Every summer, Dongting Hu, China’s second-largest freshwater lake, swells in size as flood water from the Yangtze River flows into its borders. Dams and dikes are erected around the lake’s edges to protect against flooding. But this year, not for the first time, they were overwhelmed. For three days in early July, more than 800 rescue workers in Hunan province scrambled to block the breaches. One rupture alone took 100,000 cubic metres of rock to seal, according to Zhang Yingchun, a Hunan official. At least 7,000 people had to be evacuated. It was one of a series of disasters to