LBL researchers publish book on "heat islands"

March 20, 1992

By Diane LaMacchia

In addition to its already staggering cooling bills -- over half a million dollars an hour on a hot summer afternoon -- a city like Los Angeles runs up an additional $100,000 in cooling costs per hour because it is a "heat island."

Scientists from the heat island project in LBL's Energy and Environment Division have just published a guidebook on how to control heat islands -- a worldwide phenomenon in which urban areas absorb more heat than their suburban and rural areas.

The phenomenon is caused primarily by alterations people have made to the urban landscape, which change its thermal response to solar radiation.

"The urban areas are warmer because their dark surfaces absorb more solar heat and because there is less vegetation," says Hashem Akbari, co-principal investigator of the heat island project (with Art Rosenfeld) and one of the authors of the just- released "Cooling Our Communities: A Guidebook on Tree Planting and Light-Colored Surfaces."

"There are two quick fixes for summer heat islands," Akbari says. "The least expensive is to move toward lighter colored surfaces, the way Mediterranean cities do. The other is to plant shade trees -- another ancient tradition."

Urban landscapes are typically characterized by an inability to reflect solar radiation because of dark-colored buildings and streets; surface roughness; reduced evaporation from the replacement of vegetation by hard, impermeable surfaces; and the ability to store a lot of heat.

These properties combine to make urban temperatures hotter by one to five degrees Centigrade (two to nine degrees Fahrenheit), depending on the time of day. Heat islands are a moderate asset during the winter, but in the summer they increase air- conditioning usage, exacerbate pollution and smog, and add to human discomfort. City-wide tree planting and the use of light- colored surfaces are two good ways to mitigate the heat island effect.

"We should definitely go toward reflective roofs, parking lots and streets," says Akbari. "We should shade our houses with trees and vines.

"Before the invention of mechanical air conditioning, people kept their homes cool by painting them white and keeping them shaded."

The book provides data showing that the cost of conserved energy through "whitening" and "greening" is much lower than the price of electricity to run air conditioning units.

Edited by Akbari, Joe Huang, Haider Taha, and Susan Davis, the guidebook is available through the Environmental Protection Agency for $13. It is written in non-technical language for ready comprehension by utility planners, government officials, and others interested in energy and environmental issues. To order, write to the Superintendent of Documents, P.O. Box 371954, Pittsburgh, PA 15250-7954.