Research And Analysis On The Spatial And Temporal Evolution And Driving Forces Of Urban Expansion In The Beijing-Tianjin-Hebei Region

With the continuous development of society and the acceleration of urbanization,it has led to excessive concentration of urban population,excessive development of agricultural land,and worsening of the ecological environment.The changes in urban built-up areas directly reflect the spatial aggregation of cities and the distribution of human activities.Studying the changes in the spatial contour of urban built-up areas plays an important role in urban land use efficiency and ecological environment.Therefore,conducting spatiotemporal evolution analysis and driving force analysis of urban expansion is of great significance for the sustainable development strategy of cities.This article takes 13 cities in the Beijing Tianjin Hebei region as the research object.Based on the nighttime lighting dataset from 1999to 2019,the spatial contours of five built-up areas in 1999,2004,2009,2014,and 2019 are extracted.Based on this,the spatiotemporal characteristics and driving mechanisms of urban expansion are analyzed.The main conclusions of this article are as follows:(1)This article is based on the surface coverage data of the long-term series nighttime lighting dataset,and uses statistical data and reference comparison methods to extract the overall error of the spatial contour of 13 cities in the Beijing Tianjin Hebei region in 1999,2004,2009,2014,and 2019,with a total of 5 phases of built-up areas.The overall error is controlled within 10%,and the average spatial accuracy reaches over 90%,which meets the accuracy requirements of urban expansion change analysis.(2)In terms of time,there are significant differences in the expansion speed,dynamic degree,and coordination among cities.The overall growth rate of the built-up area is relatively fast,with an average growth rate of 10.36km~2/a.However,most cities are in a slow expansion stage and their development is not coordinated.In terms of spatial form,the compactness index shows a downward trend,the fractal dimension shows an upward trend,and the stability index shows a downward trend first and then an upward trend.The urban built-up areas are increasingly scattered,and the stability has improved after 2014.The migration direction of the center of gravity in different cities is inconsistent,with significant differences.Structurally,Beijing is the first city in the Beijing Tianjin Hebei region.The"Two City Index"began to decline after reaching its maximum in 2004,and the primacy effect continue to weaken;The rank scale index is both greater than 1,and there are mega cities such as Beijing and Tianjin,with a large number of small and medium-sized cities that are immature in development;The Gini coefficient results show that the distribution of urban size is relatively reasonable.In terms of landscape pattern,the aggregation index shows a downward trend,while the landscape shape index shows an upward trend,making urban built-up areas increasingly complex.(3)There is a strong correlation between the area of built-up areas and factors such as natural environment,economy,population,transportation,and policies,indicating that urban expansion is directly or indirectly influenced by these factors;At the same time,regional GDP,fixed assets investment,fiscal revenue,total retail sales of consumer goods and total population at the end of the year are the main driving factors affecting urban expansion in Beijing Tianjin Hebei region.