中国西部冰川对近期气候变暖的响应*

中国冰川主要分布在青藏高原及周边地区,在这一广大的区域内分布有冰川46377条。研究表明,中国西部变暖显著,1950年代以来平均气温上升0.2℃/10a,其中1990年代是近千年中最暖的10年;同时,1950s以来西北各省的降水量增加了约18 ％ 。为认识这一气候变化对中国西部冰川的影响,利用遥感和地理信息系统方法,获取了近50a来5000多条冰川的变化状况。结果表明,中国西部82.2 ％ 的冰川处于退缩状态,冰川面积减少了4.5 ％ ,同时也有一些冰川处于前进状态。此外,近数十年中国西部冰川变化表现出明显的区域差异,青藏高原中部和西北部地区的冰川相对稳定,而高原周边山区的冰川物质亏损严重,处于加速退缩状态。

GLACIERS IN RESPONSE TO RECENT CLIMATE WARMING IN WESTERN CHINA

Glaciers in China are primarily located in the Qinghai-Xizang (Tibet) Plateau and surrounding high mountains. The China Glacier Inventory (CGI) indicates that there are over 46377 glaciers in Western China, accounting for 52 percent of the total area in Central Asia. Meteorological records indicate that air temperature in Western China has risen by 0.2℃ per decade, and the 1990s is likely the warmest decade of the millennium; similarly, most of Western China also has seen an increase in precipitation during the past 50 years, for example, precipitation increased by 18 ％ during the last half of the last century in northwestern provinces. Using remote sensing and Geographical Information System (GIS) methods, we have monitored the changes over 5000 glaciers in the past 50 years. We conclude that 82.2 ％ of all the monitored glaciers retreated, while the remaining glaciers were enhanced. It should be mentioned that the enhanced glaciers were not necessarily enhanced over the entire observational period; in the past two decades while regional climate warming has been much evident many of the once expanded glaciers started to retreat. As a whole, glaciers that have been monitored show a total area loss of 4.5 ％ from the late 1950s to the late 1990s. Investigation on glacier changes over the past few decades reveal some regional differences, which is mainly attributed to different dynamical responses of glaciers with different sizes and physical properties along with climate changes of that region. For example, glaciers in central and northwestern parts of the Qinghai-Xizang Plateau were relatively stable, while those in mountains surrounding the Plateau experienced extensive wastage. It is concluded that strong warming and reduced precipitation are likely key drivers for the extensive reduction of ice cover in the eastern and southern parts of the Plateau. In contrast, recent cooling in the northwestern and central parts of the Plateau may partially explain the relatively stable condition of those glaciers. The modest warming trend and increase in precipitation in the southeastern part of the Plateau could account for the modest changes in glaciers there. Although precipitation has increased in Northwest China (Tianshan, Qilian Shan, Eastern Pamirs, and so on), the strong warming may be the principal factor driving glacier retreat although large glaciers with heavy debris covering their ablation areas may also contribute to the variations of ice extent in the region. Glacier recession is a key factor in the variability of water resources in the arid river systems of Northwest China. The recent increase in discharge of these rivers may be partially related to the increase in glacial runoff caused by loss of ice during glacier retreat. Although the glaciers that we (and others) have monitored account for only 10 ％ of the total number and 24 ％ of the total area of glaciers in China, our results may be extrapolated to infer glacier changes in various mountain regions of China.