Hujan Monsun Indonesia: Karakteristik, Variabilitas dan Proyeksi Perubahannya di Masa Depan.

Abstract

Monsun secara sederhana didefinisikan sebagai variasi musiman angin dan curah hujan. Monsun menjadi dasar iklim di wilayah ekuator, di mana setiap variasi iklim yang terjadi mengacu pada kondisi normal monsun. Monsun memainkan peran penting dalam berbagai sektor kehidupan manusia, seperti pertanian, ekonomi, sumber daya air, dan ekosistem. Penelitian sebelumnya menunjukkan bahwa iklim Indonesia didominasi oleh pola monsunal, yang menjadi fondasi iklim utama di wilayah ini. Meskipun penting, pengetahuan tentang aktivitas monsun di Indonesia masih terbatas, dengan banyak fitur yang belum terungkap. Saat ini, pemantauan hujan monsun di Indonesia menggunakan Indeks Monsun Australia (AUSMI), yang tidak akurat dalam menangkap variabilitas hujan monsun Indonesia karena perbedaan karakteristik regional. Penggunaan AUSMI kurang tepat, dan penelitian ini bertujuan untuk memberikan pemahaman lebih baik tentang karakteristik dan variabilitas hujan monsun Indonesia, serta proyeksi perubahan di masa mendatang. Penelitian ini menganalisis karakteristik hujan monsun Indonesia menggunakan metode Singular Value Decomposition (SVD) pada variabel curah hujan, suhu muka laut (SST), dan angin. Hasil analisis mengungkap bahwa wilayah hujan monsun Indonesia mencakup bagian selatan dan tengah, dengan dua fase utama: musim hujan (November–April) dan musim kemarau (Mei–Oktober). Selain itu, hujan monsun Indonesia dipengaruhi oleh dipol meridional SST, anomali tekanan di Siberia dan Indo-Australia, serta angin baratan di Samudra Hindia. Untuk memahami lebih dalam karakteristik hujan monsun Indonesia, penelitian ini mendefinisikan Indeks Monsun Indonesia berdasarkan komponen angin zonal pada ketinggian 850 hPa, yang berkorelasi erat dengan curah hujan di wilayah monsun. Indeks ini lebih akurat dalam menangkap variabilitas antar tahunan curah hujan monsun Indonesia dibandingkan AUSMI. Variabilitas hujan monsun Indonesia sangat luas, dipengaruhi oleh interaksi dengan fenomena iklim global seperti El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Quasi-Biennial Oscillation (QBO), dan Pacific Decadal Oscillation (PDO). Di antara fenomena tersebut, ENSO paling banyak dikaji. Sementara itu, QBO belum banyak diteliti meskipun berpotensi memengaruhi variabilitas musiman hujan monsun Indonesia. Hasil analisis variabel iklim juga menunjukkan bahwa perubahan iklim telah berdampak nyata di Indonesia, terutama di sektor pertanian yang sangat rentan terhadap kekeringan. Penelitian ini mengkaji dampak kekeringan di masa depan akibat perubahan curah hujan monsun. Meskipun intensitas curah hujan secara umum tidak berubah signifikan, durasi kekeringan diperkirakan akan meningkat, dengan rata-rata mencapai 9 bulan di masa depan, baik pada near future (NF: 2025– 2055) maupun far future (FF: 2071–2100). Kekeringan di masa depan cenderung dimulai pada awal musim kemarau, dengan peningkatan kejadian yang dimulai sejak bulan Juni di semua skenario

The monsoon is simply defined as the seasonal variation of wind and rainfall. The monsoon serves as the foundation of the climate in equatorial regions, where all climate variations refer to the normal monsoon conditions. The monsoon plays a crucial role in various sectors of human life, such as agriculture, economy, water resources, and ecosystems. Previous studies have shown that Indonesia’s climate is dominated by the monsoonal pattern, which forms the primary basis of the country’s climate. Despite its importance, knowledge about monsoon activity in Indonesia is still limited, with many features remaining undiscovered. Currently, monsoon monitoring in Indonesia uses the Australian Summer Monsoon Index (AUSMI), which is inaccurate in capturing the variability of Indonesia’s monsoon due to its distinct regional characteristics. The use of AUSMI is less suitable, and this study aims to provide a better understanding of Indonesia's monsoon rainfall characteristics, variability, and future projections. This study analyzes the characteristics of the Indonesian monsoon rainfall using Singular Value Decomposition (SVD) on variables such as rainfall, sea surface temperature (SST), and wind. The results reveal that the monsoon region of Indonesia includes the southern and central parts, with two main phases: the rainy season (November–April) and the dry season (May–October). Additionally, the Indonesian monsoon is influenced by the meridional SST dipole, pressure anomalies in Siberia and Indo-Australia, and westerly winds in the Indian Ocean. To gain deeper insights into Indonesia's monsoon rainfall characteristics, this study defines the Indonesian Monsoon Index based on the zonal wind component at 850 hPa, which is strongly correlated with rainfall in the monsoon region. This index is more accurate in capturing the interannual variability of Indonesian monsoon rainfall compared to AUSMI. The variability of the Indonesian monsoon is extensive, influenced by interactions with global climate phenomena such as the El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Quasi-Biennial Oscillation (QBO), and Pacific Decadal Oscillation (PDO). Among these phenomena, ENSO has been the most studied, while QBO has received little attention, despite its potential impact on the seasonal variability of Indonesia’s monsoon. Climate variable analysis also shows that climate change has had a significant impact on Indonesia, especially in the agricultural sector, which is highly vulnerable to drought. This study examines the potential future impact of drought due to changes in monsoon rainfall. While the overall intensity of rainfall is not expected to change significantly, the duration of drought is projected to increase, with an average duration of up to 9 months in the future, both in the near future (NF: 2025– 2055) and the far future (FF: 2071–2100). Future droughts are likely to start in the early dry season, with an increase in occurrences starting as early as June under all scenarios.