Spatiotemporal changes and driving factors of vegetation in Yunnan based on MODIS-NDVI

【Objective】To study the temporal and spatial changes of vegetation in Yunnan and its influencing factors, so as to provide theoretical basis for regional environmental protection and ecological environment construction.【Method】 Based on MODIS-NDVI data,trend analysis,Hurst index and residual analysis were used to analyze the spatio-temporal evolution characteristics of vegetation cover in Yunnan from 2001 to 2020 on different topographic and geomorphic regionalization scales,and the effects of terrain,climate and human activities on the changes were discussed.【Result】From 2001 to 2020,NDVI in Yunnan showed an overall growth trend and the change rate of NDVI in different topographic and geomorphic regions was greatly different. NDVI in Yunnan was high in the west and low in the east,and high in the south and low in the north. The area of NDVI improvement was larger than the area of degradation at all stages,and the area of NDVI improvement was the highest in northeast Yunnan(70.84%). In the future,10.99% of the area would continue to improve,and the northeast Yunnan region had the highest proportion of continuous improvement among different regions. Terrain factors had a significant impact on NDVI. As a whole,NDVI in Yunnan decreased with the increase of altitude, and increased first and then decreased with the increase of slope. In the slope direction,NDVI presented a feature that the negative slope was greater than the positive slope. The average correlation coefficient between precipitation and NDVI in Yunnan from 2001 to 2020 was 0.0074,showing a pattern of west negative and east positive,and northeast Yunnan was most affected by precipitation. The average correlation coefficient between air temperature and NDVI was 0.0884,and southwest Yunnan was the most affected by air temperature. The changes of NDVI were mainly promoted by human activities at each stage. The change of land use had a strong correlation with the change of NDVI. A series of ecological protection projects improved vegetation,while the expansion of construction land inhibited the growth of vegetation.SuggestionImplement forest ecological construction according to local conditions to improve vegetation planting survival rate; improve the planning and management of construction land to prevent the rapid and disorderly expansion of construction land;continue to promote ecological projects and intensify efforts to protect forest lands and grasslands.