Glacier Variations In The Indus Basin Over The Past 20 Years

The Indus Basin was selected as the research object.Using Landsat OLI,ETM+,TM images and other data as data sources.Due to the large number of surface cover glaciers in the study area,automatic extraction methods are difficult to directly recognize glaciers from remote sensing images,the glacier vector boundaries of 1993,2000 and 2016 were extracted with the method of visual interpretation combined with Randoiph 6.0 Glacier Inventory Data in the study area.The characteristics of glaciers variation were analyzed during the past 20 years.At the same time,the ICESat and SRTM elevation data are employed to investigate glacier thickness change of two typical glaciers.In addition,we analyzed the temperature and precipitation characteristics of the meteorological stations of the study area over the past56 years,and combine with the grid meteorological data for further analysis.The relationship between glacial change and the climate change in the study area was also discussed.(1)From 1993 to 2016,the total area of glaciers in the Indus Basin decreased from24,778.12±464.04 km~2 to 24,017.59±436.78 km~2.The area of glaciers shrunk by760.53±637.26 km~2,accounting for 3.07±2.57%of the total area of glaciers and the annual average shrinkage rate of glacier area was 0.13±0.11%during the past 20 years.In 1993-2000 and 2000-2016,the annual average shrinkage of glaciers was 0.12±0.37%and0.14±0.16%,respectively.During the period from 2000 to 2016,the annual average shrinkage rate of glacier area was larger than that of the period from 1993 to 2000.Overall,the result indicates that the rate of glacier area shrinkage rate in the Indus Basin has shown a slight acceleration over the past 20 years.The shrinking rate of glacier area was inversely proportional to the glacier area of different size.The smaller glacier size,the intenser the glacier shrinks.Each aspect of glaciers is in a state of shrinkage.The north(4.51±2.65%)and northeast(4.15±2.85%)aspects of glaciers shrunk the most serious,the glaciers in the east aspect(1.62±2.06%)shrunk the least.The large area retreat at 3400-6000 m,and the area change of the other elevation gradients is generally small.Affected by the advance glaciers,the glacier area increased from 2200-2400 m in 1993-2000.(2)The is a difference in the shrinkage of glacier area in different mountain ranges in the study area.In 1993-2016,the glacier area in the western part of the Himalayas shrank the most serious(7.24±3.21%),followed by the Hindu Kush(6.74±3.68%),while the Karakoram glaciers appear only a slight decline(1.00±2.30%).In 1993-2000,the shrinkage of the glacier area in the Hindu Kush Mountain(2.94±3.65%)was larger than in the Western Himalayas(1.98±3.17%).At different time periods(1993-2000,2000-2016),the area of the glaciers in the Western Himalayan accelerated to retreat;the shrinkage of the glaciers in the Hindu Kush Mountain has slowed down;the glaciers in the Karakoram Mountain tends to be stable,and there is a large amount of advance glaciers in the region.There is also a difference in the shrinkage of glacier area in different sub-basins in the study area.The basins which the area of glaciers shrank greater are Swat(9.44±4.33%),Upper Indus(8.19±3.46%),and Jhelum(7.21±4.79%).The basins which the area of glaciers shrank less are Shigar(0.21±1.96%),Hunza(0.43±2.25%),and Shyok(1.51±2.23%).At different time periods(1993-2000,2000-2016),the shrinkage of the glacier area in each sub-basin appeared the trend of accelerating rate overall.(3)The rate of glacier thickness reduction in G073594E36759 N and G073308E35113 N of the study area were both faster.The rate of the glacier thickness reduction of G073594E36759 N glacier was 1.30±0.23 m/a in 2000-2006.The rate of the glacier thickness reduction of G073308E35113 N glacier was 1.18±0.42m/a in 2000-2008.At the same time,the area and the length of the two glaciers appear a large shrinkage.Compared with the research results of the elevation change of the glaciers in the Tibet plateau and its around areas,the thinning rates of the two typical glaciers are fast.The main reason is that the area of the two glaciers are smaller and the two glaciers are more sensitive to the climate change.(4)In the past 56 years,the annual average temperature in the study area appears a warming trend,and the increase of precipitation is smaller.Therefore,the overall shrinkage of the glacier area in the study area from 1993 to 2016 was mainly affected by the increase in temperature.Through the analysis of grid meteorological data,the large shrinkage of glaciers in the Himalayas in the study area is mainly due to the combined effects of increased temperatures and reduced precipitation.The shrinkage of the glacier area in the regions of Karakoram and Hindu Kush Mountain is mainly affected by rising temperature.