Distribution And Evolution Of Lakes In Qiangtang Plateau Under Climate Change

Qiangtang plateau,located in the Qinghai-Tibet Plateau,is the largest inland lake region in China.There are a large number of lakes,glaciers and frozen soil in the area.The Qiangtang plateau is accelerating its rate of change in the context of climate change with temperature rise.It is the response of the Qiangtang plateau in recent years that the increase of temperature,the melting of glaciers,the speeding up of river system,the development of alluvial fan and the obvious expansion of lakes."Melting and changing Qiangtang plateau" is increasingly getting more and more attention by domestic and foreign experts and scholars.Answering the characteristics of lake distribution,variation of lake area and water storage,change of glaciers and what is the reason are the current research priority.In this thesis,the Qiangtang plateau is the target area.Based on RS and GIS technology,using 6 different periods covering the whole area of the remote sensing images,all lakes in the Qiangtang plateau were extracted by NDWI index.And we analyzed the situation of lakes via their disappearance,emergence,expansion or contraction.Then,the area change rate and the trend rate parameters were used to characterize the degree of lake changes.Thus we can reveal the characteristics of lake evolution in the Qiangtang plateau in recent 40 years.Based on these,in order to explore the causes of lakes change,we do some analysis via watershed scale and we divided the closed drainage basin of each lake by putting forward a new method based on DEM and Google Earth.Finally,hydraulic connection of lakes and its influence on the evolution of lakes are discussed.The main conclusions of this paper are as follows:(1)Basin division results and distribution maps of the inner area of Qiangtang PlateauIn order to dividing the closed drainage basin of each lake,we put forward a new method based on DEM and Google Earth,and successfully divided each basin of more than 290 lakes.All the basins is divided into three types:single lake basin,series connection basin,and hybrid lake basin.The map of lake distribution in Qiangtang plateau was drawn up to provide the basic support for the study of Qiangtang plateau in the context of climate change.All the basin are in a total of 221,including 190 single lake basins,17 series connection basins,and 14 hybrid lake basins.(2)The evolution characteristics of lake area in Qiangtang PlateauThe total number of lakes in Qiangtang plateau is 297,294,298,296,298,298 in the six periods of 1970s,1990s prophase,1990s anaphase,2000s prophase,2000s anaphase and 2010s prophase.Lakes area of Qiangtang plateau decreased first and then increased rapidly.The total area of lakes in each period were 25821.38km2,24474.89km2,25607.57km2;28038.09km2,30080.06km2,31630.73km2.(3)The reasons for the evolution of different lake types are analyzed from the point of view of hydraulic linkage.a)If there is only one lake in a basin,the source of supply of meltwater accounted for an important part,this type of lakes is generally expanding;mainly affected by climate change under the background of temperature rising,glaciers melting faster,increase the amount of water.b)If a basin contains several lakes,and there is a hydraulic relationship between the upper and lower lakes,shrinking lakes are generally the throughput of lakes,and expanding lakes are mostly the tail lakes.c)If there is a clear tributary relationship between more than one lakes originating from the same glacier river,and there is a large river supplying one of the lakes,and the smaller river supplies another lake.In this case,the lakes which are supplied by tributaries are shrinking,while the lakes supplied by the main stream expand.The main reason is that after the increase of river flow,the scour at the river fork is more intense,leading to more water flowing into the main stream after erosion and deposition.(4)Water variation analysis of typical lake-Nam CoDuring the year of 1976-2015,Nam Co was basically at a state of expansion.The water surface area expanded from 1928.63km2 to 2018.55km2,an expansion of 89.92km2.Water storage volume increased from 98.566 billion m3 to 108.351 billion m3,an increase of 9.785 billion m3.The overall expansion is basically divided into 3 stages:slow growth period of 1976?1996,rapid expansion period of 1997-2009,and almost stagnation period of 2010?2015.