In June of this year, a Food and Agriculture Organization’s (FAO) report ranked the Mekong Basin as the world’s most productive freshwater fishery, accounting for over 15% of global annual freshwater fish catch. Meanwhile, researchers at the World Wide Fund for Nature (WWF) estimate that the contribution accounts for a quarter of the world’s freshwater catch. This inland fishery is critical to the food security of tens of millions living in Cambodia, Laos, Thailand and Vietnam, and is fuelled by the Mekong River’s natural flow cycle.
Typically, the Mekong transitions like clockwork around July from the dry season period of relatively low flow to an extreme wet season pulse bringing floodwaters that nourish the entirety of the basin.
Each year, this flood pulse drives water from the Mekong up through a tributary at Phnom Penh, expanding the Tonle Sap Lake in Cambodia to more than five times its dry season size. The Tonle Sap serves as the foundation of Mekong’s most extensive fishery. The lake’s annual expansion and subsequent dry season contraction produces an annual 500,000-tonne fish catch in the lake and dispatches migratory fish throughout the entire Mekong Basin.
The Mekong’s wet season flood pulse is also essential for riverbank agriculture which supports the livelihoods of millions who live along the banks of the river and its tributaries. On a grander scale, floods deposit nutritious sediment across the Mekong’s floodplain which stretches from northwest Cambodia to Vietnam’s Mekong Delta. However, the Mekong’s natural flow and the heartbeat of the Tonle Sap are being undermined by wet season water restrictions from dams in China and in downstream Mekong countries. When wet season rainfall levels are low, those upstream water restrictions weaken the Mekong pulse even more.
This year, the Mekong’s annual floods are once again behind schedule.
In the month of July, researchers from Chinese academic and research institutions, including Tsinghua University, produced a study (called the Tsinghua study) which claimed that during the wet season, China’s upstream dam restrictions have a positive impact on the Mekong. The study’s findings make a valuable contribution to the public discourse; however, its authors ignore the importance of the Mekong’s natural flow and the resource base produced from that natural flow.
The Tsinghua study was undertaken in response to the Eyes on Earth (EoE) study published in April which was supported by the Sustainable Infrastructure Partnership, implemented by Pact as part of the US Department of State’s Lower Mekong Initiative.
The EoE study compared actual measurements of the Mekong River Commission river gauge in Chiang Saen, Thailand to a natural river flow model derived from a wetness index which uses remote sensing data to measure all forms of wetness including rainfall, snowmelt, groundwater, evaporation, and even dew. The study found that China’s upstream dam regulation had severely altered the natural flow of the river and pointed to a massive restriction of water during the 2019 wet season at a time when downstream countries were experiencing weather-driven drought.
The EoE study concluded that China’s operations of 11 upstream dams exacerbated drought conditions in the lower basin by restricting the natural flow from China during the wet season. A follow-up investigation further determined that the two largest dams in China, Xiaowan and Nuozhadu, restricted around 20 billion cubic meters of water between July and November of 2019.
The Tsinghua study came up with results and conclusions that conform with the EoE study. Both studies model river flow across a 10-year period between 2010 and 2019, showing major releases of water from China’s dams during the dry season and major restrictions of water (compared to natural flow) during the wet season.
The Tsinghua study also determined that remote sensing precipitation measurements were a reliable way to derive river flow, especially in the absence of an inadequate surface observation network inside of China for monitoring upstream conditions over the last decade. Despite these admitted inadequacies, the authors used this limited surface data network to determine that the region experienced drought from June through August of 2019.
In contrast, the EoE study determined there was enough water in China’s portion of the upper Mekong from June through the end of 2019 to produce a Mekong pulse at Chiang Saen. These findings were corroborated by remote sensing data available from Google’s Earth Engine.
The Tsinghua study concluded that the Mekong Basin is “experiencing high frequency of drought and the proportion of drought occurring in the dry season is significantly higher than that in the wet season”. Its main hypothesis is that “the regulation of reservoirs in the Mekong Basin could play an active role in dealing with droughts” and it emphasizes the positive role China’s upstream dams can play by further restricting large quantities of water during the wet season and releasing more water during the dry season.
China’s historical experience with rivers has been colored by the need to harness and tame China’s rivers to prevent calamitous floods. For example, flooding of the Yangtze River in 1931 killed 3.7 million people and records show numerous instances throughout China’s past in which flooding killed more than one million people. These disasters have driven China’s urge to engineer and control nearly all of its free-flowing rivers. China is now exporting this historical experience to the Mekong via the Lancang Mekong Cooperation Mechanism (LMC) and research like the Tsinghua study. The mantra of the LMC is that dams and river regulation are necessary for effective flood control and drought relief.
This is a dangerous discourse for a river system in which natural flow cycle underpins the food and economic security of Cambodia, Laos, Vietnam and Thailand. Historical records in the Mekong Basin show zero cases of severe flooding which killed thousands of people, let alone millions.
The productivity of the Mekong Delta, one of the world’s major production zones of rice and agricultural products, depends on Mekong floods. Extreme flooding does occur as it did in August 2019 in northeast Thailand and southern Laos but by and large communities in the Mekong are adapted to benefit from these floods. A 2017 study by the Mekong River Commission estimated that wet season flooding provides $8 billion to $10 billion in annual economic benefits while causing less than $70 million in damages. Benefits of natural flow outweigh costs by more than 100 times.
The Tsinghua study’s conclusions, which argue for shifting China’s wet season contribution of the Mekong flow to the dry season, are based on a false (and self-serving) premise. The fact is that life in the Mekong depends on the flood pulse. Efforts to restrict the pulse in the name of “flood control” threaten the livelihoods of tens of millions of farmers and fishers downstream. The only beneficiaries of such restrictions are dam operators and electricity markets upstream in China.