
According to the state news agency Xinhua, the drought – the worst for 60 years – is due to the lack of rainfall in the area round Poyang and its tributaries. Poor weather conditions this year are partly responsible. But putting the blame on them overlooks the role played by the colossal Three Gorges reservoir, 500km upstream. The cause and effect is still not officially recognised, even if the government did admit last May that the planet's biggest dam had given rise to "problems that need to be solved very urgently".
"Every year, when the Three Gorges reservoir stores water – to power the dam's turbines during the winter – the flow rate in the Yangtze drops. This in turn increases the rate at which the level of Poyang lake falls, and the period of low water comes sooner," said Ye Xuchun, a researcher at China's Southwest University. In partnership with scientists at the Lake Science and Environment laboratory at Nanking University, he has published a comparative analysis of water levels in the Three Gorges basin and at the lake's northern extremity, near the city of Hukou, where the outflow from Poyang joins the Yangtze.
The authors conclude that the artificial regulation of the reservoir, which must be kept full to optimise electricity output, reduces the water level in the lower reaches of the Yangtze. This means that the big river no longer "plugs" the lake's northern outlet, so the other rivers feeding into Poyang simply pass through the dwindling lake and run on downstream...
Lake Poyang, seen from a NASA satellite