Green Roofs for Urban Food Security and Environmental Sustainability
By Corinne Kisner, December 2008
URBAN AGRICULTURE CASE STUDY: CHICAGO, ILLINOIS
In Chicago, Illinois, urban agriculture stems from not only the need for food security for the city’s poor, but also from the desire to mitigate the effects of climate change. While developing countries must focus on combating urban poverty, developed countries like the United States are beginning to understand and fight the threat of climate change. Just as it is a luxury to emit excessive greenhouse gases without concern for the climate, it is a luxury to have the wealth and food security to afford to spend resources protecting the environment. In a developing country where hunger is commonplace, it is unfair to ask individuals to sacrifice their food because agriculture contributes to climate change. However in a developed country, individuals free from the threat of starvation can modify their habits, perhaps spending more money to lessen their carbon footprint. With this in mind, Chicago’s urban agriculture can be understood from two angles: providing food and mitigating climate change.
Chicago is the densest city in the U.S., with a population of 2.9 million (the entire metropolitan area has a population of 9.7 million.) The poverty rate in Chicago is 20.5% and the extreme poverty rate is 9.1%. Like urban poor in developing countries, urban poor in the U.S. face food insecurity. Many can’t afford food, and even those who can afford to eat can’t always afford to be concerned with nutrition, as fast foods high in fat and sugar are generally the cheapest option. With access to land and water, the city’s poor could cultivate their own vegetables to diversify their diets and achieve higher food security. Chicago now has over 600 community gardens with a variety of educational programs, food bank services, and cooperative organization for high local involvement. The gardens, like those in Havana or Harare, provide local, sustainable food for city-dwellers and promote a healthy, self-sufficient community.
In addition to policies that promote urban agriculture for food in Chicago, the government also supports green roofs to mitigate climate change. Planting vegetation on top of a human-made structure grants cities numerous benefits in addition to the obvious aesthetic value and improved air quality. Green roofs reduce heating and cooling bills and extend the life of the roof by two to three times. Therefore the initial expense of a green roof is earned back in energy savings and avoided environmental damage. Cities concentrate impermeable surfaces like pavement and concrete, impeding storm water drainage as well as absorbing and converting solar radiation to heat; green roofs can offset these phenomena and make urban areas more sustainable and viable in the long-term.
During rainstorms, the plants and soil on green roofs absorb the water that would otherwise run off and strain the sewer system. Researchers estimate that “three to five inches of soil or growing medium absorbs 75% of rain events that are one-half inch or less.” In addition to serving as a sponge, the bacteria and fungi on green roofs also function as a filter for contaminants, breaking down and detoxifying pollutants like nitrogen and phosphorus. These services, previously provided by open spaces and wild vegetation, must now be found with intentionally-planted green roofs.
Another important problem in cities is the urban heat island effect, or the overheating of cities due to dense concentrations of asphalt that absorb solar radiation. The urban heat island effect contributes to pollution and increased energy consumption, costing the city money in cooling bills and deteriorated public health. Air conditioners and car exhaust further contribute to the heat island: the more temperatures increase, the more people rely on energy-intensive artificial cooling, providing temporary relief indoors but emitting greenhouse gases and fueling a positive-feedback loop of rising temperatures and climate change. Researchers hope that green roofs will absorb the heat that is otherwise reflected off the concrete. According to the city’s Department for the Environment, on summer days in Chicago, “temperatures atop the green-roofed City Hall are typically 25 to 80 degrees Fahrenheit (14 to 44 degrees Celsius) cooler than the adjacent county office building, which has a black tar roof.”
In order to lead by example, Chicago mayor Richard Daley, Jr. installed 20,300 square feet of vegetation on the roof of City Hall in 2001. The project is part of Daley’s vow to make Chicago the “greenest city in America” and saves $5,000 a year in utility bills. The garden contains 20,000 plants of over 150 species, mostly prairie plants native to the region, and is monitored for its success in reducing temperatures and absorbing rainwater. With City Hall as a model of green roofs’ environmental, economic and social benefits, Chicago has paved the way for other buildings to install similar projects by offering $5,000 grants for residential or small commercial green roofs. In addition to these grants, Chicago offers other financial incentives to catalyze the movement, including reduced city fees for stormwater management, a density bonus permitting developers to increase the number of units allowed on a piece of property, and expedited permits (in 30 rather than 100 days) for buildings with green roofs. Chicago, as the first city to undertake such a movement, created these policies from scratch, and they have proven effective: Chicago now leads the country in green roofs, boasting 300 such buildings for a combined 3 million square feet of vegetated roofs. Not to be outdone, Portland, Oregon and Washington, D.C. have cited Chicago’s success as motivation for their own greening. Chicago’s model of financial incentives and public education can be replicated by other cities to achieve the environmental benefits of green roofs. Perhaps in the future the two goals of urban agriculture in Chicago, increased food security for the poor and climate change mitigation, could be combined by planting food gardens on roofs. Government support for urban food cultivation similar to that for green roofs could yield admirable progress in the fight against urban poverty and food insecurity.
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Works Cited
Chicago Green Roofs, “Guide for Building Green Roofs in Chicago,” 2 December 2008.
Dawson, Donald, “Plant-Covered Green Roofs Ease Urban Heat,” National Geographic News, November 15 2002. 2 December 2008.
Department of Environment, “About the Rooftop Garden,” 2 December 2008.
Environmental Health Perspectives, “Growing Green Roofs, City by City,” June 2007. 2 December 2008.
EPA, “Heat Island Effect,” 2008. 2 December 2008.
Green Net, “Chicago’s Community Gardens,” 2008. 2 December 2008.
Greenroofs.com, “Chicago City Hall,” The Greenroof Projects Database, 2006. 3 December 2008.
Heartland Alliance, “Poverty Trends in Chicago, Illinois,” August 2008. 2 December 2008.