(TibetanReview.net, Oct27’26) – Chinese researchers have determined, based on past nearly 700-year-long data, that the Yarlung Tsangpo river – which is soon to host the largest mega dam in the world – may face increased run-off and flood risks over this century. The brunt of the devastating effect of such an eventuality will obviously fall on downstream India. This is in addition to the serious danger already being posed by the fact that the mega dam is being built on a known seismically active zone.
Using tree-ring width chronologies in the southeastern Tibetan Plateau, the team reconstructed the river’s run-off history from 1325 to 2020 and created a forecast model, reported scmp.com Oct 26.
The report said that along with climate data, this data was used to create a model that projected that river run-off would increase under future climate scenarios, along with a possible increase in high-run-off events such as floods.
“These results provide a long-term perspective on hydroclimatic variability in the Yarlung Tsangpo River and a scientific basis for assessing future water-resource risks,” the team has said in a paper published in the Chinese-language journal China Science Bulletin on Oct 8.
The researchers, who were from the Chinese Academy of Sciences and Yunnan University, have said future run-off should be considered in planning “water resource development and storage infrastructure” and in assessing transboundary water risks in the region.
China is building the dam near the end of the Yarlung Tsangpo’s run across the southern length of Tibet before it enters India as the Brahmaputra River. The world’s largest planned hydropower project is expected to have a total installed capacity of more than 60,000 megawatts upon completion – three times that of China’s Three Gorges Dam, the largest operating in the world currently.
The mega dam is being built in Metog (Medog, or Motuo in Chinese), a border county in Chinese-ruled Tibet, close to the disputed border with India’s Arunachal Pradesh state.
The Chinese team has noted that the Tibetan Plateau has been warming at about twice the rate of the global average over the past century, which had impacted the region’s ice cover and hydrological cycle. And they have said that among the rivers in the plateau, the Yarlung Tsangpo experiences the most run-off. This refers to the movement of excess water or snow over land that eventually finds its way to bodies of water or drainage systems.
Rising temperatures have accelerated glacial melting, increased permafrost degradation and shortened the duration of snow cover. Rain distribution has also become more unstable, with a rise in extreme rain events and anomalous run-off. The research was stated to indicate that the region will trend towards a wetter climate, putting the Yarlung Tsangpo more at risk of both water scarcity and flooding.
To reconstruct the river’s hydrological history, the team turned to tree rings as a climate proxy, since climate data was available only from the mid to late 20th century. Each ring signifies about a year of a tree’s life. The structure of the rings can show what kind of conditions they were formed under.
It is explained that wider rings can mean more water during the growing season, and narrower rings less. These patterns can be used to form a climate history that can cover hundreds of years, the report said, citing the US National Oceanic and Atmospheric Administration. The Chinese team has said the width and density of rings could be sensitive to moisture conditions during the growing season.
The team’s model has projected an increase in run-off in the Yarlung Tsangpo river during the 21st century, “accompanied by a possible increase in the occurrence probability of high-run-off events”.
Under the middle-of-the-road and high-emissions climate scenarios used by the UN’s Intergovernmental Panel on Climate Change, run-off (in this century) was estimated to increase by about 20% and 29% respectively compared to the reconstructed historical period of 1325 to 2020, the team has said.
This is based on the team’s model of monthly run-off at the Nuxia station, located in Milin county-level city near Medog, from 2030 to 2100.
The team has found that run-off had exhibited inter- and multidecadal variability over the last 700 years, with 14 wet periods and 14 dry periods.
Projections of the distribution of run-off are also stated to suggest that there will not only be an increase in mean run-off but also a higher probability of extreme high-run-off events.
The report said this latest study is not the only recent indication that the region will require careful management in the process of building what will be the world’s largest dam.
It noted that in June, Chinese geologists said they had found that an active fault line directly beneath the planned project could pose a threat to its integrity and urged engineers to implement measures to mitigate the risk of collapses and landslides.