlah curah hujan sebesar 5-17% pada MK1 dan 3-24% pada MK2, dan frekuensi DHK15 sebesar 2-10%.

 

The seasonal predictions are needed to adjust planting time for the following 1-2 seasons. Information on the amount of rainfall and dry spell is an appropriate parameter in agricultural planning. The research aimed to examine the skill of ensemble seasonal rainfall prediction models, to determine an optimal probability for making decisions, and to determines the skill of seasonal prediction based on optimal probability. Model verifications were assessed in Dry Season Planting (DSP)1 (February-May) and DSP2 (May-August in Monsoonal (Indramayu District) dan DSP1 (Mei-August) in Local (Bone District) Rainfall Pattern. We used Relative Operating Characteristics to evaluate the skill of probabilistic predictions. The optimal cut-point was assessed using the Youden Index, and the skill of prediction at an optimal cut point was determined using the Proportion of Correct method. In conclusion, the results show that the use of the optimal probability at the cut point in decision-making increase the skill of rainfall prediction 5-17% in DSP1 and 3-24% in DSP2. As for the frequency of DHK15, the skill increases by 2-10%.


Keywords


prediksi musim; keandalan; curah hujan; deret hari kering; peluang optimal

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DOI: http://dx.doi.org/10.31172/jmg.v21i1.618

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