In October 2013, the coastal Chinese city of Ningbo, which is home to 10 million people and the world’s fourth-largest port, was hit with a torrential flood. Wastewater systems and rivers overflowed. Five people were killed, and more than 100,000 houses were inundated with brown flood water polluted with sewage, industrial chemicals and heavy metals.  Flooding is a perennial problem in southern and central China, but in the last three decades it has gotten much worse. All along China’s coastline, cities are sprawling, and developers are paving over wetlands and hemming in rivers between concrete walls, leaving no place for floodwater to go. In summer 2020, China suffered 21 large-scale floods — the most in over two decades. More than 30 rivers swelled to their highest levels ever recorded. Authorities had to blow up smaller dams to ease pressure on the gargantuan Three Gorges Dam astride the Yangtze River, which may have been close to structural failure.