How building and street morphology affect CO2 emissions: Evidence from a spatially varying relationship analysis in Beijing

Abstract

Urban morphology plays a critical role in the reduction of CO2 emissions. Despite the growing interest in the relationship between urban form and CO2 emissions in urban sustainable development, few quantitative estimates have been made of the effects of urban morphology considering the combination of three-dimensional (3D) buildings and streets at the neighbourhood scale on CO2 emissions. To explore these effects, this study first proposes a methodological system for computing urban morphology indicators including 3D buildings, streets and their relationships. These morphological indicators quantitatively measure the extension, shape complexity, spatial compactness and irregularity of buildings and streets. Then, the urban morphology indicators and CO2 emissions are calculated for each traffic analysis zone (TAZ) to obtain their characteristics of spatial distribution, using Beijing as the study area. Ultimately, the non-stationary effects of morphological indicators on CO2 are quantified by Multiscale Geographically Weighted Regression (MGWR). The results demonstrate that each morphological factor performs a distinguishable function in different regions. The adjacency ratio, meshedness and width have strongly positive effects on CO2 emissions in the northern part of Beijing within the 6th ring road, while the covered area ratio and the linearity play a crucial negative role, implying that the complexity and sparse layout of buildings and streets are the main drivers to increase CO2 emissions. In the southern part, the length, width STD and height STD pose an apparently positive impact on CO2 emissions, while the openness poses a significant adverse effect, implying that the irregularity and fragment of buildings along streets are the primary reasons for CO2 emissions augmentation. In the densely populated area, the number, floor area ratio, and neighbour distance all exserts a robust positive effect on CO2 emissions. Interestingly, the floor area ratio poses negative effects within the 5th and 6th ring roads, which is a dense industry zone, implying the expansion of buildings can reduce industrial proportion to mitigate CO2 emissions. This study provides insights into CO2 emissions related to micro-scale morphological characteristics and suggests achievable plans for low-carbon physical urban spaces in a spatially varying manner.