Mekong Dam Monitor (Update for September 16 - 22, 2024)

 

Update for September 16-22

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 Two weeks of extreme weather in the Mekong cause flash floods and energize the floodpulse The Mekong Basin was hit again last week by another extreme weather event, this time a tropical depression coming one week after Typhoon Yagi. The two wetness maps show where the hardest hit areas were (blue/purple) with Yagi’s extreme precipitation falling over northern Laos, northern Thailand, and western Myanmar. The path of last week’s tropical depression was about 150km south of Yagi and caused flash flooding and landslides in the Lao provinces of Bolikhamxai, Khammouane, and Xaignabouli. The storm hit just as Yagi’s floodwaters were passing through central Laos, so river levels from central Laos to Stung Treng, Cambodia are currently extremely high, with some parts above flood stage. This extreme weather is bringing disastrous consequences for communities in Laos, particularly those living around tributaries, but it is pushing a robust floodpulse through the Mekong. It is too early to give a specific forecast, but these and future floods will likely result in a normal but late expansion of the Tonle Sap in the next three weeks, bringing positive consequences for the 2024-2025 Mekong fish catch.

IMAGE OF THE WEEK Yagi flooding in Chiang Rai was slightly less intense than August’s severe flooding In late August we produced a map of the severe flooding in northern Thai provinces of Chiang Rai and Phayao which showed over 1,500 square kilometers of flooding during that event. Typhoon Yagi’s flood map over the same area shows a similar yet less intense flooding pattern, with an estimated 976 square kilometers of flooding. Both images are attached for comparison purposes. We will produce more flood mapping like this for other parts of the Mekong flooded by Typhoon Yagi in an upcoming special briefing.

September Flooding August Flooding

Where is the water? Last week we observed a large cumulative restriction of flow of 1.2 billion cubic meters throughout the basin. Major restrictions came from Xiaowan (CHN, 209 million cubic meters), Nuozhadu (CHN, 154 million cubic meters), Jinghong (CHN, 148 million cubic meters), Ubol Ratana (THA, 198 million cubic meters), and Plei Krong (VNM 166 million cubic meters).

Most Impactful Dams

River Levels River levels from Chiang Saen to Vientiane are now trending back below normal levels as upstream dam restrictions reduce flow and as Typhoon Yagi’s floodwaters move downstream. River levels from Savannakhet to Stung Treng are nearing alarm or flood levels, and these high levels will last over the next week. More extreme weather could drive these levels even higher in the days and weeks to come. The Tonle Sap River level is below normal, but at the highest it has been since 2019 and trending upward.

Chiang Saen Gauge Stung Treng Gauge

Weather & Wetness The pathway of last week’s tropical depression appears clearly on the wetness anomaly map (blue/purple) isolated in central Laos. Most of the rest of the basin is still experiencing severely dry conditions even in the path of Typhoon Yagi which hit two weeks ago.

Mekong Dam Monitor in the News

• Voice of America highlighted the need for better preparedness after devastation caused by Typhoon Yagi, referencing the Stimson Center's MDM work and need for better data sharing for early warning.