Until the onset of major dam construction in the higher elevations of the Mekong basin, its lower, broader reaches constituted the world's largest inland freshwater fishery and the mainstay for the employment, food security and nutrition for 60 or more million people. Tragically, over both of the last two May-October wet seasons, the mainstream experienced unprecedented low flows. In both years the normally reliable "flood pulse" was insufficient to meaningfully reverse the flow of Cambodia's Tonle Sap River to into its Great Lake, the "beating heart" of the fishery whose annual catch is directly proportional to its volume during the flood season.
China inevitably has become a major focus of concern about extreme drought in the lower half of the river because of its construction of a massive cascade of 11 large to mega-sized dams on the Upper Mekong, which it calls the Lancang Jiang ("turbulent river"), and an almost total lack of transparency about how these dams are being operated.
The reservoir of largest of the dams in the Lancang, the 261.5-metre-high Nuozhadu dam, can hold 22 cubic kilometres of water -- as much as the other 10 dams combined. Nuozhadu acts as a huge storage tank with a "tap" that can control the flow of water to the Jinghong dam, the lowest dam in the cascade, which is the "faucet", that controls the flow to the lower half of the river.
The lower basin is now populated with scores of large dams ranging from dams with significant storage capacity to "run of the river" dams with comparatively small reservoirs in Laos, Cambodia, Thailand, and Vietnam. These also significantly affect the water level in the mainstream, but in the dry season China is the single largest source of flow. Inevitably, when their stretch of the river is abnormally low the downstream countries tend to focus upstream on China rather than the impact of their own dams and of undeniable climate change.
In July 2019, largely because of low water releases from Chinese dams, stretches of the mainstream and the Tonle Sap lake fell to their lowest levels in at least one hundred years. The Cambodian diet, which depends on fish for 75% of its animal protein, saw a 70% drop in the fish catch during the first nine months of 2020. The continuation of this trend will be an environmental and socioeconomic catastrophe of historic proportions.
There is a practical, but politically difficult way to significantly mitigate the most damaging impact of large dams on the mainstream and major tributaries alike. This issue was addressed for the mainstream only in the 1995 Mekong Agreement ratified by Thailand, Vietnam, Cambodia and Laos, which committed the countries to "the sustainable development, utilisation, conservation and management of the Mekong River Basin water" for mutual and equitable benefit.
The 1995 Mekong Agreement established three basic rules for maintaining the most critical flows in the case of permanent water development projects: "Of not less than the acceptable minimum monthly natural flow during each month of the dry season; to enable the acceptable natural reverse flow of the Tonle Sap to take place during the wet season; and to prevent average daily peak flows greater than what naturally occurs on the average during the flood season."
China and Myanmar are not parties to the 1995 agreement, but the document explicitly provided for both countries to join at a future date.
The two mainstream dams built in Laos are designed to adhere to these rules, as likely would four more under consideration. If China committed to the rules, that would go a long way towards restoring the critical core of the river's natural seasonal flows.
Despite many obvious political obstacles, bringing China into the original Mekong Agreement's rules on dams and water diversions need not be impossible. China's adherence could be achieved either through informal cooperation or, more effectively by a regional agreement delivered through the MRC or China's Lancang-Mekong Cooperation Mechanism.
The launch on Dec 15 of the web-based Mekong Dam Monitor (MDM) by the Stimson Center of Washington, DC, could materially support either alternative. The online MDM platform uses remote sensing, satellite imagery, and Geographic Information System (GIS) mapping and analysis to provide near-real time reporting on a range of indicators, including reservoir conditions to better understand the interaction of numerous factors that are contributing to the collapse of one of the once mighty Mekong.
Stimson's landmark achievement will be especially welcome to those who have long been frustrated over the previously unanswerable questions about the cause of the failure of the last two monsoons to recharge the Tonle Sap. The MDM's goal is to help promote cooperation among all Mekong riparians to optimise the operations of existing dams to approximate the natural timing and volume of its seasonal flows, not to subject China to unwanted scrutiny.
In China's case, coordinating the operation of dam floodgates and power generation to sustain the natural seasonal flow in line with the rules mentioned above would require more regularity and predictability that has not been seen so far. This need not compromise electric power generation because of the extreme size of the reservoir capacities of the Nuozhadu and Xiaowan dams in particular.
The far more daunting problem is the political one. One way to reduce concerns about national prerogatives could be by a progressive, step-by-step process. Already, in the face of downstream criticism of its dam operations, China has begun to provide more frequent data on river flows. This is still insufficient to understand what is happening to the river in a more comprehensive and real-time basis.
Ultimately, without changes in the operation of all of the Basin's dam cascades, including on major tributaries, the productivity of the river will continue to collapse and along with it the main sources not only food and livelihood security but also unwanted social instability. The latter is a potential threat that China needs to deal with to achieve its goal of basin-wide cooperative development.
Richard Cronin is a Distinguished Fellow, the Stimson Center.