Carbon Cycle Of Urban Eco-economic System And Its Regulation Through Land Use Control

Presently, under the pressure of climate change and international carbon emission reduction, how to coordinate the relationship between economic development and environmental protection, promote carbon emission reduction and develop low-carbon economy have been the most important problems confronting China’s development. Therefore, Chinese government definitely proposed the carbon emission reduction aim as "carbon emission intensity per GDP in 2020 decreases by 40 to 45 percents than that of 2005." Cities are areas where human economic activities concentrate in, in which land use and land cover changes drastically. With energy consume and fossil fuel combust intensively, the process of urbanization is bound to have a profound impact on global carbon cycle and climate change. Currently, China is in the process of quickly urbanization. Quantitatively estimating the urban carbon cycle processes not only help to establish urban carbon emission inventory standard, but also help to understand the role of urban carbon cycle in the process of regional carbon cycle process. Research on urban carbon cycle not only is the important basis of establishing low-carbon urban strategies, but also is the theoretical reference for establishing low-carbon city pattern for china’s actual conditions. Meanwhile, studying the regulation of urban carbon cycle through land use control is help to guide the low-carbon city development through territorial development, industrial adjustment, land use planning, cities and towns’arrangement and urban development pattern. This is the inevitably requirement of low-carbon development on the city level. In this context, carbon cycle of Urban Eco-economic System (UEES) and its regulation through land use control becomes an urgent research programme.Based on the summarization of research situation of carbon cycle in UEES in China and abroad, the dissertation established the theoretical framework of carbon cycle of UEES and its regulation through land use control. Then the dissertation put forword the estimation methods of carbon budget of UEES, carbon cycle of UEES, land use carbon budget and carbon effect, and land use regulation method of carbon cycle of UEES. Then, take Nanjing city as the case, the dissertation studied the carbon cycle process of UEES, and analyzed the carbon emission, carbon flux and carbon footprint of different land use types, and also analyzed the carbon emission effect of land use change. Finally, several low-carbon urban management strategies based on land use structure optimization results of Nanjing City was put forward. The main conclusions are as following:(1) The estimation method of carbon budget of UEES of Nanjing city was established, the carbon storage, carbon flux and carbon circulation of UEES of Nanjing city was systematically estimated, and the carbon cycle process of UEES of Nanjing city was preliminary analyzed. As to carbon storage and carbon flux, the results showed that the total carbon storage of Nanjing city is 6937×104t, in which the natural carbon storage account for 88%, the human carbon storage account for 12%. The human storage increased drastically from 1996, which was caused by the increase of carbon stored in building wood and urban greenbelt. The main carbon flux processes of Nanjing city are lateral carbon input and vertical carbon output, which is brought by human activities. And the proportion of the natural carbon sequestration and natural carbon emissions in total carbon flux is relatively low.As for inner carbon circulation of Nanjing UEES, the main parts are industrial processing system, urban living system, rural living system and agricultural producing system etc. The carbon come from industrial processing system mainly flow in other parts of UEES in the form of energy and products. Urban living system accept most carbon inner input, such as the energy products come from industrial processing system, food products come from agriculture producing system, and wood products come from outer city system. The carbon output from Nanjing UEES is mainly in the form of energy products, wastes and aquatic products.As for carbon circulation between urban and rural areas of Nanjing city, the direct carbon flow from rural area to urban area is wood and food products, and the direct carbon flow from urban area to rural area are mainly energy. In general, the carbon flow from urban area to rural area of Nanjing city is obviously more than carbon flow from rural to urban area. The indirect carbon (Embodied Carbon) flow from urban area to rural area in the form of industrial products is 121×104t in 2009.(2) Carbon budget and carbon cycle pressure of Nanjing city was assessed, and found that the carbon cycle efficiency is increasing but the total carbon sink of Nanjing city present a declining trend, which caused the decline of carbon compensation rate, expansion of carbon footprint and increase of carbon cycle pressure. The carbon cycle efficiency of Nanjing city was promoted mainly because the decline of per GDP carbon emission and the increase of carbon productivity. The decreasing of carbon sink of Nanjing city mainly caused by the decrease of carbon sinks of cropland ecosystem. Further, anthropogenic carbon emission amount of Nanjing city is much more than total carbon sink. The carbon compensation rate decreased from 15.34% in2000 to 6.07% in 2009, which indicate that the terrestrial carbon sink function of Nanjing city are not enough to compensate the anthropogenic carbon emissions, which caused the increase of carbon cycle pressure. The result of the dissertation also indicates that the carbon footprint and carbon deficit are both present a increasing trend. The carbon deficit of Nanjing city in 2009 is 678×104t, which is more than ten times of land areas of Nanjing city.(3) The matching relationship between land use type and carbon cycle process was established, the carbon storage and carbon flux of different land use type was determined, and Nanjing city as the case was studied. Results showed that the per unit area carbon storage of Nanjing city increased from 95 t/hm2in 1996 to 105 t/hm2in 2009. The total carbon storage of inhabitation, mining and manufacturing land is 2631×104t, which account for 38 percents in total of Nanjing city, and per unit area carbon storage is 184t/hm2. High carbon emission intensity of inhabitation, mining and manufacturing land is mainly caused by the increase of carbon stored in residential building wood and urban greenbelt, and the increase of carbon storage on per unit building area that brought by the rising of plot ratio of buildings. Carbon fluxes of per unit area of Nanjing city present an obviously increasing trend. Carbon input and output amount from inhabitation, mining and manufacturing land is the highest, the intensity of which is 218.65t/hm2 and 230t/hm2 respectively in 2009. This indicated that for the high concentration of human activities, the carbon flowing in Inhabitation, Mining and Manufacturing land is much more than other land use types.(4) The carbon emission effect of different land use types of Nanjing city was assessed, and found that carbon emission intensity, effect and footprint of different land use types of Nanjing city are quite different from each other. Anthropogenic carbon emissions of per unit area of Nanjing City is 46.63t/hm2, in which that of inhabitation, mining and manufacturing land is the highest(200.52 t/hm2). carbon footprint Per unit area of Nanjing city present a increasing trend from 2000 to 2009, in which that of inhabitation, mining and manufacturing land is the highest(47 hm2/hm2). The carbon source intensity of Nanjing city quickly increased and the carbon source intensity is 16 times of carbon sink intensity. As to the different land use types, the carbon source intensity of inhabitation, mining and manufacturing land is the highest, and the carbon sink intensity of cropland is the highest(4.73 t/hm2). Different land use types have different carbon emission elasticity. The carbon emission will increased 427t with one hectare addittion of inhabitation, mining and manufacturing land. This indicated that inhabitation, mining and manufacturing land is the most important anthropogenic carbon emission source.(5) Carbon emission increasing was impacted by many factors. In general, economic development, population and urban expansion are the main promoting factors among others. Factor decomposition result indicates that industrial carbon emission intensity of Nanjing city has an inhibitory action on the increase of carbon emission, and other factors such as economic development, population and industrial structure effect all has a promoting action. Factor decomposition of land use carbon emission of Nanjing city indicated that except for per GDP land use intensity, all the other factors such as economic development factor, land use carbon emission intensity and land use structure are positive factors, i.e., are the promoting factors for carbon emission increasing. Further, the regression analysis showed that the determinant factors of carbon emission are increasing of GDP, population and expansion of urban construction land.(6) Land use structure optimization and land use extent regulation are important strategies to facilitate carbon emission reduction. As to the land use structure regulation and control, land use structure optimization scheme base on lowest carbon emission (LUSOS-LCE) can efficiently facilitate carbon emission reduction, and the carbon reduction rate is about 8.5%. Under land use planning scheme of Nanjing city in 2020 compared with the land use structure in 2005 (base line), the carbon storage increased 344×104t, carbon emission increased 1294×104t and carbon sink decreased 3.4×104t. As to t LUSOS-LCE compared with the land use structure scheme in 2020, the carbon emission decreased 73×104t, and the carbon emission reduction potential is 8.5% percent of total carbon emission of 2020. If considering the carbon storage and carbon sink of Nanjing city under LUSOS-LCE, the carbon emission reduction and carbon sink increase totally will reach 148×104t, which showed that LUSOS-LCE scheme is the best land optimization scheme to add carbon sink and reduce carbon emission and it is obviously better than the land use structure optimization scheme based on highest carbon storage (LUSOS-HCS) and lowest carbon sink (LUSOS-LCS). Furthermore, restraint of land use extent also has a high carbon emission reduction potential.(7) Establishing low-carbon oriented land use regulation and control system is the important way to decrease urban carbon emission and strengthening the urban abilities to adapt climate change. The main low-carbon oriented land use strategies are strengthening ecological protection and enhancing the carbon sink function of city, optimizing land use structure and decreasing urban carbon footprint, exploring low-carbon land use patterns and technologies, low carbon planning and establishing policy guarantee system for low-carbon land use, etc.