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Turning Up the Heat: What is the "heat island effect" and what can you do about it?

Most people would agree that one of the best things about being human is our ability to control our environment. Whereas other creatures are at the mercy of natural forces, we can get around most of them. Too hot? Turn on the AC. Too cold? Crank up the heater. Find that mountain inconvenient to travel over? Tunnel through it.

Nowhere is the human race's mastery over the environment more obvious than in urban areas. In any large city, there are miles and miles of land that has been totally subjugated to human needs. However, we are increasingly seeing the dark side of our modification of the world around us. One of these unintended consequences is known as the "heat island effect."

The heat island effect occurs when developed urban areas have significantly higher average temperatures than the rural areas surrounding them.

The city of Los Angeles, one of the most extreme examples of this phenomenon, strikingly illustrates how substantial this difference can be. As the city has been developed over the past 50 years, its average high temperature in the summer has increased by nearly one degree per decade. Among other things, this has contributed to the city's legendary smog problem, since ozone forms more readily at higher temperatures.

There are many ways that developers can help mitigate this pesky problem, and save money while they do it. As it turns out, the same heat increases that can cause smog also cause the early aging of parking lots and roofs, as well as jack up air conditioning costs. By implementing the following strategies, shopping center owners can save money, and help the environment while doing so.

Use Reflective Material for Parking Lots The Urban Heat Island Group, a division of the United States Government's Lawrence Berkeley Laboratory, has done studies that show remarkable differences in temperature between standard blacktop paving surfaces and newly-developed reflective pavements. In one study, a patch of fresh blacktop registered a scorching 123???F on a bright sunny day, while a section of reflective asphalt in the same parking lot was a relatively cool 88???F, a difference of 35 degrees! The blacktop had a reflectivity of only 5%, while the new pavement (designed by Reed & Graham Inc. of San Jose, Calif.) reflected 51% of incoming sunlight.

Besides reducing air-conditioning costs, keeping your parking lots cool means they won't wear out as fast. As shopping center owners know, parking lots are not cheap, and can cost as much as $1,500 to $2,000 per space. The Heat Island Group's studies indicate that heat accelerates natural wear processes such as rutting.

The Mills Corp. is experimenting with a new parking system at its new Discover Mills project that will improve drainage and reduce heat retention. 5% of the spaces at the new development will be a porous Astroturf-like substance, which will have lower reflectivity than blacktop and hold more moisture for evaporative cooling.

Use Reflective Roof Material Roofs are also a major heat absorber in shopping centers, especially dark-colored roofs made with tar or asphalt. During the summer, dark roofs can make air conditioning costs soar. While such roofs can help keep centers warm in the winter, the Heat Island Group found that even so, a city like Los Angeles could have a net savings of $35 million by increasing the reflectivity of its roofs. In another study, the Florida Solar Energy Center that buildings with lighter roofs saved up to 40% on energy costs.

The latest technology in reflective roof coatings is called TPO, short for thermoplastic overlay. Ron Head, marketing and sales manager of thermoplastics for Carlisle Syntec Inc., notes that "everybody has always known that black absorbs and white reflects,"but says that the market for reflective roofing has grown recently. This growth has been spurred on by the EPA's Energy Star certification program, which requires roofing materials to have a reflectivity level of .65% or higher.

"Eventually, people will start marketing TPO roofs as being environmentally friendly," says Head, "now it's become like a floodgate's opened up and everybody is getting on board." He cites Home Depot, Lowe's, Kmart and Wal-Mart as examples of big-box retailers who have started using reflective roofing materials.

Plant and Retain trees Planting trees on your property, and retaining as much of the original tree canopy as possible does more than enhance the aesthetic value of your center. Everyone from NASA to the non-profit group American Forests have done studies that show that replacing forests with pavement is one of the leading causes of the heat island effect.

In a sense, trees sweat much like humans do to cool themselves off through a process known as evapotranspiration. A fully-grown tree can "sweat" 40 gallons of water a day, and by doing so can disperse as much heat as a space heater can generate in four hours!

Another cooling effect provided by trees is shade. A National Public Radio special on heat islands featured a scientist taking heat readings in a parking lot. The shade-free areas of the lot reached a scorching 108???F, while a patch of shade underneath a tree was only 86???F. Even after the sun went down, the shady spot was many degrees cooler than the surrounding area.

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