| Land-use change and fossil fuel consumption by rapid urbanization have severely affected the global carbon metabolism cycle.These also have influenced global climate change and the greenhouse effect.Since the high strength and complexity of the urban carbon metabolism,it plays an essential role in the global carbon metabolism cycle.Rapid urbanization is one of the main factors driving the continuous increase in carbon emissions in China.Currently,as the world's largest carbon emitter,China is faced with severe pressures to reduce emissions.To achieve the new-type urbanization development,it is essential for the government to coordinate the relationship between economic growth and low-carbon development,and build low-carbon cities effectively.In the process of urbanization,human activities such as energy consumption,industrial structure,and economic growth model are closely related to the form of land use.To some extent,reasonable urban land use management has a significant role in reducing emissions.Hence,to understand the urban carbon metabolism system on the perspective of land use could guide urban low-carbon development through land planning,industrial adjustment,urban spatial industry layout,and so on.Previous studies on urban carbon metabolism have been focused on the metabolism process among social and economic sectors and ignored the spatial pattern of the carbon metabolism process.In this way,these results could hardly regulate the critical nodes of carbon metabolism spatially.Meanwhile,existing studies on urban carbon metabolism are mainly black box studies,mostly focusing on carbon emissions and carbon sink accounting.Few studies have opened this black box to reveal the essential characteristics and operational mechanisms of carbon metabolism within urban systems.In addition,the lack of energy balance sheets at the municipal level,the research scale of urban carbon metabolism in China is relatively simple.Most current researches concentrated on the provincial and national scales.As a result,it lacked a multi-scale analytical framework at the city level,which was not conducive to the coordinated promotion of carbon reduction by multi-level primary government.On this basis,this study proposes a research framework to combine land use and urban carbon metabolism effectively,and analyzes the urban carbon metabolism process and forecasts the emission reduction potential from the macro/micro-scale.The macro/micro-scale focuses on the urban level and the sub-district level(Jiedao in Chinses),respectively.This study firstly reveals the spatial-temporal evolution of use carbon emissions and carbon sinks from 1995 to 2015 at the macro-scale,and the spatial characteristics of urban residents'travel carbon emissions in 2015 at the micro-scale.In this way,it helps to understand the effects of land-use changes on urban carbon metabolism.Based on this mechanism,the carbon flow model was constructed to track the carbon element transfer process.The self-regulation characteristics of the metabolic system are checked according to the law of biological metabolism.Then,considering the important role of urban form in the process of carbon metabolism,the relationship between urban form and carbon emissions at macro/micro scales is analyzed through econometric models.Finally,based on the simulation of urban expansion,setting target year as the final year of territorial spatial planning(2035),scenario simulation is used to forecast the urban carbon emission reduction potential at macro/micro scales.The main research and results have been concluded as follows:?:The spatial and temporal characteristics of urban emissions and carbon sinks at the macro/micro-scale:(1)At macro-scale:the corresponding relationship between land use types and different carbon emission projects was established.The spatial and temporal distribution of carbon sinks and emissions of varying land-use types in Hangzhou from 1995 to 2015 were calculated by the IPCC inventory method and empirical coefficient method.The results showed that the total carbon emissions of Hangzhou increased by 4.47 times from 297.78×10~4tC in 1995 to 1601.6×10~4tC in 2015,and the increase was mainly from carbon emissions on industrial land and the urban road and transportation land.From 1995 to 2015,carbon sinks showed a slight downward trend,which decreased by 22.29%.In addition,carbon sinks could only offset 0.66%of the total carbon emissions in the study periods.Spatially,high carbon emissions had shifted from the urban center to the southeast and east,and high carbon sinks were clustered in the northwest.(2)At the micro-scale:The carbon sinks accounting still uses the empirical coefficient method.The carbon sinks were still accounted by the empirical coefficient method,and the carbon emissions were focused on that by urban residents'daily travel on the urban road and transportation land.Based on taxi GPS data,carbon emissions by urban residents'daily travel on the main time periods(6:30-9:30,10:30-15:30,17:30-21:30 and 22:00-24:00)of a typical working day in Hangzhou were accounted by combining the questionnaire data of residents'travel modes,the specific power model of motor vehicles and the carbon emission coefficients of different travel modes.The results show that the total amount of urban residents'carbon emissions on the main time of a typical working day in 2015 was17819.12kg,and the peak emissions period was 6:30am-9:30 am.High carbon emission areas are distributed in the east,southeast,and northwest of the urban core area,and high carbon sink streets were distributed in the southwest.Carbon sinks can offset 91.89%of the total daily travel carbon emissions on the main time of a typical working day.The sub-districts with the largest value of carbon budget were concentrated in the east-central area of the urban core area.?:The processes of urban carbon metabolism process at the macro/micro-scale:(1)At the macro scale:the carbon flow by land-use changes during 1995-2015 was quantitatively tracked.And the mutualism index(M)was constructed by the ecological network utility analysis method.The M value could be used to evaluate the comprehensive effects of land-use change on urban carbon metabolism.Based on Kleiber's law of biological metabolism,the relationship between carbon emission intensity and urban size was analyzed through the panel data model.The self-regulation characteristics of urban carbon metabolism were discussed under the results of the panel data models.The results showed that from 1995 to 2015,the total amount of the negative carbon flow by land-use changes was 6.5 times the total amount of the positive carbon flow.Nearly two-thirds of the negative carbon flow came from the conversion of cultivated land to industrial land.The positive carbon flow mainly comes from the conversion of industrial land to urban other construction lands,which accounts for 70%of the total.The average value of M was less than one throughout the study period,indicating that land-use changes exacerbated urban carbon metabolism disorders.The results of the self-regulation characteristics analogy show that the relationship between the carbon emission intensity and the scale of urban land size was in line with Kleiber's law.The sublinear relation between them indicated that the higher level of landscape urbanization could more effective in the low carbon cities.(2)At the micro-scale,the study focused on whether the relationship between the carbon emission intensity by urban residents'daily travel and the scale of urban land size was in line with Kleiber's law.Meanwhile,through the control variable model,the effect of the coordination relationship between landscape and population urbanization on the emission reduction was discussed.The results showed that the carbon emission intensity and the scale of urban land size showed a near-linear relationship,which didn't conform to Kleiber's law.However,when the population density was controlled,the above relationship was in line with Kleiber's law.Carbon emission intensity by urban residents'daily travel declined as population density increases.And the benefits from the added density(such as trip savings or shortening)overshadowed the effects of urban expansion.The regression model results show that when landscape urbanization and population urbanization increased simultaneously,the emission reduction effect of population density growth could be well-reflected.However,when the speed of population urbanization was far behind that of urban expansion,the emission reduction effect brought by the population urbanization would be offset by that of landscape urbanization.?:The relationship between urban form and urban carbon emissions:(1)At the macro scale,the urban form was described from urban land use landscape pattern,and the coupling relationship between urban road distribution and urban form.And the panel data model was applied to analyze how urban form influenced urban carbon emissions.The results showed that the increase of urban construction land patches mainly led to the carbon emissions growth,and the promotion of the agglomeration degree of construction land patches contributed to reducing emissions.The higher the coupling degree between urban road distribution and urban form could lead to lower carbon emissions.The maximum patch index of construction land was positively related to carbon emissions growth,which indicated that the mononuclear urban form was not conducive to emission reduction.It reflected that compact with multinuclear urban form,and the better coupling relationship between urban road distribution and urban form contributed to emission reduction.(2)At the micro-scale:with multi-source data,the urban form at sub-district level was described from density,diversity,and road characteristics.The polynomial regression model and geographically weighted regression model were applied to explore the relationship between urban form and carbon emissions by urban residents'daily travel.The results showed that promoting road area ratio and land mix level,and reducing degree of occupational-residential segregation could help to emission reduction.Moreover,the effects of land mix level and road area ratio on travel carbon emissions had spatial non-stationarity.Improving land mix levels of inner-ring sub-districts in the urban core area and increasing road area ratio of sub-districts on the southwest,northwest,and northeast could effectively promote emission reduction.?:Scenario simulation of urban emission reduction at macro/micro scales in 2035:(1)The spatial patterns of urban land use in Hangzhou in 2035 under two scenarios of inertial scenario and the innovation scenario were simulated by FLUS model.On this basis,(1)At the macro scale:scenario simulation of carbon emission of urban construction land in Hangzhou in 2035 was carried out.And results reflected the emission reduction effects of land use control and emission reduction measures.The former included urban expansion control and land structure adjustment,and the latter contained technological reform,green low-carbon travel,and other measures.The results showed that under the inertia scenario,Hangzhou's carbon emissions reached5.67×10~7t in 2035,which was 3.68 times higher than that in 2015.Under the effective control of urban expansion,strict implementation of low-carbon land use plans and implementation of emission reduction measures,the carbon emissions of innovative emission reduction scenarios reached 2.63×10~7t in 2035,which was 53.62%lower than the inertia scenario.Meanwhile,the carbon emissions per unit GDP reached the current level of the developed countries in the world.This showed that the combination of low-carbon land-use plan and emission reduction measures was a guaranteed way to realize the emission reduction.(2)At the micro-scale:Based on the results of spatial pattern simulation of urban land use in Hangzhou in 2035,the effects of control of urban expansion and optimization of urban form optimization on carbon emissions by urban residents'daily travel were discussed.The results showed that in the inertia scenario,carbon emissions by urban residents'daily travel in the main period of a typical working day in 2035 reached 78404.13kg,which was 4.4 times of that in 2015.Under the effective control of urban expansion and optimization of urban form,this part of carbon emissions reached 45260.56 kg in 2035,which decreased by 42.27%compared with the inertial scenario.This reflected that the effects of urban land use control on emissions reduction effects were apparent.For one thing,this study greatly enriches the theoretical research system of urban carbon metabolism.For another,it expands the research dimension of urban carbon metabolism.The macro/micro research provides an essential reference for the formulation and implementation of emission reduction policies to the different levels of government. |
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