Vietnam has recorded its hottest October in 65 years, with temperatures averaging 1.74°C higher than normal. With El Nino expected to bring more unusually warm weather, the country faces growing heat risks. Rapid urbanisation in Hanoi is adding to the problem, as concrete replaces green spaces and traps more heat — also known as the urban heat island effect. Between 1998 and 2022, Hanoi's built-up area more than doubled.