| On the one hand,glaciers are one of the sensitive indicators of climate change,their area,length and thickness will change with climate change.The glaciers also provides valuable freshwater resources for agricultural irrigation and hydropower generation in the downstream areas;On the other hand,glaciers provide freshwater resources for the downstream areas,but also lead to floods,debris flows and other natural disasters.The runoff instability caused by glacier ablation will also affect the regional water resources security and sustainable development.Karakoram Mountains are the most concentrated mounain glaciers area in the middle latitudes of the world,which is located at the border of China's Xinjiang Uygur Autonomous Region,Pakistan,India and other countries.It is famous for its widespread surge-type glaciers and slight glacier mass gains.Most of the global glaciers melting trend has been strengthened with global warming in recent years,while the glaciers in Karakoram Mountains show different characteristics from other surrounding areas.Under the background of overall glacier mass loss,the glacier mass in this area shows a stable or weak increasing trend,and some glaciers terminus appeared advance which was suspected to be caused by surged.Therefore,this area has also become a hot spot for international Glaciology research.Glacier Lake Outburst Floods occurred frequently in Shaksgam Valley in the upper reaches of Yarkant River,causing serious damage to houses,bridges,roads,natural landscape and people's lives and property in the downstream.At present,there is a lack of systematic and comprehensive information on glacier change in the basin,which restricts the further study of related issues.Therefore,we extracted the glacier area in different periods from Landsat images based on the band ratio method and visual interpretation.We compared the digital elevation models of different periods for calculating mass budgets of glaciers in Shaksgam Valley,Karakoram Mountains based on the geodetic method.Then,using the meteorological data to analyze the main factors affecting the glacier changes in Shaksgam Valley.Finally,combine with the existing research,the internal relationship between glacier surge and glacier lake burst flood is discussed.Draws the following conclusions:(1)The glacier area decreased by 43.89±59.56 km2 from 2000 to 2016,with an average annual retreat rate of about 0.14±0.21%.Among them,the average annual retreat rate was 0.15±0.33% from 2000 to 2010,the average annual retreat rate was0.13±0.50% during 2010-2016.Comparing the change rate of glacier area in different periods,it can be found that the retreat rate of glacier area has slowed down in recent years.In the same period,the shrinking rate of clean ice was higher than debris-covered ice.In terms of area,large glaciers are dominant,while small glaciers are dominant in number.Compared with large glaciers,the retreat rate of small glaciers was larger,which indicates that small glaciers were more sensitive to climate change.Glaciers are mainly distributed between 4400-6300 m,the change rate of glacier area decreases with the elevation increases.The distribution and variation of glaciers in different slope directions are quite different.Glaciers are mainly distributed on the north and northeast slopes,and the shrank of glaciers on the south slope were the most serious.On different slopes,glaciers are mainly distributed in lower slope areas,and less in steep areas.The average slope of debris-covered ice is smaller than clean ice.Most of the glacier's terminus are in a stable or advanced,and most of the advancing glaciers are located in the western part of Shaksgam Valley.(2)The glaciers in the Shaksgam River Valley appear to show a weak surface thickening during 2000-2016.Glaciers experienced a thicking of 1.21±0.41 m during 2000-2016,with an average annual thicking of 0.08±0.03 m·a-1,and the overall mass gain was 0.06±0.02 mw.e.a-1.From 2000 to 2010,the average thicking was 0.74±0.40 m,with an average annual thicking of 0.07±0.04 m·a-1,and the mass gain was0.06±0.03 m w.e.a-1.From 2010 to 2016,the average thicking was 0.54±0.67 m,with an average annual thicking of 0.09±0.11 m·a-1,and the mass gain was 0.08±0.09 m w.e.a-1.Glacier first thickened and then thinned on different slopes.Glaciers thickened in the range of 5°?40°,and the glacier thinned rapidly when the slope is greater than 40°.In low-altitude areas,glaciers are mainly thinning.With the increase of altitude,glaciers thinning becomes weaker and even increases.The surface elevation changes of debris-covered ice were different from clean ice.The debris cover not only does not protect the glacier,but also accelerates the melting of glacier.(3)There is a good relationship between glacier mass change and climate change.It was found that the mean annual percent cloud cover and mean monthly(May to October)percent cloud cover were higher in the western part compared to central and eastern parts in Shaksgam Valley during 2000-2015.Compared with the eastern and central parts,the temperature of the western part decreases and the precipitation increases,which leads to the increase of glacier thickness in the western region,and the glacier terminus is mainly advance.The temperature decreased and precipitation increased during 2010-2015,which resulted in the accumulation of glacier mass in this period greater than that of the previous period.(4)The special geological structure of Shaksgam Valley has developed a series of glaciers which are orthogonal to the valley.Due to the strong activity of glaciers and the influence of climate,the glaciers surge frequently.The ice tongue blocks the valley and forms a blocking lake to intercept the flood.The water storage at the end of the ablation period exceeds the pressure of the ice lake,resulting in the collapse of ice dam and flood disaster. |
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