Temporal and Spatial Variations of NDVI and Its Driving Factors in Inner Mongolia from 1982 to 2015

Based on the data of GIMMS NDVI3g, ERA5 and land cover, the vegetation variations(1982–2015) were analyzed by using the Theil-Sen median trend analysis, Mann-Kendall test and Hurst index, multivariate linear regression and residual analysis were used to quantitatively determine the impact of climate factors and human activities on the dynamic change of vegetation. The findings indicated that from 1982 to 2015, the area with significant and extremely significant vegetation increase accounted for 8.83% and 24.01% of the total area of the study area; the area with significant and extremely significant vegetation decrease accounted for 4.20% and 5.64%, and the area without significant vegetation change accounted for 57.32%. The spatial difference of NDVI Hurst index was obvious in the study area. The vegetation overall presented reverse sustainability, but the trend was not obvious. The area with significant positive and negative correlation between annual precipitation and NDVI accounted for 31.19% and 1.52% of the study area; the area with significant positive and negative correlation between annual temperature and NDVI accounted for 18.97% and 13.74%. During 1982–2015, the vegetation restoration area caused by human activities, climate, climate and human activities integrated effects accounted for 70.43%, 7.82% and 21.75% of the total vegetation restoration area, respectively; the vegetation degradation area resulted from human activities, climate, climate and human integrated effects accounted for 51.03%, 26.28% and 22.69%, respectively. From 1982 to 2015, the vegetation in Inner Mongolia was generally in the recovery state. Areas where climatic factors were significantly related to vegetation were not the main areas of vegetation change, and human activities were the main causes of vegetation restoration and degradation.