Science

Do You Live in the Hottest City?

Summer in the city — any city — can be stifling. Peer down a wide avenue and the asphalt looks practically like it’s sizzling. But when you leave the concrete jungle and get just a little bit outside the city, the temperature drops dramatically. Maybe there’s even a chill in the air.

This isn’t your imagination playing tricks. It’s a real phenomenon called an urban heat island. At its simplest, it means that a city is warmer than its surrounding rural areas.

Climate Central, a nonprofit of scientists and journalists, looked at just how drastic these temperature differences are, and released the results in a new report “Summer in the City: Hot and Getting Hotter.” Fifty-seven of the 60 largest U.S. cities had “measurable urban heat island effects” during the past 10 years, and these places are experiencing more “searing hot days” every year. “We see uniformly that cities are hotter than their rural counterparts,” Alyson Wenward, Ph.D., of Climate Central, told weather.com.

It’s long been thought that urban heat islands happen because a city’s concrete and other dark surfaces absorb the sun’s rays and release the heat slowly overnight, according to Nick Wiltgen, a meteorologist with The Weather Channel. “They’re not holding in water, so there’s no cooling effect,” he said.

Recent studies show, however, that’s only part of it: Waste from air conditioning units on large buildings, cars and other machines also add to a city’s warmth, from the hot air pumped out through their exhaust systems. “It’s something that you can actually feel,” Wiltgen said of the urban heat island effect.

So which cities are the hottest? Climate Central, Wenward said, relied on temperature stations and their consistent, regulated temperature records to make the determinations. Las Vegas topped the list, with daily summer temperatures more than 7 degrees hotter in the city proper than surrounding areas. Albuquerque, New Mexico; Denver, Colorado; Portland, Oregon and Louisville, Kentucky rounded out the top five.

Wiltgen said he’s not surprised by Vegas, but would’ve expected to see Chicago and Phoenix higher up (they’re 31 and 18, respectively). “Phoenix is well known for having a strong urban heat island at night,” he said. As for Chicago, he surmised that this actually amps up in winter, with Lake Michigan's influence adding to the city’s own human-generated warmth.

Where does your city rank? Click through the slideshow above to find out. The first three cities — Charlotte, North Carolina; San Diego, California; and Sacramento, California — actually experienced cooler summer temperatures than their rural surroundings. Click here for the full Climate Central report.

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