CJP4W6159-14x20cm.jpg

Hydrology

Upstream flow contributes only a small portion of the total annual flow of the Mekong River. Most of the total flow volume is delivered to the Mekong from tributaries in the Lower Mekong Basin (see Table 1); however, the importance of upstream flow should not be underestimated as dry-season snow melt from China contributes to over 24% of the total flow.

Table 1. Proportional contributions to total Mekong River mean annual flow by river reach, distinguishing those made by the left and right bank tributary systems.

River Reach Left Bank (%) Right Bank (%) Total (%)
China 16 16
China – Chiang Saen 1 3 4
Chiang Saen – Luang Prabang 6 2 8
Luang Prabang – Vientiane 1 2 3
Vientiane – Nakhon Phanom 18 4 22
Nakhon Phanom – Mukdahan 3 1 4
Mukdahan – Pakse 4 6 10
Pakse – Kratie 22 2 24
Tonle Sap 9 9
Total 55 20 100

Flooding

The flood season in the Mekong River Basin lasts from June to November and accounts for 80 to 90% of the total annual flow (MRC 2010). The annual flood season is especially important in the Lower Mekong Basin where it has shaped the environment and its inhabitants.

See the sections on the People and Flood and Drought for more information.

Many of the Mekong’s key ecosystems have developed as a result of seasonal flow fluctuations. The area’s extensive wetland habitats would not exist without the annual flood. Likewise, the life-cycles of many Mekong fish species depend on it. Fish migrate to deep pools in the mainstream to seek refuge during the dry season; later, during the flood season, they migrate back to spawning and nutrient-rich feeding grounds on floodplains.

See the Fisheries section for more information.

Latest News

Laos urged to better assess impacts, provide effective mitigation measures, as Luang Prabang dam moves forwards

Cambodia, Thailand and Vietnam requested Laos to conduct rigorous transboundary impact assessments and enhance proposed measures to mitigate potential adverse impacts

Flood and drought remain key challenges for the Mekong: Report

Extreme low flows and extensive flooding of different communities along the Mekong River in 2019 and an increasing number of droughts that have occurred in many parts of the region in recent years are among the signs that the Mekong region is facing incre

New strategy to address Mekong wide challenges near finishing line

A draft Mekong basin development strategy to respond to critical environmental and social pressures from ongoing and planned developments and climate change in the Mekong River Basin has now received a greenlight from a governance body of the Mekong River