Spatial-temporal Variation And Driving Factors Analysis For The Expansion Of The Main Urban Agglomerations In China Based On Night Light Remote Sensing Datasets (1995-2015)

Urbanization is an inevitable process of social and economic development.Ur-banization has created urban civilization and material prosperity and improved the quality of human life,but it has also changed the original natural environment and caused a series of ecological,environmental and social problems.Since the 21st cen-tury,with the rapid development of economic,China is in a period of rapid urbaniza-tion,and a large number of economically developed city groups have formed.At pre-sent,the contradiction between the spatial expansion of urban agglomerations and natural environmental protection has become a hotspot in the field of geosciences.In the past two decades,with the rapid development of ground observation technology,it has become possible to monitor the spatial expansion of urban agglomerations and changes in urban morphology with long-term dynamic monitoring on a regional scale.In this paper,eight major Chinese urban agglomerations,including the Yangtze River Delta,the Pearl River Delta,Beijing-Tianjin-Hebei,Chengdu-Chongqing,Cen-tral Plains,the middle reaches of the Yangtze River,central Yunnan,and Beibu Gulf,are used as the study area.DMSP/OLS and NPP/VIIRS night light remote sensing data,based on statistical data comparison method,were used to extract the built-up areas of 8 major urban agglomerations in China in the past two decades.The statisti-cal analysis of spatial-temporal expansion,speed of expansion,intensity of expansion,spatial autocorrelation and hotspot analysis,shift of gravity center in built-up areas,landscape pattern index,and urban land use scale were used to the built-up areas ex-pansion analysis of eight major urban agglomerations in China from 1995 to 2015.Finally,the grey correlation method is used to analyze the spatiotemporal correlation analysis of driving factors such as the non-agricultural population,regional GDP,total industrial output,total investment in fixed assets,number of colleges and universities in 8 major urban agglomerations in China.The main results of this study are as fol-lows:(1)Analysis of the spatial pattern evolution of the built-up areas of the eight major urban agglomerations in China in the past two decades.The area of the built-up areas of the eight urban agglomerations is increasing year by year,and the overall expan-sion trend of“point-block-area”is presented.Among them,the Yangtze River Delta,Pearl River Delta,Beijing-Tianjin-Hebei,and Central Plains urban agglomerations have a larger expansion.The maximum growth area exceeds 1000 km~2 every 5 years;the maximum area growth in the middle reaches of the Yangtze River and the Chengdu-Chongqing urban agglomeration is between 500-1000 km~2,which is in a medium-speed development stage;the maximum area increase in the built-up area of the central Yunnan and Beibu Gulf urban agglomerations does not exceed 500 km~2every 5 years,which is relatively backward compared to other developed urban ag-glomerations.However,the built-up area and annual average growth rate are increas-ing year by year.From an overall perspective,the expansion speed of the eight urban agglomerations increased rapidly from 1995 to 2015,with a positive growth rate every five years.The overall expansion intensity shows a trend of ups and downs.(2)Analysis of the pattern and spatial and temporal changes of built-up areas.All the urban agglomerations in the paper belong to the agglomeration-oriented spatial expansion model.The spatial distribution shows positive spatial autocorrelation,and the degree of agglomeration shows fluctuations.Most of the gravity centers of urban agglomerations are located in developed cities.The center of gravity of urban ag-glomerations in the middle reaches of the Yangtze River has moved a lot.The rank of cities in the Yangtze River Delta,the middle reaches of the Yangtze River,central Yunnan,the Beibu Gulf is higher,and the scale of development is increasing.Differ-ences in the scale of urban land use among Beijing,Tianjin,Hebei,Yangtze River Delta,Pearl River Delta,Central Plains,and the middle reaches of the Yangtze River are narrowing.The Differences in land use scale among Chengdu-Chongqing,central Yunnan and beibu gulf urban agglomeration are expanding,and the built-up areas are tending to be concentrated.Analysis of the landscape pattern index at the plaque level and landscape level shows that the fragmentation of the landscape in the built-up area of the Pearl River Delta urban agglomeration gradually weakens,and the degree of separation continues to decrease.The landscape fragmentation of the other 7 urban agglomerations has increased.(3)Analysis of the driving factors for the expansion of built-up areas.Policy factors are dominant among the driving factors.Measures such as administrative division adjustment,regional development policies,and housing policy adjustments will have a direct impact on the expansion of urban built-up areas.Natural factors determine the regional industrial structure.Socio-economic factors such as non-agricultural popula-tion,regional GDP,and total industrial output have a greater impact on the expansion of urban built-up areas,while the number of colleges and universities and the total investment in fixed assets have less impact with less synchronization.