Melting permafrost reduces Yangtze River flow

Two recent scientific studies have highlighted the chronic water problems in the Yangtze River Basin. First, Chinese scientists have found that melting permafrost on the Tibetan Plateau is reducing the flow of the Yangtze River, according to an article in Nature. The amount of water entering the Yangtze River near its source on the Tibetan Plateau has fallen by 15% over the past four decades, despite melting glaciers and increased rainfall.

Permafrost  deep layers of frozen soil near the surface  is highly sensitive to climate change. The results of this five-year research project conducted by scientists from the Cold and Arid Regions Environment and Engineering Research Institute in Lanzhou, show that 10% of the permafrost that underpins the plateau has disappeared over the past decade, due to rising temperatures and increasing human activity in the region. As permafrost melts the layer of new soil “acts like a sponge, soaking up the water that would otherwise have run off into the river.” This explains why the amount of water flowing into the Yangtze has decreased so much.

Previous research by the Chinese Academy of Science has warned that thawing permafrost will lead to significant changes in surface hydrology and accelerated degradation across the plateau. Over time, rapid thinning of permafrost has dried up soil, turning swathes of the plateau’s wetlands and alpine meadow into dusty desert. This will significantly reduce downstream water supplies in the long run.

There have also been reports that melting permafrost is destabilising infrastructure on the plateau, including the 2,000-kilometre long Qinghai-Tibetan railway; no doubt giving Chinese engineers sleepless nights. Permafrost underpinning the asphalt of the Qinghai-Tibetan highway, which was built back in the 1970s, is now all near thawing point.

A second recent study, released by WWF last week, shows that lakes in the Yangtze River Basin are shrinking dramatically. These lakes could dry up completely if measures aren’t taken to stem the impacts of climate change, increased industrialization, and urbanization, the study warns.   Water resource projects have been blamed for record low levels in these freshwater lakes this year, Wang Shigang, deputy director of the Jiangzi Poyang Lake Hydrologic Bureau was quoted in China Daily as saying. This comes after the Three Gorges Dam and was blamed for the devastating drought last spring in the downstream Yangtze River.

Heedless of such criticisms, this month China completed a crucial part of the eastern section of the giant South-North Water Transfer Project, which will transfer 14.6 billion cubic metres of water from the Yangtze River to the parched provinces in the country’s north.  But as permafrost melt dries up the source of the river, and dams and development hold back water further downstream, even the traditionally “water rich” Yangtze will not have any excess water to give away.