🇮🇩Indonesia

Indonesia spans about 6°N to 11°S, forming the world's largest archipelago with roughly 1,904,569 km² distributed across more than 17,000 islands that stretch approximately 5,100 km along the Equator from western Sumatra to West Papua, encompassing Sumatra, Java, Borneo (Kalimantan), Sulawesi, Bali, the Lesser Sunda Islands (Lombok, Flores, Timor), the Maluku Islands, and Papua.

The archipelago sits astride the Pacific Ring of Fire with intensely active volcanoes including Krakatau, Merapi, Sinabung, Tambora, and Mount Agung, while the highest peak Puncak Jaya reaches 4,884 m in Papua, the highest island peak on Earth and home to the Carstensz glaciers, rare equatorial ice. The climate is overwhelmingly tropical rainforest (Af) across most islands, transitioning to tropical monsoon (Am) in monsoon-dominated regions and tropical savanna (Aw) in the dry Lesser Sundas (Sumba, Timor) and Java's eastern interior.

Jakarta on Java has highs of 31–33°C and nights around 25°C year-round with 1,860 mm rainfall in a clear monsoon pattern. Medan sees highs of 31–33°C and nights around 24°C with 2,240 mm, while Padang on Sumatra's wet coast has highs of 31–32°C and nights near 24°C with about 4,300 mm. Banjarmasin, Manado, Denpasar, Kupang, and Jayapura have highs of about 29–34°C and nights of 21–25°C, with Kupang in dry West Timor receiving about 1,440 mm, and Puncak Jaya's summit area holds retreating tropical glaciers.

ENSO dominates variability: El Niño years (1997–98, 2015–16, 2019, 2023) bring drought, peatland fires, and haze across Sumatra and Kalimantan. Heavy monsoon rain brings flooding, notably in Jakarta (2007, 2013, 2020). Major events include the 2018 Palu earthquake-tsunami, 2010 Mount Merapi eruption, 2018 Anak Krakatau collapse-tsunami, recurrent severe Jakarta floods worsened by rapid land subsidence, sea-level rise, glacier retreat, and coral bleaching.

Our archive covers 160 Indonesian cities with daily ERA5 reanalysis data going back to 1940. The hottest July afternoons are in Semarang, with average highs around 32.6°C, while Banjar has the coldest January nights, with average lows near 12.9°C. Comparing the last decade against the 1940–1970 baseline, mean temperatures across these cities have risen by about 1.3°C.