Remote Sensing Analysis Of Water Changes In Qinghai Lake In The Past 30 Years Based On GEE

Surface water provides basic resources for terrestrial life.It is essential for climate balance,hydrological cycle,and ecosystems.Lakes,as an important part of surface water,play an important role in the field of hydrology and environment,such as hydrological cycle and flood control.In addition,lakes provide important habitats and food resources for a variety of fish,aquatic life and wildlife.However,affected by climate change and human activities,the morphological characteristics and biological composition of lakes will continue to change indefinitely,which will affect the ecological environment.In recent years,under the dual effects of climate change and human activities,many lakes around the world are undergoing rapid change.These changes in the lake have greatly affected the available freshwater resources and caused a series of regional ecological and environmental problems,which have become key constraints to regional sustainable development.Therefore,extracting lake water information rapidly and accurately,and grasping distribution of lake size and dynamic changes timely have important practical significance for environmental research,management of terrestrial ecosystems,and sustainable development of human society.Spatial resolution is a key factor that restricts the accuracy of lake water extraction.Downscaling is one of the effective means to improve the spatial resolution and accuracy of remote sensing detection in combination with the principles of geography.In this paper,Qinghai Lake is used as the research area.Based on the Google Earth Engine(GEE)platform,Landsat data is down-scaled to achieve a near 30-year long-time Qinghai Lake high spatial resolution(10 m)water boundary dynamic monitoring and analysis.The area change and the spatial change of the lake shoreline,combined with the water level information extracted by the altimeter satellite ICESat,are used to estimate the water volume change of Qinghai Lake in the past 30 years.The climate impact factors of the Qinghai Lake change are analyzed.The results obtained are as follows: 1)The method for spatially downscaling the NDWI(normalized difference water index)image combined with Sentinel-2 and Landsat 8 data can effectively improve the accuracy of water extraction in Qinghai Lake.Scores,overall accuracy,Kappa coefficient and other evaluation indicators have all improved to some extent,and more detailed features can be extracted after downscaling.2)During the period of nearly 30 years from 1990 to 2018,the area of Qinghai Lake fluctuated greatly.Taking 2004 as the inflection point,it showed a trend of first decrease and then increase.Among them,during the period of 1990-2004,the climatic tendency rate was-89.6 km2 / 10 a,and the area of the lake area between 14 a decreased by 139.259 km2.During the period of 2004-2018,the climatic tendency rate was 147.4 km2 / 10 a and 15 a lake area.The area has increased by a total of 244.565 km2.3)The spatial changes of the lake shoreline mainly occurred at the sandy islands and Haiyan Bay on the eastern shore of Qinghai Lake,Haixi and Bird Island on the west shore,and the entrance of the Shaliu River on the north shore.From 1990 to 2004,the three lakeshore lines receded by 1.67 km on average.From 2004 to 2018,the three lakeshore lines advanced an average of about 2.2 km,with relatively severe fluctuations.4)The water level and area of Qinghai Lake have the same change trend,showing a trend of decreasing first and then increasing as a whole.Among them,during 1990-2004,the climatic tendency rate was-0.9 m / 10 a,and the lake surface water level decreased by 1.36 m during 14 years.During 2004-2018,the climate tendency rate was 1.4 m / 10 a,and the lake surface rose by 2.39 m in 15 years.5)Qinghai Lake's water volume change has the same trend with area and water level.In the past 30 years,it has shown a trend of decreasing first and then increasing.Among them,during the period 1990-2004,the climate tendency rate was-37.8 × 108 m3 / 10 a,and the amount of water was reduced by 58.76 × 108 m3 in 14 years.During the period 2004-2018,the climate tendency rate was 62.8 × 108 m3 / 10 a,during 15 years The amount of water increased by a total of 104.50 × 108 m3,a larger increase.6)After a comparative analysis with long-term climatic factors,it was found that during the period of 1990-2004,the main reason for the decrease of Qinghai Lake water volume was the increase of evaporation.During the period of 2004-2017,the increase of Qinghai Lake water volume was caused by the increase of precipitation and the decrease of evaporation.