Research On The Impact Of Climate Change And Human Activities On Vegetation NPP Changes In Northwest China

With the implementation of the "Western Development" strategy and the "One Belt,One Road" major initiative in the 21st century,the Northwest China has ushered in an unprecedented development opportunity,but also brought greater challenges to the ecological environment in the northwest region.Therefore,it is of vital importance to strengthen the protection of the ecological environment in the Northwest China.The net primary productivity of vegetation not only reflects the production capacity of plants,but also is an important characterization parameter for measuring the terrestrial ecological environment.In-depth study of the impact of climate change and human activities on vegetation NPP in Northwest China under the background of global change is of great significance to promote vegetation restoration,maintain ecological security,protect regional ecological environment,and establish an ecological environment in which people and nature live in harmony.Therefore,this study uses the Northwest China as the study area,based on NDVI data,meteorological data,land use data,DEM data and et al,using the CASA model and the coefficient of variation method to calculate the actual NPP and potential NPP,and the difference between the actual NPP and the potential NPP as the impact of human activities on vegetation NPP.On this basis,the spatial and temporal changes of vegetation actual NPP in the Northwest China from 2000 to 2016,the impact of land use change on actual NPP of vegetation and the impact of climate change and human activities on vegetation NPP in Northwest China were analyzed.The main research conclusions are as follows:(1)In terms of temporal change,from 2000 to 2016,the annual average and annual total NPPA of the Northwest China showed an increasing trend.The NPPA of vegetation in different provinces and different vegetation types showed a trend of increasing volatility.From the perspective of spatial distribution,the annual average NPPA of vegetation in Northwest China has gradually decreased from southeast to northwest,and then increased in the Altai Mountains and the Tianshan Mountains in the northwestern part of Xinjiang.In the trend of spatial change,the NPPA of vegetation in the northwestern region is mainly dominated by the increasing trend,and the regions with more significant increase are mainly distributed in the southeastern region.From the perspective of the stability of spatial variation,the NPPA variation of vegetation in Northwest China is in a relatively unstable state,and there is a significant spatial difference in the stability of variation.From the future trend of vegetation NPPA,the area of vegetation improvement in Northwest China will show a weak change to degraded and continuous improvement in the future,and the area of vegetation degradation mainly shows weak degradation to improved trend.(2)From the perspective of the relative contribution rate of different land use types to the change of vegetation NPPA,the sustainable land use type contributed a lot,and the grassland contributed the most;while the changed land use type contributed only 2.9%.A further study of 2.9%of the contribution of land use types in this study found that the change from grassland to cultivated land has the largest contribution,followed by the change from unused land to cultivated land,and the change from cultivated land to forest land and grassland has a relatively large contribution to the change of vegetation NPPA.From the impact of land use type change on vegetation NPPA per unit area,the conversion area of cultivated land to shrub,woodland and grassland,and grassland to shrub has the greatest impact on the increase of vegetation NPPA.(3)From the influence of climatic factors on the NPPA of vegetation,it was found that there was a positive correlation between vegetation NPPA and temperature in most areas of Northwest China,and only a small part of the area showed a negative correlation;in most areas,vegetation NPPA and precipitation showed a positive correlation.In particular,the positive correlation between the northwestern part of the Northwest China with less precipitation is more obvious;96.45%of the regional vegetation NPPA is positively correlated with solar radiation,especially in the Loess Plateau and Qinba Mountains,the positive correlation with solar radiation is more obvious.Vegetation NPPA is proportional to the area of positive correlation and negative correlation between sunshine hours and relative humidity;the negative correlation ratio between vegetation NPPA and annual average wind speed is greater than the positive correlation ratio.(4)From the spatial distribution of the influence of human activities on NPP,the areas where human activities have a negative impact on vegetation NPP are mainly distributed in the transitional area of forest land to the cultivated land at the foot of the mountain,while the areas where human activities have a strongly positive imapct are mainly distributed in the oasis region of the Tarim River,Shiyang River,the northwestern part of the Qilian Mountains and the the source regions of three rivers.From the change trend,the positive change of human activities on vegetation NPP in the northwest region accounts for 52.35%of the total area,of which the positive change is more significant mainly distributed in northern Shaanxi,Daba Mountain in southern Shaanxi,southeastern Shaanxi,oasis of Tarim River and cultivated land in northern Tianshan,and the negative change accounts for 48.65%of the total area.The negative change of human activities on vegetation NPP is obvious mainly distributed in the surrounding areas of cities and towns.(5)According to the spatial distribution of relative contribution of climate change and human activities to vegetation NPP change in Northwest China,it is found that climate change is the dominant factor for the increased of vegetation NPPA,while human activities is the dominant factor for the decrease of NPPA.Among the contributions of climate change and human activities to the increase of vegetation NPPA in the changes of different land use types,the contribution of climate change in the land use types that remain unchanged is greater than that of human activities,while the contribution of human activities to the increase of vegetation NPPA in the conversion of other land use types to cultivated land and unused land to woodland and shrub is significant.However,among the contributions of climate change and human activities to the reduction of vegetation NPPA in the changes of different land use types,the contribution of human activities is obvious.The significant factors affecting NPPA in Northwest China were the number of rural population,effective irrigation area,and agricultural fertilizer application,temperature and precipitation.The factors that have significant effects on vegetation NPPA in Xinjiang are precipitation,effective irrigation area and agricultural fertilizer application.The factors have significant effects on vegetation NPPA in Qinghai Province are the temperature,the number of rural population,the amount of agricultural fertilizer applied,and the number of livestock at the end of the year.The factors that have a significant impact on the vegetation NPPA in Gansu are the amount of agricultural fertilizer applied,the number of rural population and the effective irrigated area.The factors that have a significant impact on the vegetation NPPA in Ningxia are effective irrigated area,rural population,agricultural fertilizer application and precipitation.The factors that have a significant impact on the vegetation NPPA in Shaanxi are the number of rural population,the amount of agricultural fertilizer applied,solar radiation,and the number of livestock at the end of the year.