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Water: Green Infrastructure

Reduce Urban Heat Island Effect

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Why Green InfrastructureHow to Resources
Why Green Infrastructure
Urban heat islands occur when cities replace natural land cover with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat. Trees, green roofs and vegetation can help reduce urban heat island effects by shading building surfaces, deflecting radiation from the sun, and releasing moisture into the atmosphere.[1][2][3]

Climate change will likely lead to more frequent, more severe, and longer heat waves during summer months (see 100-degree-days figure (JPG)). The City of Chicago expects to see 30 more days per year rise above 100°F under “high” greenhouse gas emissions scenarios. Under lower emissions, Chicago’s new summer heat index is expected to increase to around 93°F by the end of the century – similar to current summer conditions in Atlanta, GA.[4] City reports outline worries that intense summer heat could lead to uncomfortable conditions for residents, as well as reduced tourist attraction in summer months.[5]

Extreme heat events often affect our most vulnerable populations first. There are a number of tools available to help communities map the benefit of reducing heat-related stress on their community. For example, the Institute for Sustainable Infrastructure (ISI) recently developed a risk-based spreadsheet economic companion tool to its EnvisionTM Sustainable Infrastructure Rating System, called the Business Case Evaluator (BCE) for Stormwater. The tool includes estimates for the value of a comprehensive list of benefits, including reduced heat-related morality rates. For more information and to download the BCE for stormwater management, click here Exit EPA Disclaimer or from ISI here Exit EPA Disclaimer. An example of the BCE's use can be found here (PDF) (86 pp, 19MB, About PDF)Exit EPA Disclaimer

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How To
Plant trees and build green roofs to reduce urban heat island effect. Luckily, since we know what causes contribute to urban heat island effect, it is possible to control it. Although space in urban areas is limited, small green infrastructure practices can easily be integrated into grassy or barren areas, vacant lots or street rights of way. Green roofs are an ideal heat island reduction strategy since they provide both direct and ambient cooling effects.[6]

Planning for heat island mitigation can take many forms. City officials in Louisville, Ky., recently awarded a $115,700 contract for a tree canopy assessment that will inform ways the city can use trees to address urban heat, stormwater management, and other concerns. “Knowing where we lack canopy, down to the street and address level, will help our efforts exponentially”, remarked Mayor Greg Fischer.[7]

Just add water. Build green infrastructure improvements into part of regular street upgrades and capital improvement projects (CIPs) to ensure continued investment in heat-reducing practices throughout your community. Make traditional water quality practices do double duty by adding trees in or around green infiltration-based practices such as roadside planters to help boost roadside cooling and shading.Transform your community one project at a time by planting native, drought-tolerant shade trees and smaller plants such as shrubs, grasses and groundcover wherever possible.

Some communities may consider adopting requirements that oblige developers to maintain or improve street tree coverage in the right of way. Private development incentives such as the Portland, Ore., Ecoroof Program (PDF) (2 pp, 844K, About PDF) Exit EPA Disclaimer can also offer benefits. Portland’s program reimburses private property owners $5 per square foot of green roof created. The city also provides resources and technical assistance to small businesses interested in entering the green roof industry.

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U.S. EPA Urban Heat Island Program – CA clearinghouse for resources, tools and educational materials on heat island effects, as well as a compendium of mitigation strategies.

Federal Funding Compendium for Urban Heat Island Adaptation (PDF) (90 pp, 849K, About PDF) Exit EPA Disclaimer – The Georgetown Climate Center's compendium of federal funding opportunities related to urban heat island effects.

Reducing Urban Heat Islands: Compendium of Strategies - Green Roofs (PDF) (29 pp, 4MB, About PDF) – General EPA resource, contains a compendium of available outside resources.

iTree Exit EPA Disclaimer – A U.S. Forest Service analysis tool for urban forest managers. It uses tree inventory data to quantify the dollar value of annual environmental benefits such as energy conservation, air quality improvement, carbon dioxide reduction, stormwater control, and property value increase.

Survey of Green Roof Incentive Policies (PDF) (54 pp, 1.56MB, About PDF) Exit EPA Disclaimer – From D.C. Greenworks.

EnvisionTM Sustainable Infrastructure Rating System – Business Case Evaluator (BCE) for Stormwater Exit EPA Disclaimer - Includes value estimates for a comprehensive list of green infrastructure benefits, including reduced heat-related morality rates. Also available from ISI here Exit EPA Disclaimer.

The Value of Green Infrastructure for Urban Climate Adaptation (PDF) (52 pp, 2MB, About PDF) Exit EPA Disclaimer - This Center for Clean Air Policy report evaluates the performance and benefits of a variety of green infrastructure strategies that assist with community climate resiliency including eco-roofs, green alleys and streets, and urban forestry.

Green Works for Climate Resilience (PDF) (76 pp, 2MB, About PDF) Exit EPA Disclaimer - A Community Guide to Climate Planning: This guide from the National Wildlife Federation includes planning resources related to extreme heat mitigation.


1. Rosenzweig, C., Solecki, W., & Slosberg, R. (2006). Mitigating New York City’s heat island with urban forestry, living roofs, and light surfaces. A report to the New York State Energy Research and Development Authority. Full text: http://www.fs.fed.us/ccrc/topics/urban-forests/docs/NYSERDA_heat_island.pdf (156 pp, 4MB, About PDF) Exit EPA Disclaimer.

2. Santamouris, M. (May 2014). Cooling the cities–a review of reflective and green roof mitigation technologies to fight heat island and improve comfort in urban environments. Solar Energy. Vol. 103, Pages 682–703.

3. Bowler, D. E., Buyung-Ali, L., Knight, T. M., & Pullin, A. S. (2010). Urban greening to cool towns and cities: A systematic review of the empirical evidence. Landscape and urban planning, 97(3), 147-155.

4. Katherine Hayhoe, Texas Tech University; Donald Wuebbles, University of Illinois at Urbana-Champaign. (May 18, 2008). Chicago Climate Change Action Plan – Climate Change and Chicago: Projections and Potential Impacts, Executive Summary. Online Resource. Available: http://www.chicagoclimateaction.org/pages/research_reports/8.php Exit EPA Disclaimer.

5. City of Chicago. (2008). Chicago Temperature Impacts Fact Sheet. Online resource. Available: http://www.chicagoclimateaction.org/filebin/pdf/factsheets/Chicago_Temperature_Impacts_Fact_Sheet_June_2008.pdf (2 pp, 42K, About PDF) Exit EPA Disclaimer.

6. Oliveira, S., Andrade, H., & Vaz, T. (2011). The cooling effect of green spaces as a contribution to the mitigation of urban heat: A case study in Lisbon. Building and Environment, 46(11), 2186-2194.

7. Bruggers, James. (May 7, 2014). Study to examine Louisville’s trees. The Courier-Journal. Online resource. Available: http://www.courier-journal.com/story/tech/science/environment/2014/05/07/louisville-tree-canopy-study/8804855/ Exit EPA Disclaimer.

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