| The special and complex natural geographical environment has laid a good foundation for the storage of water resources in the Qinghai-Tibet Plateau(QTP).With widespread snow mountains,crisscross glaciers,dense lakes,the sources of many rivers and nourishing billions of people,the QTP lives up to the reputation as the"Asian Water Tower".Lakes in the QTP are important carriers of water resources in the"Asian Water Tower".In the plateau environment,their revenues and expenditures are mainly affected by the solid water resources such as glaciers,ground ice in permafrost,and the collection and evapotranspiration of surface water and groundwater.The change of lakes area and quantity also reflects the change of regional climate to a certain extent.Under the background of the obvious climate change in recently,the evolution of lakes and the change of river runoff in the QTP have a great impact on the regional ecological environment,it is urgent to study the evolution trend of lakes and their eco-environmental effects in the QTP.The evolution of lakes has experienced a process from natural driving to human and natural driving.To explore the evolution process of lakes in the QTP and the driving forces of their dynamic changes,based on Remote Sensing(RS)and Geographic Information System(GIS)technology,this paper extracted the lake data of the QTP from 1980s to 2020,and divided the lakes into tectonic lake,glacial lake,thermokarst lake,dammed lake,fluvial lake,and artificial lake according to different causes.The number,area,and spatial changes of tectonic lakes,thermokarst lakes and glacial lakes in the QTP from 1980s to 2020 were studied,and the driving forces of the dynamic changes of lakes and their eco-environmental effects were analyzed.The main conclusions are as follows:(1)In the past 40 years,the number and area of lakes in the QTP have changed significantly in the process of overall warming and increased precipitation volatility in most regions.The number of lakes increased continuously from 70005 in the 1980s to 143582 in2020;the lakes area showed a trend of decreasing(during 1980s-1990)-accelerating growth(during 1990-2020),decreased from 41347.84km~2 in the 1980s to 40441.4km~2 in 1990,and then increased to 54634.44km~2 in 2020.From 1980s to 1990,the number of lakes decreased because of the drop of temperature and precipitation in most areas;From 1990 to 2020,the increase of lake area was mainly due to the significant rise of temperature,precipitation and glacier melt water.(2)The area of tectonic lakes decreased from 1980s to 1990 and continued to expand from 1990 to 2020.The total area increased by 11388.13km~2,and the number increased from1089 to 1451.In terms of spatial distribution,the tectonic lake changed mainly occurred in the inner basin.Combined with the annual precipitation and mean temperature,it was found that the temperature and precipitation increased significantly in these regions,which was the direct reason of the area and quantity of the tectonic lakes.(3)Permafrost region is a region where thermokarst lakes development.The number of thermokarst lakes increased from 60834 to 120374 from 1980s to 2020,and the area increased from 932.5km~2 to 1713.57km~2.In space,it is mainly concentrated in the Hoh Xil region and the Beiluhe river area,where the terrain is flat.Significant climate warming has led to extensive degradation and even melting of permafrost.The increase of ground ice melt water and precipitation has doubled the number and area of thermokarst lakes in the permafrost regions of the QTP.(4)Thermokarst lake is a typical geomorphic unit in the process of permafrost degradation,and it is also the type with the most significant changes in the number and area of lakes in the QTP.Therefore,this study selected the evaluation indexes as point density,permafrost stability type,annual average precipitation,surface temperature,soil moisture,snow area,Normalized Difference Vegetation Index(NDVI),and slope,refered to the previous researcher's experience and expert evaluation to determine the index weight,and obtained the thermokarst lake susceptibility zoning map of permafrost region in the QTP by using the comprehensive evaluation method.The high susceptibility zones accounted for 19.02%,mainly distributed in the southwest of Qinghai Province,the central of QTP,including the Hoh Xil region.(5)Glacial lakes are formed by glaciation,and the main recharge source are atmospheric precipitation and glacial melt water.The number of glacial lakes increased from 8002 to 20329 from 1980s to 2020,and the lakes area increased from 900.1km~2 to 1620.5km~2.The spatial changes were mainly in the Tanggula Mountains,the Himalayan Mountains,the West Kunlun Mountains,and the southern margin of QTP.(6)NDVI,lake ecosystem service value and glacier lake outbreak flow(GLOF)were used to evaluate the eco-environmental effect of the QTP.Overall,the NDVI of the QTP was increased.The NDVI difference between 2000 and 2019 was used as the index to evaluate vegetation degradation and improvement,which showed that the vegetation improvement area accounts for 37.58%.As an independent ecosystem,the lake ecosystem service value in the QTP was increasing with the increase of lakes area.The rise of temperature and the extensive degradation of glaciers have resulted in the increasing of GLOF,which is harmful.(7)As a resource,lakes in the QTP have important ecological service functions such as water conservation,biodiversity maintenance and regional ecological protection.Among them,thermokarst lake and glacial lake are often regarded as adverse geological phenomenon,and their evolution process,especially the occurrence of GLOF,has potential or direct harm to regional major projects and ecological environment,which should be given enough attention in relevant regional planning,engineering construction and environmental protection.The results can provide basic lake data for the Second Tibetan Plateau Scientific Expedition Program,for clarifying the relationship between lake and the freeze-thaw environment.It is helpful to promote the scientific understanding of the evolution of lake ecosystem under global warming,serve the rational development and management of lake ecological resources,and provide fundamental support for disaster prevention and mitigation of the thermokarst lake and GLOF. |
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