Interrelationships And The Evolutionary Model Between Urban Land Expansion And Population Growth

Urbanization is the most important social change in the world in the 21^st century.The persistently growing urban population drives urban land to expand outward.Urban population and land are the two most important elements of a complex urban system,which are the topics of this dissertation.The research goal of this dissertation is to quantify and model the interrelationship between urban land and population and promote urban development.The main research contents are the characteristics,rules and mechanisms of urban land expansion and population growth,and responses to the practical problems of land management in urban development in China.In terms of time series,it has been widely found that urban land expansion is faster than population growth,that is,land urbanization is faster than population urbanization,which will directly lead to a decrease in urban population density(defined as the ratio of urban population to built-up area)over time.Taking the temporal decline in urban population density as a starting point,this dissertation firstly examines the characteristics,laws and quantitative model of urban population density decline over time.Then,this dissertation analyzes the influencing factors and mechanisms of the temporal decline in urban population density,which is the key to further understand the law and mechanism of density decline,and also the basis for regulating the declining rate of urban population density.From the time-series relationship between urban land and population in individual cities to their cross-sectional relationship in urban systems,this dissertation investigates the differences of time-series and cross-sectional relationships between urban land and population and their evolutionary correlations over time.Finally,based on the predictions of future urban land demand considering the scenario of density decline,this dissertation proposes three strategies for slowing down the decline in urban population density over time and the path choice of China's future land urbanization.The main findings are as follows:1.The decline in urban population density over time is a widespread fact and a general trend and the exponential model can quantitatively describe the trend and speed of urban population density decline over time.(1)This dissrtation firstly uses the urban population density data in 1990,2000 and 2014 of 200 global cities to illustrate the wide-ranging facts and general trends of the decline in urban population density over time.From2000 to 2014,the urban population density of Chinese large,medium and small cities decreaesed by 3.58%annually.International comparisons show that urban population density declines fastest in Chinese cities within major countries and regions such as the United States,Europe,India and Africa.(2)This dissertation proposes an exponential model of urban population density decline over time.The exponential model can quantitatively describe the trend and speed of the decline in urban population density over time.Taking 35 major cities in China as an example,the exponential model can fit the temporal trend of urban population density from 2001 to 2015 well,with an average adjusted R² of 0.68.(3)The applicability of the exponential model is verified by the urban population density from 1910 to 2000 in 20 major cities in the United States,with an average adjusted R² of 0.83.The density of the 20 major cities declined annually by 2%in the 20^th century.The good ability of the exponential model to fit the decline in urban population density over time suggests that the exponential model can predict future urban population density,which has important applications in urban land demand forecasting.(4)This dissertation derives the temporal variation of urban population density from the spatial distribution model of urban population density.This establishes the relationship between the spatial distribution and temporal variation of urban population density,and also gives the theoretical proof that urban population density declines over time.2.The temporal variation of urban population density is affected by many factors and the compact urban form and expansion pattern can effectively slow down the decline in urban population density.Based on the analysis of urban population density and related data in 1990,2000 and 2014 in 200 global cities,it is found that:(1)the urban population size will not affect the declining rate of density,but the larger the size of the built-up area,the slower the density decline.The impact of urban population growth rate on density change is not stable,but the growth rate of built-up area is significantly correlated with the annual change rate of urban population density.The rapid urban expansion significantly increases the density decline over time.In addition,the higher the initial urban population density of the city is,the faster it will decrease over time thereafter.(2)In terms of urban form,the higher the degree of fragmentation of the built-up area,the faster the urban population density declines;the higher the compactness of the built-up area,the slower the density declines.The increase in the proportion of the infilling expansion pattern can slow down the density decline,while the increase in the proportion of the edge-expansion and outlying expansion pattern accelerates the density decline.(3)In terms of socio-economic factors,the higher the per capita GDP is,the slower the decline in density is;and the higher the GDP growth rate is,the faster the density declines.The higher the level of urbanization is,the slower the decline in density is;the faster the rate of urbanization increases,the faster the density declines.(4)From the perspective of the operability of land management and urban planning,the influence of urban form and expansion pattern on the declining rate of urban population density has the most practical significance.The multivariate regression model shows that only the urban form indicators and proportions of expansion patterns can explain the 33%variations of the annual change rate of urban population density.The compact urban form and expansion patterns can effectively slow down the decline in urban population density over time.3.The temporal development of urban elements in individual cities will not follow the cross-sectional law of the urban system,and the evolutionary model of urban systems effectively unifies the temporal and cross-sectional relationships between urban elements and population.(1)Taking 275 prefecture-level cities in China as examples,this dissertation analyzes the the differences between temporal and cross-sectional relationships of built-up area and population from 2000 to 2016.The results show that the cross-sectional scaling law is very stable,while the temporal scaling law has significant fluctuations.(2)The evolutionary model of urban systems proposed in this dissertation uses the graphic language to visually demonstrate the essential difference between the cross-sectional scaling law and the temporal development path of individual cities.Therefore,the temporal development of urban elements will not follow the cross-sectional scaling law of the urban system.The evolutionary model of urban systems explains the self-consistency of the temporal and cross-sectional relationships between urban land and population,and establishes the dependence between the cross-sectional scaling law and the temporal development of individual cities.The evolutionary model of urban systems divides the increase of urban land with population increase into two parts:basic increment and excess increment.The basic increment is caused by the cross-sectional scaling law,while the differences of excess increment among different-sized cities determines the change of the cross-sectional scaling exponent.(3)The interrelationships between urban population and GDP,household electricity consumption and road length in Chinese prefecture-level cities from 2000to 2016 confirm the two main findings that the temporal development of urban elements is intrisincly different from the cross-sectional scaling law and the validity of the evolutionary model of urban systems.The use of road traffic congestion data from 1982 to 2014 in 101 cities in the United States also confirm the two main findings.Using the total floor area(residential building area)and population data in Shanghai from 2005 to 2017,this dissertation extends the urban scaling studies from a system composed of multiple cities to a system composed of different sub-areas within the city,and the evolutionary model still applies.4.The decline in urban population density has significantly increased the demand for urban land in the future and the livable compact urbanization paradigm is a realistic choice for China's land urbanization.(1)Taking the decline in urban population density over time into consideration,this dissertation forecasts the urban land demand in 2030 in China.Compared to the scenario that urban population density does not decline,due to the decline in density,the future urban population have to occupy extra 68,000 km²,42,000 km² and 19,000km² under the high-speed scenario(density declines by 3%per annum),the medium-speed scenario(2%)and the low-speed scenario(1%),respectively.(2)The rapid decline of urban population density will accelerate urban sprawl,increase land resource consumption,and threaten urban and regional sustainable development.Based on the results and findings,this dissertation proposes three strategies to slow down the decline in urban population density over time,including:maintaining the density around urban centers,advocating a compact expansion pattern,and adapting to specific urban land use types.(3)From the perspective of game theory,this dissertation analyzes the“Prisoner's Dilemma”of the high-low density dispute in urban development,and proposes that the livable compact urbanization paradigm is the realistic choice of China's future land urbanization.