Heat island effect: Cities heat quickly, cool slowly, so nights don’t bring much relief

Wednesday, July 7, 2010

Heat islands: Cities heat quickly, cool slowly

NEW YORK — Hot town, summer in the city? No kidding.

The high temperatures blanketing the Northeast and mid-Atlantic regions of the country are making many people miserable, but those in New York City, Philadelphia and other dense, built-up areas are getting hit with the heat in a way their counterparts in suburbs and rural areas aren’t.

Cities absorb more solar energy during the day and are slower to release it after the sun sets, making for uncomfortable nights and no real relief from the heat. And because they haven’t cooled down as much overnight, mornings are warmer and the thermometer goes right back up when the sun starts beating down the next day.

Scientists have known for years about so-called heat islands, urban areas that are hotter than the less-developed areas around them.

Cities are just “not well designed to release that summertime heat,” said William Solecki, geography professor at Hunter College and director of the City University of New York’s Institute for Sustainable Cities.

The lack of nighttime relief can make the daytime high temperatures even more difficult for people to take as the days pass and the heat continues, he said.

That’s “where you start to have real problems, if your body’s not cooling down,” Solecki said. “You’re not getting that break.”

Deaths blamed on the heat included a 92-year-old Philadelphia woman whose body was found Monday and a homeless woman found lying next to a car Sunday in suburban Detroit.

The heat-islands effect is significant in the East because “we have a large population living in heavily built-up areas with lots of concrete and lots of steel, good absorbers of heat,” National Weather Service spokesman Sean Potter said.

And there’s nothing like the extreme heat of the past couple of days to make it obvious to everyone.

On Tuesday, the temperature hit 103 degrees in New York City and 102 in Philadelphia, soared past the century mark in Boston, Washington, D.C., and Newark, N.J., and broke records in Providence, R.I., and Hartford, Conn.

The heat-island effect occurs because cities, with their numerous building surfaces and paved roads, absorb more of the solar energy coming from the sun during the day than places that are less built up. At night, those types of surfaces don’t release that accumulated energy as quickly.

Cities also are very dry places, due to the lack of greenery and vegetation that could help bring moisture into the area and keep temperatures down, said Stuart Gaffin, an associate research scientist at Columbia University who focuses on urban climatology and environment.

All that combines to make cities risker places for people during times of extreme heat, he said.

“For me,” Gaffin said, “this is the scariest kind of weather.”

Associated Press writer Jim Fitzgerald contributed to this report from White Plains, N.Y.

will not be displayed