近40年来青藏高原湖泊变迁及其对气候变化的响应

湖泊对气候波动有敏感记录。本文以GIS和RS技术为基础，在野外实地考察的基础上，从20世纪70年代、90年代、2000年前后和2010年前后4期Landsat遥感影像中提取了青藏高原所有湖泊边界信息，建立了青藏高原湖泊空间数据库。分析表明的青藏高原面积大于0.5 km2的湖泊总面积变化：（1）从20世纪70年代至90年代增加了13.42%; （2）从20世纪90年代至2000年前后增加了4.86%; （3）从2000年前后至2010年前后增加了13.04%。可见，近40年来，青藏高原湖泊个数和面积均呈增加的趋势。气象数据分析表明，青藏高原气候出现了由暖干向暖湿的转型，表现为气温升高、降雨量增加和蒸发量减小。笔者选取了研究区内面积大于10 km2的时间上合适做比较的所有湖泊，逐一分析了其在4个时期的动态变化情况，并根据变化结果进行了分区。不同时期的湖泊变迁具有区域差异性：（1）从20世纪70年代至90年代，西藏北部、中部、藏南、青海羌塘盆地和青海东部湖泊呈萎缩趋势; （2）20世纪90年代至2000年，青海北部湖泊萎缩; （3）2000年至2010年，除藏南外，青藏高原其余地区湖泊全面扩张。不同补给源的湖泊对气候变化的响应模式不同：（1）气温主要影响以冰雪融水及其径流为主要补给源的湖泊，如色林错、赤布张错等; （2）降雨量主要影响以大气降雨和地表径流为主要补给源的湖泊，如青海羌塘盆地; （3）蒸发量直接影响湖泊水量的散失，在青藏高原总体蒸发量减小的大环境下，部分地区因升温引起的湖泊蒸发效应超过了降水和径流量增加，湖泊出现萎缩的现象，如羊卓雍错流域。总之，地质构造控制了湖泊变迁的总格局，而短时间尺度的湖泊变迁主要受气候因素的影响。此外，湖泊动态变化还受冰川、人类活动、湖盆形状、补给和排泄区等因素的影响。

Change of the lakes in Tibetan Plateau and its response to climate in the past forty years

The levels and surface areas of lakes are indicators of climate change and climate variability. The authors extracted surface extent of all lakes in the Tibetan Plateau from Landsat remote sensing images of the 1970s, of the 1990s, around 2000 and 2010 based on RS and GIS and developed the lake spatial database in combination with on the spot investigations to a few representative lakes. The results show that the total surface area of lakes, each of which has an area larger than 0.5 km2, increased by 13.42% during the period of the 1970s to the 1990s, increased by 4.86% during the period of the 1990s to around 2000, and increased by 13.04% from 2000 to around 2010. It showed that lakes in the study area keep the expanding trend in the past forty years. We found that the climate of the Tibetan Plateau changed from warm dry to warm wet gradually characterized by increasing temperature, precipitation, and dropping evaporation through the meteorological data. Meanwhile, all lakes, each of which has an area larger than 10 km2, suitable for the surface area changes analysis were selected to compare the dynamic changes one by one, and the division of these lakes into expansion area and atrophy area was made according to dynamic changes. The variations of the lakes differ from area to area in different periods, and the response to climate is strong. In practical terms, between the 1970s and the 1990s, lakes in north and middle Tibet, southern Tibet, Qinghai Qiangtang Basin and east Qinghai were shrunk whereas lakes in other places tended to expand. From the 1990s to 2000, lakes in north Qinghai were shrunk. From 2000 to 2010, most lakes in the study area except southern Tibet expanded. Different climate parameters can produce different effects in different areas: temperature mainly affects lakes which rely on glacier melt water runoff for supply, such as Siling Lake and Chibuzhang lake; precipitation mainly influences lakes recharged by precipitation and surface runoff, such as Qinghai Qiangtang Basin; evaporation brings about water loss of all lakes, which influences areas with evaporation effect caused by raising temperature surpassing the increase in precipitation and runoff, such as Yamdrok Lake. Tectonic activities play an important role in the evolvement of lakes in long time scales, controlling the big pattern. While the climate shapes lakes more directly in short time scales. Besides, The dynamic changes of the lakes also can be influenced by other factors, such as glaciers, human activities, lake basin shape, open or closed systems and catchments.