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  • 22 Nov 2014

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Portland hotter during the summer because of urban heat island effect

Portland’s summertime weather is considerably warmer because of the “urban heat island effect” — and more so than most other large U.S. cities — according to a new study by Climate Central.

Only three other large cities have registered more temperature gains from the urban heat island effect since 1970, according to the report by Climate Center, a Princeton, New Jersey, nonprofit research and journalism organization.

Urban heat islands are areas where a preponderance of concrete, asphalt, and buildings, and the corresponding loss of trees and other foliage, make cities hotter than surrounding areas.

According to the report, Portland’s urban heat island effect caused an average temperature increase of 4.8 degrees Fahrenheit during the summers since 1970, compared to nearby rural areas.

Las Vegas, Nevada, topped the list, at 7.3 degrees. Albuquerque was second-highest among the large cities, at 5.9 degrees, and Denver was third at 4.9 degrees. The report looked at data for 60 cities.

On the worst days, temperatures can be as much as 19 degrees warmer in Portland than in surrounding rural areas, researchers found.

Nighttimes are warming faster than daytimes, they found, with an average difference among the cities of 4 degrees. Daytime temperatures, on average are 2.5 degrees warmer.

“Climate change is warming the entire planet, rural and urban areas alike,” said Alyson Kenward, lead author of the report.

However, cities are heating even more.

“Urban heat islands have hotter days, far hotter nights, and more extremely hot days each summer than adjacent rural areas,” Kenward said. “Without greenhouse gas reductions cities will continue to get hotter, with potentially serious consequences.”

To read the full report, called Summer in the City: bit.ly/1AyiBo6.

Steve Law can reached at 503-546-5139 or This email address is being protected from spambots. You need JavaScript enabled to view it..

Twitter: @SteveLawTrib

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