China, already the world’s largest generator of electricity from river water trapped by giant dams, recently announced plans to nearly double its hydropower capacity by 2020.
This is good news for those concerned about China’s impact on climate change. Coal, the dirtiest of the fossil fuels, is now the main source of energy for China.
But South-east Asia and South Asia, which depend on the regular flow of major rivers that start in China, will be watching closely where the new Chinese dams are built and how the huge amounts of water in their reservoirs are regulated.
These decisions can affect the flow of water in trans-boundary rivers that begin and run for much of their course in China, such as the Mekong, South-east Asia’s longest river, and the Brahmaputra, which winds for 1,700km through the highlands of Tibet before crossing into India and Bangladesh.
When all the generating units began running last month at the Xiaowan hydropower dam on the Chinese section of the Mekong in south-western Yunnan province, China’s hydropower capacity became the world’s largest.
Xiaowan is the fourth of eight dams being built on the upper Mekong. Its completion brought China’s nationwide hydropower generating capacity to just over 200 million kilowatts.
Chinese officials say that had they not tapped hydropower, thermal plants of equivalent capacity would have been built, burning 288 million tonnes of coal annually and releasing 855 million tonnes of carbon dioxide and 5.4 million tonnes of sulphur dioxide into the atmosphere each year. Hydropower produces no toxic air pollutants or carbon emissions.
China aims to generate 15 per cent of its power from non-fossil sources by 2020, up from 7.8 per cent at present. It has also promised to cut its carbon emissions per unit of economic output by 40 to 45 per cent by then. As the most competitive renewable energy, hydropower is the key to achieving emission cuts in China, although rapid expansion of nuclear power will also help.
Mr Zhang Guobao, director of the National Energy Administration, told the official Xinhua news agency last month that hydro projects with another 70 million kilowatts capacity were under construction.
If done well, hydropower can be a sustainable and non-polluting power source. However, blocking rivers with massive dams and reservoirs can create serious social and environmental problems, including displacement of local communities, forest and wildlife habitat destruction, and preventing movement of migratory fish. There is also the risk of damage or even a catastrophic breach in an earthquake.
Because of such concerns, the central government in China had put a freeze on dam building. However, in July, Beijing gave the go-ahead to two hydropower projects, one in Yunnan and the other in Tibet. They were the first approvals in more than two years.
Will intensified dam building result in lax regulation? Mr Zhang said that even as China accelerated hydropower development, approval procedures would be stricter and focus on issues like the environment and the rights of people relocated to make way for the projects. He did not say where all the new dams would be constructed.
India is concerned that China may decide to meet some of its hydropower needs by building giant dams on the upper reaches of the Brahmaputra River, although Beijing has denied this. But China now appears certain to finish its planned cascade of dams not only on the upper Mekong, but also on the upper Salween River before it flows into Myanmar.
For downstream South-east Asian states - Myanmar, Laos, Thailand, Cambodia and Vietnam - this raises two points of concern. The first is how much water will be impounded in Chinese reservoirs behind the dams in these projects.
The second is how hydropower operators, all of them state-owned firms, will regulate the flow of water once the reservoirs hold enough water and the generating units are ready to run.
The four completed dams on the upper Mekong have a capacity to hold back over 18 billion cubic metres of water. This is 70 per cent of the total storage capacity of all reservoirs on the Mekong and its tributaries. After the fifth upper Mekong dam at Nuozhadu is finished in 2014, China’s share will rise to nearly 90 per cent.
There are two basic ways of regulating the outflow of this water. One is to hold it back in the wet season to prevent flooding downstream and to release it in the dry season when it is most needed by farmers and others.
The other way is to release more of the turbid water in the wet season before the sediment has a chance to settle in the reservoir, and store extra water in the dry season to make up for these releases.
Chinese hydropower operators reportedly prefer the latter method because it evens the flow of water throughout the year and increases both the reliability and efficiency of electricity generation.
However, it raises the risk of wet season flooding and dry season water shortages for downstream states in South-east Asia.
The writer is a visiting senior research fellow at the Institute of Southeast Asian Studies in Singapore.