Himalayan glaciers are among the fastest retreating glaciers in the world due to the effects of global warming.

This may result in water shortages for hundreds of millions of people who rely on glacier-dependent rivers in China, India and Nepal, warns the World Wide Fund for Nature (WWF), the global conservation organization.

A new WWF report "An Overview of Glaciers, Glacier Retreat and Subsequent Impacts in Nepal, India and China" reveals that Himalayan glaciers are retreating at a rate of 10-15 metres per year.

"The rapid melting of Himalayan glaciers will first increase the volume of water in rivers causing widespread flooding," said Jennifer Morgan, director of the WWF's Global Climate Change Programme.

"But in a few decades this situation will change and the water level in rivers will decline, meaning massive economic and environmental problems for people in western China, Nepal and northern India."

Declining figures

The Qinghai-Tibet Plateau is the most concentrated glacial centre in the middle and low latitudes of the world, covering an area of 104,850 square kilometres, including 23,000 square kilometres in India, 16,933 square kilometres in Pakistan, 5,322 square kilometres in Nepal, and 49,873 square kilometres in China.

The largest glacier cover is in the Himalayas, amounting to 34,660 square kilometres.

Glaciers have been used as a tool by scientists to monitor the climate for many years. Snow, glaciers and permafrost are especially sensitive to changes in atmospheric conditions because of their proximity to melting states.

"Temperature changes in glacial regions are commonly earlier and more evident than other areas on Earth. So they are considered the most directly visible signals of global warming," said Professor Shen Yongping of the Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, who completed China's portion of the report.

Comparative analysis of satellite data obtained in 1986 and 2000 shows that glaciers and firns in the headwater region of the Yangtze River are retreating, from 899.13 square kilometres in 1986 to 884.4 square kilometres in 2000.

"From these figures it can be seen that glaciers in the Yangtze River source region have a relatively small recession rate, approximately 1.7 per cent," said Shen.

However, because the glacial retreat in the region occurred suddenly after the mid-1990s, it is quite evident that the stream flow in the Yangtze has greatly increased in recent years.

The most evident glacial retreat has occurred in the Nyaingentanglha Mountains of the southeastern part of Tibet Autonomous Region. Unlike the cold glaciers around the headstream of the Yangtze River, the typical temperate maritime glaciers in that region are much more sensitive to increasing temperatures, according to Shen.

Impact of retreat

Himalayan glaciers feed into seven of Asia's greatest rivers, including the Ganges, Indus, Brahmaputra, Salween, Mekong (the Lancang River in China), Yangtze and the Yellow River. These rivers sustain hundreds of millions of people in the Indian subcontinent and China with water for drinking, irrigation and industry.

As glacier water flows dwindle, the energy potential of hydroelectric power will decrease causing problems for industry, while reduced irrigation means lower agricultural output.

The report warned that the accelerated melting of glaciers will cause an increase in river levels over the next few decades, initially leading to more incidence of flooding and landslides. In the longer-term, however, as the volume of ice available for melting diminishes, a reduction in glacial run-off and river flows can be expected.

Global warming over the past half century has led to an accelerated retreat of the glaciers and the enlargement of many glacial lakes, according to the WWF report.

A retreating glacier's meltwater is hemmed in by the glacier's terminal moraine. When the volume of water becomes too great for the moraine to support, the glacial lake bursts its banks.

"The flood can cause devastating damage to downstream agriculture and livestock, and frequently results in the loss of life," said Shen.

Nearly 229 glacial lakes have been identified in Tibet's Aru Basin, of which 24 are potentially dangerous.

Over the past 15 years, the degradation of wetlands on the Qinghai-Tibet Plateau has been severe. As the permafrost melts deeper underground, the water also sinks.

"That is why we have seen in the past decade many lakes in the headstream Yangtze River region shrinking quickly, some even on the brink of drying up," said Shen.

The lake area has shrunk by 196.54 square kilometres, which is roughly 7.5 per cent of the lake's total area.

Lake shrinkage has mainly occurred in the region around the headwaters of the Yangtze River, where lakes have diminished by 10.64 per cent, and at the source of the Yellow River, where a figure of 5.28 per cent has been recorded.

Accompanying the sinking of water levels, the area of high-cold swamp meadow has also decreased sharply by 24.36 per cent, mainly around the source of the Yangtze River.

Around the source of the Yellow River, desertification has increased by 25.65 per cent, with an annual expansion rate of 1.83 per cent, thereby falling into the category of regions suffering from severe desertification.

"Climate change is a major factor affecting the environmental changes in headwater regions, but human activities aggravate the already degraded ecosystem," said Shen.

Overgrazing and highway construction on the plateau have led to the severe shrinking of vast expanses of meadow.

"The bare land absorbs more heat and amplifies the effect of increased temperatures in glacial regions," he said.

So strengthening the protection of the already fragile ecosystem on the plateau is crucial in mitigating climate change, Shen said.

(China Daily 03/24/2005 page13)