Glacier And Glacial Lake Change In The Mt.Xixiabangma Region Over The Past 40 Years

Glaciers are important freshwater resources,feeding many rivers on the Tibetan Plateau.Due to the increasing warming trend,global glaciers show retreat trend,which has resulted in a series of water availability and seasonality issues as well as glacial hazards.It is important to improve the prediction ability of glacier change and its potential impact.The Mt.Xixiabangma region is located in the middle of the Himalayas,available glacier inventory data is lacking and glacier mass balance results are different here.Based on Hexagon KH-9,Landsat and the first Chinese Glacier Inventory,glaciers area change were investigated.By employing geodetic methods based on digital elevation models(DEM)derived from Topographic Maps,the Shuttle Radar Topography Mission(SRTM)DEM and TerraSAR-X/TanDEM-X(TSX/TDX),glacier elevation change and mass balance were obtained.From 1974 to 2018,the glaciers were generally in a state of retreat,with a retreat rate of 0.60±0.10%a^-1.Comparing glaciers change in different periods,we can find that the retreat rate of glaciers has accelerated.The area shrinkage rate of debris-covered glaciers and debris-free glaciers are different,debris-free glaciers show a higher shrinkage rate.Glaciers change show a normal distribution at different elevation,and glacier area changed most at the elevation band of 5400-5500 m.Glaciers area change on different slopes show a unimodal distribution,and glaciers area change is small in steep areas.Glaciers area change varies greatly in different aspects,glacier retreat most in the east direction,and retreat least in the northwest direction.The area and number of small glaciers are greater than those larger glaciers and more sensitive to climate change.The glaciers have different shrinkage rates on different slopes,the glaciers on the south slope have a larger retreat rate than those on the north slope.By 2018,there are 236 glacial lakes which area equals or greater than 0.01 km².The total glacial lakes area is 41.89±4.38 km²,and the largest one is 5.48 km².The number of glacial lakes has doubled,and the glacial lakes has increased by 18.69±4.42 km²,with a area growth rate of 80.56%.The glacial lakes are mainly distributed in the range of5000-5500 m,with a characteristic of large number and small scale.The number and area of glacial lakes on the north slope are more than those on the south slope.Among the different types of glacial lakes,the number of glacier-fed but unconnected lake is the most,and the area of debris-free glacier connected lake is the most.Glacier-fed but unconnected lakes are with the greatest number increase,and debris-covered glacier connected lakes are with the greatest area increase.After assessment,we found that TOPO DEM performed well and have the potential to assess glacier volume change in previous stage.Based on TOPO DEM,we derived that the overall elevation change in the Mt.Xixiabangma region was-14.12±0.52 m from1974-2012,corresponding to an annual thinning rate of-0.38±0.08 m a^-1 and the mass loss was-0.36±0.10 m w.e.a^-1.From 1974 to 2000,the average thinning rate was-0.37±0.04 m a^-1 and the mass loss was-0.33±0.17 m w.e.a^-1.While a more severe thinning rate of-0.41±0.07 m a^-1 and a more negative mass balance of-0.37±0.09 m w.e.a^-1occurred in 2000-2012.From 1974 to 2012,the glaciers experienced an accelerated thinning rate.The glaciers exhibited a heterogeneous thinning pattern in the Mt.Xixiabangma region.The glaciers on the northern slope experienced a more severe mass loss of-0.41±0.10 m w.e.a^-11 from 1974-2012 compared to mass loss of-0.26±0.10 m w.e.a^-1 on the southern slope during the same time.Debris-covered glaciers show a more severe mass loss than debris-free glaciers.Lake-terminating glaciers show a more severe mass loss than non-lake-terminating glaciers.Geomorphological setting and climate are necessary conditions for the development of glaciers.Glaciers change has an inevitable relationship with climate.The retreat of glaciers in the Mt.Xixiabangma region is the result of climate change,and the impact of temperature on glaciers change is greater than the impact of precipitation and geomorphological setting.