The weather in some of the world’s most densely populated cities is swinging from droughts to floods and back again as rising temperatures play havoc with the global water cycle, a study commissioned by the charity WaterAid showed on Wednesday. “There will be winners and losers associated with climate change,” said Michael Singer of the Water Research Institute at Cardiff University, one of the authors of the study. China’s eastern city of Hangzhou and Indonesia’s capital of Jakarta topped the list of cities suffering from “climate whiplash”, or a rapid succession of prolonged floods and droughts, the study showed.