The Three Gorges and Gezhouba, two of China's top hydropower plants, have closed capacity by as much as two-thirds, state media said on Tuesday, as torrential rains across the south triggered drastic steps to ease pressure on the Yangtze River.
Days of heavy rainfall have pushed water levels in more than 60 rivers in southern China above warning levels. Floods have damaged crops, forced hundreds of thousands from their homes and killed at least 33, while the north has wilted in a heat wave and drought-like conditions.
The Three Gorges dam is the world's biggest power station by far, with an installed generation capacity of 22,500 megawatts (MW), equivalent to about 20 coal-fired stations.
The two power stations in Hubei province have stopped 26 generators, due to flood pressure in the middle and lower reaches of the Yangtze River, Asia's longest river, the state-run Xinhua News Agency said, citing the Three Gorges Corp, the world's largest hydroelectric power producer.
Hydropower is China's second largest electricity source after coal. The shutdowns have cut capacity by 13.52 gigawatts (GW) to just 7.5 GW. The Three Gorges plant has reduced capacity to 6 GW from 18.12 GW, while Gezhouba, some 38 kms (23 miles) away, has halved capacity to 1.5 GW from 2.9 GW.
Phone calls to Three Gorges were unanswered.
Hydropower schemes can shut during times of high rainfall to prevent flooding downstream or to protect their turbines.
Such measures are frequent during the rainy season in China's south, but Li Rong, power analyst with consultancy SIA Energy, said the size of the current shutdown was unprecedented.
He estimated it at 200 GW hours of daily electricity output, about 40 percent of demand in Shanghai, China's most populated city, during the summer peak season.
While the heavy rainfall has led to short-term power shutdowns, it is also helping to replenish reservoir levels in the country's south, which had been falling in recent months, hurting output of hydro power.
Most of the nation's hydro power plants are located in the southern provinces of Hubei, Hunan, Sichuan and Guizhou.
Any prolonged closure of the generators will renew concerns about higher demand for coal to fuel the nation's thousands of thermal power plants as a weeks-long heatwave scorches the north.
Traders said that it would take at least a dozen large fossil fuel or nuclear power stations to make up for the hydro restrictions.
In recent weeks, Beijing has urged coal mines to ramp up output to ensure electricity supplies during peak hours as a prolonged bout of hot weather across the north has boosted demand for air conditioning.
On Tuesday, coal for export from Australia's Newcastle terminal hit their highest since April, with mining outages tightening supply amid strong northern hemisphere summer demand.
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