Dry weather complicates water diversion

Less than a year from the start of water diversion from a sprawling reservoir in central China to northern regions including Beijing, questions are surfacing about whether the once-soggy south has enough water to help ease shortages in the acrid north.

The worries have been rekindled after the Danjiangkou reservoir stretching across Hubei and Henan provinces, the water source for the central route of China's massive south-to-north water diversion project, failed to start water storage as scheduled in a dry autumn season.

After eight years of construction, the height of a dam originally completed in 1973 has been raised by 14.6 meters to 176.6 meters to enable the Danjiangkou reservoir to store up to 29 billion cubic meters of water. At full capacity, the reservoir has an area of 1,022 square km and is the second largest in China only after the Three Gorges.

The heightened dam passed quality checkups organized by the State Council, China' s cabinet, in late August. Afterward, the reservoir was ordered to start storing water from the Hanjiang River, the largest tributary of the Yangtze River, in an expected autumn flood season in September and October.

An annual average of 9.5 billion cubic meters of water in the reservoir is designed to flow all the way to 19 major cities and more than 100 counties in the north beginning in October next year.

The autumn flooding, however, did not come as expected, as the Hanjiang River basin, which stretches westward to Shaanxi Province, experienced a rainless autumn and many upstream dams held more water to brace for potential severe winter and spring droughts.

As a result, the volume of water flowing down into the Danjiangkou reservoir averaged just 446 cubic meters per second in September, down 70 percent from the same period of normal years, according to latest data.

Meanwhile, the reservoir was ordered to discharge no less than 800 cubic meters of water per second in September and no less than 600 cubic meters per second in October to meet demand in the lower reaches. The gap drove down water levels in the reservoir by more than three meters over the two-month period to 144.15 meters, about five meters lower than the dead storage level.

As the dry winter kicks in, the water level is expected to keep falling in the coming months and could drop by another nine meters to a rarely seen low of 135 meters next May. The reservoir dropped to 134.7 meters in May 2011 when it was hit by a once-in-a-century drought.

Historically, China's south has always been rich in water resources and often battled severe flooding while the north often suffered severe water shortages. But over the past couple of years, many regions in the south of the country have become new victims of drought while the northern regions have begun to receive more rain.

Li Weijing, chief scientist of the climate research program under the China Meteorological Administration, said it is very likely that the south will see more droughts in the future while the north could receive more rain.

In the 1980s and 1990s, the rain belt lay in the Yangtze River reaches and regions to the south of the river, while as of 2003, the rain belt started to move northward. That tendency has become more obvious over the past couple of years, Li said.

This year's dry autumn in the Hanjiang River basin reinforced worries among experts and the general public that if the south becomes drier in the future, it could pose challenges to China's water diversion efforts.

In addition, quickening urbanization and robust economic growth along the Hanjiang River have boosted the demand for water, intensifying the scramble.

Officials close to the water diversion scheme have moved to reassure naysayers. Zheng Shouren, chief engineer of the Yangtze River Water Resources Commission under the Ministry of Water Resources, said the dry autumn forced the Danjiangkou reservoir to delay water storage to the flooding season next summer, but the scheduled water diversion in October is unlikely to be affected.

The heightened dam can help store more water in rainy years to make up the gap in dry years, said Zheng.

But he acknowledged that the south has entered a less rainy period and said that the building of a series of dams upstream to block more water calls for integrated river basin management.

The viewpoint was echoed by Wang Hao, head of the water resources department with the China Institute of Water Resources and Hydropower Research.

Wang said all upstream tributaries and reservoirs should be put under integrated water regulation so as to balance supply downstream to the Danjiangkou reservoir.

In dry years, the water project should divert less water to the north to ensure the meeting of local water demand first, he said, adding other big reservoirs along the thousands of canals and pipelines to the north can help supplement the water supply.

Several experts, including Wang, said that with the authorities planning to increase the volume of water diverted from the Danjiangkou reservoir to 13 billion cubic meters a year, they should consider building a canal to divert water from the Three Gorges reservoir on the Yangtze River to supplement the Danjiangkou resource.

The south-to-north water diversion project, first envisioned by China's late chairman Mao Zedong, was designed to consist of eastern, central and western routes, with an estimated overall cost of 500 billion yuan (82 billion U.S. dollars) and a construction period of 40 to 50 years.

The project aims to transfer 44.8 billion cubic meters of water annually from the country's south, mainly the Yangtze River reaches, to quench the water shortage in the north.

Construction of the eastern and central routes began in December 2002 and December 2003 respectively, and water diverted via the central route will mainly supply Beijing. Hundreds of thousands of local residents have been relocated to make way for the project.