关键词: 西藏, 那曲, 湖泊, 水位变化, 气候变化

Abstract:

Inland lake is a sensitive indicator of climate change. Because lakes in high mountain region are in natural status and are little affected by human activities, their changes can reflect climate conditions. In this paper, four inland lakes (Bamucuo, Pengcuo, Dongcuo and Nairipingcuo) area changes in area and factors causing the water level growth are analyzed using remote sensing data and climate data from meteorological stations near the four lakes. For lake area changes from 1980 to 2005, the TM and CBERS remotely sensed data and topographic map at 1:100,000 scale in 1975 are used in this study. The meteorological data including temperature, rainfall, evaporation (1971-2004), snow depth and land frost depth from four meteorological stations Naqu, Anduo, Bange and Dangxiong which are the closest to the four lakes are used in this study. Based on the lake area information derived from a digitized 1:100,000 scale topographic map in 1975 and satellite remote sensing data from 1980 to 2005 georeferenced using topographic map, it is found out that four lakes' areas increased in 1980 compared with 1975, by 9.8 km², 9.7 km², 12.9 km² and 3.9 km², respectively. In 1988, the four lakes retreated and their areas are equivalent to the areas in 1975. The areas of Bamucuo, Pengcuo, Dongcuo and Nairipingcuo notably increased during the last 30 years from 1975 to 2005. Their areas increased by 48.2 km² (25.6%), 38.2 km² (28.2%), 19.8 km² (16.2%) (compared with 2004) and 26.0 km² (37.6%). The lake area increase has been more obvious since 2000. The analysis of climate changes for the last 40 years shows that annual mean temperature and precipitation increased significantly, while evaporation, maximum land frost depth and maximum snow depth decreased. For instance, the mean temperature increased by 0.28 ^oC/10a from 1961 to 2004; rainfall witnessed a big fluctuation from 1961 to 1994 and the maximum and minimum rainfall occurred in this period. The rainfall has been increasing since 1994. Evaporation decreased by 130 mm/10a from 1995 to 2004. The maximum land frost depth reduced 10 to 40 cm and the maximum snow depth decreased as well. The result based on the relationship between lake area changes and climate variation shows the main factors which are directly related to lake water level are rainfall, ice snow defrost and land frost. The indirect factors of lake area changes are temperature, lake size, catchment's area, land formation of lake basin, surface features etc.

Key words: Naqu of Tibet, lake, lake area change, climate change