Originating from the Qinghai-Tibet Plateau in China, the river is called the Lancang River in China and the Mekong River when it flows through the lower reaches before emptying into the sea.

"China's hydropower stations are beneficial to flood control and drought relief during wet and dry seasons," said Lu Guangsheng, dean of the Institute of International Relations at Yunnan University.

Tian Fuqiang, a professor of hydraulic engineering at Tsinghua University, said that China only accounts for 13.5% of the water flowing out of the Mekong's estuary, which means China's hydropower projects had a limited impact on the amount of water in the Mekong River Basin.

"Hydropower projects do not consume water resources, but use water energy, and they can regulate natural runoff," Tian explained, adding that China's development of the Lancang River is mainly meant for hydropower, which is a clean source of energy. He noted that there are also reservoirs and hydropower stations on the main streams of Laos.

The Lancang hydropower cascade has a positive impact on the discharge and water level of the Mekong mainstream, according to a joint research conducted by the Mekong River Commission, the Lancang-Mekong Water Resources Cooperation Center, China Institute of Water Resources and Hydropower Research, and the International Water Management Institute.

Data from the report shows that due to the regulation of Lancang hydropower cascade, the monthly discharge and water level of Chiang Saen station, the first hydrological station of the Lancang River entering the Indochina Peninsula, in dry season of 2012-2013 were higher than the multi-year averages.  

Monthly distributed rainfall over the Lancang-Mekong River Basin [Source: Mekong River Commission]

In 2019, the Mekong River Basin suffered from extreme drought as the water flow decreased significantly. At the same time, Yunnan province in the Lancang River Basin also suffered from a severe drought. From the upper reaches to the lower reaches, extreme weather had a serious impact on production and livelihoods throughout the basin.

A 2022 report by China Renewable Energy Engineering Institute largely attributed the drought to a shortened rainy season, reduced monsoon rainfall, and the El Niño phenomenon, which led to abnormally high temperatures and strong evaporation.

Despite significantly reduced natural precipitation, Nuozhadu and Xiaowan hydropower stations, two major cascade power stations along the Lancang River, discharged all the runoff and the water previously stored in their reservoirs to increase the water flow downstream during dry seasons in 2019, the report said.

According to data provided by the report, the reservoirs used their storage to replenish water to the downstream by 17 billion cubic meters in 2019, accounting for 14.7% of the annual average runoff at Chiang Saen station. 

China has managed the cascade hydropower stations along the Lancang River in a scientific manner, giving full play to their role in disaster prevention and mitigation, which helped Mekong countries effectively cope with drought and avoid major disasters in a year of severe drought, said Li Guoying, China's minister of water resources, at the 4th Mekong River Commission Summit.

To achieve sustainable development of hydropower projects in the Lancang-Mekong Basin, Lu suggested ramping up efforts to enhance transparent data sharing.

For example, China has made good on its promise to share year-round hydrological data of the Lancang River with the launch of an online information sharing platform on Nov. 30, 2020.

Lu said it is also important to introduce more digital technologies and more mature models under the Lancang-Mekong Cooperation Mechanism to provide and share reliable data, which will help to increase the accuracy and efficiency of decision-making.

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