Impacts of Climate Change, Sand Mining, and Hydropower Dams on the Mekong River–Tonle Sap Lake Interaction System

The Mekong River–Tonle Sap Lake interaction system plays a vital role in supporting livelihoods in the region through the reverse flow phenomenon. During the flood season, a substantial volume of water flows from the Mekong mainstream into the Tonle Sap Lake floodplain, which is then gradually drained during the dry season to provide additional water to the Vietnamese Delta. This interaction is critical for fisheries and agriculture, benefiting approximately 20 million residents across the Tonle Sap Lake and Mekong Delta regions.

However, since 2010, extensive dam construction in the upper Mekong River and local sand mining activities have significantly altered the flow regime, weakening the interaction in two key aspects: the duration of reverse flow and the volume of nutrient-sediment water entering the lake. Utilizing an integrated modeling framework comprising hydrodynamic and hydrological models, this study found that while the Tonle Sap Lake system demonstrated resilience to climate change between 2010 and 2024, the influence of human interventions has been profound.

Our results indicate that the average annual reverse flow volume, which was approximately 43 km³ during the historical period (1980–2000), has declined by about 25% to an average of 30 km³ in recent years. Additionally, the duration of the reverse flow has shortened by approximately 20 days. These changes underscore the dominant role of anthropogenic stressors in disrupting the Mekong River–Tonle Sap Lake system.

To sustain this critical interaction, urgent measures are needed to regulate local sand mining and foster transboundary collaboration with upstream states regarding dam operations and future reservoir construction. Such actions are essential to maintaining flow regimes that approximate natural conditions and securing the livelihoods of millions in the region.