Universities, EPA Work to Cool Heat Islands

By Ryan Newhouse

If only all islands could be like those in a Jimmy Buffet song: warm, sunny, uncrowded and relaxed. Unfortunately, a new kind of island—while it usually qualifies as warm—is anything but peaceful. These smog-inducing, weather-changing islands are actually metropolitan areas, known as here miles of blacktops and paved surfaces trap heat and affect local climate conditions.

Studies on the UHI show that urban air and surface temperatures can measure 2-10°F warmer than surrounding rural areas. Heat islands increase the magnitude and duration of heat waves within cities and increase energy consumption for air conditioning and refrigeration. It has been estimated by the Heat Island Group that the heat island effect costs the city of Los Angeles $100 million per year in energy-related expenses.

Urban Heat Island ProfileHeat islands are formed when natural lands are replaced with pavement, buildings and various other infrastructures. According to a report published by the Brookings Institution in Washington, DC, between 1982 and 1997 the amount of land consumed for urban development in the United States increased by 47%, while the nation’s population only grew by 17%. The effects of heat islands on local climate systems can include decreased and altered wind speeds and direction, reduced visibility, less evaporation (up to 50%), 200% greater heat storage, less snow and more thunderstorms.

Heat islands greatly raise the rates at which pollutants, such as nitrogen oxides from vehicle emissions, “cook” in the ozone, creating one of the main ingredients of smog. Looking again at Los Angeles, the ground-level ozone raises from an acceptable level at 70°F to an unacceptable level at 90°F.

When researchers work to address UHI, they generally look at two strategies: increasing vegetation and increasing albedo (solar reflective) surfaces. Working with David Sailor, a mechanical and materials engineering professor for Portland State University (PSU), the EPA funded a project to develop an Urban Heat Island Mitigation Impact Screening Tool (MIST), which can be used by public officials in assessing the potential of urban heat island mitigation strategies to affect the urban climate, air quality, and energy consumption within their cities.

“The challenge is that it is a time-intensive, costly procedure to assess [the air quality of] large cities,” says Sailor, “so the EPA wanted a tool that was easy to use,” and that led to the creation of a free web-based program that anyone can use as a screening tool to assess potential for UHI mitigation.

MIST users simply input the city they want to model, define which mitigation strategy to test (i.e. increase/decrease vegetation, increase/decrease albedo surfaces, or a combination of both), and the tool will estimate the strategy’s impact.

In 1997, the EPA launched the Heat Island Reduction Initiative (HIRI), which focuses on turning research on heat islands into practical information that communities can use to develop heat island projects, programs and policies. In support of the initiative, the EPA has funded several university-based research projects, like the one at PSU, for heat island reduction strategies. From urban planning and testing to the development of cutting-edge building materials, partners of the HIRI are findings ways to cool things down.

One promising avenue of research on UHI is determining the effects of increased vegetation in urban areas. According to an article published by the Heat Island Group, one properly watered tree can “evapotranspirate” 40 gallons of water a day, which offsets the heat equivalent produced by one hundred 100-watt light bulbs burning 8 hours a day.

Dr. Robert Berghage, an associate professor of horticulture at Penn State University and director of the school’s Green Roof Research Center, has been monitoring the effects of green roofs on campus. A green roof is just that, a roof with green plants growing on its surface, which provides albedo and helps with storm-water management, as well as helping to keep the building itself at a lower temperature in the summer.

“We have about an acre of green roofs on campus,” says Berghage, that are spread over five different buildings, literally. The largest green roof is about 10,000 square feet. “It sounds like a lot,”” he explains, “but when you consider all the flat roof buildings we have on campus it’s a drop in the bucket.”

“A regular flat black rooftop in central Pennsylvania can reach 175-185° F in the summer,” Berghage says, “but a green roof stays close to the ambient temperature, and that translates into a cooler building. A green roof building is also 20-30° F cooler inside than the ambient temperature outside.” Large buildings can also save 20-30% of the electricity required for air conditioning with a green roof.

“From a societal standpoint,” says Berghage, “if we put a lot of green roofs in communities, it would shave the peak demand for energy usage, and then you would save the need for additional infrastructure to provide the power for those peak demand times.”

Theoretically, green roofs can last two to three times longer than a blacktop roof, perhaps even longer. “At Penn State, we replace a blacktop roof once every 15-17 years,” says Berghage. The major obstacle for green roofs, however, is cost. “Green roofs cost more than twice as much as a blacktop roof,” Berghage explains.

Heat island mitigation still has a long way to go, at least according to a report by Eva Wong, former EPA Heat Island Reduction Program manager. In the report, Wong writes: “Despite this progress in research and implementation, heat island mitigation policy has not advanced significantly…Few decision makers (e.g., state and local officials from departments of Energy, Environment, Public Works, Planning, and Health) consider heat island mitigation strategies amongst other traditionally considered options.”

Of course, cities have much to offer in the way of sustainability: public transit, opportunities for experimentation and innovation, sometimes even smaller per-capita carbon footprints. However, as research continues to lead to new innovations, it will become even more important for universities and scientists to raise awareness of the technologies available to urban planners, city officials and contractors that can reduce their local urban heat islands, save energy, and fill their cities with a little more green space.

See More:

University of Florida Garden Spans Entire Rooftop The Gainesville Sun

The Dark Side of SummerThe Village Voice

Urban Ecology: Taking Measure of the Coming Megacity’s Impact Science Daily