Distribution And Variation Of Glacial Lakes In High Mountain Asia Since 1990

Glacial lake is an important part of the cryosphere,which can store glacial meltwater and regulate runoff,and is also one of the precious fresh water resources in the plateau.In the context of global warming,glaciers in the High Mountain Asia show a rapid shrinking trend,while glacial lakes on the whole show an expanding trend.The increasing frequency of disaster events such as glacial lake outburst has attracted extensive attention of scholars.As the glacial lake is usually located in the alpine mountains,it is difficult to make field investigation,so remote sensing has become one of the important means of glacial lake research.The distribution of glacial lakes is closely related to glaciers,and the changes of glacial lakes can also reflect the changes of glaciers to a great extent.Therefore,all lakes within 10 km from glaciers are considered as glacial lakes in the most current research.However,it also contains some lakes that are not affected by glaciers.In order to solve this problem,this study used multi-source remote sensing data to extract all the lakes within 10 km of the glacier in High Mountain Asia around 1990 and 2020.Meanwhile,the drainage basin of each lake was extracted,and the lakes whose glacier area accounted for more than 5%of the lake drainage area were regarded as glacial lakes.The glacial lakes are classified from two perspectives of the type of dam body and the contact relationship with glaciers.The present distribution and temporal and spatial variation of glacial lakes in High Mountain Asia are analyzed in detail.At the same time,combined with CRU reanalysis data,the causes of glacial lake change are discussed.The preliminary conclusions are as follows:（1）In 2020,10,894 glacial lakes with an area greater than 0.01 km² developed in High Mountain Asia,with a total area of 1,026.4±121.7 km².Glacial lakes are mainly distributed in Eastern Himalaya,Inner Tibetan Plateau,Southeastern Tibetan Plateau,Hengduan Shan,Western Himalaya and Western Tianshan Mountain.The number of glacial lakes in Qilian Shan,Hissar Alay,Western Kunlun and Eastern Kunlun is relatively small.Moraine-dammed lakes are the main type of glacial lakes in High Mountain Asia,accounting for 68.7%of the total number of glacial lakes.They are mainly distributed in Himalaya,Inner Tibet Plateau,Southeastern Tibet Plateau and Hengduan Shan.The number of ice-dammed lakes is small,accounting for 1.7%of the total glacial lakes,mainly distributed in Inner Tibetan Plateau,Karakoram,Eastern Kunlun and Western Kunlun.The number of supraglacial lakes accounts for 3.1%of the total glacial lakes,mainly distributed in Eastern Himalaya and Karakoram.The number of other-dammed lakes accounts for 26.5%of the total glacial lakes,and their distribution is relatively average in High Mountain Asia.Ice-dammed lakes account for18.9%of the total number of glacial lakes,while ice-unconnected lakes account for77.9%of the total number of glacial lakes,which is more than ice-connected lakes.（2）The vertical regularity of glaciers and glacial lakes in High Mountain Asia is similar,and the distribution is almost normal.Glaciers are mainly distributed in the altitude range of 4700-6200 m and glacial lakes in the altitude range of 4300-5800 m,accounting for 74.9%of the total number of glacial lakes.Ice-dammed lake has the highest elevation,mainly distributed above 5300 m.The second was the moraine-dammed lake,which mainly distributed in the altitude range of 4300-5800 m.The third is other-dammed lake,mainly distributed in the altitude range of 3900-5200 m.The supraglacial lakes are distributed evenly at different elevations.In High Mountain Asia,the elevation of glaciers and glacial lakes increases with the decrease of latitude.（3）From 1990 to 2020,the glacial lake area in High Mountain Asia expanded at a rate of about 6.0 km²·a^-1,showing a trend of higher in the south and lower in the north over Tibetan Plateau.The area expansion rate of glacial lakes in Himalaya,the Southeastern Tibet Plateau and Inner Tibet Plateau is relatively high,while the expansion rate of glacial lakes in Hissar Alay,Western Kunlun,Eastern Kunlun and Qilian Shan is relatively low.The glacial lakes have an obvious expansion trend within the altitude range of 4300-5500 m.Moraine-dammed lake is the main contributor of glacial lake expansion in High Mountain Asia.The ice-dammed lake showed a slight negative growth in area.The area of supraglacial lake and other-dammed lake changes little on the whole.Ice-connected lake also expanded more than ice-unconnected lake.From 1990 to 2020,a total of 2,656 new glacial lakes were added in High Mountain Asia,including 2,169 moraine-dammed lakes,60 ice-dammed lakes,294 supraglacial lakes and 133 other-dammed lakes,1,162 ice-connected lakes and 1,200 ice-unconnected lakes in which.A total of 541 glacial lakes disappeared,including 322moraine-dammed lakes,41 ice-dammed lakes,140 supraglacial lakes and 38 other-dammed lakes,132 ice-connected lakes and 269 ice-unconnected lakes in which.During the study period,680 glacial lakes were converted from ice-connected lake to ice-unconnected lake due to glacial retreat.（4）According to CRU reanalysis data,the overall temperature change rate in High Mountain Asia was 0.29℃/10a,showing a significant increasing trend.The overall change rate of precipitation was 4.32 mm/10a,and the precipitation showed an increasing trend in most regions.Through analysis,the direct influence of temperature and precipitation changes on glacial lake changes in High Mountain Asia is relatively small,but temperature changes can indirectly influence glacial lake changes through glaciers.Glaciers affect glacial lakes mainly by providing supply sources and by providing sufficient topographic conditions for the expansion of glacial lakes due to retreat,which are mainly reflected in three aspects:the significant expansion of ice-connected lakes,the large increase of glacial lakes and the transformation of the contact relationship between glacial lakes and glaciers.In addition,the dam type of glacial lake also has a certain effect on the change of glacial lake.（5）Compared with other studies,the number and area of glacial lakes studied in this study are the smallest.However,from the perspective of the changes in the number and area of glacial lakes,the selection method of glacial lakes in this paper can better identify the glacial lakes that are more sensitive to climate change and strongly affected and replenished by glaciers in High Mountain Asia.Some non-glacial lakes not affected by glaciers are excluded,which is conducive to more accurate and in-depth study of the feedback between glacial lakes and glaciers.In addition,compared with other studies,this study not only updated the glacial lake boundary of High Mountain Asia in 2020,but more importantly provided the glacial lake classification list under the two classification systems of glacial lake dam type and glacial lake and glacier contact relationship,so as to provide a detailed basis for future glacial lake outburst risk assessment.