| Urbanization is the most important milestone in the development of human history and is widely considered as a key engine for socio-economic development.Rapid urbanization has brought unprecedented opportunities for human beings;however,it also directly or indirectly gives rise to challenges to a sustainable future for humanity and nature through the continuous urban expansion and the growth of energy consumption and greenhouse emissions,consequently causing an imbalance between the economic,environmental and social systems.Therefore,establishing socially,economically,and ecologically sustainable cities requires quantitative analysis of the characteristics of various intricate urban attributes,such as urban scale,economic development,infrastructure services,and natural resources,and the dynamic coupling relationships among them.Zipf’s law,Gibrat’s law,and urban scaling law,as significant theories of new urban science research,compose the paradigm and theoretical fundamental for revealing urban structure,growth dynamics patterns,and evolution mechanisms.Meanwhile,the 2030 Sustainable Development Goals（SDGs）,as the strategic framework for global sustainability,are of great significance in guiding the implementation of the urban sustainable development agenda.As the largest developing country,China is beset by severe problems,such as imperfect market mechanisms,unbalanced regional development,and a severe ecological environment,and there is an urgent need to provide a conceptual layout of future urban development and sustainable urban development path.How to integrate the concept of sustainable development into urban development and how to analyze the current situation and contradictions of sustainable development in China from the perspective of social,economic,and environment can provide a scientific basis to improve the quality of the urban environment and realize regional sustainable development,as well as provide scientific reference for other developing countries.This study uses urban expansion（such as urban area and population growth）as the entry point to explore the development and evolutionary patterns of China’s urban systems and their coevolutionary trends with socio-economic and ecological indicators,and evaluate the level of sustainability of China’s urban development in China’s prefecture-level and above cities.The main results are as follows:（1）In general,China’s urban expansion shows a rising periodic exponential trend from 1987 to 2017,with evident inter-and intra-regional disparities.At the national level,the total urban areas of prefecture-level cities and above showed a rising exponential trend（142293.5 km2 in 2017）and phased characteristics during the study period,which is intimately related to China’s national strategies for economic and social development.In terms of the spatial pattern.the speed,and scale of urban expansion（AE and AGR）in China show an unbalanced pattern,i.e.,"high in the east and low in the west",with the coastal region having a more evident AE（27.1-79.18）and the Yangtze River basin having a higher AGR.Analysis of variance（ANOVA）is used to analyze the variations in urban expansion among different city categories over five time periods from 1987-2017,and the results show that the urbanization process differs among regions,especially in the southwest and northwest regions,where are significantly different from other regions in different periods.Likewise,there are differences in urban expansion among cities even under the same category,most notably in the Western,Central,and Southern regions.In a word,China has experienced an unprecedented development of urbanization with a tendency to slow down.The current regional development in China is characterized by complexity and diversity,which requires high attention and a proactive and scientific approach to regional and urban planning and achieving sustainable growth.（2）The city size distribution in China differs significantly from Zipf’s and Gibrat’s law,which is relevant to shifts in urbanization policies.The city size distribution in China does not conform to the theoretical linear distribution,that is,both large and small cities are smaller than the expected value of Zipf’s law,showing a downward trend of collapse.The Zipf coefficients calculated by distinct urban size indicators are different.Specifically,the Zipf coefficient is less than 1 for urban areas（0.561-0.693）and greater than 1 for year-end（1.062-1.283）and non-agriculture populations（1.0211.2）.However,it is noteworthy that due to the transformation from a centrally planned economy to an emerging market economy system and the change of urbanization strategy,the Zipf coefficient gradually converges to 1 in time.Moreover,China shows a clear pattern of converging urban growth from 1987 to 2018 with a 95%confidence interval of[-0.17,-0.12],in other words,the larger cities grow slower while the smaller cities grow faster,therefore contradicting Gibrat’s law of proportionate growth which states that growth of a city is independent of its absolute size.The impact of China’s urban development policies on the applicability of Gibrat’s law in Chin is verified through DID,we found that China’s urban development changes with the shift of macro-urbanization policies,which impacts the validity of Gibrat’s law in China.As a result,our results suggest that implementing a master plan for sustainable development in the new era can bring maximum benefit to our human being,and that urbanization should be promoted in accordance with objective rules and the government should take the responsibility and reduce unnecessary interventions in land-use planning.（3）To some extent,Bettencourt’s urban scaling theory is not applicable to China,a rapidly urbanizing country,and temporal scaling may not collapse in the curve of transversal scaling.Research based on the urban scaling law in western developed countries highlights that urban expansion slower than population growth—shows sublinear behavior（β=2/3）.However,in our study,it is found that the increase in urban areas progressively exceeded its urban population growth,leading to a superlinear scaling(βmean=1.94).In addition,the infrastructure indicators（e.g.,number of hospitals and high schools）scale sublinearly or linearly with population,contradicting their expected regimes.Whereas the scaling exponent of China’s economic output attribute（e.g.,GDP and total wages）and the population is significantly larger than western developed countries like the United States and Germany,with βmean of 1.37 and 1.36,respectively.The above results indicate that China does not follow the urban development theory proposed by Bettencourt and has its own unique development model.However,it is essential to point out that the scaling exponent tends to level off over time as it evolves,indicating that the Chinese urban system is moving toward integration with the global economic system（e.g.,western counterparts）and attaining a balanced and sustainable development under the control of national governance.The temporal scaling of urban attributes usually evolves in the same direction as the crosssectional scaling of the urban systems but with significantly different values,which highlights the correlation and contradiction between the temporal scaling and transversal scaling.The similarities and differences demonstrate the correlation and contradiction between the spatial and temporal scaling exponents and illustrate unequivocally that individual temporal dynamics do not collapse in the universal curve of urban systems.Finally,we assess and compare the performance of different cities by calculating SAMIs that eliminates the size effect,the results reveal that the economic output efficiency of the eastern region is higher than that of the western regions with the same population.The sparsely populated regions such as the northeast and Xinjiang occupied a larger area than other regions with the same population.（4）The comprehensive level of sustainable urbanization in China continued to increase during the period between 2000 and 2015（31.52-56.45）,showing a spatial heterogeneity of "High East.Low West",with the degree of coordinated development between the social and economic subsystem weakening,while the degree of trade-off between the environmental subsystem and the other two subsystems remains unchanged.China’s overall trend of urban sustainable development may be classified into three stages:slow decline,steady rise,and rapid increase after a rebound.Specifically,the level of sustainable development of the three subsystems（i.e.,social,economic,and environmental）is constantly improving.In terms of the results of provincial analysis,the sustainable development level in China presents an increasing trend on the whole from west to east,changes in different provinces have an offsetting effect and therefore present minor changes at the national level,from which it can be posited that the degree of changes in sustainable development indicators at the national level tends to mask changes in the level of sustainable development in each province.The evaluation results of the sustainable development levels of municipalities show that the Yangtze River Delta,Beijing-Tianjin-Hebei,and Pearl River Delta economic zones are regions with high economic development levels,and the socially sustainable development levels show a pattern of high in the east and low in the west,while the Shandong Peninsula and the peripheral areas of the Central Plains urban agglomeration have higher environmental sustainability scores.Finally,the synergies and trade-offs among the three SDGs categories are analyzed by using the MFA function.There is a statistically significant positive correlation between social and economic SDG categories（RV=0.32）in 2000,demonstrating a synergistic effect between the two,which weekend in 2015（RV=0.12）;while there are statistically significant trade-offs between the environmental SDG category and the other two（RV=-0.2,RV=-0.15）,and this relationship also gradually weakened in 2015.The assessment of urban sustainable development levels at municipal,regional,national perspective unfolds a comprehensive picture of sustainability,which provides precise guidance for future improvement of regional sustainable development policies,and novel insights for other countries with a shared prospect,while confirming that a paradigm of balanced and coordinated social,economic,and ecological development is a realistic option for future urbanization.As a typical developing country,China’s urban expansion does not follow the urban laws（Zipf,Gibrat and urban scaling law）commonly found in developed countries,which is of phase,regional and hierarchical characteristics.Meanwhile,disorderly and haphazard land development has intensified the contradiction with socio-economic development and ecological environmental protection.This paper helps to better understand the structure of urban system and predict the trajectories of future urban development,so as to enrich and improve the theory of urban scaling law and form a new urban science theory with Chinese characteristics.Furthermore,the relevant research results of this paper provide a scientific basis for optimizing urban spatial structure,promoting national new type urbanization,and realizing regional integrated development,and provide new ideas for exploring the transformation path of cities to social-economic-ecological coordinated and balanced development. |
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