ZHANG Shu-ping, ZHANG Hu-cai, CHEN Guang-jie, CHANG Fen-qin, CAI Yan-feng, ZHENG Qian
In this paper, all the materials adapted are as follow: 1) meteorological data from three stations nearby Ngangla Ringsto, namely, Gaize, Shiquanhe and Pulan, from 1973 to 2010; 2) Landsat remote sensing images covering the water area of Ngangla Ringsto in 1973, 1976, 1990, 2000, 2001, 2002, and 2009, which were used to extract the information of lake changes, and images covering the whole catchment in 1976, 1990/1992, 2000 and 2009, which were used to gain the information of glacier changes in the drainage basin. On the base of above information, the changes in climate, lake and glacier during the past 40 years were analyzed, and the relationship between every factor that causes the lake area change of Ngangla Ringsto was preliminarily studied. It is fond that: (i) during the past 38 years, the lake area of Ngangla Ringsto decreased before 2000 and increased after that, with a general trend of increase; (ii)The glacierized area in the catchment has shrunk and consistently contributed the Ngangla Ringsto during that time span; (iii) After comparing the changing tendencies of temperature, annual precipitation and maximum of potential evaporation at the three meteorological stations, the data from Gaize Station is chosen as a reference to analyze the cause of the lake area change in Ngangla Ringsto. The result shows that in every changing stage it is a gap between the annual precipitation and maximum of potential evaporation in the catchment that controls the change in the lake area of Ngangla Ringsto. When the water input from precipitation and constantly increasing melt water is less than the amount of evaporation in the catchment, the lake area will decease, but when the water from the glacier melting and frozen soil thawing in a accelerated speed due to the rapidly rising temperature plus gradually increasing precipitation in the catchment finally surpasses the output from evaporation, the lake begins to expand.
