🇱🇦Laos

Laos spans 13°55′–22°30′N as a landlocked Southeast Asian country (approximately 236,800 km²) on the Indochinese peninsula bordering China, Vietnam, Cambodia, Thailand, and Myanmar, dominated by the Annamite Range running along the Vietnamese border (Phou Bia 2,819 m, the country's highest peak), the rugged northern highlands of Phongsali and Houaphanh, the central Bolaven Plateau (a fertile coffee-growing volcanic upland), and the Mekong River valley along the Thai border (the country's spine, with Vientiane and Luang Prabang). The climate is uniformly tropical monsoon — tropical savanna (Aw) across the Mekong lowlands, tropical monsoon (Am) on the wet eastern Annamite slopes, and a humid subtropical (Cwa) tendency at higher northern elevations.

Vientiane averages 21°C in January and 30°C in April with 1,640 mm rainfall almost entirely from the southwest monsoon May–October, with the severe pre-monsoon hot season April–May regularly above 38°C. Luang Prabang records 21°C in January and 28°C in April with 1,360 mm. Pakse on the Bolaven margin averages 23°C in January and 30°C in April with 2,030 mm.

Sam Neua in the high north registers 16°C in January and 26°C in April with 1,500 mm — among Laos's coolest cities. The Bolaven Plateau and the windward eastern Annamite slopes receive 3,000–4,000 mm. Major events include the severe July 2018 Xe-Pian Xe-Namnoy hydropower dam collapse during a tropical-depression-driven flood (over 71 deaths, displacing thousands), recurrent severe Mekong floods in 2008 and 2018, the severe 2019 and 2020 multi-year droughts shrinking the lower Mekong, intensifying pre-monsoon heatwaves above 42°C (Laos broke 43.5°C at Vientiane in May 2023), and accelerating Mekong delta upstream-impact compounded by increasing Chinese damming.

Our archive covers 2 Lao cities with daily ERA5 reanalysis data going back to 1940. The warmest July averages occur in Vientiane, around 31.5°C, while Vientiane records the coldest January nights near 16.2°C. Comparing the last decade against the 1940–1970 baseline, mean temperatures across these cities have risen by about 1.5°C.5°C at Vientiane.