Summary: Green-roof zoning laws may provide a solution to the Urban Heat Island Effect, which contributes to anthropogenic climate change through heat pollution originating from large cities. US legislators may follow the lead of Stuttgart, Germany, where exemplary city-greening zoning laws have greatly reduced urban pollution.
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By Gabriela Steier, Esq.
Green-roofs are an overlooked solution to the complex problem of heat pollution, which contributes to anthropogenic climate change. As Catherine Malina wrote in a Georgetown International Environmental Law Review article in 2011, however, green-roof zoning laws could be effective and cost-efficient options to mitigate heat pollution from urban microclimates known as
The UHIE is a problem in major cities around the world, but the US could learn from Germany’s examples to mitigate the resulting heat pollution. Stuttgart , Germany, for example, is the hub of major car producers Audi and Mercedes-Benz, and is known as “the cradle of the automobile.” It would resemble Detroit in the US, but for the major distinguishing factor that Stuttgart has prevented a mass exodus and post-industrialization impoverishment. Stuttgart is leading the city-greening way.
One method of city greening is roof greening, planting vegetation atop buildings to offset some of the UHIE . Thus, the important and novel approach here suggests green-roof zoning laws to reduce the UHIE.
Targeting Climate Change with Green-Roofs
The UHIE affects public health and contributes to climate change. According to the US Environmental Protection gency (EPA) , the UHIE occurs in metropolitan areas and “can affect communities by increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, heat-related illness, . . . mortality, and water quality.” In fact , “[o]n sunny summer days, city roofs and pavement, which are dry and exposed, may be 50-90°F hotter than natural surfaces, which are shaded or moist.” Correspondingly , the World Health Organisation (“WHO”) “estimates that the warming and precipitation trends due to anthropogenic climate change of the past 30 years already claim over 150,000 lives annually,” especially where the UHIE is the greatest. In fact, EPA estimates that “a city with 1 million people or more can be 1.8-5.4°F (1-3°C) warmer than its surroundings” during the day and 22°F (12°C) in the evening. Predictions based on the 1995 Chicago and 2003 Europe heatwaves anticipate 25-31 percent higher frequencies and 72-76 percent longer heatwaves by 2090. Studies in the largest metropolitan areas in the US also confirm the links between mortality, the UHIE, and climate change.
According to meteorological simulations , green-roofs can cut the urban global warming contributions in half and could reduce urban carbon emissions dramatically. A recent report published by the National Academy of Science explains that,
continued conversion of existing lands to urban landscapes has the potential to drive significant local and regional climate change, compounding global warming. At the same time, how cities choose to expand and develop will be critical to defining how successful society will be in adapting to global change. Because cities are, in a real sense, fundamental units of both climate change adaptation and mitigation, development choices in the coming century will lead to either significant exacerbation or significant reduction in the impacts of global change.
Additionally, as noted in Malina’s article, Michigan State University researchers “found that a square meter of vegetation captures 375 grams of carbon, which suggests greening Detroit’s rooftops could remove as much carbon from the atmos the Urban Heat Island Effect (UHIE), urban heat absorption and radiation on impervious surfaces, such as concrete, asphalt and brick.phere as taking 10,000 mid-sized SUVs and trucks off the road for a year.”
Green-roofs buffer some stormwater, sequester carbon, and improve water quality in flood-prone regions. Notably, global urbanization facilitates UHIE accumulation, thereby driving climate change by up to 4°C. According to the United Nations Environment Programme , “30-40% of all primary energy is used in buildings” contributing greatly to fossil fuel use and climate change, especially in the US, where 82 percent of people live in cities. Cutting these figures in half through green-roofs would mitigate climate change significantly.
Correspondingly, in the US, land use laws aim at environmental protection after urban development but no specific regulation addresses the UHIE. The EPA maintains a Heat Island Reduction Program, which merely provides non-binding guidance for local action. Through green-roofs , the overall energy consumption of the building is lowered, and green-roofs “provide a beneficial environmental modification that reduced building energy needs and protects against two current public health stressors: high summertime heat and ground-level ozone . . . . ” Strikingly, although the business and environmental cases for green-roofs have been established and despite the surge in green construction, no streamlined approaches of government intervention have emerged to support and incentivize green-roofs.
Green-Roofing Benefits to Offset the UHIE
In Stuttgart, the Federal Nature Conservation Act (BNatSchG), the Nature Conservation Act of the state of Baden-Württemberg (NatSchG), and the federal German building code (BauGB) govern the preservation of green spaces, including green-roofs. The overarching general principle of the federal BNatSCHG is “to permanently safeguard (1) biological diversity, (2) the performance and functioning of the natural balance, including the ability of natural resources to regenerate and lend themselves to sustainable use, and (3) the diversity, characteristic features and beauty of nature and landscape. . . . ” These German laws create a culture of city greening that extended to Stuttgart’s roofs and even industrial buildings. Accordingly, Stuttgart’s Urban Climatology Office implemented these provisions by mapping the UHIE and establishing specific city-greening zoning based on the climate atlas maps. Figure 1 Stuttgart’s Climate Atlas Map . This classified thermal map illustrates the highest UHIE in Stuttgart. Red and orange zones have the greatest variance from normal temperatures and overlap with the most densely populated areas with the least vegetation where the UHIE is most significant. Green and blue areas show the coolest regions which coincide with green areas and woods.
In the US, green-roof policy insufficiently targets the UHIE. Such policy includes pilot projects, financial incentives, and command-and-control strategies, which lack behind Stuttgart’s model in practicality, likelihood of success, and legislative impact to create a culture of city greening resembling the one in Stuttgart. First, pilot projects are only examples and curtail setting national roof-greening trends without effective green-roof legislation. Second, general financial incentives ineffectively reduce market barriers – or else there would be more green-roofs in the US.
Portland, Oregon, for example, actually used zoning in its direct financial incentive program, and are somewhat successful, but these plans generally do not create a lasting commitment and ignore the underlying reason of mitigating climate change. Third, current building regulation is opaque, inconsistent, and unpopular with developers. In sum, legal tools in the US exist to promote green-roofs but local legislation could complement them to overcome current shortcomings.
Rethinking Zoning
US zoning laws may follow Stuttgart’s implementation of the BNatSchG, NatSchG and BauGB through green-roof zoning legislation. By analogy, local legislative action, informed by the EPA’s heat island effect program, may target microclimates to mitigate climate change by tailoring US zoning laws to regional city-greening requirements. Ideal green-roof zoning laws would combine features already nested in municipal urban agriculture, impervious overlay zoning, or tax codes. Boston Zoning Code § 89(5) , for example, allows both open-air and greenhouse rooftop farming. Additionally, green-roofs slow stormwater runoff in mapped districts that zone for total impervious cover limits. Urban farms on roof tops, for example oasify barren roof surfaces, thereby effectively using otherwise lost space. Applied to megapolitan heat islands, reversing the heat desertification by planting roof top gardens, it may also help to expand urban farming.
Overall, green-roof zoning laws put climate change mitigation control in the hands of communities and provide benefits that extend far beyond their target cities. Comprehensive city-wide green-roof acts from Toronto or New York’s tax abatement should proliferate green-roofs to offset the respective city’s heat pollution. Minneapolis , for instance, incentivizes green-roofing indirectly by offering utility fee reductions for managing stormwater quality or quantity. Correspondingly, Philadelphia offers green-roof tax incentives of one quarter of the construction cost, thereby removing market barriers. Lessons from these cities could be easily translated across metroplitan areas in the US. In following Stuttgart’s example, green-roof zoning can mitigate climate change while improving urban resilience to environmental impacts. Green-roof zoning offsets urban heat pollution by literally putting “green on top.”
Gabriela Steier, Esq., joined the Vermont Law School as an LLM Fellow in Food and Agriculture Law in August, 2015. Originally from Germany, she and earned a B.A. from Tufts University, a J.D. from Duquesne University, and pursues a doctorate in comparative law from the University of Cologne, Germany. Prior to joining the Vermont Law School, she worked as a Legal Fellow at the Center For Food Safety in Washington, D.C., where she focused on food safety, public health, pollinator protection, animal welfare, international trade, and GMO issues domestically and in the European Union. She has published widely on international food law and policy and has earned several awards for her work. In her free time, she enjoys sharing healthy and delicious foods with friends and family, painting, traveling, and nature walks. This paper is devoted to my father, mentor and best friend, Prof. Dr. Liviu Steier with heartfelt gratitude for brainstorming with me and for all of his support. Warm thanks go to Dr. Regina Steier and Fany Sontag with love and to Morrice for his patience. Special thanks to my classmates and to Professor Craig Pease for their helpful suggestions and insightful critiques of earlier drafts in the Vermont Law School’s LLM Seminar Fall 2015.
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