Mekong Dam Monitor (Update for September 9 - 15, 2024)

 

Update for September 9-15

Notable changes on the Mekong in the last week. Visit the Monitor home for more, including Burmese, 中文, Khmer, ພາສາລາວ, ไทย, and Tiếng Việt translation.

SPOTLIGHT As Typhoon Yagi Brings a 30-year Flood, Transboundary Dam Coordination Improves But Early Warning Does Not Typhoon Yagi has brought what many are calling a 30-year flood to the Mekong Basin in Thailand, Myanmar, and Laos. River levels at Luang Prabang exceeded flood stage from September 11-15, Chiang Khan from September 12-15, and Vientiane/Nong Khai from September 12-17. The MRC forecasts Nakhon Phanom will exceed flood stage from September 18-19 as the floodpulse moves downstream. No excessive flooding is forecasted for Cambodia and Vietnam’s Mekong Delta. The MDM team plans to produce more analysis on the impacts of the floods and dams in the coming weeks. From preliminary review, we observed increased and effective communication between the governments of China, Laos, and the Mekong River Commission regarding coordinated dam operations. The MRC published an announcement from China’s authorities regarding reduced outflow from the Jinghong Dam as a method for reducing the impact of Typhoon Yagi. Satellite imagery and MDM analysis confirmed flow reduction from China and concludes this could only have been done with sophisticated operation of multiple upstream dams. Some (but not all) dam operators in Laos provided public announcements on social media in Lao and English language regarding reservoir releases prior to the arrival of Typhoon Yagi. Both developments are an improvement over past practice.  It is not clear to what degree those messages were received by vulnerable communities downstream of these dams. It is also not clear to what degree dam operations helped or hindered flooding around Luang Prabang, Laos. Certainly, the presence of more than 10 dams near and in the upstream vicinity of Luang Prabang (on the Nam Ou, Nam Khan, and Mekong mainstream) added complexity and vulnerability to communities affected by the flooding. Throughout affected areas in Myanmar, Thailand, and Laos, local people voiced concerns over lack of proper guidance and early warning in preparation for the flooding despite Typhoon Yagi being forecasted a week in advance. This has near term importance as Typhoon Yagi is not likely to be the last typhoon of 2024.   The images in this Spotlight provide insight to some areas which were flooded. In Chiang Rai City, Thailand, flooding on the Kok tributary was worse and more sudden than the August flooding three weeks prior and could have been related to the inability of an irrigation dam downstream of the city to clear sudden flood waters. Social media users made false claims of a dam burst upstream in Myanmar’s portion of the Kok tributary. We confirmed via satellite imagery that there are no dams in Myanmar on the Kok tributary.

Although the river did not exceed flood stage at Chiang Khong, Thailand (below), some low-lying areas such as Niwat Roykaew’s Mekong School were flooded by about one meter of water.    The Nam Tha 3 Dam, a small run of river dam in Luang Namtha, Laos, overtopped and caused severe flooding for a few days in the center of Luang Namtha town and the airport south of the town (below). After the dam overtopped many locals feared the Nam Tha 3 Dam would breach, but it did not.

Low lying areas of Vientiane, Laos, experienced flooding. Peak flooding imagery for Vientiane is not currently available.

Nong Khai, Thailand and islands in the Mekong also experienced extreme flooding. Nong Khai floods have yet to peak.

IMAGE OF THE WEEK August Floods Provided Little Help to Mekong Floodpulse – Will Typhoon Yagi? The waters from the severe flooding in northern Thailand from late August hit the Tonle Sap confluence at Phnom Penh, Cambodia around September 8, but this did little to energize reverse flow and cause the Tonle Sap Lake to expand. In early September, seasonal inundation only expanded by about 500 square kilometers compared to the end of August, leaving the Mekong floodpulse still far behind schedule and relatively weak. Typhoon Yagi’s floodpulse will hit the Tonle Sap confluence around September 23 and could cause a greater expansion of the Mekong Floodpulse.

Where is the water? Last week we observed a large cumulative restriction of flow of 1.24 billion cubic meters throughout the basin. Major restrictions came from Huangdeng (CHN, 122 million cubic meters), Nuozhadu (CHN, 154 million cubic meters), Nam Ngum 1 (LAO, 312 million cubic meters), and Xenamnoy (LAO, 192 million cubic meters).

Reservoir Storage Over Time

River Levels Typhoon Yagi created extremely high river levels, some over the flood stage from Chiang Saen to Nakhon Phanom along the Thai-Lao border (see Spotlight).  River levels are now starting to gradually recede as the floodpulse moves downstream. River levels in Cambodia are near normal for this time of year.

Chiang Saen Gauge Stung Treng Gauge

Weather & Wetness The pathway of Typhoon Yagi appears clearly on the wetness anomaly map (blue/purple), and while large its effects are fairly isolated to northern Thailand, northern Laos, Shan State in Myanmar, and southern Yunnan province. Most of the basin remains in extreme drought including the headwaters, northeast Thailand, and most of Cambodia.

The larger wetness anomaly map of Asia shows the broader pathway of Typhoon Yagi, including areas of extreme wetness in northern Vietnam in the Red River Basin as well as the extent of Yagi’s storms in Myanmar covering nearly all of Shan State.

Mekong Dam Monitor in the News The Bangkok Tribune highlighted recent flooding in Thailand, citing MDM data to indicate China's dam operations had no negative influence on the flood situation. AFP published a fact-check to debunk viral social media claims that a dam burst in China contributed to the flooding n Thailand and Laos back in August.