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27-Aug-2016 16:06
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In The Spotlight

Scientists warn that Yangtze River Delta will experience 'big droughts'

By Wu Chong

After China's worst drought in a decade, water in its longest river--the Yangtze--has fallen to its lowest levels in nearly a century and a half.

Ships have run aground and nearby lakes have dried up. Falling water levels-- in January, the lowest since Qing officials began recordkeeping in 1866-- have also exacerbated water pollution in one of China's most heavily-used waterways.

Drought hitting the midstream area of the Yangtze River in 2003.

This may be only the beginning, warn Chinese climatologists, who say that extreme weather and glacial shrinking are likely to cause even more "big droughts" in the Yangtze River Delta in the near future.

"I'm more than 50 percent sure that in the first 30 years of the 21st century, the delta and the middle and downstream areas of the river will experience big droughts," says Dr. Jiang Tong of the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences.

Such droughts would have significant implications for the region, which feeds a population of more than 400 million and contributes nearly half of China's total economic output.

Last fall, Jiang and his research team published several studies in the Chinese journal, Advances in Climate Change Research, predicting a significant decrease in annual rainfall in the river's downstream and midstream regions until the year 2030.

According to the study, rainfall would increase again after 2030, a change directly related to global carbon emissions levels.

Depending on which of three separate emissions models they used, however, Jiang's team found sharp fluctuations in rain levels and distribution.

Under the lowest emissions condition, rainfall might actually increase at a rate 7.47 percent higher than the average annual rate of increase, "most conspicuously in summer and winter," according to Jiang.

But the risk for drought shattered many of Jiang's previously-held assumptions.

Before, Jiang and many of his colleagues assumed that an increase in global temperatures would surely lead to an increase in total and extreme precipitation. But their studies, including one from 2005 that measured global historic river levels, have since shown otherwise.

Jiang Tong, a researcher from the Nanjing Institute of Geography and Limnology, researching the effects of climate change on lake levels and rainfall patterns in Xinjiang.

In that study, Jiang and his team conducted an analysis on the observation data of about 1,000 rivers in the world, finally focusing on 195 without dams and reservoirs but with more than 40 years of hydrological records. Their results were surprising: only 27 of these rivers witnessed an increase in peak flows, while 31 of them saw a decrease. The remaining 137 saw no change in their peak flows.

"The research suggested that the previous, 'theory,' which said climate change would lead to expedited hydrological cycling and increased floods, was only an assumption," Jiang says.

But most Chinese researchers agree that it is still too early to draw any solid conclusions. Luo Yong, deputy director of China's National Climate Center, says that while Jiang's research is consistent with previously-observed monsoon patterns, "all available climate models have shortcomings."

Luo bases his own model on predictions from the Intergovernmental Panel of Climate Change and on historic climate change patterns, which show China's rain belt shifting from north to south an average of once every 60 years. After its last southward shift-- in the late 1970s-- the monsoon is due for another shift north around the year 2020, Luo says.

"According to the prediction of the Intergovernmental Panel of Climate Change, global warming will bring more rains to lands at the middle and high latitudes," Luo says.

Many studies have warned that delta regions in Asian countries are among the areas most vulnerable to the effects of climate change. The Yangtze River Delta, dubbed China's "cradle of rice and fish," draws particular attention from Chinese researchers because it has nurtured the fastest-growing regional economy in the country.

"We have established well-round facilities and solutions to floods for this area, but so far, nothing has been done to prevent droughts," Jiang says.

Drought hitting the midstream area of the Yangtze River in 2003.

According to the climatologist, the effects of those droughts will be far-reaching. In addition to affecting the growth of trees and of local crops in autumn and early spring, drought will also bring problems to water transportation.

For a large river like the Yangtze, those problems may be compounded by shrinking glaciers.

Although only about 10 percent of the Yangtze's water supply comes from melting glaciers upstream, that supply could be lost once glaciers shrink beyond a certain point.

Glacier shrinking also leads to more exposure of land surface in the water source areas and may result in vegetation regression, says Liu Shiyin, a researcher at the Cold and Arid Regions Environment and Engineering Research Institute. This, in turn, affects the entire water cycling system.

Results would be worse in areas like the Tarim Basin, where glacier melt contributes nearly 40 percent of the water content in some rivers and up to 80 percent in many tributaries.

A recent study led by Liu found that glaciers in China's western areas shrank by 7.4 percent on average from 1999 - 2002, a much higher rate of decline than that of 40 years ago.

"The melting speed has expedited even since the 1990s, according to our preliminary study," says Liu, who is currently analyzing new data collected between 2002 and 2007.

All of this spells bad news for the Yangtze River.

"If the two elements-- glacier shrinking and rainfall decrease-- happen to overlap in the same time period, it will be a really bad situation," Luo says.

Meanwhile, Jiang is also analyzing new data against his models of liquid flows and silt in the tributaries of the Yangtze River. He hopes his conclusions will lead to solutions in adapting China's rivers to climate change. But Jiang is still cautious.

"We definitely need more and further studies to find out the truth."

Wu Chong is a freelance journalist who has written for China Daily and She is also an editor for Global Environmental Review, a Chinese electronic magazine about environmental news.