The Study Of Glacier Changes And Its Impact On Runoff In The Sugan Lake Basin In The Northwest Inland

In recent years,the water resources have gradually become the constraint factor for the maintenance and development of the oasis system in northwestern China.Unlike other arid regions,the arid inland river basins in Northwest China have many mountains,which block and uplift water vapor,make the precpitation in mounntainous areas more abundant,and develop abundant glaciers,snow and frozen soil,which become an important source of runoff in mountainous rivers.According to the survey,in the early 1960s,the number,area and reserves of glaciers in arid inland areas of Northwest China accounted for more than 40%of the glaciers in China,mainly distributed in the Kunlun Mountains,Tianshan Mountains,Qilian Mountains and other mountains,while the annual glacier melting water in inland river basins was as high as 39%of the national glacier melting water.In the past half century,the temperature in the inland arid area of northwest China has increased significantly,aggravating the melting and retreating of glaciers,affecting the transformation of hydrological cycle elements in the basin,thus changed the composition and structure of water resources in the arid inland area.All these will make the contradiction between supply and demand of water resources in the region more acute.Therefore,it is particularly urgent to study the process of conversion and change between hydrological components in the arid inland regions of the northwest,especially the impact of glacial ablation on runoff under climate change.Located in the western Qilian Mountains,the Suganhu Basin is an important passage for the Silk Road.Glaciers are flourishing in the study area,and the area of glaciers and ice reserves occupy the higher proportion of the total glaciers in the Qilian Mountains.Therefore,it can be used as a typical area for the study of inland river glaciers in the northwest.(1)Based on Landsat remote sensing images,the 10 glacier data in Suganhu basin from 1989 to 2016 was extracted by using the band ratio threshold method.Items of glaciers were divided by referring to the rules of glacier cataloguing,and single glacier reserve was calculated by using the empirical formula.The results shown that in the past 30 years,the area of glaciers has been significantly ablated,and the retreat rate was about-1.61 km2/a(-0.5%/a).The annual rate of glacial retreat shown a trend of "slow-faster-fast".Smaller glaciers(<0.1km2)were gradually disappearing.(2)Based on the meteorological station data,the topographic correction of climatic factors was carried out,and the relationship between the glacier area and average temperature in the glacial melting period(July-August),average annual precipitation were analyzed.The results shown that the increase of temperature was the dominant factor of glacier retreat in Suganhu Basin,while the variations in glaciers are less sensitive to changes in precipitation than air temperature.The linear determinant coefficient(R2)between glacier area and mean temperature in glacier melting period was slightly larger than that in the whole Suganhu basin,while the determinant coefficients of glacier area and temperature in each meteorological station were quite diffe re nt.(3)The terrain factors including elevation,slope and aspect were extracted by digital elevation data(DEM),and the distribution of glacier with topographic conditions was analyzed.The results shown that area of glaciers was concentrated in the altitude range of 4900-5200m,and the glaciers were most distributed in the range of 5000-5100m,and gradually decrease to both sides;Within different elevation zones,as the altitude increases,the rate of decline in glacier area was gradually decreasing.In addition,as far as the distribution of glacier area was concerned,the northwest slope direction was obviously larger than the northeast slope direction,and its quantity distribution was just the opposite.This shown that the northwest slope direction was conducive to the development of larger glaciers,which was due to the water vapor transport under the influence of westerly circulation and southwest monsoon,but the retreat speed of glacier area was less than the South slope.The distribution of glacial area increases first and then decreases with the increase of slope,an d it was most suitable for glacier development between the slope of 1-20°.There was a strong negative linear correlation between glacial area and temperature at elevation zones,and the fine regression models were established.The retreat of glaciers in different altitudes depends mainly on the increase in temperature,while the rate of retreat is affected by altitude.(4)The distributed hydrological model of Water and Energy transfer Process in Large river basins(WEP-L),which considers the melting process of mountain glaciers,can well simulate the variations of precipitation,glacier and snow melt-water runoff from 2000 to 2016,and reveal their future variations.The conclusions are as follows:WEP-L model could well describe the water cycle process in the mountainous area of Suganhu Basin.Under the current conditions(2000-2016),the average annual runoff in the simulated mountainous area is 48.03 mm,ice runoff accounts for 23%,snow melting runoff for 29%,rainfall runoff for 48%.Since 2000,the surface runoff has shown a non-significant upward trend.The annual average change rate of runoff was about 0.018 mm/a,which was mainly attributed to the increase of glacial meltwater caused by the increase of precipitation and temperature during this period.In addition,the comparative analysis of the glacial area monitored by remote sensing,the Second Chinese Glacier Inventory and the simulate d glacial reserve shown that the three data were highly consistent.(5)The regression relationship between glacier area and air temperature of glacier-covered areas at each elevation zone was analyzed;and based on the relationship to predict glacier area in the future.Referring to the national climate model prediction results,the glacier area of 2041-2070 and 2071-2100 were forecasted respectively in the baseline period of 1989-2016.The forecasting results shown that the glacier area will continue to shrink in the future,and the glacier area ablation forecasted by elevation zones would be slightly smaller than the change in entire glacier-covered areas.In terms of runoff forecasting,the WEP-L model was used to set three different climate scenarios for the future 2041-2070 and 2071-2100 based on the current year 2000-2016.The results of mountain runoff forecast shown that when the temperature increased by 1.4?in the future,the runoff would decrease by 6.2%;when the temperature increased by 2.5? in the future,the runoff would decrease by 10.2%;The increase in temperature made it increase in glacial meltwater,and part of the snowfall has been converted into rainfall,resulting in a decrease in snowmelt runoff,and an increase in rainfall runoff.And the higher the air temperature,the more the runoff would be reduced.At the same time,considering the increase of temperature and precipitation,the future change of mountain runoff was more complicated.In the future,increasing precpitation by 5%and temperature by 1.4? would decrease the runoff by 2.7%.In the future,increasing precpitation by 8%and temperature by 2.5? would reduce the runoff by about 2.8%.When the temperature remains unchanged,the increased precipitation increased the runoff,while the precipitation intensified the accumulation of glaciers,resulting in a slight decrease in melt runoff.In general,the response of runoff to temperature was stronger than that of precipitation.The decrease of runoff in the future was mainly attributed to the continuous decrease of snow cover and snowmelt runoff and the increase of evapotranspiration under the temperature rising,while the glacier melt-water runoff would occupy a larger proportion of the total runoff in the study area in the future and continue to increase.Rainfall runoff always occupies the largest proportion.