What is an urban heat island?

Urban heat islands are urban areas that are hotter than surrounding rural areas.  Factors that contribute to heat islands include the removal of local vegetation and natural surfaces as well as the addition of heat absorbing surfaces like dark roofs and pavements.  Many US cities are urban heat islands with temperatures between 2 and 15° Fahrenheit hotter than their surroundings (Akbari 1996).  Utah urban areas that are landscaped present a special case because much of the surrounding areas are actually dry, hot desert.  However, within Utah urban areas there are localized high-temperature patches caused by the same factors that cause urban heat islands.

Urban heat islands are expanding with spreading populations and new building construction.  Since 1940, summertime temperatures of many cities have climbed steadily by 0.25 to 1 degree Fahrenheit per decade (Akbari, 1994).  As temperatures increase, the need for air conditioning increases, this places more demand for power generation.  Los Angeles, for example, experienced one of the largest ever observed heat island cause and effects.  This city experienced a peak cooling demand increase of 1.5% for every rise of 1 degree Fahrenheit (Akbari 1993).  Power plants must generate the additional electricity to meet these peak-cooling demands, and in the process, they also produce air pollution.  One of the main compounds released into the atmosphere, as a byproduct of power generation is the greenhouse gas, carbon dioxide.

The increase in temperatures also increases the rate of release of volatile organic compounds (VOCs) into the urban environment.  VOCs enter the atmosphere as a byproduct of transportation and industry fuel consumption as well as from biogenic sources.  Certain VOCs, when combined with nitrogen oxides (NO_x) and in the presence of sunlight, react to form ground-layer ozone.  This pollutant is a powerful oxidizing compound and is the major contributor to summertime smog. 

The Environmental Protection Agency and other partners funded the Marshall Space Flight Center’s Global Hydrology and Climate Center’s fly-over project, to locate hot spots in four target cities including Salt Lake City.  In July of 1998, National Aeronautics and Space Administration (NASA) sent a Lear jet equipped with thermal (infrared) imaging equipment to take aerial photography of the Salt Lake City valley.  The results of the data showed, in part, that areas near bodies of water, tree-lined roads, and significantly vegetated spots can be 60-70 degrees cooler than areas near vast asphalt paved parking lots and large buildings with dark colored rooftops.  These results generated by NASA and other heat island researchers, assist groups such as the Utah Energy Office to promote and implement Cool Communities strategies. 

To help decrease urban temperatures and prevent the consequences of higher temperatures, the Cool Communities program suggest the following strategies:

Although it is advisable to plant woody species to reduce energy consumption, a word of clarification must be mentioned about the water they require.  Utah is the second driest state in the United States; and we are justifiably reminded to conserve water.  Most officials in the plant and water industries agree that improper irrigation procedure is the largest water waster in Utah.  Although plants consume water, the amount of water used by plants is insignificant compared to the amount that ends up in gutters and sewers.  By far, the most efficient way to save water is to properly irrigate, not to remove or reduce vegetation.  Even if plants are removed, the amount of water saved would be insignificant compared to the amount of energy consumed by not maintaining plants. 

Youth in Utah are educated about urban heat islands and Cool Communities strategies through the “Kool Kids” program. 

The Kool Kids Program Kit offers four lesson plans, overheads, test questions, experiments, and hands-on research tools.  The lesson plans include the following:

Lesson One ­ Geography of the Wasatch Front

     Concept:  Urban, suburban, and rural communities are the three main types of developed environments.  All three of these environments have both common and unique land cover types.  Each land cover may affect local air temperatures differently because of unique thermal properties.

Lesson Two ­ The Urban Heat Island Effect

     Concept:  An urban heat island is the result of replacing local vegetation with dark, heat absorbing surfaces.  The associated increase in summertime temperatures increases the use of energy for air conditioning and affects the level of air pollution.

Lesson Three ­ The Urban Heat Island Effect and Air Quality

     Concept:  Increases in urban temperature directly contribute to ozone levels and indirectly to other greenhouse gases. 

Lesson Four ­ Landscaping and Urban Forestry

     Concept:  Trees and other landscaping plants can be used to mitigate the urban heat-island effect and its resultant health and environmental problems.

TEACHER RESOURCE KIT INFORMATION

The TEACHER RESOURCE KIT is available for check out by Utah educators from the Utah Energy Office, Jordan School District and National Energy Foundation.  By appointment, energy experts may also be scheduled to give brief overviews of urban heat islands and illustrate the kit to students and communities at energy and community fairs, educational seminars, and in classroom settings.  Contact the Utah Energy Office to learn more about Kool Kids and Cool Communities programs. Here is information for checking out the TEACHER RESOURCE KIT nearest you:

UTAH ENERGY OFFICE
Department of Natural Resources
1594 West North Temple, Suite 3610
Salt Lake City, Utah 84114
801-538-7200

JORDAN SCHOOL DISTRICT
9150 South 5th West
Sandy, UT 84047
801-567-8770
duane.devey@jordan.k12.ut.us

NATIONAL ENERGY FOUNDATION
3676 California Avenue, Suite A117
Salt Lake City, UT 84104
801-908-5800
koolkids@nef1.org