Relationship between Urban Form and Urban Sustainability

The world is experiencing a rapid urbanization process since decades ago, and more than half of the world’s population now are living in urban areas. United Nations has projected that the population growth in urban areas will continue and result in more than 66% of the population living in cities by the year of 2050. Although cities are bringing economic growth and development across the world, especially in high-income countries, this rapid pace of urbanization has also led to resource depletion and environmental degradation over the past decades, as well as other urban problems, such as urban poverty and social inequality, local climate change, non-renewable energy consumption, Greenhouse Gas (GHG) emission and biodiversity decline, most of which are argued to be associated with fast urbanization and urban sprawling development. Modern societies have adopted sustainable development as the strategic plan and development model to response to the growing economic, social and environmental issues in global environment. An increasing number of research have been done on the topic of sustainable development since the Brundtland Commission Report proposed the definition of sustainable development in 1987. Since then, a limited but growing literature is emerging that looks into the relationship between urban form and urban sustainability, proposing the question of whether there is a sustainable urban form, and if so, how to achieve it. It is now generally accepted that there are correlations between urban form and urban sustainability in a variety of ways, but no consensus has been made. Moreover, potential research gaps exist in terms of the definitions and measurements of both urban form and urban sustainability concepts, as well as there is a lack of systematic and comprehensive theoretical framework on the relationship between urban form and urban sustainability, neither there are enough empirical studies in U.S. context with up-to-date data. By asking the central research question “how and to what extent does urban form influence urban sustainability?”, this dissertation aims at exploring the relationship between urban form and urban sustainability; explaining the mechanisms of the potential correlations by systematically reviewing theoretical underpinnings and synthesizing a comprehensive theoretical framework; empirically examining the relationship between multiple urban form elements with a wide range of urban sustainability outcomes with secondary data; identifying the trade-offs among different dimensions and aspects of urban sustainability under different urban form scenarios; and addressing an identified gap in the literature of a dearth of U.S. empirical studies by conducting an empirical study in a U.S. study area. To fulfill the research objectives, I first conducted a systematic and comprehensive literature review on the research topic, which not only summaries the existing theories, findings and conclusions in the field, but also identifies the potential research gaps in the literature. A theoretical framework on the relationship between urban form and urban sustainability was created to illustrate and visualize the theoretical correlations between a selected group of urban form elements and a wide range of urban sustainability outcomes. Empirical analysis is employed to test the theoretical framework and the hypothesized correlations between urban form elements and urban sustainability outcomes, using the secondary data in Florida at Census Place scale. Multiple regression analyses are conducted for a total of 204 models in economic, social and environmental dimensions of urban sustainability, in three time periods: 2007 and 2012 cross-sectional, and 2007-2012 panel estimation. The results and findings of this dissertation indicate that overall, the central research question of this Dissertation appears to have been answered in the affirmative: urban form is shown in this study to have a statistically significant effect on urban sustainability outcomes. Specifically, the four selected urban form elements: density, concentration, land use mix and connectivity all have significant associations with one or more urban sustainability outcomes in a variety of models. Moreover, this dissertation posits the hypothesis that there are potential interaction effects between urban form elements in terms of their effects on urban sustainability, and the empirical findings support my hypothesis with multiple significant results from models with interaction effects, which contributes to the theoretical understandings on the relationship between urban form and urban sustainability. Besides, there are some expected correlations between urban form and urban sustainability from the theoretical framework that are either show non-significant results, or even with results against the theoretical expectations. These results call for research outside Florida and at different geographic scales to further explore the relationships between such urban form elements and urban sustainability outcomes. Furthermore, the evidences from the empirical analysis in Florida imply that there are some correlations between urban form and urban sustainability, especially between land use mix and a wide range of social and environmental sustainability outcomes, have not been widely discussed in the literature, but showing significant results in Florida places, which also calls for more extensive research. Finally, the research finds that there is no urban form element that is benefiting all urban sustainability outcomes, which indicates the existence of the trade-offs among different aspects and dimensions of urban sustainability. Therefore, there is no straight-forward solution from urban form to improve urban sustainable development, and it has to consider the specific situation in each place, and also promoted with other urban sustainability policies. The completion of the dissertation is able to contribute to theory through the establishment of a comprehensive theoretical framework, the identification of unexpected and under-explored correlations between urban form and urban sustainability, the proposition of the interaction effects between urban form elements and the definition and measurement of urban form. This study is also contributing to practice and U.S. cities by collecting and integrating enormous secondary data at Census Place scale in Florida, the provision of significant evidence on the correlations between urban form and urban sustainability, as well as the discussion on the potential interaction effects between urban form elements, and the trade-offs among different aspects and dimensions of urban sustainability.