Dams and floods

The ‘3 S’ River Basin in Cambodia is where three rivers meet. By 2050, more frequent and intense flooding will be the norm for the basin’s 3.4 million people, according to a new study by scientists from the US National Aeronautical and Space Administration (NASA). 

The NASA study, ‘Diagnosing challenges and setting priorities for sustainable water resource management under climate change’, used water resource data and climate projections to model 24 different scenarios showing the impacts of increased flooding under different reservoir management measures. The study also analyzed a unique element—surveys on water governance conducted by NASA partners from Conservation International—for balancing tradeoffs of sustainable water use and climate uncertainty. The study showed that dam operators will need to cope with new flood patterns that could include more frequent floods and more intense flood seasons. Rainfall is expected to increase by around 6 mm a year between 2025-2050. 

The authors warn that the increase in floodwaters being discharged through reservoirs and spillways could damage the structural integrity of dams and may require expensive upgrades to dam infrastructure, proving a burden to governments. They conclude that dam operators will face “the near-constant need to manage flood waters in reservoirs further down the cascade,” and that their ability to mitigate downstream flooding by holding back water will be limited. Water resource management practices will need to factor in the predicted impacts of climate change on water resources. 

Three important rivers

The Se Kong River flows from Laos, and the Sre Pok and Se San rivers from Vietnam’s central highlands. The three rivers meet in Cambodia before flowing into the main stem of the Mekong River. Together, the ‘3 S’ rivers deliver around 20% of flow and 25% of sediment load into the Mekong River system. Climate impacts will require increased management and cooperation. To manage the increased flood risk under climate change, the upstream countries­—Laos and Vietnam— will need to coordinate with Cambodia, the downstream country. 

Map: A new NASA study has modeled 23 hydropower dams in the Se Kong, Se San, and Sre Pok River Basin (78,714 km2), located within the Mekong River Basin.

Source: NASA

Governing flood risk

The scientists discuss the projected water resource management needs in the context of the Freshwater Health Index developed by Conservation International, which includes detailed ratings of governance and stakeholder engagement in the region. The Index suggests that water resource governance, including transboundary cooperation, is currently not as strong as it needs to be. The authors call for transparency and cooperation in water resource management, saying these are foundational to Mekong countries’ ability to adapt to a changing flow regime.

“Our assessment reveals that the basic building blocks of good water governance, such as financing, information sharing, and enforcement, require substantially more attention in the coming years,” their report states. “It will be of little use...to invest in costly infrastructure if there is not a similar commitment to strengthening water governance and management in the region.”

Source: Mohammed, I.N., Bolten, J.D., Souter, N.J. et al. Diagnosing challenges and setting priorities for sustainable water resource management under climate change. Sci Rep 12, 796 (2022). https://doi.org/10.1038/s41598-022-04766-2