Spatially And Temporally Resolved Monitoring Of Global Glacial Lake Changes Based On Multi-source Remote Sensing

Glacial lake is a natural lake formed by glacial movement or mainly supplied by glacial meltwater.As a derivative of glacier movement,the dynamic evolution process of glacial lake is a true portrayal of glacier and climate change,and also accelerates the melting of its contact glacier,which plays an important role in the surface water cycle and the evolution effect of glacier disaster.In recent years,the rapid expansion of glacial lakes has gradually affected the lives of residents downstream of mountain glaciers,so it is urgent to master the complete list of glacial lakes and their spatio-temporal variation characteristics.Since the area or volume of glacial lakes has not been carefully assessed on a global scale before,the temporal trends of the amount of water stored in these glacial lakes and the change of glacial lakes are not clear,which further results in that the role of glacial lake surface interception in regulating global sea level rise has been difficult to estimate.In order to deeply understand the spatial distribution,dynamic change trend and fresh water storage of alpine glacial lakes,it is particularly important to obtain a complete,accurate and relatively unified spatial inventory data of glacial lakes.At the same time,it is extremely urgent to monitor the temporal and spatial changes of glacial lake area and water level in typical regions of glacial lake distribution(alpine and polar regions),which can provide effective data support and theoretical basis for later studies on risk assessment and early warning of glacial lake outburst and estimation of water budget of sea level change.In view of the above objectives,this paper carries out remote sensing cataloging and monitoring analysis of glacial lakes from three aspects.The main research contents and results are as follows:(1)Based on multi-source remote sensing,geospatial data and literature data,and through strict quality control,this study cataloged the spatial distribution and max＿extent of 117,352 glacial lakes covering(near)the world for many years(1984-2019).According to the location relationship between glacial lakes and glaciers and whether they are replenished by modern glacier melt water,we superimposed high-resolution Images of Google Earth and used visual interpretation to classify glacial lakes into glacier-fed lakes and non-glacier-fed lakes.On the basis of glacial lake cataloging data,remote sensing data products were used to obtain the annual water area of these glacial lakes.The glacial lake water volume was estimated by fitting the empirical relationship between glacial lake water area and volume.The spatial distribution and temporal evolution of glacial lake area and volume were analyzed.The research shows that the total area of global glacial lakes is 24755.84±2971.33 km~2,and the total water volume is estimated to be 432.51±91.05 km~3.In terms of overall distribution quantity and area,glacial lakes are mainly distributed in Greenland,High Mountain Asia and Cordillera mountains in western America.From the perspective of different types of glacial lakes,the global glacial lakes are mainly glacier-fed lakes,and the altitude zone<1000 m is the active zone of glacial lakes.The analysis of glacial lake area change rate from 2000 to 2019 shows that glacial lake area in high latitudes has changed faster than that in middle and low latitudes in the past 20years.(2)Taking the Typical Alpine Region Alps as a case area,based on remote sensing data products,the annual area of glacial lakes in recent 20 years since 2000 is extracted,and the temporal and spatial variation characteristics of ice lakes in Alps are analyzed from different ice lake types,different elevation zones and different size grades.According to the research,498 glacial lakes(≥0.01 km~2)were identified in the Alps in 2019,with a total area of 33.77±6.94 km~2,mainly distributed in the central and western parts of the Alps(the junction of Italy,Switzerland and France).Almost half of the lakes are located at an elevation of 2250-2750 m,and the average elevation of small glacial lakes is higher than that of large glacial lakes.During the study period,the area and volume of the glacial lake increased in three stages.The area not in contact with the glacier accounted for the largest increase,and the area of the ice lake had the largest relative change(47%).(3)Taking Greenland,a typical polar region,as an example,the temporal heterogeneity of Greenland glacial lake is analyzed from the perspective of glacial lake water level by using ICEsat-2 laser altimeter data.The results show that there are 48,307 glacial lakes in Greenland,with a total area of 10681.75±347.11 km~2.During the study period(2018.10-2021.10),the glacial lake(≥1 km~2)was effectively observed for 2 to 36 months,and the average number of observed months was 12.The median seasonal variation range of glacial lake water level was0.32 m.Affected by glacial melt water,the median seasonal water level change of glacial lakes fed by glacial meltwater was 0.68 m,which was significantly higher than that of glacial lakes not connected with glaciers(0.27 m).On the whole,the spatial pattern of high seasonal water level change in northeast Greenland and low seasonal water level change in southwest Greenland is presented.