Monitoring the quantity of water flowing through the Upper Mekong basin under natural (unimpeded) conditions

This can clearly be seen in the annual cycle of the residuals, which are negative in the wet season and positive in the dry season. When the largest of the dams, Nuozhadu, and its reservoir were completed, the lack of water during the wet season is most pronounced after the largest generators began operating. 

 

The dams greatly expand institutional capacity to regulate the river flow, with corresponding impacts downstream that need to be addressed through holistic solutions. The six dams built since the commissioning of the Nuozhadu Dam in 2012, are compounding the alteration of natural river flow as the reservoirs are filled and water is released. One of the greatest consequences occurred in 2019, when the Lower Mekong recorded some of its lowest river levels ever throughout most of the year. Using the wetness index to predict natural flow, it is evident that there was above-average natural flow originating from the Upper Mekong. The residuals demonstrate excess flow in the dry season, presumably to support electrical produc-tion in early 2019, while the flow during the wet season was severely restricted as the Lower Mekong received record lower levels of rainfall. The severe lack of water in the Lower Mekong during the wet season of 2019 was largely influenced by the restriction of water flowing from the upper Mekong during that time. Cooperation between China and the Lower Mekong countries to simulate the natural flow cycle of the Mekong could have improved the low flow conditions experienced downstream between May and September of 2019. If the wetness index is used as a guide to simulate natural flow, then all communities along the Mekong basin could benefit from maintaining the integrity of the Mekong River.