Post by red on Jul 31, 2006 6:55:41 GMT -8
Cooling cities' heat islands
Construction techniques, landscaping can reduce temperatures
By Elise Kleeman Staff Writer
As development replaces Southern California's natural vegetation and soil, more of the sun's heat is absorbed, creating urban heat islands.
In the megalopolis the region has become, with housing stretching solidly from the desert to the Pacific Ocean, daily temperatures can be boosted anywhere from 3 to 7 degrees.
"Los Angeles' downtown area has heated up since the 1930s by something like 6 degrees Fahrenheit," said Hashem Akbari, an engineer at the Lawrence Berkeley National Laboratory and head of its heat island research program.
On average, California cities have warmed by 2 degrees in the past 50 years, he said, and the impact goes beyond the thermometer.
"During the summer, when you have higher urban temperatures, that increases the demand for air conditioning, adds to the discomfort of citizens and increases the amount of smog," Akbari said.
Electricity use spikes, water is in greater demand and even milk production at dairy farms slows, said Jay Golden, director of the National Center for Excellence on SMART Innovations for Urban Climate and Energy at Arizona State University.
"Ten, 15 years ago, when we were starting this research area, basically no one was talking about it," Akbari said. But with temperatures this summer reaching record levels in many California cities, more attention is being drawn to the problem.
There are, fortunately, some solutions, if city planners get to work fast, experts say.
Cities are about 50 percent pavement and 25 percent roof area, Akbari said - two surfaces that can be replaced with materials that reflect more of the more sun's heat instead of holding it long into the night.
"There has been a lot of effort by manufacturers to try to bring cool roofing products into the market," he said.
Until about five years ago, a cool roof meant one that was painted white. Now many researchers and labs - including the Lawrence Berkeley Laboratories - have been working together to create reflective roofing surfaces in a variety of colors and materials.
For materials such as metal and clay tiles, efforts have been quite successful, without any significant price increase. Less successful have been efforts to engineer more reflective asphalt shingles, which are used on most houses, and which also cost about 8 percent more when more reflective, Akbari said.
The benefits could be enormous. For every extra percentage point of sunlight the roof reflects, its surface will be about 1 degree cooler. That alone could reduce air-conditioning bills for a house by about $100 a year not to mention reducing the heat generated by air-conditioning units in use.
Another avenue of research is into lighter colored pavements. Concrete, for example, is more than twice as reflective as asphalt.
Narrower streets are also being encouraged in new developments, along with the planting of more shade trees.
"Trees are probably the best thing we can do to reduce the heat island," said Heather Merenda, a planner in Santa Clarita's environmental services division. It's a delicate balance, though. Heavily watered landscaping can also absorb heat, said climatologist Bill Patzert of Jet Propulsion Laboratory. He favors native, drought-tolerant plants. In rapidly growing Santa Clarita and a number of other cities, new parking lots are required to include shade trees.
But most cities in the Los Angeles area have not passed ordinances to decrease the heat island effect, said Dwight Steinert, director of the Los Angeles chapter of the Association of Environmental Professionals, though change is coming.
"We'll probably start seeing it in city council meetings and board of supervisor meetings and at the state level too," said Josh Meyer, a project manager at the nonprofit Local Government Commission, which advocates environmentally friendly planning.
Interest had waned during the cool summers following the 2000-01 California energy crisis, he said, but with the recent statewide heat storm, interest is returning "in a big way."
www.sgvtribune.com/news/ci_4116231