The Impact Of Climate Change And Human Activities On Vegetation NDVI And Lake Area In Qinghai Lake Basin

Vegetation is one of the important components of the surface ecosystem and an important indicator for evaluating regional ecology.The Normalized Difference Vegetation Index(NDVI)is the best indicator to describe the vegetation coverage.The Qinghai Lake basin is a typical ecologically fragile area in China,and the vegetation in the basin has important ecological value.The study of the temporal and spatial evolution of vegetation coverage in this area has become a hot topic in relevant fields.Lake is one of the important components of surface water,which plays an important role in regulating regional climate and hydrological cycle and maintaining the balance of regional ecosystem.The lakes are also sensitive to global climate change and can be used as an indicator of ecosystem changes.In this paper,using remote sensing technology,based on Google earth engine(GEE)and long-time series Landsat satellite remote sensing images,the temporal and spatial variation characteristics of vegetation NDVI and Qinghai Lake area in Qinghai Lake Basin and the relationship between them and influencing factors were studied.It is expected to provide reference for vegetation restoration and ecological environment policy formulation in the Qinghai Lake Basin.The main research work of this paper is as follows:(1)Based on GEE platform and Landsat5,7,8 surface reflectance products,Spatio-temporal characteristics of vegetation NDVI in Qinghai Lake Basin from 1990 to 2019 were studied.The results showed that the annual average NDVI of vegetation in Qinghai Lake Basin increased significantly from 1990 to 2019 at the rate of 0.0285/10a(P<0.05);vegetation cover in Qinghai Lake Basin is gradually increasing from west to East as a whole;high and medium-high vegetation cover areas account for about half of the area of the Basin,and the proportion of high vegetation cover areas has increased significantly in recent 30 years.(2)Based on GEE platform and Landsat 5,7,8 surface reflectance products,this paper combines the Otsu algorithm(OTSU)and the improved normalized water index(MNDWI)to more accurately automatically calculate the threshold to distinguish between water bodies and non-water bodies,and then achieve Extraction of the water area of Qinghai Lake.The result shows that the area of Qinghai Lake decreased significantly at a rate of 6.76km2/a from 1990 to 2003(P<0.05),and increased significantly at a rate of 18.1km2/a from 2004 to 2019(P<0.05);The spatial changes of the water area of Qinghai Lake are mainly concentrated in Shadao Lake on the east bank and Bird Island and Haixi Island on the west bank;the irregularity of the shoreline of Qinghai Lake has increased significantly in the past 30 years.(3)Using Inverse Distance Weighted(IDW and linear regression to study the characteristics of temperature and precipitation changes in the Qinghai Lake Basin from 1990 to 2019.The residual analysis method is used to study the impact of climate change and human activities on the NDVI of the Qinghai Lake Basin vegetation on the pixel scale,and the correlation analysis method is used to explore the response relationship between the Qinghai Lake area change and the climate.The result shows that in the past 30 years,the Qinghai Lake Basin has an obvious warming and humidification trend;the impact of climate change and human activities on the change of vegetation NDVI is mainly promoted,and the common driving of the two is the main reason for the change of vegetation NDVI;Qinghai Lake area change and precipitation are significant Positive correlation,little correlation with temperature.