Energy efficiency is critical to household resiliency before, during, and after an extreme weather event, and it is integral to a long-term energy strategy. As advancements in building technology and structural development improve energy efficiency, the incorporation of green infrastructure (GI) is becoming increasingly popular because it offers considerable benefits with minimal impact on development. GI addresses two concerns that most American households are likely to experience: excess precipitation and high temperatures. GI not only reduces energy consumption but also offers an added layer of protection from weather events.
GI is the incorporation of green, or natural, elements into the built environment to enhance the management of water sources by gray infrastructure systems. Examples include urban tree canopies, rain gardens, planter boxes, bioswales, buffer strips, constructed wetlands, riparian zones, and green roofs. GI largely helps reduce the volume of excess stormwater because vegetation expels 3.2 percent of surface runoff from incoming precipitation, whereas impervious surfaces expel 12 percent.1 Reducing stormwater runoff also prevents untreated water from carrying pollutants, such as pathogens and heavy metals, into area water systems.2 Impervious surfaces often cause flooding because they are unable to absorb excess water into surrounding surface areas. Impervious surfaces also increase temperatures in urban areas, a phenomenon known as the urban heat island effect. Impervious surfaces alone are 3.4°F ±–1.08°F warmer than surrounding surfaces during summer.3 The urban heat island effect results in temperatures that are 1.8°F to 5.4°F higher than surrounding rural boundaries during the day; this difference can be as high as 22°F in the evening with the release of stored heat from building materials and road surfaces.4
On top of managing water sources, GI also provides a passive cooling system that reduces land surface temperatures and air temperatures through evapotranspiration. During this process, water evaporates through plant leaves and is released into the atmosphere as water vapor, and the cooler water vapor absorbs the surrounding heat.5 Consistently, studies measuring land surface temperatures during the warmer months find that areas with larger areas of green surface cover are cooler than other urban areas; on average, parks are found to be 1.69°F cooler.6 Shade from trees also saves energy in residential buildings; shaded suburban residences use between 4.8 percent and 19.3 percent less energy than do houses with no shade.7 Economically speaking, reducing outside heat by even a few degrees offers considerable cost savings because it reduces energy demand and consumption. For example, in Gainesville, Florida, trees are estimated to have generated $1.9 million in energy savings each year, based on 2007 electricity retail prices.8
GI is not without faults; it can have detrimental effects if an evaluation of it measures only its direct impact. For example, a dense tree canopy can inhibit the dispersion of particle air pollution in city neighborhoods, leading to air quality problems9, or a large tree located on the south side of a house in a northern city could increase energy consumption because it blocks valuable warmth from sunlight during the colder months.10 With factors such as these kept in mind, the direct and indirect benefits of GI can be achieved and maximized through thoughtful planning.
Lahouari Bounoua, Ping Zhang, Georgy Mostovoy, Kurtis Thome, Jeffrey Masek, Marc Imhoff, Marshall Shepherd, Dale Quattrochi, Joseph Santanello, Julie Silva, Robert Wolfe, and Ally Mounirou Toure. 2015. “Impact of urbanization on US surface climate,” Environmental Research Letters 10:8, 084010.
- U.S. Environmental Protection Agency. “Benefits of Green Infrastructure: Water Quality and Quantity” (www.epa.gov/green-infrastructure/benefits-green-infrastructure). Accessed 22 March 2017.
- Bounoua et al., 1.
- U.S. Environmental Protection Agency. “Heat Island Effect” (www.epa.gov/heat-islands). Accessed 1 May 2017.
- U.S. Geological Survey. “Evapotranspiration — The Water Cycle” (water.usgs.gov/edu/watercycleevapotranspiration.html). Accessed 13 May 2017.
- Diana E. Bowler, Lisette Buyung-Ali, Teri M. Knight, and Andrew S. Pullin. 2010. “Urban greening to cool towns and cities: A systematic review of the empirical evidence,” Landscape and Urban Planning 97, 147–55.
- Ram Pandit and David N. Laband. 2010. “A Hedonic Analysis of the Impact of Tree Shade on Summertime Residential Energy Consumption,” Arboriculture & Urban Forestry 36:2, 73–80.
- Francisco Escobedo, Jennifer A. Seitz, and Wayne Zipperer. 2012. “The Effect of Gainesville’s Urban Trees on Energy Use of Residential Buildings,” EDIS series FOR 211, University of Florida, Institute of Food and Agricultural Sciences Extension.
- M. Demuzere, K. Orru, O. Heidrich, E. Olazabal, D. Geneletti, H. Orru, A.G. Bhave, N. Mittal, E. Feliu, and M. Faehnle. 2014. “Mitigating and adapting to climate change: Multi-functional and multi-scale assessment of green urban infrastructure,” Journal of Environmental Management 146, 107–15.
- Won Hoi Hwang, P. Eric Wiseman, and Valerie A. Thomas. 2016. “Simulation of Shade Tree Effects on Residential Energy Consumption in Four U.S. Cities, ” Cities and the Environment 9:1, article 2.