By Chris Buckley
LAKE HONGHU, China (Reuters) - China's drought along its biggest river, the Yangtze, is for some scientists a demonstration of how global warming could increasingly disrupt the complex dance of air flows, rains and waterways that feeds dams and farming heartlands.
Many older farmers around Lake Honghu, part of the drought-stricken Yangtze River basin, said summers and winters had seemed warmer in the past decade, and some said overall rainfall had shrunk, although impressions varied.
Few blamed global warming, not a widely understood idea in rural China, although one offered his own twist.
"This is all related to global warming. In the past few years it's been getting warmer and the rain has been less than before, and it comes at different times," said Li Shenguang, a fish trader working the shrinking waters of Lake Honghu.
"It's related to the Japanese nuclear leak and the volcano eruption in Iceland," he added.
Climate experts would certainly dismiss those explanations and they mostly avoid blaming specific extremes of weather on global warming. They say their work tracks trends, not particular events. The drought parching much of the Yangtze, the world's third-longest river, is no different.
But the months-long dry spell across parts of central and eastern China, and severe drought in the usually lush southwest province of Yunnan last year, amount to signs of what global warming could bring, said Liu Changming, a prominent hydrologist at the Chinese Academy of Sciences in Beijing.
"I think there is a link to climate change," Liu told Reuters. "In recent years, the trend seems to be that China's south, which generally has abundant water, has experienced more drought and extremes in weather.
"We can't be sure of how much of this drought can be ascribed to climate change, but at least climate processes and atmospheric circulation have been abnormal recently," he said.
Food prices worldwide could double in 20 years as the output struggles against slowing gains in crop yields, global warming, and demand from growing populations and economies, the charity Oxfam said in a report this week.
China is a huge grain producer and consumer, and even the relatively limited drought along the Yangtze has made global traders sit up.
Evidence that climate change is unsteadying or shifting production or making it more costly to adapt and keep up yields could magnify concerns.
Research indicates global warming could increase precipitation in much of the Yangtze River basin and southern China in coming decades, said Lin Erda, director of the Agriculture and Climate Change Research Center of the Chinese Academy of Agricultural Sciences in Beijing.
But rainfall patterns could become more uneven.
"You could have a situation where average precipitation volume doesn't show a big change, but extremes of lows and highs, of major floods and droughts, could increase," said Xia Jun, a water expert at the Chinese Academy of Sciences whose research includes the effects of global warming.
"A severe drought such as this could be followed by severe flooding, which is what happened in 1998," said Xia.
Indeed, a 2010 study of the Three Gorges Dam found that rainfall in the dam area has declined since the 1990s, especially in the past decade, and future patterns could be more unsteady.
For a few decades at least, the upper Yangtze will also absorb more water from glaciers melting in the Himalayas and other mountain ranges. Those flows may then peter out.
"Droughts in dry seasons and floods in wet seasons are more likely on the Yangtze above the Three Gorges, with increased torrential downpours and other extreme weather events that will have negative consequences for managing the dam," said the study sponsored by China's meteorological administration.
(Reporting by Chris Buckley; Editing by Nick Macfie)