China's Lancang reservoirs play key role in flood mitigation

The cascade reservoirs in the Lancang River in China played a significant role in mitigating floods and droughts in Mekong River countries in 2021, a report has found.

The Mekong River, known as the Lancang River in China, is a vital waterway that stretches across China, Laos, Myanmar, Thailand, Cambodia and Vietnam.

For the Lancang River Basin, 2021 was a relatively dry year. Compared with the long-term average, precipitation in the basin in the year was 11.6 percent lower and the annual runoff dropped by about 20 percent, Zhou Dongni from the Bureau of International Cooperation, Science and Technology of the Changjiang Water Resources Commission said.

As the bureau released its "Report of the Hydrological Situation in the Lancang-Mekong River Basin in 2021", she also noted uneven distribution of rainfall in the basin through the year.

About 74.5 percent of annual precipitation in the basin happened in the rainy season, which lasts from May to October, she said. Precipitation in August, the rainiest month, was 50 times more than the driest month, March.

Research from her team showed, however, cascade reservoirs in China had greatly relieved Mekong countries from the adverse impacts of potential floods and droughts.

"Without the regulation of cascade reservoirs, during the dry season the monthly average discharge of Chiang Saen station would have decreased by 60 to 83 percent," she said.

In March, the driest month, discharge at the station in Thailand would be only be 290 cubic meters per second, "which may bring great adverse impacts on riparian residents' life", she said.

During the flood season, the water levels of the Mekong's mainstream would rise significantly without the operation of cascade reservoirs in China, she said. In Chiang Saen station, the monthly average discharge would have increased by 23 to 51 percent.

"Therefore, the regulation effect of Lancang cascade reservoirs is significant by storing flood water during the rainy season and supplementing extra water during the dry season on the downstream in 2021," she noted.