The term 'green infrastructure' is growing broader in U.S. cities

Jan. 7, 2022
A nationwide analysis of the term 'green infrastructure' across 122 U.S. cities found that, while stormwater-specific definitions are still most popular, the term is quickly becoming generalized.

A new nationwide analysis of 122 plans from 20 U.S. cities, published today in Frontiers in Ecology and the Environment, found that many plans fail to explicitly define green infrastructure.

The study is the first systematic review of the use and definition of the green infrastructure concept in U.S. city plans — and the authors suggest that the term may no longer be specific to stormwater infrastructure.

With all of the concepts outlined in the study’s 122 plans, the authors developed a synthetic definition of green infrastructure to guide future research and planning. The authors hoped that a shared definition could help cities and researchers adopt a more consistent view of green infrastructure:

Green infrastructure (GI) refers to a system of interconnected ecosystems, ecological–technological hybrids, and built infrastructures providing contextual social, environmental, and technological functions and benefits. As a planning concept, GI brings attention to how diverse types of urban ecosystems and built infrastructures function in relation to one another to meet socially negotiated goals.

Lead author Zbigniew Grabowski, who completed the work as a postdoctoral associate at Cary Institute of Ecosystem Studies, explained, “Green infrastructure is broadly understood to be a good thing, but many city plans lack a clear definition of what it actually is. Hydrological definitions dominate. This narrow view can limit project funding and cause cities to miss out on vital social and ecological services that more integrative green infrastructure can provide.”

Green infrastructure has its roots in 19th century landscape design. Its original conceptualization was broad, taking in parks, trail systems, gardens, and other natural landscape features that provide benefits for people and the environment. This shifted in 2007, when the U.S. Environmental Protection Agency defined green infrastructure as a set of best practices for managing stormwater, to meet Clean Water Act regulations.

The team’s nationwide analysis explored several aspects of city planning: the type of city plans that define green infrastructure, how it is defined, and the functions and benefits assigned to green infrastructure projects. Twenty medium-to-large U.S. cities, representing the major biomes, were included. 303 different city plans were collected and screened for references to green infrastructure, with 122 meeting criteria for analysis. These included comprehensive/strategic, sustainability, watershed restoration, and climate plans.

Some of the assessed cities included: Atlanta, Austin, Baltimore, Chicago, Denver, Detroit, Louisville, Miami, Milwaukee, New Orleans, New York City, Philadelphia, Phoenix, Portland, Sacramento, San Juan, Seattle, St. Louis, Syracuse, and Washington DC.

The team found that 39 percent of plans that refer to green infrastructure do not define what it is. Of those that do, stormwater concepts predominate (59 percent); followed by landscape concepts (17 percent); ‘integrative’ – which combine stormwater and landscape concepts — contribute 15 percent; and miscellaneous definitions contribute 9 percent.

Across even those plans containing definitions, 57 percent of plans had several different definitions within themselves, indicating that green infrastructure means different things to city planners across the US.

What qualifies as green infrastructure also varied widely. Across GI definitions, the team identifies 693 different types of acceptable installations. The features most commonly included trees (90 percent), rain gardens (75 percent), ‘other stormwater facilities’ (55 percent), blue-green corridors (60 percent), and green roofs (65 percent). Some cities went so far as to include green energy and alternative transportation technologies within their definitions of GI.

Green infrastructure benefits identified by city plans include water quality, recreation, health, city livability, and property value. Across cities, social benefits were those most commonly cited in plans, followed by environmental, economic, built environment, and ecological benefits. Some cities also identified more specific benefits: such as recovery from extreme weather events (in Washington DC), new business opportunities (in Miami), and social revitalization (in Atlanta).

Coauthor Timon McPhearson, a research fellow at Cary Institute and Director of the Urban Systems Lab at The New School, concludes, “The U.S. is poised to make large scale, needed, investments in urban infrastructure. To ensure these investments build environmental resilience in a way that benefits the lives of all urban residents, we’ve put forth a more comprehensive definition of green infrastructure, to guide planning, policy, and practice — with the goal of facilitating more equitable urban greening.”