| This paper takes Nagqu grassland as the research object,based on the MODIS NDVI remote sensing data from 2001 to 2015,combined with the local climate and human factors,the maximum value composite(MVC)method,the mean method,the stability analysis method and the correlation analysis method were used to study the effects of The temporal and spatial evolution of NDVI in northern Tibet and its influencing factors from 2001 to 2015,so that the majority of scholars can understand the latest changes of grassland in northern Tibet,provide the reference for the rational development of animal husbandry and scientific utilization of grassland resources.The main results are as follows:(1)The Normalized difference vegetation index(NDVI)of Nagqu region was basically maintained at 0.11 from December to April of the next year.And the peak of NDVI was mainly concentrated at July to September in the whole growing season.And NDVI value showed a low value nearly three years.In the past 15 years,the vegetation index in Nagqu area had little change in the interannual period,which was between 0.18 and 0.21.(2)There is obvious spatial difference of vegetation NDVI in Nagqu,showing the trend of high in the East and low in the west.Vegetation index has obvious succession law in the month,which is the green wave gradually progressed from east to west in January to August,and gradually reduced from west to east in September to December.The best season for vegetation coverage in Nagqu from July to September.NDVI values of pixels in the eastern region are poor,while it is relatively stable in the central and western regions.The significant reduction in vegetation index was mainly concentrated in the junction of Amdo County,Nagqu county and Sog County,and at the junction of Bangor county and Xainza county.(3)From 2000 to 2015,in Nagqu region,the annual average temperature is 0.91?,the annual average precipitation is 523.39 mm,the annual average evaporation of 1507.76 mm,the annual average relative humidity of 50.6%.In the overall trend,the annual average temperature is on the rise,while the annual precipitation is decreasing,the annual evaporation showed a slow downward trend,the average annual relative humidity showed a larger downward trend.From the data point of view,the climate of Nagqu region was warm and dry trend.(4)Based on the region data,the average NDVI of the same month of years has a significant positive correlation with monthly average data of years of temperature,precipitation and relative humidity over the same period.The correlation is the largest with the monthly average relative humidity of years.and it is not obvious with the evaporation.Based on the site data,there are significant positive correlations between average NDVI of the same month of years and the temperature,precipitation and relative humidity over the same period.It is most significant correlations with relative humidity in the Bangor,Amdo,Xainza,Biru,Lhari sites.There is positively correlated with the four meteorological factors,and the correlation coefficient is the highest with the air temperature in Nagqu station.(5)Nagqu area NDVI was negatively correlated with the population density;NDVI of Amdo and Xainza weather stations showed a significant positive correlation with the population density.It is significant negative correlation in the Lhari site.And there is a inapparent positive correlation between NDVI and population density in Nagqu,Sog,Bangor stations.Another,NDVI of Biru station is indistinctive negative correlated with its population density.(6)From 2008 to 2012,the number of livestock stocks in year-end decreased sharply,which had a significant positive effect on the growth of grassland vegetation.There was a significant positive correlation between Normalized vegetation index and annual livestock slaughter number,but there was no significant negative correlation with the regional gross domestic product(GDP). |
PDF Full Text Request