Green Infrastructure and Climate Change: A One Water Approach

Scott Turner and David Rouse

Scott Turner, PE, AICP, LEED AP ND is Director of Planning at Environmental Partners in Quincy, MA. We co-wrote this article for the American Planning Association’s Water and Planning Network.

Over the last 20 years the term green infrastructure has taken on a range of meanings and different scales of application in planning and design practice. Mark Benedict and Ed McMahon of The Conservation Fund defined green infrastructure as “a strategically planned and managed network of wilderness, parks, greenways, conservation easements, and working lands with conservation value,” typically at the regional scale (Benedict and McMahon, Green Infrastructure: Linking Landscapes and Communities, Island Press, 2006). More recently, the U.S. Environmental Protection Agency (EPA) defined green infrastructure as “a stormwater management approach that mimics natural hydrologic processes,” typically at the local and site scales. Common to both definitions is the notion that green infrastructure provides environmental, economic, and social co-benefits.

Applications of green infrastructure – be they regional or site-specific – are becoming more widespread. At the same time, climate change concerns have become prominent in our day-to-day lives and green infrastructure has become an acknowledged climate change adaptation strategy. The American Planning Association’s (APA’s) Water and Planning Network calls for planners and allied professionals to adopt an integrated approach to water resource management known as “One Water.” This narrative describes the role that green infrastructure can play in helping our cities and regions address the impacts of climate change within the context of One Water. While the focus is on adaptation, it should be noted that green infrastructure can also play a role in climate change mitigation (e.g., by sequestering carbon).

As the earth’s temperature continues to rise, the impacts of climate change have become more apparent. Projections regarding these impacts are continually being developed and updated based on factors such as carbon emission scenarios, population, land use/land cover, and transportation patterns. The International Panel on Climate Change (IPCC), comprised of scientists and climate change experts from industry and nongovernmental organizations, has studied and reported on climate change causes, impacts, mitigation, and adaptation since 1990. The IPCC is currently updating its “Climate Change 2014: Synthesis Report” and is scheduled to next release a comprehensive report in 2022. The IPCC’s most recent reports, “Special Report on Climate Change and the Land” (August 2019) and “Special Report on the Ocean and Cryosphere in a Changing Climate” (September 2019), are available at https://www.ipcc.ch/reports/.

Cities throughout the world are producing climate change studies and planning documents . U.S. cities such as Boston, New York, and San Francisco, among others, are evaluating the long-term impacts of climate change and exploring ways to adapt and become more resilient to climate change. These impacts are difficult to quantify and are largely dependent on our ability to cut global carbon emissions. However, virtually all studies project significant impacts at the local scale, for example increased flooding due to more intense storm events and (in coastal environments) sea level rise and storm surge.

Impacts such as increased flooding and more severe droughts will significantly affect water resources. Although drinking water, wastewater, and stormwater have traditionally been addressed in separate professional “silos,” the interrelated nature of water resources is prompting planners and water professionals to think of water more holistically. PAS Report 588, Planners and Water (Cesanek, Elmer, and Graeff, APA 2017) describes One Water as the idea that “all water within a watershed is hydrologically interconnected and is most effectively and sustainably managed using an integrated approach.” For example, the quality of stormwater runoff contributes to the overall water quality of rivers, streams, and wetland resources. These resources in turn impact the quality of water supplies. High rates of runoff generated by significant storm events result in  increased erosion and sedimentation, which impacts the quality of water resources and therefore drinking water supplies, as well as increasing downstream flooding.

Traditional grey infrastructure systems collect and rapidly convey stormwater downstream, typically with little or no treatment or detention, thus exacerbating downstream flooding. Older cities such as New York, Philadelphia, Boston, and Washington, DC have combined storm-sanitary sewer overflow (CSO) systems. During high rainfall events, storm sewers overflow into the sanitary sewers, resulting in mixing of stormwater with untreated sewage and water quality degradation when they discharge into rivers and streams. In instances when CSO water is stored and then pumped to a wastewater treatment plant, additional stresses are placed on the facility. The likelihood of combined sewers mixing sanitary and storm water increases as the intensity of storm events – exacerbated by climate change – increases.

Many water and wastewater treatment plants, which are considered critical infrastructure systems, have been built in low-lying areas in close proximity to water supply sources and wastewater discharge outfalls. Facilities located in or near floodplains or in coastal areas subject to sea level rise and storm surge are particularly vulnerable to higher intensity storms exacerbated by climate change.

Green Infrastructure as a Climate Change Adaptation Strategy

While the concept of green infrastructure was developed independently of concerns about the impacts of climate change, it is finding widespread application as a climate change adaptation strategy across scales, from region to city, neighborhood, and site. Viewed as a regional open space network that conserves natural ecosystem values and provides benefits for people, green infrastructure can build resilience to shocks (e.g., major flooding events) and stresses (e.g., rising temperatures) associated with climate change. For example, preservation of forested lands in the upper reaches of a watershed both increases groundwater recharge, thus improving the quality and quantity of drinking water supplies, and reduces runoff into rivers and streams that contributes to downstream flooding.

The Regional Green Infrastructure Framework developed for the Greater Baltimore Wilderness Coalition (GBWC) by a team led by The Conservation Fund, with APA as co-principal investigator, demonstrates how green infrastructure can be used as a climate change adaptation strategy at the regional scale. Prepared with the support of a Hurricane Sandy Coastal Resiliency grant administered by the National Fish and Wildlife Foundation, the framework identified the following five strategies for using green infrastructure to enhance community and regional resilience to coastal storms and climate change.

1. Natural Resource Protection: Preserve lands with valuable and vulnerable resources providing hazard mitigation and other co-benefits, including floodplains, wetlands, forest, stream systems, steep slopes, hydric and highly erodible soils, and important habitat areas.
2. Urban Forest Enhancement and Restoration: Maintain, enhance, and restore tree canopy in urban and suburban communities to reduce stormwater runoff, ameliorate the urban heat island effect, and improve air quality.
3. Multi-Benefit Green Stormwater Infrastructure: Retrofit developed areas to reduce impervious surface and incorporate best management practices such as bioretention areas, green streets, and green roofs in order to reduce vulnerability to flooding.
4. Critical Infrastructure Protection: Use green infrastructure to reduce extreme weather risks to critical infrastructure, including key transportation corridors, power production and transmission facilities, hospitals, and emergency management centers.
5. Coastal Defense: Preserve/restore natural habitat and introduce nature-based practices (e.g., living shorelines) to protect against coastal flooding, storm surge, and sea level rise.

At the local/site scale, many cities are implementing green stormwater infrastructure as a climate adaptation strategy (equivalent to the GBWC’s regional resilience strategy #3). New York City, Washington DC, Philadelphia, and Boston are currently working towards complying with EPA Consent Decrees that require a reduction in combined sewer overflows to nearby rivers and streams. Green stormwater infrastructure plays a significant role in each city’s strategy to reduce CSO discharges.

In New York City, for example, the New York City Department of Environmental Protection (NYC DEP) is constructing thousands of rain gardens/bioswales throughout the city. These installations collect stormwater close to where it is generated, treating and infiltrating it into the ground before it can be discharged to the City’s combined sewer overflow system. While the rain gardens do not completely eliminate stormwater discharge to combined sewers, particularly during larger rainfall events, they do reduce the amount and frequency of stormwater discharge and preserve capacity in the existing grey infrastructure system by removing the first 1-2 inches of rainfall. The majority of smaller storms (about 90% of all storms) can be handled by the rain gardens, thus reducing downstream discharges, flooding, and erosion and sedimentation impacts. Effectively, this citywide network improves capacity in the existing grey infrastructure system to handle storms with increased intensity as a result of climate change. The NYC DEP has spent over $600 million on its green infrastructure program since 2012 and has committed over $1 billion through 2029 to expand this system.

Philadelphia and Washington, DC have invested similarly in meeting water quality goals. Philadelphia has implemented its “Green City, Clean Waters” program to manage stormwater by building and maintaining public stormwater infrastructure and by regulating private development.  Green City, Clean Waters calls for an investment of $2.4 billion over the next 25 years in public infrastructure. Green City, Clean Waters is increasing green stormwater infrastructure in Philadelphia, making it a significant portion of the EPA mandated goal to reduce the amount of polluted stormwater overflows discharging into the creeks, streams, and rivers by 2035. By using green stormwater infrastructure, residents will not only see clean water improvements, but also other “triple bottom line” benefits, including more green spaces, reduced heat island effects, and more local jobs to maintain the sites. 

Rain gardens are not the only site-specific green stormwater infrastructure strategy utilized to adapt to climate change impacts. Other strategies include bioretention basins, pervious paving systems (such as pavers, asphalt, and concrete pavement), rainwater harvesting cisterns, underground infiltration systems, and green roofs. These systems collect stormwater runoff at its point of generation, thus preserving downstream water quality and reducing erosion and sedimentation impacts. Installing different types of green stormwater infrastructure in sequence enhances water quality treatment, infiltration, and reduces discharges to CSO systems or downstream water resources.

In addition to managing stormwater, site-scale green infrastructure mitigates the urban heat island effect by reducing impervious surfaces and increasing vegetative cover in developed areas.  Studies have shown that nature-based solutions such as street trees in urban areas encourage activity along developed streetscapes, thus providing social benefits and stimulating economic development.

Green infrastructure solutions, at both the regional and site scales, are increasingly becoming part of our built and natural environments and important tools to help communities adapt to climate change.  Past approaches to managing stormwater have considered urban stormwater runoff to be a waste product to be collected, conveyed, and discharged without treatment into natural systems.  Collecting, treating, and infiltrating stormwater at its source using green infrastructure approaches provides multiple environmental, social, and economic benefits.  Green infrastructure has already arrived in many of our nation’s older cities.  Over time, as the impacts of climate change become more intense, we will see green infrastructure become an increasingly important adaptation strategy, as part of a One Water approach.