Study On Remotely Sensed Monitoring Of The Synergic Evolution Of Glaciers-glacial Lakes And Their Response To The Climate Change In Alatau Mountains,Central Asia

Due to the global warming,most of the glaciers in the Tianshan Mountains are shrinking,and the shrinking rate has accelerated in recent years.The formation of glacial lakes comes from glacial meltwater and atmospheric precipitation,so the change of glacial lakes is related to glaciers and climate change.The flood and debris flow caused by glacial lakes outburst is one of the common natural disasters in alpine areas,which poses a serious threat to the life and property safety of the downstream residents.Therefore,it is of great importance to dynamically monitor glaciers and the glacial lakes,and reveal the synergistic evolution between them and their response to climate change.The Alatau Mountains in Central Asia are located in the western part of the Tianshan Mountains.About two-thirds of the glaciers are located in the northern part of Kazakhstan,and there is a lack of glaciers inventory.In addition,in recent years,glaciers in this region have largely melted,forming many glacial lakes,and there is a lack of reports on monitoring of glacial lakes.In this paper,Landsat satellite images were used to extract glaciers and glacial lakes boundary information from 1990 to 2018 in the Alatau Mountains,Central Asia.The spatiotemporal variation characteristics of glaciers and glacial lakes from 1990 to 2018 were analyzed,and the potential climate driving factors of glaciers-glacial lakes co-evolution were discussed in the Alatau Mountains,Central Asia.The main conclusions are as follows:(1)The spatiotemporal variation characteristics of glaciers in the study area in recent 30years are revealed.(1)From 1990 to 2018,the percentage of area changes(PAC)of glaciers was-26.61%of the Alatau Mountains in Central Asia,and the annual percentage of area changes(APAC)of glaciers was-1.06%/yr,which indicates that the glaciers show obvious retreat trend in the past 30 years.The rate of glaciers retreat has been increasing year by year,especially in the last 10 years.(2)The retreat of glaciers in this area is mainly distributed below the altitude of 3600 m,and the rate of glacier retreat is different in different periods.The trend of glacier retreat is consistent from 1990 to 1999 and from 2011 to 2015.Glaciers are more stable at high altitudes and retreat faster at low altitudes.(3)The glaciers are mainly small glaciers in this area.The area of glaciers of all scales has retreated,and the rate of glaciers area retreat increases with the increase of glaciers scales.(4)The retreat rate of the glaciers in the east,southeast,southwest and west slope is relatively large,and the retreat rate in the west slope reaches the maximum 34.63%.(5)The southern glaciers have faster retreat rate and annual average rate of change than the northern glaciers.(2)The spatiotemporal variation characteristics of glacial lakes in the study area in recent30 years are revealed.(1)From 1990 to 2018,the PAC of glacial lakes was 24.52%,and the APAC of glacial lakes was 0.76%/yr.The number of glacial lakes increased significantly in the past 30 years,and the area of glacial lakes continued to increase,showing obvious expansion trend.(2)The expansion area of glacial lakes is the largest in the range of 3200?3400 m altitude,accounting for 51.05%of the total expansion area of glacial lakes.(3)Small glacial lakes dominate the distribution of glacial lakes.The area of glacial lakes with a scale of<0.01 km~2accounts for 5.66%of the total area,and the number of glacial lakes is up to 99,accounting for32.14%of the total.(4)The growth rate of glacial lakes in the north,northeast,east and northwest directions is higher than that in the southeast,south and southwest directions,which may be due to the influence of the south direction topography and less melting of glaciers,resulting in a slower growth rate of glacial lakes.(5)Compared with the southern glacial lakes,the northern glacial lakes have faster expansion rate and annual average rate of change.(3)The spatiotemporal variation characteristics of climate in the study area in recent 30years are revealed.From 1990 to 2018,the average temperature of the Alatau Mountains in Central Asia changed significantly,with a warming tendency slope of 0.037°C/yr,showing a significant upward trend.The temperature in winter showed an insignificant downward trend(the slope was-0.016°C/yr),and the temperature in summer increased significantly with a slope of 0.199°C/yr.The annual average temperature change rate gradually decreases from north to south.The summer average temperature change rate presents a spatially decreasing trend from two center points to the surroundings.The winter average temperature change trend is consistent with summer.The study area has shown a trend of higher and higher summer temperatures and lower and lower winter temperatures in the past 30 years.The average annual precipitation,summer precipitation and winter precipitation all show a decreasing trend.Precipitation in the west of the study area generally decreased,while precipitation in a small part of the east increased.(4)Based on the analysis of climate change characteristics in the study area over the past30 years,the potential climate driving factors of glaciers-glacial lakes co-evolution are discussed.Glaciers of the Alatau Mountains in Central Asia showed a retreating trend from1990 to 2018,and glacial lakes showed an increasing trend.The retreat of glaciers and the expansion of glacial lakes have an inseparable relationship with temperature and precipitation.The temperature in the study area showed an overall rising trend from 1990 to 2018,which would inevitably lead to glacier melting and retreat.The decrease of precipitation also reduces the supply of glaciers,leading to the retreat of glaciers,and also increases the water supply of glacial lakes.However,the decrease of precipitation does not lead to the shrinkage of glacial lakes,which indicates that the expansion of glacial lakes is closely related to the melting of glaciers,and it also proves that the water supply of glacial lakes mainly comes from glacial meltwater.The retreat of glaciers leads to the expansion of glacial lakes.Under the background of global warming,the continuous retreat of glaciers is likely to lead to glacial lakes outburst,which is also consistent with the phenomenon that glacial lakes outburst has occurred continuously in recent years.