Study On Glacier Change In Pumqu Basin Based On Multiple-Source Remote Sensing Data Monitoring

Glaciers are indicators of climate change and play an important role in the earth’s climate system.In recent decades,glaciers in High Asia have retreated rapidly.The continuous retreat of glaciers will not only lead to changes in surface runoff,but also cause natural disasters such as glacial lake outburst,flood and debris flow.Pumqu basin is located in the core area of Qomolangma National nature reserve,with a large number of mountain glaciers.The type of glacier with a large area is debris covered glaciers.This type of glacier is widely distributed in the Himalayan Mountains.Previous studies have shown that its change state is more stable than that of clean glaciers,and there are few studies on the change of this type of glaciers.Under the background of global warming,whether the glaciers in this region are in a state of continuous accelerated retreat and whether the debris covered glaciers also show an obvious change trend need to be further studied and discussed.Taking Pumqu basin as the study area,based on multi-source remote sensing data,this paper systematically obtains the glacier cataloging information in this area in recent 20 years,including the change of glacier area,surface velo city and surface elevation,and analyzes the change trend of debris covered glaciers and overall glacier in this area.The main contents and research results of this paper are as follows:(1)Using 83 Landsat remote sensing images,the three periods of glacier boundary information in Pumqu basin in 2000,2010 and 2020 are extracted,and the temporal and spatial variation characteristics of glacier area in Pumqu basin from 2000 to 2020 are analyzed.In 2020,there are 631 glaciers in Pumqu basin,with a total area of 1171.48±54.68 km2.Among them,26 are debris covered glaciers,covering an area of 563.00 km2.Over the past two decades,the number of glaciers in the study area has decreased from 667 to 63 1.The total area of glaciers has decreased by 91.32±30.46 km2(7.23%),and the average annual shrinkage rate is 0.36%/a.Among them,the area of debris covered glacier has decreased by about 13.66 km2,and the average annual shrinkage rate is 0.12%/a,which is far less than the area shrinkage rate of clean glaciers(0.60%/a).The analysis of 2000-2010 and 2010-2020 shows that the glacier retreat rate in Pumqu basin has changed from 0.40%/a to 0.33%/a in recent 20 years,indicating that the glacier retreat rate in this basin has slowed down.The glacier area is affected by its size.Compared with large-scale glaciers,the area retreat rate of small-scale glaciers is larger,among which the retreat rate of glaciers with the size of 1-2 km2 and 2-5 km2 is the most serious.In addition,the area change rate increases first and then decreases with the increase of altitude.(2)Based on 64 Landsat series optical images,the interannual glacier surface velocity information of the 2000-2020 long time series of glaciers in Pumqu basin was obtained.For the debris covered glaciers in the basin,the monthly glacier surface velocity information of surface debris covered glaciers in Pumqu basin from 2018 to 2020 was obtained by using 184 scene sentinel-1a radar images.From 2000 to 2020,the overall surface movement speed of glaciers in the basin showed a slowing trend,changing from 8.78 m/a to 7.88 m/a.The area covered by debris is the area with the slowest glacier movement rate.For glaciers larger than 1 km2,with the increase of area,the overall average surface movement speed also accelerates;The area with the fastest flow velocity is mainly concentrated below 4500 m above sea level,which shows a decreasing trend with the increase of altitude.The larger the glacier slope is,the higher the movement speed of the glacier surface is.The greater the slope of the glacier,the higher the movement speed of the glacier surface.The monthly surface velocity information of the debris covered shows an obvious seasonal variation trend,and the velocity in summer is significantly higher than that in winter.From the average value of monthly velocity in these three years,the glacier velocity is the slowest from November to February of the second year.From March,the glacier velocity begins to accelerate gradually,and the average velocity reaches the maximum from May to September.After October of each year,the velocity begins to decline again,and the glacier velocity drops to a relatively gentle state.(3)Based on SRTM DEM and Tan DEM,the glacier surface elevation changes in Pumqu basin from 2000 to 2014 were estimated.From 2000 to 2014,the average surface elevation change of the whole glacier in Pumqu basin was about-8.39 m,with an average annual change rate of-0.60 m/a.The accumulated ice reserves lost in the past 14 years have reached 427.98 km3,showing a state of material loss.With the increase of altitude,the glacier surface elevation decline rate increases first and then decreases,and the fastest decreasing area is mainly concentrated in the altitude zone of 5000-5400 m,which is 1.12 m/a.Compared with the larger glaciers,the surface elevation of the smaller glaciers decreased more obviously,and the average surface elevation of the glaciers with a scale of<0.1km2 decreased the most,which was 0.86m/a.On the whole,the change rate of surface elevation of surface debris covered glaciers of the same size is higher than that of clean glaciers.The corresponding annual change rate of debris covered glaciers of 1.0-5.0 km2,5.0-10.0 km2 and ≥10.0 km2 are-0.74 m/a,-0.60 m/a and-0.65 m/a.The corresponding annual retreat rate of clean glaciers is only-0.58 m/a,-0.58 m/a,-0.27 m/a.