Mekong River water levels between Jinghong hydropower station in China’s Yunnan province and the Mekong Delta in Vietnam fell in recent weeks to worrying levels, says the Mekong River Commission (MRC).
The MRC has observed a 25 percent drop in average rainfall since last November, while outflow from Jinghong has been fluctuating wildly, falling to half its normal levels on several days in January.
The fluctuations have made it “challenging for authorities and communities to prepare for and respond to possible impacts”, says to Dr Winai Wangpimool, Director of the MRC Secretariat’s Technical Support Division.
In early January, China’s Ministry of Water Resources notified the four Lower Mekong countries that the outflow from Jinghong would be restricted to 1,000 m³/s from 5 to 24 January due to the maintenance of power grid transmission lines. The Ministry, however, did not specify the river water level before the outflow restriction nor the volume to be restored on 25 January.
“Continuing this flow pattern could have an impact on river transport, fish migration, agriculture and river weed collection,” Dr Winai said. “To help the Lower Mekong countries manage risks more effectively, we call on China and the Lower Mekong countries themselves to share their water release plans with us.”
Last year, China agreed to share year-round water level and rainfall data with the MRC and pledged to notify the MRC and its Member Countries of any abnormal rise or fall in water levels or discharge, and provide relevant information on factors that might lead to sudden flooding.
The significantly lower levels have also changed the river’s colour from its usual brown to blue-green. The lower flow means less sediment is being washed downstream and the resulting clarity of the water is leading to the formation of algae on the riverbed.
Experts at the MRC are concerned that the increased clarity could lead to changes in the river’s productivity, with less food available for aquatic insects, invertebrates and small fish.
The 12th longest in the world, the Mekong River runs through China, Myanmar, Laos, Thailand, Cambodia and Vietnam. Heavily dammed in China, changes to its flow have had a noticeable impact on the river’s ecology and on the downstream communities dependent upon it for food, fresh water and livelihoods.
Plans to build another dam in Laos have already brought widespread criticism from environmental groups and the Thai authorities.