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Pittsburgh’s stormwater is managed through a combined sewer system, which is the common way to manage stormwater in much of the eastern United States. One pipe is used for both wastewater flushed from sinks and toilets as well as rainwater collected in stormdrains. This combined system leads to overflow of untreated water into the rivers during heavy storm events. While one solution is to upgrade the city infrastructure, another means for managing stormwater, that is also used on Carnegie Mellon’s campus, is called green infrastructure.  

Green Infrastructure, as defined by the Clean Water Act, is a " range of measures that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters.” 

Examples of green infrastructure include nature-based solutions such as green roofs. These systems act as sponges. Vegetation slows or stores water when it rains. The water is either absorbed and used by the plants, allowed to infiltrate into the ground, or released back into the system later preventing the waste treatment facilities from being overwhelmed all at once. 

Temperatures are higher in urban areas than in rural areas because much of the natural vegetation has been removed and replaced with surfaces that absorb heat, such as roofs, roads, and other paved surfaces. Vegetation has a natural cooling effect, so introducing more vegetation, even on a roof, is a simple and effective way to reduce heat islands. 

Vegetation’s natural cooling effect is due to evapotranspiration. This is the combined processes which move water from the Earth's surface into the atmosphere, via evaporation and transpiration. Evaporation is when water moves from the soil into the air as a gas. Transpiration is when the water taken in through the roots of plants is emitted through their leaves. Together, evapotranspiration cools the air by using heat from the air to evaporate the water. 

Plant life on green roofs transforms what otherwise might have been a concrete or paved roof that trapped heat into a space where vegetation actually reduces the air temperature around it.

Green roofs also provide temperature-related benefits to the building underneath it. Reduced surface temperatures allow less heat to flow through the roof and into the building. Building temperatures remain more constant resulting in lower heating and cooling needs. 

References:
U.S. Environmental Protection Agency. (2008). Reducing urban heat islands: Compendium of strategies. Draft. .

Replacing pavement and other hardscape with vegetation improves habitat connectivity. Even vegetation on top of buildings and integrated into rooftops. CMU green roofs emphasize planting native species, which increase habitats for insects and fauna that rely on local plant life. The campus green roof with deeper substrate provided habitat for the insects and animals that burrow in the soil, providing more habitat to survive, especially over the winter. 

Increasing the variety of plant and animal species benefits ecosystems by making them more resilient. This is especially significant in otherwise urban environments that can lack robust green spaces for flora and fauna to flourish.

The biophilia effect refers to the positive psychological and physical health benefits, such as reduced stress and improved cognitive function, that humans experience when connecting with nature.  

Studies show that people who regularly interact with or even just have a view of plants and green spaces have improved physical and psychological health benefits. This includes lower blood pressure, improved immune function, and reduced stress hormones. In addition to positive health outcomes, research has found that when workers have access to windows with a view of nature or sunlight, they have higher productivity and improved attention span. Students have shown improved behavior and learning outcomes as well.

The green roofs on CMU’s campus are often on lower-level areas of the roofs, which allows them to be visible from multiple vantage points both inside and outside. Because the roofs aren’t limited to the very tops of buildings, the campus community can see and engage with these additional green spaces and hopefully reap the psychological and physical benefits of doing so.

References:
Miola, L., Boldrini, A., & Pazzaglia, F. (2025). The healing power of nature. Biophilic design applied to healthcare facilities. Current Opinion in Psychology. 64. .

Ríos-Rodríguez, M.L., Testa Moreno, M., & Moreno-Jiménez, P. (2023). Nature in the Office: A Systematic Review of Nature Elements and Their Effects on Worker Stress Response. Healthcare (Basel). 11(21). . 

DeLauer, V., McGill-O'Rourke, A., Hayes, T., Haluch A, Gordon, C., Crane, J., Kossakowski, D., Dillon, C., Thibeault, N., & Schofield, D. (2022). The Impact of Natural Environments and Biophilic Design as Supportive and Nurturing Spaces on a Residential College Campus. Cogent Soc Sci. 8(1). .