| In recent years,with global warming and the intensification of human activities,vegetation degradation,grassland desertification and other problems are particularly prominent,which have become an important issue restricting the sustainable development of regional and global social economy.As an important part of terrestrial ecosystem,vegetation connects the material circulation and energy flow of each circle and is an important route of water circulation and biogeochemical circulation.Research on vegetation ecological protection based on vegetation coverage is conducive to further understanding of the evolution law of vegetation ecosystem,which is of great significance to the restoration of the ecosystem,as well as the practical guidance of vegetation construction and regional sustainable development.Now with the emergence development and mature of remote sensing technology,a wide range and high resolution remote sensing satellite image for regional and even global provide the technical support for the dynamic monitoring of vegetation coverage,and the use of vegetation spectral reflectance of the characteristic differences with other land cover types have developed a number of different vegetation index(NDVI and EVI,SAVI,etc.),NDVI performance for the growth of vegetation and the status of the cover,vegetation green degree has an irreplaceable role.At present,NDVI has been widely used in global or regional remote sensing monitoring of large-scale vegetation,especially in the study of surface vegetation characteristics in arid and semi-arid regions.Nalengler River basin is located in the southwest margin of Qaidam Basin in Qinghai Province,and is located in the arid region in the west..In this region,precipitation is scarce and evaporation is intense.Vegetation is very sensitive to the change of hydrothermal conditions,and vegetation coverage has always been an important factor to evaluate the ecological environment in this region.Based on the NDVI and meteorological data of Nalengler River basin in 1987-2016,combined with the meteorological data in the basin and the underground water level data,adopting the method of information entropy to explore the vegetation coverage and meteorological factors(temperature,rainfall,relative humidity)of space-time distribution and variation characteristics of the research period in the study area.Based on this,the Person correlation coefficient method is used to analyze the relationship of the vegetation coverage,air temperature,rainfall,relative humidity and the embedded depth of groundwater level,the main conclusions are as follows:From 1987 to 2016,the vegetation coverage of The Nalengler River Basin was mainly reduced.The areas with reduced vegetation coverage accounted for 55.91% of the study area,and the areas with increased vegetation coverage accounted for 44.09% of the study area,mainly distributed in the front edge of alluvial fan.There is a spatial correlation between vegetation cover and meteorological factors in The Nalengler River Basin,but the correlation is weak.Areas with a significant positive correlation between air temperature and vegetation cover accounted for 12.25% of the study area,areas with a significant positive correlation between rainfall and vegetation cover accounted for 0.26% of the study area,and areas with a positive correlation between relative humidity and vegetation cover accounted for 0.65% of the study area.Therefore,temperature is a relatively prominent influencing factor of vegetation change in this study.The groundwater level was divided into different gradients according to the depth.The average groundwater level of each gradient was significantly negatively correlated with the average NDVI value corresponding to each gradient,and the correlation coefficient reached-0.7.Global warming does not make the meteorological conditions in the study area beneficial to the overall vegetation ecosystem.On the contrary,the increase of temperature may lead to the intensification of drought in most regions.The vegetation variation trend in the ecosystem regions dependent on groundwater is mainly influenced by the melting water of snow and ice in kunlun Mountains under the condition of climate warming,and vegetation growth shows a trend of improvement... |
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