NASA sees a hot time in the old town

By DAN WHIPPLE, UPI Science News

BOULDER, Colo., Aug. 20 (UPI) -- It has been about 200 years since a British scientist wandering through London discovered the urban heat island effect, which causes cities to be considerably warmer than the surrounding countryside.

In 1820, naturalist Luke Howard calculated nights in the city were 3.7 degrees Fahrenheit warmer and days 0.34 degrees F. cooler than in the country. He attributed the difference to city fuel use.


Now the National Aeronautics and Space Administration is using space-age technology and satellite data to answer the burning question: Why are there still so many black roofs?

The agency reckons it might be just about time to promote light-colored roofing material and more trees to help cool things down in a warmer, more energy intensive world.

"We know that this heat island effect has been heavily studied in urban climatology. We are using satellite data sets to quantify urban heat," Dale Quattrochi, senior research scientist at NASA's Marshall Space Flight Center in Huntsville, Ala., told United Press International. "We're capitalizing on the taxpayer's dollar to bring it back down to Earth to help control the environment."


NASA's research shows concrete, asphalt, dark roofing and a lack of vegetation contribute to urban heat islands -- domes of trapped heat that are growing in most major metropolitan areas, keeping temperatures up to 10 degrees F. warmer overnight than in suburbs or woodlands.

The United Nations has predicted by 2025, 60 percent of the world's population will live in cities. Although cities occupy only a tiny portion of Earth's land area, they are considerably hotter than the surrounding countryside and, subsequently, urban households and buildings require more energy for cooling.

Heat islands also may have global impact. Research from the University of Maryland earlier this summer indicated land use changes in the United States could be contributing twice as much as to global climate change as previously thought. Part of the problem is although the effects can be continental and even global, land use decisions usually are made at the local level. Quattrochi said NASA has been working with local decision makers to "see what we can do to mitigate these effects."

Eugenia Kalnay, a meteorology professor at the University of Maryland, first quantified the heat island effect on global climate changes. "This is a very important question," she told UPI. "County governments or state governments should include the heat issues from land use changes in their plans."


Quattrochi said the research has identified a couple of key actions. "One is to plant more trees in the right places," he said. "We are assisting policy makers and tree-planting organizations to plant the right kids of trees in the right places."

Surprising, this is not just a matter of plunking down any tree at any place. In the southeastern states, for instance, Quattrochi said certain kinds of oaks and pines emit high levels of volatile organic compounds and can exacerbate the production of ground-level ozone. So it is better to plant hickory and maple, he explained.

"Trees provide shade," he said. "They also intercept solar energy that would otherwise be used to heat up the ground. This helps cool the air even more."

Another important action, according to NASA, is lightening surfaces in the city.

Quattrochi said black roofs are more tradition than anything else. "A number of roofing materials are available that reflect energy back to the open sky, 60 to 70 percent," he said, adding that many Eastern and Mediterranean cities have light roofs to aid in cooling.

Putting down more concrete instead of asphalt also can reduce the heat island effect, although Quattrochi said asphalt manufacturers are beginning to produce cooler materials as well.


Studies by the Department of Energy's Lawrence Berkeley National Laboratories in California suggest mitigation strategies for urban heat island effects could save $5 billion to $10 billion in energy costs annually in the United States. Reductions in ozone and smog could save another $5 billion. Los Angeles alone could save $530 million a year from smog reduction and energy efficiency.

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