Change And Risk Assessment Of Glacial Lake In Southeast Of Tibetan Plateau

With the continuous change of global climate,the glacial lake outburst disaster is increasingly prominent.Glacial lakes are widely distributed in southeastern of Tibet Plateau,which are the key areas of glacial lake disasters.In this paper,GF-1/2 and Landsat series satellite images are used as the main data sources to extract the glacial lake boundary in 1985,2000 and 2019 by NDWI method.From the scale,altitude and distance from the mother glacier,the change of glacial lake was analyzed,and the overall characteristics of the change of glacial lake in the four basins in the southeast of Tibet Plateau were analyzed.Finally,the risk of 3457 glacial lakes is evaluated.The main conclusions are as follows:(1)In 1985,there were 3253 glacial lakes in Southeast of Tibet Plateau with a total area of 207.82km2;in 2000,there were 3466 glacial lakes with a total area of 221.80km2;in 2019,there were 3457 glacial lakes with a total area of 232.38km2.According to the three-level watershed division,glacial lakes are mainly distributed in Menggu drainage basin of Nujiang River,and the number of glacial lakes in anbaqu and chayuqu drainage basins is the least.There are the largest change of glacial lake area in Yigongzangbu and Kalongzangbu drainage basins and the largest number of newly added and disappeared glacial lakes.(2)The change rate of glacial lake area is inversely related to its scale and distance from its mother glacier.The glacial lake area with small scale and close to its mother glacier changes greatly.At the same time,the newly added and disappeared glacial lakes are mainly small-scale glacial lakes close to the mother glaciers.There is also a certain relationship between the change rate of glacial lake area and the altitude.The glacial lake with great change in the southeast of Tibet Plateau is generally within the altitude range of 4800-5200m.(3)The change of glacial lake area is mainly related to the influence of altitude,glacier melt water supply,climate change and glacial lake's own factors,among which glacier melt water supply and climate change are dominant.The change of glacial lakes in Menggu drainage basin of Nujiang River is mainly affected by glaciers and other factors play an auxiliary role;the change of glacial lakes in laizi paixiang drainage basin of Brahmaputra River is mainly affected by glaciers and precipitation,but the retreat of glaciers is an important reason for the large number of glacial lakes in the basin;the change of glacial lakes in Yigongzangbu and Kalongzangbu drainage basins is mainly affected by glaciers and precipitation,both of which play a greater role in the change of glacial lakes in the basin;the change of glacial lakes in danbaqu and chayuqu drainage basins The glaciation is mainly affected by glaciers.The glaciers in the basin retreat less,the annual temperature is low and the precipitation is rare,which leads to the small number and stable change of glacial lakes.(4)A typical glacial lake was selected in four basins to analyze the leading factors of its change:the main reason for the expansion of No.1 glacial lake is precipitation;the main reason for the expansion of No.2 glacial lake is the increase of glacial melt water caused by the rise of temperature and a large amount of precipitation;the main reason for the expansion of No.3 glacial lake is the high temperature.In recent years,the rising temperature has caused the glacial retreat and melting water to flow into the glacial lake.The precipitation in the area which the No.4 glacial lake located in is less,and the glacier melt water supply is difficult due to the terrain restriction,which leads to its small change.(5)The risk assessment results of 3457 glacial lakes in Southeast of Tibet Plateau are as follows:1163 glacial lakes without risk,accounting for 33.64%of the total;1556 glacial lakes with low risk,accounting for 45.01%of the total;579 glacial lakes with medium risk,accounting for 16.75%of the total;159 glacial lakes with high risk,accounting for 4.60%of the total,of which 22 glacial lakes are surrounded by houses,roads and other facilities within 20km.Basin 3 is the main distribution area of middle and high risk glacial lakes.