Bloom and gloom: how glacier melt greens the desert but dries up Tibet

PUBLISHED : Sunday, 02 August, 2009, 12:00am
UPDATED : Sunday, 02 August, 2009, 12:00am

Climate change is having profoundly different impacts on China's two westernmost regions, Tibet and Xinjiang .

While Tibet is mired in a deepening drought, and will continue to suffer declining water resources in future years, the water table is on the rise in Xinjiang and the dry climate is gradually becoming more humid.

Glaciers in Tibet have been melting for decades. From 1971 to 2002 they shrank by 5.3 per cent, and between 2003 and 2008 they shrank a further 10 per cent.

On the face of it, the melting of the glaciers should mean that Tibet becomes wetter, with icy water filling rivers, ponds and wetlands.

But according to research by a team from the Wuhan-based Institute of Geodesy and Geophysics under the Chinese Academy of Sciences, between 2002 and 2007 Tibet had suffered a drop in total water resources - ice, snow, surface and underground water - equivalent to a 30mm reduction in rainfall.

This year Tibet has experienced its worst drought in three years, with some monitoring stations not recording rainfall for more than 200 days, and temperatures up to 2.3 degrees Celsius higher than normal, Xinhua reported in June.

Xin Yuanhong , who has been tracking glacier movement in Tibet since 2005 as chief engineer of the Water Resources and Geology Institute in Qinghai, said that while rivers and lakes directly beneath glaciers were filling up, elsewhere they were drying up and disappearing. This matters because the Qinghai-Tibet Plateau is the source of three of China's major waterways, the Yangtze, Yellow and Lancang (Mekong) rivers.

The scientist said the government had spent more than 7 billion yuan (HK$7.9 billion) trying to reverse the trend of drought by planting trees and grass in the region but it was having little effect. 'Mother Nature has the upper hand. Once she starts, we will have to wait until she finishes.'

The research from the Wuhan institute, which was the most comprehensive assessment of water resources in the region and made use of data from a US satellite, reconstructed the variations in the past half-decade.

It showed that while Tibet was drying up, Xinjiang's water reserves were growing at a rate equivalent to a rise in rainfall of 10mm per year.

The finding backs up a controversial 2002 book by geologist Shi Yafeng, who wrote that Xinjiang had been growing wetter since 1987.

Professor Shi recorded an expansion in green foliage, a drop in sandstorms and a surge in damage caused by floods - which had not been seen in the region for decades. The book was criticised in academic circles because it flew against the conventional wisdom that such changes were short-term fluctuations and that Xinjiang would remain arid.

History suggests that Xinjiang has not always been so arid. In about 100BC, Han dynasty historian Sima Qian wrote in his masterpiece Shiji that the vast region that now comprises Xinjiang and the western part of Gansu province was home to rich and powerful nations populated by millions along the Silk Road. He recorded huge lakes, forests, farms and even bamboo fields - all suggesting a lusher climate than exists today.

Ice cores retrieved from the Tianshan mountain range show that the temperature 2,000 years ago was considerably higher than today. According to a model constructed by meteorologist Zhao Zongci, of the National Climate Centre, the warm weather today could be helping humid air rise over the Himalayas and travel farther inland, creating additional precipitation in Xinjiang.

Not all scientists are convinced.

Wang Tao, director of the Cold and Arid Regions Environmental and Engineering Research Institute, said the increase in water resources cited by the Wuhan team was not enough to alter Xinjiang's desolate landscape fundamentally.

'Even if there was some transition, it would be a long-term process without an immediate impact. Xinjiang will remain extremely dry for a long time,' he said.

On the ground, all the people know is that this year is one of the best in decades.

Chen Dongliang, an apple farmer in Aksu, said the water level in his well had been rising steadily. 'The weather is good - I can't remember it being so good for years,' he said. 'I am expanding my orchard.'