This year's flood peak is forecast to occur in late September and early October, at alert level 1. At present, according to the Southern Institute of Water Resources Planning, the water source from the Mekong River flowing into the Mekong Delta through Kratie station (from June 1 to August 24) has only reached 107 billion cubic meters, compared to the average of many years, 27.8 billion cubic meters lower. This causes the river water level to be low, on August 24 it was 15.7m, 2.9m lower than the average of many years. On the same day, the water level at Tonle Sap Lake reached 4.7m, 2.93m lower than the same period of many years. Tonle Sap Lake, a natural reservoir for the lower Mekong region (Cambodia and the Mekong Delta of Vietnam), is lacking more than 14 billion cubic meters of water compared to the average of many years. This leads to low water levels flowing into the upper Mekong River.
The water level at the headwaters of the Mekong River is still nearly 1m lower than normal, the flood has not yet reached the Mekong Delta.
Downstream of the Mekong River, the water level on the Mekong River is affected by water from upstream and tides. On August 23, on the Tien River at Tan Chau, the highest water level reached 2.01m, 0.96m lower than the same period many years ago; similarly, on the Hau River at Chau Doc station, it was 0.59m lower.
One of the reasons is that last week the rainfall in the lower Mekong region was low due to the weak southwest monsoon. The average rainfall was about 25mm, with some places in Cambodia and the Central Highlands of Vietnam receiving about 75mm.
The main reason is that the hydropower dams upstream of the Mekong have stored a huge amount of water in the past week. According to the MDM (Mekong Dam Monitoring Project), the highlight of the past week was that the dams on the tributaries have stored a huge amount of water, 3.8 billion cubic meters, to fill their reservoirs. Of these, five hydropower dams have stored more than 400 million cubic meters of water, namely Nam Ngum 2 (2 billion cubic meters), Nam Ngum 1 (410 million cubic meters), Nam Ngiep 1 (581 million cubic meters), Nam Theun 2 (520 million cubic meters) and Xekaman 1 (450 million cubic meters).
"This is the largest water storage in a week at Lao hydropower dams since 2020. Water storage activities during the rainy season will be detrimental to Mekong communities because they lower the Mekong River water level and reduce the benefits of Mekong flood flows," MDM experts commented.
Across the Mekong basin, rainfall has improved in the upper reaches, but widespread drought conditions in Laos, northeastern Thailand and Cambodia remain widespread.
According to data from the Mekong River Commission (MRC), the total flow to Stung Treng, Cambodia in July 2023 was 34.18 billion cubic meters, only about 57% of the average flow before the dams. Currently, seasonal flooding has occurred in some low-lying areas of the lower Mekong (mainly in Cambodia), with the flooded area at the end of July reaching only about 10,700 km 2 , 4,000 km 2 less than the average of many years.
Experts predict that this year, the flood in the West will be late and at a low level. The highest flood peak of the year only reached alarm level 1 and ended early. Meanwhile, high tides are forecast to increase, causing deep saltwater intrusion, making the drought and salinity situation more severe. Farmers should take proactive precautions.
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