Research On The Evolution Characteristics And Influencing Factors Of Chengdu-Chongqing Urban Agglomeration

Urban agglomeration,also known as city cluster,is formed by cities of different types,functions and scales in a certain region.There is one or more mega-cities as the core and developed transportation,communication and other kinds of infrastructures within the region.After reform and opening-up,China's industrialization and urbanization have been developing rapidly,the number and scale of cities have been growing,and the cities have been interacting with each other frequently through various flows of elements such as transportation,information,knowledge,energy,etc,contributing to the formation and evolution of urban agglomerations in China.So far,China has basically formed 20 urban agglomerations with different sizes,scales and development degrees,forming a new spatial organization pattern of “5+9+6”,namely five national urban agglomerations,nine regional urban agglomerations,and six local urban agglomerations.Urban agglomerations,as the main form of space to promote China's new urbanization,have gradually developed into new regional units for China to participate in global competition and international division of labor.With the close connection of cities,the internal structures of urban agglomerations have also transformed from simple hierarchical scale structure to complex network structure.Researches on urban agglomerations has gradually shifted from the study on the hierarchical scale structure of urban system to the study on the network structure of urban agglomerations.Chengdu-Chongqing urban agglomeration is located in the west of China and the upper reaches of the Yangtze River.It is an important platform for the development of the west,a strategic support for the Yangtze River Economic Belt,and an importantbattlefield for the country to promote new urbanization.Depending on its important strategic positions,Chengdu-Chongqing urban agglomeration has developed into one of the five national urban agglomerations.However,the development level and comprehensive strength of Chengdu-Chongqing urban agglomeration are far inferior to those of the Yangtze River Delta urban agglomeration,Pearl River Delta urban agglomeration and Beijing-Tianjin-Hebei urban agglomeration in the east coast,and is also lower compared with the urban agglomeration in the middle reaches of the Yangtze River.As a typical “dual-core” urban agglomeration,the development and evolution of Chengdu-Chongqing urban agglomeration has certain particularity.To explore the development and evolution characteristics of Chengdu-Chongqing urban agglomeration and reveal its evolution laws and development problems are conducive to the scientific and reasonable allocation of the spatial resource of Chengdu-Chongqing urban agglomeration.It is also beneficial for promoting the optimization and reorganization of urban agglomeration structure,realizing the integration and high-quality development of urban agglomeration,and promoting the coordinated development of eastern,central and western regions in China.Based on the research framework of “theoretical analysis-empirical research-policy export”,following the logical route of “node-axis-network” of urban agglomeration's development,this paper studies the evolution characteristics and influencing factors of Chengdu-Chongqing urban agglomeration.Firstly,it systematically reviews the research progress related to urban agglomeration concept,urban agglomeration development and Chengdu-Chongqing urban agglomeration at home and abroad,and introduces the core concepts and basic support theories.Secondly,it analyzes the general development circumstances of the urban agglomeration.Thirdly,from three perspectives,namely scale structure,urban connection and network structure,this paper applies primacy index model,fractal model,modified gravity model,membership model and social network analysis method to quantitatively reveal the evolution characteristics of Chengdu-Chongqing urban agglomeration.Finally,it explores the influencing factors of evolution of Chengdu-Chongqing urban agglomeration,and puts forward several suggestions to the optimization of Chengdu-Chongqing urban agglomeration.The main conclusions are as follows:(1)Since the founding of the People's Republic of China(1949),the urban development of Chengdu-Chongqing region has experienced six periods: the embryonicperiod of urban development(1949-1978),the period of rapid urban growth(1979-2000),the period of transformation from “administrative region” to “economic region”(2000-2005),the period of formation of Chengdu-Chongqing Economic Zone(2006-2010),the period of construction of Chengdu-Chongqing Economic Zone(2011-2015)and the period of formation and construction of Chengdu-Chongqing urban agglomeration(2016-2020).After the year 2020,the region has entered the construction period of Chengdu-Chongqing Economic Circle.(2)From the perspective of scale structure,from 2000 to 2017,Chengdu-Chongqing urban agglomeration has presented a typical dual core structure model centered on Chengdu and the main urban areas of Chongqing.The scale structure of the urban agglomeration evolved from the typical “pyramid structure” of “wide base and narrow spire” to the “spindle structure” of “wide tower body,narrow base and narrow spire”.The scale structure of urban agglomeration has fractal characteristics.During the study period,the disparity of urban population distribution has widened.Chengdu,as the primary city,has a stronger population monopoly position,and the scale “fault” appears between the core and non core cities.Although the scale structure of the high-level sequence cities presents an optimization trend,the overall scale structure has not evolved mature,and a coordinated urban system has yet not been formed.(3)From the perspective of urban connection,from 2000 to 2017,the strength of urban connection of Chengdu-Chongqing urban agglomeration has been continuously improved,and the improvement rate has experienced transformation from growth to continuous deceleration.At the same time,the gap of urban connection strengths has also been constantly expanding,the level of urban connection has become more complex and advanced,and the urban connection shows a multi-level network development trend in space.Moreover,there is also “fault” problem in the development and evolution process of urban connection.The overall direction of urban connection always points to Chengdu and the main urban areas of Chongqing,showing a typical“center periphery” spatial pattern.(4)Cities(nodes)and urban connection(axes)constitute the network structure of Chengdu-Chongqing urban agglomeration.From the perspective of network structure,from 2000 to 2017,the network density of Chengdu-Chongqing urban agglomeration gradually increased,and the network became more and more close.The network spacestructure has experienced three basic stages,namely “polar nucleus breeding stage”,“point-axis diffusion stage” and “network organizing stage”.It has evolved from a two-center radial simple structure to a two-center high-level radial complex network structure.During the research period,the overall network centralization degree of the urban agglomeration has improved,but the overall network centralized characteristic is not obvious,which reflects the urban agglomeration's non single core spatial pattern.While the single city centrality in the network has been increasing,the regional disparity in the centrality have also been widening,showing the “center-periphery”feature with Chengdu and the main urban areas of Chongqing as centers.During the research period,the network sub structure of the urban agglomeration has kept relatively stable,forming four agglomerated sub groups,namely,the agglomerated sub group centered on Chengdu,the agglomerated sub group centered on the main urban areas of Chongqing,the agglomerated sub group centered on Wanzhou in the northeast of Chongqing,and the agglomerated sub group formed by the cities outside the main axis of Chengdu Chongqing.In terms of core-periphery structure,the urban agglomeration network has always been showing a “half circle ladder” core-periphery structure,and the influence of radiation and agglomeration in the core area of the network has been relatively stable,but the disparity of urban radiation and agglomeration impact has expanded.(5)To promote the optimization of Chengdu-Chongqing urban agglomeration,first,we need to appropriately increase the scale of the main urban areas of Chongqing to avoid the “dual core imbalance”;second,we need to repair the “fault” of the urban scale and the urban connection to promote the coordinated development between large,medium and small cities;third,we need to fill the “central depression” and repair the“collapse of the edge area” to promote the balanced development of the region;finally,we need to build an integrated development system and mechanism to achieve regional integration.