🇮🇩Indonesia

Indonesia spans 6°08′N to 11°08′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 tallest point in the Pacific and home to the Carstensz glaciers, Asia's only 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 averages 27°C year-round with 1,860 mm rainfall in a clear monsoon pattern. Medan records 27°C with 2,250 mm, while Padang on Sumatra's wet coast sees 26°C with 4,460 mm. Banjarmasin, Manado, Denpasar, Kupang, and Jayapura average 27°C with 2,500–2,710 mm and 1,440 mm respectively, and Puncak Jaya summit averages −5°C with retreating tropical glaciers.

ENSO dominates variability—strong El Niño years (1997–98, 2015–16, 2019, 2023) bring drought, peatland fires, and haze across Sumatra and Kalimantan. La Niña amplifies monsoon 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 (land subsidence ~25 cm/year), sea-level rise, glacier retreat, and coral bleaching.

Our archive covers 161 Indonesian cities with daily ERA5 reanalysis data going back to 1940. The warmest July averages occur in Semarang, around 32.6°C, while Banjar records the coldest January nights 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.