Spatiotemporal Change Analysis of Annual Average NDVI in Qinling Mountains as Ecological Security Barrier and Dividing Line between Geography and Climate

Abstract

Based on Google Earth Engine cloud platform and MOD13Q1-NDVI images, this paper analyses the spatiotemporal variation characteristics of vegetation cover in Qinling area and its five watersheds from 2000 to 2020 from the perspectives of annual average NDVI. The results show that: 1) Since 2000, the vegetation cover in Qinling Mountains has shown a fluctuating growth trend, with annual average NDVI above 0.4, the maximum value in 2016 and the minimum value in 2001. There are obvious differences in the annual average NDVI of the five major basins, the fluctuation range of the Danjiang River Basin is the largest, the fluctuation trend of the Hanjiang River Basin and the Jialing River flow is similar, and the annual average NDVI of the Nanluo River Basin as a whole is the lowest. 2) The change characteristics of annual average NDVI in the four five-year periods from 2000 to 2020 are different, the decreasing area of annual average NDVI in the first two five-year periods is obviously larger than the increased area, and the degree of vegetation cover continues to worsen; in the third five-year period, the annual average NDVI increased almost in the whole study area, and the vegetation cover improved rapidly. The change range of annual average NDVI in the fourth five-year period is the smallest, and the proportion of unchanged area is more than half.