Urban Heat Islands

Worries over Urban Heat Islands

Left Photo: An infrared image of downtown Atlanta, which is notably hotter than surrounding areas. The composition of the urban landscape raises temperatures.

ATLANTA, Aug. 20 This city is covered by a thick blanket of smog ground-level ozone an increasing health hazard this summer. It’s no surprise to scientists at NASA, who have detected what they call the urban heat island effect in Atlanta and other cities.

AS OUR cities grow, we?re going to keep increasing the amount of heat that we put in the air, and I expect to see more and more problems with ozone, said Jeff Luvall of the Global Hydrology and Climate Center.

Infrared pictures of metropolitan Atlanta show the hot spots of the heat island, an island created by expanding miles of concrete and dwindling green space. During a 19-year building boom in the city, 380,000 acres of trees were cut down some 55 acres a day.

Temperatures in urban areas can frequently be as much as 10 to 12 degrees higher than the ambient temperature in a rural area with the same weather,said Gordon Kenna of Georgia’s Cool Communities program, a non-profit group which aims to reduce urban temperatures.

These bubbles of hot air created by urban environments can create unnatural weather patterns, bringing rain and thunderstorms to areas far from the city center, where the heat was generated.

As cities continue to grow, cutting down trees and paving the landscape, scientists say more and more urban heat islands will appear. But they say there are ways to diminish the heat-island effect.

For example, suggested Dale Quattrochi of the Global Hydrology and Climate Center: Installing or painting surfaces light color, for example white colored surfaces or highly reflective surfaces(reflective roof coatings), that reflect this heat to the open atmosphere as opposed to absorbing it and re-radiating it later.

DRAMATIC RESULTS

In Atlanta, Jeff Luvall, a NASA scientist, measures the temperature of two samples of roofing material one dark, the other light.

Let’s … try the dark material first, Luvall said. Let’s see what it is. 128? 129? 129 degrees. … The light material’s down to 113. So we?ve got a 15 degree difference. Fifteen degrees just on this quick test here.

Roofing industry consultants say the difference can be even more dramatic with light colored roofs 60 to 70 degrees cooler in direct sunlight.

The real savings comes from reducing air conditioning expenses. On an average structure the cost difference between a white and black roof can be recouped in a matter of a year or two, said roofing consultant Patrick Downey.

That’s one reason Atlanta’s Woodruff Arts Center decided to replace its old, dark roof with a new, white one.
We’re going to have a significant savings on our utility bills, insisted the Center’s Michael Sterling.

The savings don’t stop there, especially if architects and builders adopt reflective roofing as an industry standard, because as the demand for electricity to cool buildings goes down, utility companies don?t have to generate as much power.

That helps to reduce ozone less ozone, less smog. A clear case, scientists say, where less is better on the urban heat island.