&EPA
United States
Environmental Protection
Agency
SMART GROWTH
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
population.
Urban Heat Island Profile
Rural Commercial Urban Suburban
Residential Residential
Downtown Park
Suburban
Residential
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
grow.
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
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Smart Growth Factsheet Series
roofs, can also mitigate urban heat
islands while increasing the energy
efficiency and attractiveness of
commercial and residential
buildings.
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:
http://www.cityofchicago.org/Environment/
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
neighborhoods.
Resources
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
342:1397-99.
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
6205J)
Office of the Administrator (MC
1808)
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."
Printed on 100% recycled/recyclable paper with a minimum 50% post-consumer fiber using vegetable-based ink.
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