This blog post was written by Maddie Monroe as part of the Spring 2018 UGA Urban Ecology class.
As humans increase in numbers and continue to use resources, natural geographic systems and the organisms that rely on them will be increasingly affected by anthropogenic effects (Douglas and James, 2015). Urban Heat Islands are one consequence of how human modification of the environment has affected climate within cities. The heat islands are the warmer urban temperatures compared to the surrounding non-urban areas which is usually due to increased urbanization in the area because of the presence of impervious surfaces (Douglas and James, 2015). When humans modify the geological landscape, they also impact the hydrologic systems due to the implementation of combined sewer systems and impervious surfaces. Climate change scenarios also project that urban regions will have to manage increasing extreme temperatures and precipitation events (Foster et al., 2011). The increases in extreme weather events will also strain the ecosystem services that would be provided by the environment.
According to The Center for Clean Air policy, resilient urban systems are characterized by their “ability to bounce back from impacts,” and include elements of, “flexibility, diversity, sustainability, adaptability, self-organization, self-sufficiency, and learning.” A holistic view for managing the effects of climate change and creating a more resilient urban system could come from the use of green infrastructure. The Environmental Protection Agency classifies green infrastructure as, “us[ing] vegetation, soils, and other elements and practices to restore some of the natural processes required to manage water and create healthier urban environments.”
One way an urban center could utilize green infrastructure is through the implementation of eco-roofs. Eco-roofs are used to respond to extreme precipitation and temperatures, and three different types of eco-roofs exist: green, white, and blue. Green roofs are covered with plants and other vegetation typically on top of a waterproof membrane, green roofs can protect the underlying roofing material from wind damage and UV rays in addition to regulating temperatures outside of the building. The roofs can reduce storm water runoff by 50-60% by channeling the water and allowing the green space to absorb more water, as well as, helping with carbon sequestering because of the increase in green space in urban areas. The largest benefit comes from mitigating the urban heat island effect. Green roofs can reduce surface temperature by 30-60ºC and ambient temperature by 5ºC (Foster et al., 2011).
An example of an effective green roof. Photo credit: Green City Growers
White roofs are great at alleviating rising temperatures as well because they reduce the Albedo effect of traditional roofs. These roofs have been painted white or have reflective material so that the sun’s rays are not absorbed as much into the materials. The white roofs can reflect 80% of the sun’s rays as compared to only 6% on a conventional black roof (Foster et al., 2011).
An example of a white roof that will reduce the albedo effect of the sun’s rays, Photo Credit: Charles + Hudson
Blue roofs slow or store storm water runoff by using flow controls to regulate, block, or store water. These controls include downspout valves, gutter storage systems, and cisterns. The water collected could be used for non-potable uses like landscaping, gardening, or direct groundwater recharge.
An example of the components of an effective blue roof, Photo Credit: Philadelphia Water.
Green alleys and streets are other examples of green infrastructure that can be implemented in cities. The increased urbanization in cities also has an increase in impervious surfaces which in turn leads to localized flooding. Permeable pavement is a strategy that can be implemented in order to reduce the flooding that is caused by extreme weather events because it allows the water to filter through the pavement instead of becoming standing water. The permeable pavement also tends to be cooler because it has a higher reflectivity, lower capacity for absorbing heat, and greater evaporative capacity (Foster et al., 2011). Permeable pavement can be implemented in many major cities; it just requires forethought and thoughtful planning. Rain gardens along alleys and streets can also reduce the loads on existing sewer systems, so they also provide water conservation benefits for the city. A rain garden is a garden of native shrubs, perennials, and flowers that are placed along the sides of streets and alleys in a small slope. It is designed to temporarily hold and soak in rain water runoff that flows from roofs, roads, and other surfaces until the natural system can handle the water. This alleviates the strain on sewer systems which do not have the capacity to handle increasing storm water and sewage.
Urban Forests. Photo credit: Luana Vargas/International Society of Arboriculture.
Increasing the number of trees in urban areas also serves as a common and cost effective green infrastructure practice.” Trees would help in collecting and filtering the storm water runoff. They can also absorb pollutants in the air, provide wind breaks to protect buildings from wind damage, and regulate the heat island effects through shading and evaporation (Foster et al., 2011). Urban forestry allows for the planting of trees along any roads, streets, or green spaces that are managed by the local governments. They can also help with erosion control in areas that will have increasing flooding due to extreme weather events.
There is a National Green Value Calculator that compares the performance, cost, benefits of green infrastructure. This could be a helpful tool for cities and individuals who want to implement green infrastructure into cities or homes. The practice of green infrastructure can help mitigate the effects of climate change in urban areas.
Examples of cities that have implemented green infrastructure in positive ways:
“Portland invested $8 million in green infrastructure to save $250 million in hard infrastructure costs. A single green infrastructure sewer rehabilitation project saved $63 million, not counting other benefits associated with green practices such as cleaner air and groundwater recharge benefits. Portland’s Green Street projects retain and infiltrate about 43 million gallons of water per year and have the potential to manage nearly 8 billion gallons, or 40% of Portland’s runoff annually. Portland estimated that downspout disconnection alone would lead to a reduction in local peak CSO volume of 20%,” (Foster et al., 2011).
“New York City’s 2010 Green Infrastructure Plan aims to reduce the city’s sewer management costs by $2.4 billion over 20 years. The plan estimates that every fully vegetated acre of green infrastructure would provide total annual benefits of $8,522 in reduced energy demand, $166 in reduced CO2 emissions, $1,044 in improved air quality, and $4,725 in increased property value. It estimates that the city can reduce CSO volumes by 2 billion gallons by 2030, using green practices at a total cost of $1.5 billion less than traditional methods,” (Foster et al., 2011).
Definitions:
Urban heat islands – The generally warmer urban temperatures compared to those over surrounding, non-urban, areas.
Hydrologic systems – The continuous process by which water is circulated throughout the Earth and its atmosphere (the water cycle)
Combined sewer systems – The collection of rainwater runoff, domestic sewage, and industrial wastewater into one pipe.
Ecosystem services – benefits obtained from the regulation of ecosystem processes such as climate regulation, natural hazard regulation, water purification and waste management, pollination or pest control.
Green infrastructure – incorporates both the natural environment and engineered systems to provide clean water, conserve ecosystem values and functions, and provide a wide array of benefits to people and wildlife
Carbon sequestering – the long term storage of carbon in plants, soils, geologic formations, and the ocean
Albedo – the ratio of solar radiation on a surface to the amount of that radiation that is reflected back to the atmosphere
References:
Douglas, Ian, and Phil James. Urban Ecology: an Introduction. Routledge, 2015.
Foster, Josh, et al. “THE VALUE OF GREEN INFRASTRUCTURE FOR URBAN CLIMATE
ADAPTATION .” Center for Clean Air Policy, Feb. 2011,
ccap.org/assets/The-Value-of-Green-Infrastructure-for-Urban-Climate-Adaptation_CCAP-Feb-2011.pdf.
“What Is Green Infrastructure?” EPA, Environmental Protection Agency, 14 Aug. 2017,