The project will divert six trillion gallons of water a year from the Yangtze, seen from Wuhan, Hubei Province.Credit...Gilles Sabrie for The New York Times DANJIANGKOU, China — North China is dying. A chronic drought is ravaging farmland. The Gobi Desert is inching south. The Yellow River, the so-called birthplace of Chinese civilization, is so polluted it can no longer supply drinking water. The