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Research indicates that cities could significantly lower their carbon dioxide (CO2) emissions by optimizing their urban design. However, it is crucial to note that the relationship between urban design and emissions varies across different contexts, making broad generalizations problematic.
With atmospheric CO2 concentrations reaching unprecedented levels, projections estimate that an additional 2.5 billion individuals will move to urban environments globally by 2050. This trend intensifies the urgency for energy-efficient urban planning, given the critical correlations between rising CO2 levels, energy consumption, and climate change.
Despite the pressing need for research focused on energy-efficient urban models, existing studies typically examine urban form on a macro scale, often lacking standardization and focusing on a limited variety of urban characteristics. To tackle this gap, a collaborative team from Hiroshima University, Shiraz University, and Northern Arizona University undertook a detailed study analyzing the impact of urban form on carbon emissions in three distinct U.S. cities.
The findings of their research were published in the November 2024 edition of the Journal of Environmental Management.
“While it is widely acknowledged that urban form influences CO2 emissions, previous studies have largely examined this relationship on a broad level,” noted Ayyoob Sharifi, a professor at the IDEC Institute at Hiroshima University and a co-author of the study. “Our research utilizes the Local Climate Zones (LCZ) framework to explore this relationship at a more granular level.”
The LCZ framework provides a systematic way to categorize urban settings, consisting of ten built types (such as low-rise buildings, high-rises, and heavy industry) and seven natural categories. This framework has proven valuable in assessing urban heat islands. In their study, the research team applied the LCZ framework to classify the urban environments of Baltimore, Maryland; Indianapolis, Indiana; and Los Angeles, California, leveraging satellite imagery and remote sensing techniques.
These three cities were strategically selected based on their differing climates and population densities. Los Angeles experiences a warm, dry climate with minimal temperature variation, whereas Indianapolis is characterized by a cold, humid climate, and Baltimore features a mixed, humid climate. Notably, Baltimore has the highest density of inhabitants, while Los Angeles and Indianapolis share similar population densities, although Los Angeles encompasses a considerably larger geographical area.
The selection of diverse urban environments aimed to assess whether variations in LCZ could explain differences in CO2 emissions throughout the year or across specific seasons, considering both population density and climate factors. CO2 emissions were quantified using data from the Hestia Project, which tracks fossil fuel emissions at street and building levels on an hourly basis within cities.
While the study provided valuable insights into the influence of LCZ on CO2 emissions, the researchers found that drawing general conclusions across these urban settings was challenging. “Our results underscore the intricate and variable nature of the relationship between urban form and CO2 emissions. Variations are influenced by numerous factors, including climate conditions and the particular size and function of a city. Thus, patterns observed in one city are not necessarily applicable to others, which indicates that universal solutions for optimized urban design may not exist,” Sharifi explained.
Crucially, the research highlighted the significance of urban green spaces. “Without well-planned and sufficient open and green areas, even densely populated urban environments may struggle to effectively reduce CO2 emissions,” Sharifi asserted.
The research team is committed to further exploring the connection between LCZ and urban CO2 emissions with the aim of curbing urban reliance on fossil fuels. They propose refining the LCZ framework and investigating additional contributors to urban fossil fuel consumption—approaching specific sectors such as transportation, residential, and commercial—to identify clearer patterns between LCZ categories and emissions.
“Our objective is to expand our studies to include data from a broader range of cities worldwide to enhance our understanding of the association between LCZ types and CO2 emissions across various climatic and socioeconomic landscapes,” Sharifi concluded.
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