Volume Change Of Glacial Lakes In The High Mountain Of Asia And The Retention Of Ice Melt Water

Glaciers is in a state of retreat generally,with the background of rising global temperature.Part of glacial meltwater doesn’t flow out of the cryosphere with the surface runoff system,but is temporarily retained by glacial lakes,causing the sustainably increasing quantity and area of glacial lakes.Such part of glacier meltwater retained by glacial lakes play a significant role in water resource of Alpine mountainous areas,which crucially impact the maintaining of regional ecosystem balance.Otherwise,accumulated glacier meltwater can also trigger glacial lake outburst flood,leaded to destructive natural disasters such as debris flow and landslide,which seriously threatens the downstream resident and property security.Based on landsat8remote sensing image,the second glacier inventory data set of China,Randolph Glacier Inventory 6.0 and SRTM digital elevation model data,this paper investigates the glacial lakes High mountain of Asia（HMA）in 2020,and establishes the glacial lake inventory database of HMA in 2020.At the moment,based on the measured data of the average depth,area and water volume of the glacial lake collected,empirical formula for estimating the average depth-area-volume of the glacial lake suitable for different length-width ratio level is established,and the glacial lake water storage of HMA in 1990 and 2020 are calculated.Finally,0.25°×0.25°grid is established based on ERA5 meteorological data,retain glacier meltwater of glacial lakes of HMA in recent 30 years is calculated,and contribution of glacier mass loss to the water volume of glacial lakes and the retention capacity of regional glacial lakes are evaluated combined with the relevant glacier change data.There are 31680 glacial lakes in HMA,with area of about 2094.5±2.3 km²and water storage of about 52.5 Gt in 2020.Among them,the area and water volume of glacier-fed lakes account for 71%and 80%of the total area and total water resources of glacial lakes in the study region,respectively（with area of 1493.9±2.0 km²and water storage of 41.8 Gt）,and the area and water volume of non-glacial-fed lakes are 600.7±1.1 km²and 10.7 Gt,respectively,which accounts for 29%and 20%of the total area of regional glacial lakes and total water storage,respectively.From 1990 to 2020,the water volume of regional glacial lakes increased by 8.1 Gt,of which 95%came from glacial-fed lakes（7.8 Gt）,and non-glacial-fed lakes increased by 0.4 Gt,accounting for only 5%of the total increased water volume of regional glacial lakes.The southern Tibetan Plateau is not only the region with the most abundant glacial lake water storage,but also the fastest change in glacial lake water volume.The east Himalaya and the inner Tibet are the regions with the fastest change in glacial-fed lakes and non-glacial-fed lakes respectively,with an average annual increasing rate of about 0.06 Gt yr^-1and 0.01 Gt yr^-1.Over the past 30 years,glacial-fed lakes with increased area（increased water volume）in HMA have retained 8.2 Gt of glacier meltwater,accounting for about 92%of the total increased water volume of the corresponding glacial lakes,indicating that more than 90%of the increased water volume of these glacial-fed lakes is contributed by glacier meltwater,while other factors contribute less than 10%to the water volume of glacial-fed lakes.About 3.1%of glacier meltwater is retained by glacial lakes in High-Mountain Asia from 1990-2020,of which Karakoram is the region with the weakest capacity of glacial lake retained glacier meltwater.In recent 30 years,the amount of retained glacier meltwater accounts for only 0.4%of the regional glacier mass balance,while West Kunlun Mountain is the area with the strongest retention capacity.The proportion of glacial lake retained glacier meltwater accounts for 7.3%of the regional glacier mass balance.