A research team led by Prof .LI Xin from the Cold & Arid Regions Environmental and Engineering Research Institute under CAS recently appealed to the authorities to set up an early warning system for the possible floods due to glacial lake outburst in China's alpine hinterland.
The global climate change is an irresistible trend and a challenge facing today's world, says Dr. CHE Tao, a member of the team. As reported by the Intergovernmental Panel on Climate Change, the average global temperature is to go up by 1.4-5.8ºC by 2100 while the annual average temperature in China's West has seen a rise up to 2ºC over the past century.
From their glacier-monitoring work surrounding the Mt. Xixiabangma on the Sino-Nepali borderline, the group found that, due to the on-going global warming-up trend, the total area of the glacial lakes is increasing.
Many glacial lakes are dotted with the Qinghai-Tibet Plateau, and along with the glaciers, they act as the sources or head waters of many large rivers on the Roof of the World. The glacial lakes are mostly formed from the build-up of melt water when end moraines block the water flows. The majority of the Plateau's glacial lakes are dammed by unstable moraines, which were formed during the Little Ice Age. Occasional collapses of a moraine would soon release the lake's stored water, causing flooding downstream along the river route.
This phenomenon, known as a glacial lake outburst flood (GLOF), is an eruptive and potentially precarious event and a problem of common occurrence on the high-elevation massifs of the mighty Himalayas, covering the bordering areas of China, Nepal, India, Pakistan and Bhutan. In the course of the on-going deglaciation to modify Hamalayan valleys, this is one of most devastating processes as a mountainous hazard for the local inhabitants, note the researchers.
By using multitemporal remote sensing images on the flooding and breakdown events of glacial lakes in the Himalayas and the Xinjiang Uygur Autonomous Region, a long-standing survey by Dr. Che and his colleagues revealed that the glaciers on the eastern slope of the Mount Xixiabangma are undergoing a drastic decrease during the past 27 years, leading to the increase of the glacial lakes areas.
The total area of Jicongpu Glacier in the southern slope of Mt. Xixiabangma, for example, has reduced by 7.29% with a retreat speed of 57,099 square meters per year, according to the scientists. They also found that the ice tongue at the glacier's foot have lost 16.6% of its total volume with an averaging withdrawal speed of 48 meters each year. Another example is the Lumchimi Glacial Lake on the northern slope of the Mount. Its total area grew up to 117.79%, an increase of 79,048 square meters in its yearly rate. The Reqiang Glacier on the Mount's northern side has dwindled 22.9% of its coverage, averaging about 63,000 square meters in its annual shrinkage speed and it ice tongue went down by 27.56%, roughly reaching 71 meters in annual reduction rate. The glacial Lake Gangxi Cuo in the Mount's north swelled up by 878.14% in total area, averaging about 73,425 meters each year. (See Figure)
According to Dr. Che, the lakes are stemmed by the moraine (rock debris) at the end of glaciers. But the naturally-formed barrier is always fragile and unstable. The situation becomes increasingly aggravated due to the further glacial retreat and the glacial lake inflation as a result of the warming-up process. The disastrous breakdown and flooding risk are unavoidable and it is necessary to introduce an early warning system to defuse the possible ecological collapse. The scientists urge related administrations to keep an eye on the potential dangerous situation by strengthening the monitoring capacity. As the first step for the reduction of the possible calamities, they suggest, efforts should be made to establish a precautionary system for the dangerous glacial lakes in Western China.
