NEW YORK/NEW DELHI: Destructive flooding of the Brahmaputra will probably be more frequent than previously estimated, even without factoring in the effects of human-driven climate change, says a new study which assembled a chronology of the river’s flow for the last seven centuries.
According to a study, published in the journal Nature Communications, the long-term baseline conditions of the river, which flows under a variety of names through Tibet, India and Bangladesh, is much wetter than previously thought. The scientists, including those from Columbia University, in the US, said earlier estimates presumed the baseline of natural variations in river flow mainly based on discharge gauge records dating only to the 1950s.
Amid increasing concerns over China building a major hydropower project on the Brahmaputra river in Tibet, India too plans to construct a multipurpose reservoir in Arunachal Pradesh to offset its impact, a senior official of the Jal Shakti ministry said on Tuesday. T S Mehra, Commissioner (Brahmaputra and Barak), in the Jal Shakti ministry said the multi-purpose 10,000 MW hydropower project is under consideration. “This project will help offset the impact of the hydropower project by China,” he said.
The proposed Upper Siang project will be able to take the excess load of water discharge and can even store water in case of any deficit, he added. The river, also known as Yarlung Zangbo flows from Tibet into Arunachal Pradesh, where it is called Siang and then enters Assam. Last week, Yan Zhiyong, chairman of the Power Construction Corp of China, said Beijing will “implement hydropower exploitation in the downstream of the Yarlung Zangbo” and the project could serve to maintain water resources and domestic security. “There is no parallel in history...
It will be a historic opportunity for the Chinese hydropower industry,” Yan told a press conference. Reacting to this, Brahma Chellaney, a strategic affairs expert and author of the book Water- Asia’s New Battleground, tweeted India is facing China’s “terrestrial aggression in the Himalayas, maritime encroachments on its backyard and, as the latest news is a reminder, even water wars” on Monday. While some scientists believe a warming climate could intensify the monsoon rains in coming decades, and in turn increase seasonal flooding, the team sought to determine how much more often big floods might happen in the future.
They first looked at records from a river-flow gauge in northern Bangladesh which showed an average discharge of about 41,000 cubic metres per second from 1956 to 1986, and 43,000 from 1987 to 2004. The study noted that in the big flood year of 1998, when 70 per cent of Bangladesh went underwater, this peak discharge more than doubled.
The scientists also looked at data from the rings of ancient trees sampled at 28 sites in Tibet, Myanmar, Nepal and Bhutan — at sites within the Brahmaputra watershed. Since the rings grow wider when the soil moisture is high, researchers could indirectly piece together rainfall and resulting river runoff during these years.
Based on the analysis, they assembled a 696-year chronology, running from 1309 to 2004, and found that the widest rings lined up neatly with known major flood years. According to the scientists, anyone using the modern discharge record to estimate future flood hazard would be underestimating the danger by 24 to 38 per cent, based solely on natural variations.