城市化是影響全球碳循環的最重要的由人類活動主導的影響因素之一。本質上，城市碳儲存和碳釋放，無論以人工的（如能源消耗、建築物、廢物等）或自然組成部份（如城市綠色植被，城市土壤等），都與城市緊密相關。在城市碳循環中，無論人工或自然組成部份都是同等重要，因為在研究中必須同時考慮兩者的貢獻。然而，已有的研究過於片面，且大多數集中于城市能源利用和碳排放方面。該研究試圖將城市系統作為一個整體，定量地探討城市人工及自然組成部份對二氧化碳排放量的貢獻。 / 首先，我們提出一個基於過程的“城市土地的定義，以表述城市土地動態變化的本質，并運用閾值方法成功提取所定義的“城市土地。我們運用多源的遙感數據，包括夜晚燈光影像，LandSat影像及Modis影像，分析城市化過程及相應的土地利用/覆蓋變化。總體而言，在過去25年間，中國城市用地擴張了3.8倍，農田和林地是城市土地擴張的主要來源。 / 其次，以經過校準的夜晚燈光數據作為指示變量，我們開發了一個自上而下的分解模型來估算城市尺度下化石燃料消耗導致的二氧化碳排放。在中國快速城市化的背景下，城市二氧化碳排放量占全國總排放量的比例大幅增加。與農村地區相比，由於較高的收入水平，生活方式的改變及更便利地獲得電力能源，中國城市的人均排放量遠高於全國平均量。這與發達國家的情景截然相反。另外，由於當地經濟規模和結構的影響，東部地區的人均碳排放量低於西部地區。結果還表明，快速增長的經濟和城市化是二氧化碳排放量增加的主要驅動力，且能源效率在2000年之後反而呈現增長趋势，也是促進二氧化碳排放量增加的主要原因。如果國家宣佈并嚴格執行更嚴格的可持續發展目標，則經濟結構及能源結構調整將在減碳方面發揮作用。 / 第三，本研究還根據儲存-變化方法，估算了城市系統的自然組成部份，也就是城市植被和土壤的碳儲存和釋放。結果表明，儲存於城市植被和土壤中碳量與城市化石燃料排放的碳量相當，且城市土壤是主要的碳庫，儲存了約93%的碳。隨著城市不斷擴張，由於大量自然植被被破壞，城市植被變成碳源并向大氣釋放碳；而城市土壤則變成碳庫，吸收了大氣中部份的二氧化碳。鑒於中國未來持續的城市化過程，該研究結果為城市管理者提供了科學依據，以通過提高城市植被和土壤的碳儲量，吸收部份化石燃料燃燒排放的二氧化碳。 / 最後，我們還運用格蘭傑檢驗分析小尺度氣候變量對二氧化碳增加的響應。結果表明，在中國城市化較低地區，氣溫與二氧化碳變化存在雙向格蘭傑因果關係；而在快速城市化地區，如東部沿海城市，僅存在氣溫變化導致二氧化碳排放量增加的單向格蘭傑因果關係。該研究首次在城市尺度解釋了氣候對二氧化碳增量的響應關係。總體而言，本論文綜合地探索了中國快速城市化背景下，城市人工及自然組成部份對二氧化碳排放量的共同貢獻。這些研究結果為當地政府建設低碳城市提供了科學依據和決策支持。 / Urbanization is undoubtedly one of the most significant anthropogenic forces affecting global carbon cycle. Carbon storage and release through anthropogenic (e.g. energy consumption, building, waste) and natural components (e.g. urban vegetation and soil) are intrinsically coupled in urban areas. Both anthropogenic and natural components are equally important for understanding the carbon cycle in urban areas and have to be considered simultaneously. Present studies however mostly one-sided and primarily focus on anthropogenic emissions. Given the substantial scientific gaps, this study aims to build better knowledge on the contributions of urban areas to the increasing atmosphere CO₂ emissions at an urban scale, considering both anthropogenic and natural components simultaneously. / First, a process-based definition of urban areas is proposed to capture the inherent dynamics of urban areas, and a threshold technique is developed to map the defined urban areas in this study. Multi-sensor remotely sensed data are used to analyze the dynamic urbanization and related land use/cover conversions. Overall, urban areas have increased by 3.8 times over the studied period of 1985-2010. Croplands and forests are the major sources of the growing urban areas. / Second, taking calibrated nighttime light imagery as a proxy variable, we develop a top-down model to estimate fossil fuel CO₂ emissions on the urban scale. Driven by the rapid urbanization in China, the contributions of urban areas to the CO₂ emissions have increased substantially. In contrast to the developed counties, per capita CO₂ emissions in urban China are higher than the national average, due to higher income, change in lifestyle and easy access to electricity, whereas per capita CO₂ emissions in eastern China is lower than that in western China, due to the diverse scale and structure of local economy. Our analysis also reveals that the booming economy and urbanization are major drivers of the increasing fossil fuel CO₂ emissions, while the decoupling effect of energy efficiency reverses in the post-2000 period caused by the booming economy. It is foreseeable that economic reconstruction and energy structure would play a significant impact on carbon reduction if stricter environmental targets are released. / Third, carbon storage and change in natural components of urban areas, in particular, urban vegetation and soils, are also estimated in this study. A stock-change method is applied in this study. This study identifies that the amount of carbon storage in urban areas is comparable to that emitted from fossil fuel burning, and urban soils are the major carbon pools in urban areas. Along with urban expansions, urban vegetation becomes sources of carbon due to loss of biomass, whereas urban soils act as sinks of carbon because increasing urban areas enhance the carbon storage in them. Given the foreseeable urbanization in China, our study has implications for urban managers to enhance carbon storage through urban vegetation and soils, hence offsetting CO₂ emissions from fossil fuel burning. / Finally, a local temperature response to the increasing CO₂ in urban areas is analyzed by local Granger causality test. Bidirectional Granger causality presents between surface air temperature and carbon variables in less urbanized regions of China. In the rapid urbanization areas such as eastern coastal regions, only presents the Granger causality from surface air temperature to the fossil fuel CO₂ emissions. This is the first attempt to offer insights of local temperature variables response to the increasing CO₂ across urban China. Our integrated results are novel in exploring the contributions of expanding urban areas to CO₂ emissions across China, including anthropogenic and natural components of urban areas simultaneously. We believe that our findings have clear significance for local governments who strive for constructing low-carbon cities. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Meng Lina. / Thesis (Ph.D.) Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 203-218). / Abstracts also in Chinese.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_1077646 |
| Date | January 2013 |
| Contributors | Meng Lina (author.), Huang, Bo , active 2014 (thesis advisor.), Chinese University of Hong Kong Graduate School. Division of Geography and Resource Management, (degree granting institution.) |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography, text |
| Format | electronic resource, electronic resource, remote, 1 online resource (xix, 218 leaves) : illustrations (chiefly color), maps (chiefly color), computer, online resource |
| Coverage | China, China, China |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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