| As the typical inland arid and semi-arid areas,Northwestern China is not only important areas for ecological construction in my country,but also one of the more sensitive areas for global changes.With the development of the society and economy,the economic level of Northwestern China is gradually increasing,but the ecological environment of the whole region has been destroyed,and the ability of grasslands,forests,and wetlands to conserve the ecological environment had declined.However,since the implemention of the ecological project in returning farmland to forest and grassland,the ecological environment of the five northwestern provinces has been restored.With the help of vegetation NDVI(Normalized Difference Vegetation Index),which is an important key parameter of terrestrial ecological process,relying on meteorological monitoring data,geospatial data cloud platform,and geographic information system software,this study explored the interannual scale and spatial distribution of the dynamic changes of vegetation coverage in Northwestern China,analyzed the driving forces that affected the changes from natural and human factors.The main results are as follows:(1)In terms of inter-annual changes,the annual average value of vegetation NDVI showed an increased trend in Northwestern China from 2000 to 2018.In the seasonal changes,vegetation NDVI changed significantly in different seasons,with the highest change rate of vegetation NDVI in summer and autumn while lower in spring,and vegetation growth rate was relatively slow,while NDVI in the growing season showed an increasing trend.(2)In terms of spatial variation,the spatial distribution of vegetation NDVI in Northwest China was significantly different,and the overall characteristic was increased from northwest to southeast.High-value areas of NDVI are concentrated in the Qinling Mountains of Shaanxi,the Qilian Mountains in Qinghai Province,and the Longzhong Plateau in Gansu.Low-value areas are distributed in the deserts and Gobi areas of southern Xinjiang,and sands in northern Shaanxi.Vegetation NDVI which varied and increased slightly are distributed in central Qinghai,Northern Xinjiang,Southern Ningxia basically,vegetation NDVI with significant reduction are mainly distributed in arid areas such as sandy land and Gobi,while areas with significant increase in vegetation are mainly distributed in the plains and valleys of southern Shaanxi,as well as the oasis on both sides of the Tianshan and Kunlun Mountains.(3)Among the natural factors,vegetation,precipitation,dryness and humidity index all had an impact on the vegetation NDVI,but the impact of temperature and precipitation was more significant.The areas with negative correlation between vegetation NDVI and temperature are mainly distributed in the agricultural and pastoral transition zone in northern Xinjiang and northwestern Gansu.The areas with positive correlation with temperature are mainly distributed in southern Xinjiang,western Qinghai,southeastern Gansu and northern Ningxia.The areas with positive correlation between vegetation NDVI and precipitation are mainly distributed in oasis areas in central Xinjiang,eastern Qinghai,southeastern Gansu,and northern Shaanxi,areas which had negative correlation with precipitation are mainly concentrated in the desert hinterland and Gobi in central Xinjiang.(4)Among the human factors,the area of arable land,grassland,and construction land in Northwest China had shown an increasing trend from 2000 to 2018,while the area of wood land,water area and unused land had shown a decreasing trend,which is connected with large-scale urban expansion during the process of transformation.Human activities had positive and negative impact on the change of vegetation coverage.The areas where human activities promote vegetation NDVI are mainly distributed in northern Shaanxi,eastern Qinghai,and eastern Gansu.The areas where human activities had a destructive effect on the change of vegetation NDVI are mainly distrubuted in the important urban areas of Weinan Valley. |
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