Study On Changes Of Lake Areas Since 2000 And Its Response To The Climatic Factors In Tibetan Plateau

Plenty of lakes in the Tibetan Plateau are sensitive to climate change and play an important role in natural water circulation and water balance.Using MODIS MOD09A1?MODIS MOD13A1 and SRTM DEM as data sources,the lake boundaries over 50 km~2 in high flow period and the NDVI in the Tibetan Plateau are extracted from 2000 to 2016.The patterns and trends of lake area changes are analyzed from three aspects,namely,internal and external flow zoning,main sources of recharge,and the salinity of the lakes since 2000.Meanwhile,combining with meteorological data in Tibetan Plateau in recent 36 years,according to the meteorological elements zoning of change trend,the relationship between the lake area changes and the climatic factors and its influence on the variation of NDVI in different ranges of vegetation in Tibetan Plateau are primarily discussed.The main conclusions are as follows:(1)138 lakes more than 50 km~2 are overall tend to expand significantly,with2340.67 km~2 increased in area and a growth rate of 235.52 km~2/a.Among them,dilated lakes,shrunken lakes and stable lakes are accounted for 67.39%,12.32%and 20.29%,respectively.The expansion trend of inflow lakes is significant,while the outflow lakes is less significant.Lakes with glacier water as the main source of recharge are expanded significantly,so do lakes with surface runoff and river recharge as main sources.Saline and semi-saline lakes also present a trend of expansion.As for the freshwater lakes,the three types of expansion,atrophy,and stabilization are relatively balanced.(2)The temporal and spatial trends of NDVI in the Tibetan Plateau during 2000-2016,interannual,different elevations and vegetation around the lake indicate that vegetation grow most vigorously during the year from the 161th to the 273th day(June-September).However,it grows slowly during the 337th day-the 49th day of the following year(December-February).The trend during the year was characterized by a unimodal type.The NDVI shows a significant upward trend for many years(a=0.006/10a,R~2=0.6034).The mean value of the NDVI was significantly different at different elevations,and the annual average NDVI decreased significantly with the elevation.The overall NDVI of 138 lakes within the range of lake area change showed a weak reduction trend(a=-0.0013/10a) in the past 17 years,while the overall NDVI of the 1km buffer range outside the lake's range of variation slightly increased(a=0.0015/10a).(3)Under the background of the Tibetan Plateau climate presenting a warmer and more humid tendency,there is a significant regional correlation between the change of lake area and climatic factors.The results of change trend zoning of air temperature and precipitation indicate that the degree of lake expansion of Zone ?(78.18%) where air temperature and precipitation are increasing significantly is greater than that of Zone ?(66.67%)where air temperature decreases and precipitation increases.The following are Zone ?(60.78%) with increasing air temperature and precipitation,Zone ?(58.83%) in which air temperature is decreasing and precipitation is increasing,and Zone ?(50.00%) with increasing air temperature and decreasing precipitation in Tibetan Plateau.(4)The analysis of lake area changes'impact on vegetation NDVI shows that the expansion of lake area has a significant impact on the NDVI of vegetation in the range of lake area.The NDVI of the vegetation around the lake in the Tibetan Plateau from 2000 to 2016 showed a significant reduction trend.The shrinking of the lake area has a significant impact on the vegetation NDVI within the range of lake area changes.The NDVI of the vegetation around the lake in the Tibetan Plateau from 2000 to 2016showed an obvious upward trend.When the lake area is approaching stable,the NDVI of the vegetation area has a downward trend and an upward trend,while the main trend is upward.In the past 17 years,the overall range of NDVI including the range of lake area change and the 1 km buffer range showed an increasing trend.The NDVI shows a significant growth trend in the expanding lakes.The NDVI shows an increasing trend in atrophic lakes.The NDVI shows an increasing trend in stable lakes.It can be seen that the change of vegetation NDVI outside the range of lake area is less directly affected by the change of lake area while is greatly affected by other factors.It can be seen from the average annual vegetation NDVI of each district.For vegetation that has no direct impact on the change of lake area,the farther the lake,the smaller the direct impact of the lake on vegetation,and the greater the vegetation is affected by other factors.(5)The response of lake area change to climate change shows that the recharge of glacier melt water caused by air temperature rise has a significant effect on the expansion of lake area in Zone ?,?,and ?.In addition,the rate of lake expansion is significantly increasing due to the increase of precipitation.The lake area expansion in Zone ? and ? is mainly affected by the increase of precipitation.On the whole,air temperature mainly affects lakes with glacier melt water as the main source of recharge and precipitation mainly affects lakes with precipitation and surface runoff as the main sources of recharge.