基于生态网络效用的城市碳代谢空间分析——以杭州为例

城市碳排放占全球碳排放总量的78%,通过模拟生物代谢来剖析城市碳代谢机理从而控制城市碳排放是缓解全球气候变暖危机的关键。为研究杭州城市化过程中土地利用变化对城市碳代谢的综合作用,以4个时间段(1995—2000,2000—2005,2005—2010,2010—2015)为例,建立了一个"碳流"模型来分析城市生态系统中自然和人工分室在城市碳代谢正负"碳流"产生中的作用,之后利用生态网络效用方法分析"碳流"产生的生态关系及其空间分布,同时利用互惠指数M综合评价土地利用变化对城市碳代谢的综合作用。结果显示(1)净"碳流"在研究期间持续呈现负值且在2000—2005年间达到峰值,负"碳流"主要源自耕地与工业用地之间的转换,正"碳流"主要源自工业用地与城市用地之间的转换。(2)1995—2000年互惠指数(M)呈现先增加后减少再增加的变化趋势,M平均值小于1,说明土地利用变化对城市碳代谢的综合作用是消极的。(3)竞争关系集聚在高负碳代谢密度分室,互惠共生关系主要集聚在高正碳代谢密度分室。(4)从1995—2000至2010—2015,以每5年为时间间隔,生态关系分布空间变化如下:掠夺限制生态关系呈现向西北、西南和南部方向蔓延—西北方向移动—东南方向移动的变化趋势,竞争生态关系呈现东南方向移动—南部和西北部方向蔓延—零星分布的变化趋势,互惠共生生态关系呈现向东南方向移动—暂时不存在—零星分布的变化趋势。研究结果为低碳城市发展提供了理论依据。

Analyzing urban carbon metabolism based on ecological network utility: a case study of Hangzhou City

Seventy-eight percent of the total global carbon dioxide emissions come from urban areas, which consume 70% of global energy. Land-use and cover changes contributes one-third of the urban carbon emissions. Thus, understanding the mechanism of urban carbon metabolism through simulating process of biological metabolism could help to control carbon emissions in urban areas; this is the key to mitigating the crisis of global warming. As part of the goal of reducing carbon emissions, the goal of this study was to understand how land use changes during urbanization influenced carbon metabolism. This study used Hangzhou as an example, and developed a spatially explicit model of carbon transfer between components of an urban system, and then used the ecological network utility analysis to explore the structure and function of the network, and determine effects of ecological relationships among components that resulted from carbon flows, their spatial distribution, and their changes over four time periods (1995-2000, 2000-2005, 2005-2010, 2010-2015), and finally used the mutualism index (M) to judge whether land use changes had positive effects on urban carbon metabolism. The results showed that:(1) Based on the empirical coefficient model, the carbon metabolism was determined; the net carbon flow continued to have negative effects during the study period and reached a peak in the period of 2000-2005, which indicated a serious imbalance in the urban carbon metabolism. The negative carbon flow mainly came from the transition between cultivated land and industrial land, and the positive carbon flow was mainly from the transition between industrial land and urban land; (2) During the period 1995-2015, the mutualism index (M), which indicated synergistic effects among components in the urban carbon metabolism, increased at first, then exhibited a downward trend, and finally began to grow again. In addition, the average value of M was less than 1, indicating that the comprehensive effect of land use change on the urban carbon metabolism was negative; (3) Competitive and mutualistic relationships were distributed differently among components of the urban carbon metabolism:the competitive relationships accumulated in negative metabolism components with high carbon emission density, such as industrial land and highway and railway, whereas the mutualistic relationships accumulated in positive metabolism components of high carbon sequestration density, such as forest land; (4) Based on the ecological network utility analysis, the study indicated that the change in the spatial distribution of ecological relationships resulted from carbon flow between components of urban carbon metabolism. For 1995-2000 and 2010-2015 (at intervals of five years), the trends of the three ecological relationships were as follows:the exploitation relationship exhibited changes spreading northwest, southwest, and south, moving towards to the northwest and the southeast; the competitive relationship exhibited trends moving towards the southeast and spreading to the south and northwest in a scattered distribution. The mutualistic relationship exhibited a trend moving to the southeast with a non-scattered distribution. Our research results provide a theoretical basis to plan adjustments to the city''s land use structure to achieve the goal of a low carbon city.