中国城市体系的演变与发展路径优化

Evolution of China’s Urban System and Optimization of Development Paths

针对近三十年来中国城市体系人口分布的两极分化现象,本文构建一个综合的量化空间均衡模型,阐释向心力的集聚效应、离心力的通勤成本、区位基础以及迁移摩擦对城市规模和城市体系演变的影响。理论模型推演、结构式估计和反事实模拟的结果表明:改善通勤成本或降低迁移摩擦会使特大及以上城市人口持续增长,导致城市体系分布更加集中;均等化集聚效应会显著驱动中小城市人口增长,使城市体系分布向均匀化演变;区位基础的舒适度或生产率均等化将促进中小城市人口增长,而消除城市间房价差异则有助于提升特大及以上城市人口规模。反事实政策评估的结果表明,城市体系均匀化分布会促进社会公平但降低社会总产出,而城市体系集中化分布会提高社会总产出但有碍社会公平。因此,本文兼顾效率与公平,提出未来中国城市体系宜采取“稳两头、促中间”的结构优化道路:以外围中小城市的社会公平和超大城市的经济效率为基础;重点促进都市圈和城市群地区的中小城市发展,引导城市体系由“哑铃型”向“橄榄型”结构转变,构建大中小城市协调发展的格局。

Over the past thirty years of urbanization in China,there has been an imbalance in the development of cities,with a marked trend towards polarization in the distribution of the urban system.This imbalance in cities’size and their growth,and even polarization,can lead to an unreasonable spatial distribution of the population,resulting in some economic and social problems.This paper aims to theoretically reveal the evolution characteristics and driving mechanisms of China’s urban system and to propose future optimization paths in terms of development strategies.This paper constructs a comprehensive quantitative spatial equilibrium model to explain the agglomeration effects of centripetal forces,and the impact of commuting costs,locational fundamentals,and migration frictions of centrifugal forces on the evolution of city size and urban system.Using data from the national population censuses and city statistical yearbooks from 1990 to 2020,the paper conducts structural estimation and counterfactual simulations.The results demonstrate that eliminating differences in congestion effects or migration frictions would lead to a more concentrated distribution of the urban system,while eliminating differences in agglomeration effects or locational fundamentals would lead to the evolution of the urban system towards homogenization.Specifically,improved commuting costs or reduced migration frictions would cause sustained population growth in mega-cities,resulting in a more concentrated urban system;equalizing agglomeration effects would significantly drive population growth in small and medium-sized cities,leading to a more even distribution of the urban system;equalizing the amenity or productivity of locational fundamentals would promote population growth in small and medium-sized cities;and equalizing housing prices would lead to polarization in urban population distribution.These results remain robust after adjusting for sample and indicator measures,accounting for variable endogeneity,and testing parameter sensitivity.This paper then analyzes the changes in equilibrium welfare and output caused by the evolution of the urban system towards either homogenization or concentration based on the quantitative spatial equilibrium model,and explores optimization paths of China’s future urban system from the perspectives of both efficiency and equity.The results indicate that a more homogenized distribution of the urban system reduces output gap between large cities and small and medium-sized cities,as well as between urban clusters and peripheral areas,promoting social equity but lowering total output.Moreover,a more concentrated urban system increases total output but undermines social equity.To achieve a balance between both goals,this paper attempts to simulate and evaluate various policy mixes that aim to simultaneously enhance equilibrium welfare,total output,and the balance of economic development.Based on the above conclusions,this paper proposes a structural optimization path of“stabilizing the development of two ends and promoting the development of the central part”for the urban system.This involves maintaining the reasonable size of peripheral small and medium-sized cities oriented to social equity to ensure the“lower tail”of the urban system;controlling the population scale of mega-cities moderately oriented to economic efficiency to establish the“upper tail”of the urban system;and promoting the development of small and medium-sized cities in metropolitan areas and urban clusters into medium and large-sized cities,and guiding the transformation of the urban system from a“dumbbellshaped”to an“olive-shaped”structure,so as to make up for the“intermediate short boards”of the urban system and foster a coordinated development of large,medium,and small cities.The marginal contributions of this paper are as follows.(1)It eclectically constructs a comprehensive quantitative spatial equilibrium model that systematically explains the mechanisms of urban system evolution from four perspectives:agglomeration effects,congestion effects,locational fundamentals,and migration frictions(reflecting the institutional factors unique to China’s urbanization).(2)Using counterfactual policy evaluation,it explores optimization paths of the future urban system.Using counterfactual simulations to estimate the impact of differentiated policy interventions on equilibrium welfare and output,this paper proposes a structural optimization path of China’s future urban system that balances efficiency and equity by“stabilizing the development of two ends and promoting the development of the central part”.(3)We abopt a scientific approach to measure market potential and its internal components,taking into account both transportation distance and transportation time,as well as considering the differences in potential total demand across various sub-market regions.