United States
Environmental Protection
           EPA 430-F-03-001
                   Smart  Growth   and
                   Urban   Heat   Islands
      Development patterns of the
      last 50 years have had both
      positive and negative impacts
on communities across the country.
One concern has been steadily
increasing urban temperatures due to
the effects of "urban heat islands." A
heat island is an umbrella of air, often
over a city or built-up area, that is
warmer than the air surrounding it.

The urban heat island profile shown
here demonstrates that heat islands
are typically most intense over dense
urban areas. The profile also shows
how parks and other vegetated
sections within a downtown area may
help to reduce heat islands.

In general, summertime heat islands
raise air conditioning demand, air
pollution levels (particularly smog),
and greenhouse gas emissions. They
also increase the incidence of heat-
related illness and mortality. In fact, in
an average year, approximately 1,100
Americans die from extreme heat ~
the leading weather-related killer in the
United States.2

Heat islands augment this public
health threat by directly increasing
temperature and indirectly raising
ground-level ozone concentrations.
Those at significant risk from extreme
heat and ozone exposure include the
elderly, children, and individuals with
pre-existing respiratory disease.
Residents who live in homes with
dark-colored roofs and no air
conditioning may also be more
vulnerable than the general
                                         Urban Heat Island Profile
                                     Rural   Commercial    Urban   Suburban
                                                   Residential  Residential
                                               Downtown    Park

                    Source: EPA 1992
                                   Because urban design plays a large
                                   role in heat island formation, smart
                                   growth development strategies provide
                                   an opportunity to reduce heat islands.

                                   Smart growth is development that
                                   enhances both a community's economy
                                   and environment through strategies to
                                   help citizens make informed decisions
                                   about how and where they want to

                                   In addition to mitigating the heat island
                                   effect, smart growth provides a
                                   framework for increasing regional
                                   environmental protection, enhancing
                                   community character, and
                                   strengthening local economies. Here
                                   are four smart growth solutions that can
                                   achieve these goals:
 Reducing off-street parking and
  using porous paving materials:
  Surface parking lots replace natural
  vegetation with pavements that
  transfer heat to the surroundings.
  Providing on-street parking and
  planning compact, pedestrian-
  oriented development promotes
  transportation choices and can
  minimize the size and number of
  parking lots.

 Planting, preserving, and
  maintaining trees and vegetation:
  Trees and vegetation contribute to
  the beauty, distinctiveness, and
  material value of communities by
  incorporating the natural
  environment into the built
  environment. In addition, they cool
  surrounding areas by increasing
  evapotranspiration - a natural
  process that draws heat from the air
  to convert water in the leaf structure
  to water vapor. Planted adjacent to
  homes and buildings, trees provide
  shade, cool the interior, and reduce
  air conditioning energy demand.
  Trees and vegetation planted along
  medians and sidewalks can
  decrease evaporative emissions
  from cars and filter pollution from
  the air. Rooftop gardens, or green
                                  Everyone wins. Residents get better homes, lower energy bills, and
                                  cooler neighborhoods with plenty of green space. Narrower streets and a
                                  shorter pipeline means lower installation costs, so the developer gets a
                                  subdivision that's cheaper to build. And the City ends up with less streets
                                  to maintain and a standard for future development that maintain the
                                  community's existing high quality of life.
                                  J.D. Hightower, City Planner for Escalon, CA
                                  Currents - An Energy Newsletter for Local Governments January/February 1999
        Smart    Growth   Factsheet    Series

         Smart    Growth    Factsheet    Series
    roofs, can also mitigate urban heat
    islands while increasing the energy
    efficiency and attractiveness of
    commercial and residential
    Promoting infill and higher-
    density development:
    Development within existing
    communities can preserve open
    space and help offset heat islands
    and their consequences. A 2001
    report found that for every acre of
    brownfield redevelopment, 4.5
    acres of open space is preserved.
    Additional research found that
    compact development contributes
    less heat energy to the
    surrounding air than low-density
    dispersed growth patterns.3
Case Study

Chicago is a leader in urban forestry and heat island mitigation. The city
has adopted an open space impact fee ordinance that requires new
residential development to contribute a proportionate amount of open
space or recreational facilities, or to pay fees that ensure community
residents of continued access to greenspace. Chicago also replaced a
10,080 ft2 conventionally paved alley with a light-colored permeable
gravel pave system, which has eliminated chronic flooding without
requiring the installation of a sewer system. In addition, between 1991 to
1998 Chicago planted over 500,000 trees and achieved a citywide tree
count of 4.1  million. Chicago's Bureau of Forestry now plants a minimum
of 5,000 new trees per year and plans to install - in addition to 120 miles
of existing median planters - 280 miles of new median planters by
2005. In June 2001, Chicago amended its energy code to include
requirements for reflective or green roofs. See:
    Increasing public education and
    outreach: Heat island mitigation
    strategies should reflect local
    variation in the built environment,
    as well as local preferences and
    attitudes. Policies should be
    tailored to meet these needs,
    based on stakeholder input, and
    effectively communicated to the
    public.  Committees formed to
    address urban heat mitigation
    should include representatives
    from citizen groups, local
    government, non-governmental
    organizations, universities, and
    others concerned about how the
    community grows.  A lead
    organization should be  appointed
    to disseminate information to the
    community, solicit feedback, and
    incorporate issues  and  concerns
  into action plans. Working together, communities can address urban
  heat islands while enhancing the quality and character of their


  For more information on heat islands, see www.epa.gov/heatisland,
  www.hotcities.org, and http://eetd.lbl.gov/Heatlsland.
  For more information on smart growth, see www.smartgrowth.org and
  www.epa.gov/smartgrowth. Additional information on the relationship
  between the environment and the built environment can be found in
  "Our Built and Natural Environments: A Technical Review of the
  Interactions between Land Use, Transportation, and Environmental
  Quality." EPA 231 -R-01 -002.
   "Cooling Our Communities - A Guidebook On Tree Planting and Light-Colored Surfacing"
   U.S. Environmental Protection Agency 22P-2001, January 1992.
   Kalkstein, LS, 1993. Health and Climate Change: Direct Impacts in Cities. The Lancet
   Stone, B., and M.O. Rodgers. 2001. "Urban Form and Thermal Efficiency: How the Design
   of Cities Influences the Urban Heat Island Effect." Journal of the American Planning
   Association 67 (2) 186-198.
    To learn more about Smart Growth and the Smart Growth
    Network,  please go to  http://www.smartgrowth.org.
                                              Office of Air and Radiation (MC

                                              Office of the Administrator (MC
                                              EPA 430-F-03-001
"EPA's mission is to protect public health and the environment. EPA works with state and local decision makers to evaluate, promote, and implement
integrated, common-sense strategies that capitalize on public health and air quality improvements, while encouraging economic growth.  Studies have
demonstrated that mitigating heat islands provide clear environmental and financial benefits including improved local and global air quality, reduced heat-
related illness and death, and increased energy savings."
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