Climate, human activities identified as key causes of Mekong flow changes

The Mekong River Commission (MRC) and its upstream counterpart, the Lancang-Mekong Water Resources Cooperation Center (LMC Water Center), presented their Phase 1 findings on Southeast Asia's most important waterway at the 13th MRC Regional Stakeholders Forum last Thursday in Laos.

The MRC and LMC Water Center agreed to the joint study in late 2019, as they expanded upon previous collaboration.

As this Phase 1 report notes, "In both 2016 and 2019, joint studies conveyed objective information about the severe droughts to the public and made scientific evaluations of the effects of water supplement from the Lancang (the name of the Mekong in China) reach to alleviate the drought conditions on the Mekong reach."

According to the report, "two key factors contribute to hydrological changes in the Lower Mekong River Basin (LMB): natural factors, including precipitation patterns, evaporation rates, soil properties and topography; and human activities, such as infrastructure development, water management, land cover and land-use changes. These two factors interact and influence the amount, timing and water distribution within the basin."

For the study, the two sides split their research into two time periods, when water storage dramatically increased from one period to the other: 2000–2009 when the LMB accumulated 20% of its storage; then 2010–2020 when 80% of it was collected – at a time of growing irrigation demands, declining rainfall, and generally drier, drought-induced conditions.

While storage increased over time, to some 27% of the mean annual runoff (MAR), or the average amount of water that flows down a particular river per year, at Stung Treng Province in Cambodia, the study found it is low compared with river basins in other drought-prone regions of the world, such as the Colorado River basin, which typically holds storage of more than 200% of the MAR.

The study offers recommendations, particularly a short-term recommendation that urges the riverine neighbors to jointly study the different impacts of development and climate change along key parts of their common river, as well as to share critical data – including real-time sharing of storage levels and hydropower operations.

"As global climate change and the associated droughts and floods will play an increasingly important role in driving the basin’s hydrological conditions, it is critical for basin countries to share more information on meteorological flow conditions, extending to tributaries," it said.

Phase 2 of the study will embrace the recommendations, predict future trends in the evolving hydrology, and propose strategies for the riparian states to adapt to climate and demographic changes – and continue their support for the basin’s sustainable management and development.