Remote Sensing Monitoring And Hazard Risk Assessment Of Glaclal Lakes In Bedezangbu River Basin

In the context of global warming,the melting glaciers on the Tibet Plateau has accelerated,glacial lakes change significantly,these changes affect the frequency and intensity of glacial lake oustburst events,glacial lake outburst floods(GLOFs)pose a new threat to people's lives,property and infrastructure construction in key areas.Remote sensing investigation and hazard risk research of glacial lakes in key areas could provide scientific and technological support for improving China's disaster prevention and mitigation capacity.The Bidezangbo river basin in Nyingchi,Tibet was selected as the study area toconduct a systematic study on remote sensing monitoring and hazard risk of glacial lakes.Based on Landsat and Sentinel remote sensing images,in this study,we collect 5periods glacial lake data in year of 1988,1999,2008,2015 and 2019 by an object-oriented method,the techniques of GIS and statistics were applied to complete the analysis of the regulations of glacial lake changes in the past 3 decades,the GLOFs events in study area and surrounding areas,the glacial lake hazard risk assessment model was established and employed to assess the glacial lake hazard risk.The main conclusions and results are as follows:(1)Glacial lakes are widely distributed in the Bidezangbo river basin,with a high development level,and have great spital differences in distribution.In 2019,there were254 glacial lakes cover a total area of 15.58±2.10km~2,the maximum glacial lake hold an area of 1.40km~2.The distribution of glacial lakes is characterized by more northeast and less southwest,mainly distributed in the northern part of the basin.The glacial lakes have an average elevation of 4733meters,concentrated distributed between 4500 meters and 5000 meters,erosion lakes and terminal moraine lakes are the most dominant types of glacial lakes.(2)The number of glacial lakes in Bidezangbo river basin increased,and the area of glacial lakes expanded rapidly.From 1988 to 2019,the number of glacial lakes increased from 193 to 254,the area of glacial lakes expanded from 12.46±2.36 km~2to15.58±2.10km~2,the increase rate and the area expand rate are31.61%and 25.06%,respectively.There were 44 newly emerged lakes,8 disappeared lakes and 186perennial glacial lakes from 1988 to 2019.The total area of newly emerged and disappeared glacial lakes was 0.53km~2and 0.1km~2,respectively.The area of the perennial lakes in 1988 and 2019 is 13.35km~2and 14.64km~2,respectively.Climate change is the primary driving factor of the increasing number and the rapid expansion of glacial lakes.The temperature increased significantly from 1988 to 2019 in study area.(3)This study found two unreported GLOFs events,occurred in 2012 and 2018.According to the remote sensing images,the time of the GLOFs occurrence was identified,the changes in glaciers and glacial lakes,and the impact of GLOFs on the downstream are analyzed,and extreme rainfall is the trigger factor of GLOFs.The case studies in the study area provide a basis for determining the key parameters of hazard risk assessment.(4)The hazard risk assessment results indicate that,54 glacial lakes of which the254 glacial lakes in the study area have potential threats,31glacial lakes belong to low hazard risk,10 glacial lakes are in the level of medium hazard risk,13 glacial lakes are in the level of high hazard risk,and 2 high risk glacial lakes potentially threaten Sichuan-Tibet railway,monitoring and early warning of glacial lakes need to be strengthened,and the ability to prevent and mitigate GLOFs needs to be improved to ensure the safety of major projects.