PROYEKSI CURAH HUJAN DI WILAYAH JAWA–NUSA TENGGARA MENGGUNAKAN MODEL REGCM5 BERBASIS DATA CMIP6

Abstract

Wilayah Jawa – Nusa Tenggara rentan terhadap dampak perubahan iklim, terutama variabilitas curah hujan musiman yang memengaruhi sektor pertanian. Penelitian ini mengevaluasi kinerja tiga model iklim CMIP6 (EC-Earth3, CMCCESM2, NorESM2-MM) terhadap data observasi CHIRPS periode historis menggunakan diagram Taylor dan Taylor Skill Score. Model EC-Earth3 menunjukkan performa terbaik dan dipilih sebagai input utama untuk simulasi dynamical downscaling dengan RegCM5. Faktor koreksi berbasis metode delta-ratio dihitung dari keluaran RegCM5 dan EC-Earth3, diterapkan pada seluruh model CMIP6 untuk periode historis dan proyeksi. Koreksi bias terhadap data observasi CHIRPS juga dilakukan untuk meningkatkan akurasi. Proyeksi curah hujan periode 2026–2055 berdasarkan skenario SSP2-4.5 dan SSP5-8.5 menunjukkan penurunan intensitas curah hujan musim hujan (DJF) sekitar 18% dan peningkatan curah hujan musim kemarau (JJA) sebesar 22%. Kondisi ini berpotensi berdampak signifikan pada sektor pertanian, dengan wilayah pesisir Pulau Jawa paling rentan terhadap perubahan tersebut.

The Java–Nusa Tenggara region is vulnerable to the impacts of climate change, particularly seasonal rainfall variability that affects the agricultural sector. This study evaluates the performance of three CMIP6 climate models (EC-Earth3, CMCC-ESM2, and NorESM2-MM) against CHIRPS observational data for the historical period using the Taylor diagram and Taylor Skill Score. EC-Earth3 model demonstrated the best performance and was selected as the primary input for dynamical downscaling simulations using RegCM5. A correction factor based on the delta-ratio method was calculated from RegCM5 and EC-Earth3 outputs, and applied to all CMIP6 models for both historical and projection periods. Bias correction against CHIRPS data was also performed to improve projection accuracy. Rainfall projections for 2026–2055 under SSP2-4.5 and SSP5-8.5 scenarios indicate a decrease in wet season (DJF) rainfall intensity by approximately 18% and an increase in dry season (JJA) rainfall by 22%. These changes could significantly affect agriculture, with coastal areas of Java being the most vulnerable to such impacts.