Macro Process Modeling And Mechanism Analysis Of Urban Growth

Urbanization is the most important urban transformation and a major challenge in the 21 st century.In the process of global urbanization,the influx of large numbers of people into cities has prompted the continuous expansion of urban land.The urban land expansion around the world has accelerated changes in land cover and habitat and has had a major impact on regional and global climate change,biodiversity,and cultivated land.Urban growth has become one of the most noticeable events in terms of speed and scale.Urban population growth,land expansion,and infrastructure expansion are important components of urbanization.Taking urban growth as the theme,we proposed a model quantifying the macro process of urban growth.And we analyzed mechanisms of the macro process of urban growth and discussed land growth management in future urban development.One challenge of urban growth researches lies in the understanding of the laws and mechanisms of urban growth,which requires comprehensive analysis from multiple perspectives.Previous studies have generally found that urban land density(defined as the ratio of urban built-up area to available land area)decreases from the city center to the periphery.Taking the distance decay law as an entry point,we first proposed a Geographic Meta-process Model(GMP model)quantifying the macroprocesses of urban land growth.Then we quantified the macro-process of urban physical elements and social elements based on the proposed GMP model,which is the key to further understanding urban growth.Then we analyzed the macro-process mechanism of urban growth from the perspective of self-organization theory.Finally,coupled macro and the micro model predicts the future demand for urban land growth and simulates the spatial distribution of urban land in multiple scenarios,and predicts the growth of urban multi-elements.The main conclusions are as follows:1.It is a common phenomenon that urban land density declines with the increase of distance from the urban center.The geographic meta-process model can quantitatively characterize the decline of urban land density and describe the macro process of urban land growth.(1)We first use the urban land density distribution data of 112 cities in the world in 1990,2000,and 2014 to explain the distance decay law of urban land density.(2)Taking urban land density as a spatial variable,a geographic meta-process model(GMP model)is proposed based on the following principles: From a spatial perspective,urban growth can be regarded as the accumulation of continuous geographic meta-processes,each process leads to the urban land expansion and increase of urban land density in the remaining available space;the probability of new urban land following the law of distance decay from the city center to the city edge.(3)The results of fitting urban land density in 112 cities around the world in 1990,2000,and2014 show that the GMP model not only fits well the spatial distribution of urban land density but also measures the intermediate process of urban land growth.(4)An international comparison of urban compactness shows that cities in developing countries and regions,such as Latin America and the Caribbean,Sub-Saharan Africa,and South and Central Asia are generally more compact,and the urban land in developed countries with rich land resources are more dispersed.From 1990 to 2014,the urban compactness of most sample cities remained stable over time,indicating that compact cities are more likely to grow in a compact pattern,while sprawling cities are more likely to continue a decentralized expansion pattern.It reflects the path dependence and historical inertia of the urban expansion pattern.2.The densities of urban physical elements and social elements decrease with distance,but the density of social elements decreases significantly faster than physical elements.Social elements are usually more concentrated than physical elements.Taking the Chinese major cities Beijing,Shanghai,Guangzhou,and Shenzhen in 2015 and 2017 as examples:(1)we proposed an improved local contour tree method to identify the hierarchical structure of the centers of urban multi-elements.The physical elements and social elements both exhibit a multi-center structure,but the spatial development of social elements lags behind the expansion of physical elements.(2)Using the GMP model to fit the density distribution of urban multi-elements,it is found that the density of physical elements and social elements both show a significant downward trend with the increase of the distance from the city center,but the density curve of social elements decreases faster than physical elements.(3)From 2015 to 2017,the simulation of the macro process of urban multi-element growth found that urban multi-element compactness is stable over time,that is,urban elements with compact forms tend to grow in a compact pattern,while elements with sprawl forms are more likely to grow in a decentralized pattern,which also reflects the path dependence and historical inertia of the macro-process model of urban multi-factor growth and is consistent with the conclusions of Chapter 3.(4)An analysis of the spatial distribution and agglomeration degree of urban multi-element found that the social elements have a higher agglomeration degree than the physical elements in both the macroscopic spatial pattern and the distribution of circle density.3.The growth of urban elements shows the characteristics of self-organization and fractal.The difference in the macro-process of the growth of different factors is determined by the different superposition of in unit space: the superposition of elements in unit space is high,the concentration degree is high.(1)First,based on the spatial attraction mechanism and sand pile model from the perspective of urban selforganization growth,the theoretical assumptions of the macro-process mechanism of the growth of different urban elements are proposed.Then the spatial attraction-sand pile city model is proposed.According to the theoretical model,the multi-factor growth of cities is simulated,and the 207 cities in China is used to verify the correctness of the theoretical explanation of the macro-process mechanism of multi-factor growth in cities.(2)As the spatial superimposition degree of the simulated urban elements increases,the fractal dimension decreases and the degree of spatial concentration increases.The simulation results are consistent with the model assumptions.When the urban space can be superimposed(a single grid can accommodate more particles),urban elements tend to be concentrated in the central area,resulting in an increase in the degree of concentration.(3)When the urban transportation level is higher,the radius of interaction or survival of various elements is larger,there will be more likely to exist in the periphery of the city,then the degree of spatial filling of the elements will increase,and the concentration degree will decrease.(4)The high-quality spatial location data and land-use data of 207 prefecture-level cities in China are used to verify the macroprocess mechanism analysis theory of urban multi-factor growth.The empirical results show that physical elements can be superimposed with low degree,the two-dimensional plane space distribution is highly filled,and the concentration is low;the social space element is high in superimposition degree,and concentration degree is high.4.Urban elements are predicted and simulated under multiple scenarios by coupling macro and micro models.(1)Using the land use data of Wuhan in 1989,1995,2001,2007,2011 and 2016,and using the GMP model to quantify the characteristics and laws of the macro-process of urban expansion,urban land growth and population growth have a strong positive correlation,showing an exponential growth relationship.(2)Based on the macro process law of urban land growth in Wuhan,based on the predicted population of Wuhan in 2030,three growth scenarios(compact pattern,sprawl pattern,and average pattern)are forecasted.The amount of urban land growth under the compact model is significantly lower than that under the sprawl expansion pattern.(3)Coupling the macro and micro model,we simulate the spatial distribution of urban land in Wuhan under multiple scenarios in 2030.Finally,on the basis of reviewing the land growth patterns of major cities,it is proposed that the compact pattern is the development path choice for future urbanization of land.