In the United States and globally, urban areas are experiencing an unprecedented rate of population growth. More than 80 percent of the U.S. population now lives in urban areas, a number that is expected to continue to increase for the foreseeable future. Globally, since 2007, more than half of the world’s population has been living in urban areas and the figure is estimated to exceed 70 percent by 2050 (UN, 2013). During 2000-2050, developing regions could add 3.2 billion new urban residents, a figure larger than the world’s population in 1950 and double the urban population added during 1950-2000. By 2050, the world urban population could reach a total of 6.25 billion, 80 percent of whom may be living in developing regions, and concentrated in cities of Africa and Asia (UN, 2013).
The concentration of people, investment, and resources in cities has the potential for both positive and negative consequences. Despite the synergy for creativity, innovation, economic development, and social and community well-being, cities also can experience disproportionate levels of air and water pollution, loss of biodiversity, and increased rates of concentrated poverty. Cities also face challenges that can overwhelm their efforts to achieve sustainability. For example, sustainable1 urban areas require improved access to public services, renewable as well as conventional sources of energy, adequate employment for their residents, equity both economically and culturally, as well as increasing resilience against the growing impact of natural hazards. In addition, growing urban populations place increasing stress on existing infrastructure and demand for new infrastructure, while aging and deteriorating infrastructure creates further waste and inefficiencies within cities; however, addressing such challenges is hindered by financial stresses and competition for monetary resources that pressure many government budgets (Global Cities Institute, 2015). Sustainability must also consider the enormous flows of materials, energy, financial resources, and wastes into and out of cities. Despite these challenges, urban centers have the potential to capitalize on their growth and innate diversity in becoming the world’s leading lights in terms of sustainability.
The definition of a city, let alone a “sustainable city,” is controversial. Cities are extremely diverse in terms of their size, spatial structure, employment patterns, level of economic development, natural resource availability, and social fabric. In addition, each country defines a city according to its own criteria, including a combination of administrative, population size or density, economic, and urban characteristics (e.g., paved streets, water-supply
1 In the United States, sustainability is commonly defined as follows: “to create and maintain conditions, under which humans and nature can exist in productive harmony, that permit fulfilling the social, economic, and other requirements of present and future generations” (National Environmental Policy Act of 1969 [NEPA, 2000]; Executive Order 13514 [White House, 2009]).
systems, sewerage systems, and electric lighting), while temporal and spatial data gaps make accurate prediction of urbanization and size of city populations difficult (UN, 2013). In the United States, it has become increasingly challenging to delineate urban versus nonurban areas, further complicating how to clearly define sustainability issues and boundaries. As was discussed in a recent National Research Council (NRC) workshop on urban sustainability, the American landscape has become, in a crucial and enduring sense, a single entity: it is borderless, though often a separated amalgam of people and places (NRC, 2010). And in many senses, the country itself is borderless given the enormous flows across its international boundaries.
Several definitions of urban sustainability have been discussed over the years. For example, concepts of a sustainable city were reflected in the 1992 Rio de Janeiro Conference on Environment and Development (UN, 1993). The 1992 Rio Declaration integrated the economic, social, environmental, and governability dimensions of sustainability and argued for the eradication of unsustainable patterns of production and consumption, the eradication of poverty, and the role of the state, civil society, and international community in protecting the environment. Furthermore, in 1997, the Habitat Agenda (UN, 1997), adopted by the United Nations (UN) Conference on Human Settlements, noted similar concerns expressed in Agenda 21 with respect to the multiple dimensions of development, and discussed urban sustainability as requiring a harmonious integration of economic, social, and environmental issues (UN, 2013). In 2002, the World Urban Forum also affirmed that addressing economic, social, environmental, and governance issues was integral to the creation of sustainable cities and noted that the inability to address the integration of these issues would prevent the achievement of sustainable development (UN-Habitat, 2002).
In discussing sustainable development, Satterthwaite (1992) stated, “sustainable cities should meet their inhabitants’ development needs without imposing unsustainable demands on local or global natural resources and systems.” Burger et al. (2012) stressed biophysical constraints at the global level when considering sustainability. In this view urban sustainability is a fluid concept with the goal of devising policies that will improve living and working conditions for present and future generations (NRC, 2010). In the most general terms then, urban sustainability can be thought of as the measureable improvement of near- and long-term human well-being achieved through actions across environmental (resource consumption and environmental impact), economic (resource use efficiency and economic return), and social (social well-being and health) dimensions (Box 1-1).
Although cities concentrate a diverse mix of people and resources, it is also clear that cities themselves are not sustainable without water, energy, raw materials, food, and other resources from nonurban areas, and likewise the regions in which they are located depend on cities for resources. The resources needed to support urban life often originate at great distances from their final points of consumption, thereby extending the spatial reach of their impacts on global climate change. Cities that develop an island or walled-city perspective, where sustainability is defined as only activities within the city’s boundaries, are by definition not sustainable.
Whatever the precise definition, cities across the world are embracing the concept of urban sustainability, including addressing the challenges of rapid population growth and its impacts on limited natural resources. An
impressive number of urban sustainability initiatives are currently under way or planned by local, regional, state, and federal governments; academia; the private sector; and nongovernmental entities.
While there is no single approach to urban sustainability, innovative methods now being developed in some cities may be transferable to others. It is valuable to assess practices being implemented in specific urban and metropolitan regions to determine whether and how they might be adapted and applied in other urban areas. Significant, albeit otherwise unrecognized, opportunities may exist to strengthen collaborative learning across cities to the broader benefit of worldwide urban, and nonurban, communities.
Recognizing the importance and timeliness of these issues, the U.S. Environmental Protection Agency, the John D. and Catherine T. MacArthur Foundation, and the National Aeronautics and Space Administration formally requested that the National Academies of Sciences, Engineering, and Medicine undertake a study that used examples from metropolitan regions to understand how sustainability practices could contribute to the development, growth, and regeneration of major metropolitan regions in the United States. An ad hoc committee was asked to provide a paradigm that incorporates the social, economic, and environmental systems that exist in metropolitan regions that are critical in the transition to sustainable metropolitan regions (see Box 1-2 for the full statement of task). This paradigm could then serve as a blueprint for other regions with similar barriers to sustainable development and redevelopment.
To accomplish its task, the Committee on Pathways to Urban Sustainability held several fact-finding meetings and committee meetings. The first meeting, held in February 2015 in Washington, DC, included presentations from the study sponsors focusing on their interests and perspectives on the topic. As part of its evidence-gathering process, the committee also organized two public data-gathering meetings in different metropolitan regions to examine issues relating to urban sustainability. These meetings were held in April and July 2015. The April meeting focused on sustainability issues in the Los Angeles metropolitan region; the July meeting focused on Chattanooga, Tennessee. These two cities were chosen as the sites for the committee’s public data-gathering meetings due to their diverse characteristics in terms of size, geography, and varied sustainability challenges, such as related to water and air quality. The committee developed an agenda for each meeting in consultation with regional stakeholders so that the invited presentations and discussions reflected place-based knowledge and approaches to sustainability. During these fact-finding sessions, the committee heard speakers from industry, nongovernmental organizations, academia, and local and regional governments on innovative and successful actions cities have undertaken to address their sustainability challenges, as well as approaches that did not have their intended outcome. The committee also heard presentations and received information from key individuals who met with the committee and reviewed a large body of written material on urban sustainability concerns and practices in other cities, including literature that informed the committee on how cities could further strengthen their sustainability efforts. The report is focused on the United States, as required by the statement of task, but also acknowledges global linkages and other urban sustainability efforts in other parts of the world.
After this introduction, this report begins with a chapter on indicators and metrics for urban sustainability intended to guide city profiles and based on a review of a very large literature on urban sustainability indicators. A following chapter describes a set of guiding principles that help to establish the boundaries of an urban system while recognizing the constraints on urban sustainability. The statement of principles is followed by a high-level decision framework, and an urban sustainability “roadmap” that then inspires a series of city profiles, which serve as “guideposts” to highlight the opportunities and challenges in their associated specific urban contexts. The
committee chose to denote this conceptual structure as a framework—an urban sustainability roadmap—rather than a paradigm to better relate to decision-making processes and flows experienced by urban sustainability practitioners and stakeholders. The additional seven city profiles, New York City, New York; Vancouver, British Columbia; Philadelphia, Pennsylvania; Pittsburgh, Pennsylvania; Grand Rapids, Michigan; Cedar Rapids, Iowa; and Flint, Michigan, were selected to reflect the diversity of U.S. urban contexts along dimensions of city size and density,
geographic location, primary industries, and the key challenges to sustainability such as water scarcity, air quality, and social issues. Each profile provides a brief description of an urban area including relevant metrics and then outlines two to three noteworthy sustainability efforts the city undertook along with other relevant issues discovered during the committee’s research. The city descriptions end with a series of observations and recommendations based on that city. The final chapter distills these city observations and recommendations in view of the principles outlined earlier to produce a series of generalizable recommendations for a new approach to urban sustainability.