A Study On The Relationship Between Compactness And Energy Efficiency In Large Cities

Since the reform and opening up,China's urbanization rate has increased from 17.92%in 1978 to 57.35%in 2016,and it has been rapidly advancing at a rate of half a percentage higher than the world average every year.In the process of urbanization development,there are many inevitably problems such as extensive use of land,disorderly expansion of cities,and excessive energy consumption.In recent years,environmental problems such as smog caused by large energy consumption have seriously affected the quality of urban residents' life,and the problems are more serious for large cities.Based on the connotation of compact cities,this paper establishes a comprehensive index system of compactness from four dimensions of land use,population,economy and infrastructure.We measure the energy efficiency and compactness of 29 large cities in 2003-2014 with the stochastic frontier analysis method and entropy value method,then quadrant map approach is introduced to explore the relationship between urban compactness and energy efficiency.Through the measurement of compactness and energy efficiency of large cities in 2003-2014,the author found that urban compactness and energy efficiency data have similar characteristics:(1)Trends of the two were similar during the study period,and both had a V-shaped gap near 2011.(2)Urban compactness and energy efficiency are increasing with the expansion of the city.(3)The urban compactness and energy efficiency values of the east,west and central regions are in a trapezoidal decreasing trend.These analyses show that urban compactness and energy efficiency are closely related.The results of the quadrant map analysis show that cities with higher scales are mainly based on high-level coordination,and cities with lower scales are mainly low-level coordination.Urban compactness is positively correlated with energy efficiency,which confirms the assumption that compact cities can improve energy efficiency.The dense population is conducive to the scale effect,which makes the energy consumption of lighting,cooking,heating,air conditioning and home appliances more efficient;the large concentration of population and enterprises will also improve the energy efficiency of the production process;At the same time,the high-density population ensures the flow of people needed for public transportation,which is conducive to the scale effect of public transportation and reduce the energy consumption of transportation.Therefore,urban compactness has a promoting effect on energy efficiency in a certain range.In addition to urban compactness,there may be other urban energy efficiency factors that interfere with the objectivity of the quadrant analysis results.After eliminating the interference factors,this paper re-does the quadrant graph analysis.The analysis results also give the conclusion that cities with high compactness are generally more energy efficient,which also verifies the assumption that the compact city can increase urban energy efficiency.Finally,the paper narrows the scope of energy consumption to the energy consumption of urban residents,and divides energy consumption into two major sectors of energy consumption according to energy use,and studies the actual effect of urban compactness on residents' energy consumption separately.The study found that compactness has a significant negative correlation effect on both residential and transportation energy consumption.From 1986 to 2017,national urban built-up area has expanded four-fold,while the population urbanization level is only twice that of the original.This low-density urban development model has led to changes in residents' behavior patterns,which affect the urban energy consumption.Therefore,it is of great significance to improve the national urban compactness.First,improve the relevant laws and regulations around the "compact city" theory,use the law to constrain the developer's land development cycle,and achieve efficient and intensive use of land.Second,reduce the single function area of the city,and integrate several spatial areas with single functions and isolation into a composite functional area to realize the mixed use of land.Third,strengthen the construction of public transport-oriented infrastructure,especially to strengthen the construction of inter-city railway facilities,while making full use of underground space to build a "three-dimensional city"combining ground transportation and underground transportation.The innovations of this paper focus on the construction of the comprehensive index system of urban compactness,the determination of the specific form of urban energy efficiency model and the research ideas.In the past,the indicators of urban compactness were too single,and it was difficult to accurately reflect the connotation of compact cities.Therefore,when selecting indicators,this paper selects 20 secondary indicators that meet the connotation of compact cities from the four dimensions of land use,economy,population and infrastructure to build a complete comprehensive evaluation system of urban compactness,which covers density indicators,structural indicators and efficiency indicators as much as possible.The one-sidedness of using a single indicator is effectively avoided.In order to avoid the problem of model setting,a five-step model setting test was carried out.First,check if the data is suitable for using a random frontier model.The second and third steps examine the specific form of the model.The fourth step checks whether the technical invalid item obeys the semi-normal distribution or the truncated normal distribution,the last step is checking whether energy efficiency has a time-fixed effect.Five steps ensure the scientific of energy efficiency estimates.The research ideas are innovative.Firstly,the paper explains the impact of compact cities on energy efficiency by explaining the internal mechanism of urban compactness affecting energy efficiency.The relationship between urban compactness and energy efficiency is difficult to express in a functional form.The main influencing factors of energy efficiency are cluster analysis,and then use the quadrant graph method to demonstrate the relationship between urban compactness and energy efficiency again.Finally,the scope of energy consumption is reduced to the urban residents' living consumption,which measures influence level of compact city on urban transportation and residential energy consumption.The theory echoes the empirical evidence,from shallow to deep,more comprehensive and complete discussion of the relationship between compact cities and energy efficiency.