气候变化对西藏湖泊变迁的影响(1973-2017)

The Influence of Climate Change on Lake Variations of the Tibet Plateau in the Period of 1973–2017

西藏湖泊众多,其水位和面积变化对气候波动有敏感记录。本文运用RS和GIS技术,以1973-1977年、1989-1992年、1999-2001年、2008-2010年和2017年5期遥感影像为底图矢量化了西藏所有湖泊边界,建立了湖泊空间数据库。以湖泊空间数据为基础,分析了1973-2017年西藏湖泊面积动态变化特征,结论如下:从20世纪70年代至2017年,西藏湖泊总面积持续增加,共增长了47.23%;从20世纪70年代至90年代,研究区北部和中部湖泊呈萎缩的趋势,其余地区呈扩张的趋势;从2000年至2017年,西藏湖泊呈持续扩张的趋势。另外,笔者分析了研究区年平均气温、年降雨量和年蒸发量的变化特征。1981-2017年,西藏气候向暖湿方向发展,主要表现为气温升高、降雨量增加和蒸发量减少。气候变化对不同地区不同时期湖泊变迁影响显著:(1)西藏北部和中部湖泊主要以冰川、冰雪融水和地表径流为主要补给源。20世纪70年代至90年代,气温和降雨量波动较小,引起这些地区湖泊萎缩的主要原因为冰川和冰雪融水补给的减少。(2)从20世纪90年代至2017年,气温和降雨量增加、蒸发量减少,导致研究区湖泊呈现全面扩张的趋势。

There are a large number of lakes on the Tibet Plateau whose levels and surface areas are indicators of climate change and climate variability. The surface extents of all lakes in the study area were delineated from Landsat images obtained in 1973–1977, 1989–1992, 1999–2001, 2008–2010 and 2017 based on RS and GIS. The dynamic changes of lake surface areas from 1973 to 2017 were analyzed. The total surface area of these lakes increased, and the total surface area increased by 47.23% during 1973–1977 to 2017. More especially, during 1973–1977 to around 1990, lakes whose areas decreased were mainly distributed in the northern and middle parts of the Tibet Plateau, whereas lakes elsewhere tended to expand. Since 2000, most lakes have expanded. Additionally, average annual temperature, total annual precipitation and total annual evaporation were analyzed. Over the past four decades, the climate has become warmer and wetter, characterized by rising temperature and precipitation as well as dropping evaporation. Lake variations differ from area to area in different periods, and the response to climate fluctuation is strong.(1) During the 1970 s–1990 s, lakes in northern and central Tibet Plateau was mainly recharged by glaciers, snow melt water and surface runoff. During this period, there were slight fluctuations in temperature and precipitation. Lakes in these areas shrank without enough glaciers and snow melt water to supply.(2) During the 1990 s to 2017, lakes throughout the study area showed the tendency of expansion due to increasing temperature and precipitation as well as decreasing evaporation.