Analysis of the spatial-temporal change and impact factors of the vegetation index in Yulin, Shaanxi Province, in the last 17 years

Vegetation index is an important method to study regional vegetation changes. The present study is based on MODIS/Terra NDVI remote sensing data,and analyzes the spatial-temporal changes and impact factors of the NDVI in August from 2000 to 2016 at pixel scale in Yulin City of Shaanxi Province. The results showed that vegetation index increased in approximately 96. 44% of the land area in the Yulin city,and the area with increasing NDVI between 0-0.02/a accounts for 93.63% of the land area of Yulin city. The area with significant increasing trend accounts for 80.72%.The complex linear regression analysis showed that meteorological factors play a positive role in the growth and evolution of vegetation,and human activities also make the vegetation index to become more uniform. The area where the human activities restrain the growth and evolution of the vegetation covers 45.04% of area of Yulin. It is mainly distributed in Fugu County,which is located to the north of Yulin and most areas of the southern and western parts of Yulin. The area where human activities promote the increase of the vegetation index accounted for 54.96% of area of Yulin,which indicated that inmore than half of the region,human activities have played a positive role in the growth of vegetation. In these areas,the effects of forest conservation,returning farmland to forests,and returning pasturage to natural grassland are greater than those in other areas.