URBAN HEAT ISLANDS

Cause, Cost, and Correction

IMPROVING OUR CITIES

CAUSE

As world population increases so does urbanization, compounding the seriousness of city environmental problems.

Urban areas have the darker surfaces of streets and buildings and less vegetation than rural landscapes. These two factors combined raise temperatures creating a phenomenon known as an "urban heat island."

COST

Urban heat islands (UHI) result in adverse climate, worsened habitability, and greater energy demand for cooling.

While increasing emissions fill the air with precursor chemicals; higher urban temperatures accelerate the production of smog. These conditions result in increased illness, lost work and health care costs.

Expanding the generating capacity to meet the future demand for cooling energy involves significant financial investment.

According to studies conducted by the US Department of Energy at Lawrence Berkeley National Laboratories in Berkeley, California, mitigation strategies for the reduction of urban heat island conditions could save five to ten billion dollars in energy costs annually within the United States. Reductions in ozone and smog could save another five billion dollars in medical costs and lost work. Los Angeles, alone, could save $175 million per year in energy load reductions, and another $355 million from smog reduction, for a total of $530 million annually.

CORRECTION

Within the urban area some places, of course, are hotter than others. These sites should be identified and targeted for correction in logical order.

Site identification can be precisely established by satellite imagery and aerial photography with computer enhancement (showing various heat levels ranging from hot reds to cooler blues). (Washington DC Map.)

Once identified, correcting over-heated areas can be accomplished at considerably lower cost than the consequent expense associated with unrestrained urban heat island expansion.

Dark, heat-retaining, roofs and street pavements can be resurfaced with cooler, more reflective coatings during routine maintenance to deter the build up of heat. Trees and other vegetation can be planted to cool the ground and air through shade and evapotranspiration. Together, these strategies will reduce ambient temperatures, improve our air quality and reduce the demand for cooling energy.

The incentives for UHI management apply to governments, utility companies, non-governmental organizations and individuals. They include: 1) postponing or eliminating the expense of building new power production facilities and reducing the need to implement more costly emission control measures; 2) improving air quality by off-setting the production of smog from pre-cursor chemical emissions from power plants, automobiles and other sources; 3) reducing illness and the ensuing health care costs associated with air pollution and thermal stress; 4) improving the habitability and comfort of human settlements by moderating extreme temperature episodes; and 5) improving water quality and reducing storm water management costs by increasing urban vegetation and decreasing storm water run-off volumes.

UHI management programs can identify and prioritize opportunities for land and surface cover changes that will improve the urban environment. Computer models can simulate the results of proposed actions. And a cost/benefit analysis can quantify the economic and social profit that can be obtained.

UHI management programs will utilize remote sensing technology and computer geographic information systems (GIS) to identify potential land cover change in terms of surface composition, albedo (reflectivity) and vegetation that can moderate urban temperatures. New surface coatings on roof tops and parking lots, shade tree plantings and other increased vegetation, along with future urban designs incorporating greenways and forested areas will moderate urban temperature extremes. In this way cities will become more comfortable to live in and their environments more sustainable.

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