| As one of the most important geographical units affected by global climate change,lakes are sensitive to climatic changes and are considered“indicators”of climate and the environment.Taking the global lakes as research objects,using 2001-2016 MODIS250 meters per 16 day composite NDVI data,according to the spectral characteristics of lake water and background,considering the lake's geographical location,size and clarity of lake boundary,this paper extracted the areas of 186 lakes with its'areas more than400 km~2,and the spatial-temporal characteristics of the lake areas were analysed.Meanwhile,changes in the spatial-temporal characteristics of the water levels of 204global major lakes were systematically analyzed using satellite altimetry data(Hydroweb product)from 2002 to 2010.A long time series of information database for lake changes were established.Additionally,the temporal and spatial variation characteristics of global temperature,precipitation,evapotranspiration,land cover and population density were analyzed combined with the Global Land Assimilation System(GLDAS)data(temperature,precipitation and evapotranspiration),land cover data and population density data.On this basis,taking the arid and semi-arid area along the Silk Road as an example,the temporal and spatial variations of the lake areas and their influencing factors were analyzed,and the responses of the lake areas to the impact factors were also researched.The basic conclusions are as follows:(1)A comparison of the Qinghai Lake area extracted from MODIS data and Landsat data found that the areas extracted by the two data had a high correlation(p<0.01).However,the lake areas based on MODIS data were underestimated in summer and overestimated in winter.Therefore,the extraction of lake area using the annual average MODIS data can eliminate seasonal fluctuations caused by different properties of the underlying surface at different seasons.The advantage of high time resolution of MODIS data was also considered,which can better reflect the long change trend of lake area.(2)The study of lake area showed that 80%of the lakes were shrinking,and only20%of the lakes were expanding.The areas of 78%of the lakes had small change intensity,and their change rates were between-5-5km~2/a.The lakes with expanding area were mainly distributed in high mountains or plateau regions.The analysis of lake level showed that about 60%of the lake had the water level increasing,and 40%of the lake decreasing.The change rates of water level in about 71%of the lakes were between-0.3-0.3 m/a,which indicated that the change rates in the water level of most lakes were not obvious.The lakes with rising water level were mainly distributed in the high alpine and coastal regions,while the lakes with decreasing water levels were concentrated in the valley and the plain.(3)Global temperature(+0.0523?/a),precipitation(+1.1641mm/a)and evapotranspiration(+2.7889mm/a)showed an increasing trend from 2001 to 2016.The areas of construction land(+22.46×10~3km~2/a),grassland(+15×10~3 km~2/a)and cultivated land(+3.51×10~3 km~2/a)were increasing,while the areas of bare land(-19.73×10~3km~2/a),forestland(-9.93×10~3 km~2/a),wetland(-6.24×10~3 km~2/a)and water body(-5.08×10~3 km~2/a)were decreasing from 2001 to 2015.The change rates of population density in most parts of the world were distributed in the-5-5 people/5a from 2001 to2015,indicating that the population density in the regions had a small change.(4)In the arid and semi-arid areas along the Silk Road,the total area of the 24lakes decreased by 22189.7 km~2 in the past 16 years.And of 15 lakes reduced their areas,while only 9 lakes increased.The temperature(+0.0813?/a),precipitation(+2.05mm/a)and evapotranspiration(+1.21mm/a)in the lake basins increased with a undulation from 2001 to 2016.The main types of land cover in the basins were grassland,followed by bare land,cultivated land and forestland,and the proportion of wetland and construction land was very small in 2001-2015.The areas of 5 land cover types such as construction land(+22.02×10~3 km~2/a),forestland(+6.42×10~3 km~2/a),farmland(+7.61×10~3 km~2/a),grassland(+6.24×10~3 km~2/a)and wetland(+0.8×10~3km~2/a)increased,while the area of bare land(-1.42×10~3 km~2/a)and water body(-1.76×10~3 km~2/a)decreased.The population density was increasing in most of the basins in2001-2015.The analysis of lake areas and impact factors correlation found that the temperature was the main factor affecting lake areas change in the arid and semi-arid areas along the Silk Road.Changes in land cover and increase in population density mainly affected lakes in the central and western regions of the region,and the impact on the lakes located in the plateaus was not obvious. |
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