Urban Heat Island Effect Is Making NYC Warmer

Depending on who you ask at Gothamist, summer either sucks or is the most delightful time of the year. What’s not up for debate, though, is that right now this city feels hotter than, say, a wide-open field upstate.

But why does New York, especially Manhattan, heat up so much in the summer, without fail? It’s because of the “Urban Heat Island Effect.”

The Environmental Protection Agency describes heat islands as urban areas, populated with over a million people, where the average air temperature is 1.8 to 5.4 degrees warmer than surrounding areas (and 22 degrees warmer at night).

“Buildings, infrastructure, streets—the concrete, cement—they’re all absorbing the heat and making it warmer,” Jessica Spaccio, a climatologist at Cornell’s Northeast Regional Climate Center, told Gothamist.

Because our many tall buildings—which also restrict airflow—and streets absorb heat, rather than reflect it, this spikes surface temperatures. In 2015, scientist Brian Vant-Hull mapped the city’s distribution of heat.

The preliminary study showed that downtown Manhattan was warmer than uptown, and also found evidence of a “lightbox” effect where sunlight reflected off large glass buildings in Midtown was making those areas significantly warmer than neighboring areas.

As it gets hotter in the city, Spaccio said, “We’re using the air conditioning and we’re using more electricity and building back into our troubles.”

While all of this built-up heat “will eventually dissipate,” Spaccio confirmed, it will take longer “than an area that doesn’t have that infrastructure… Rural areas have open areas so heat can escape.”

Wind will also travel more easily in those areas, she noted, and “vegetation helps too—trees create shade and evaporation from soil and leaves has a cooling effect.”

Increasing green vegetation in dense, urban areas is one of the most obvious cooling strategies to lower the risk of heat wave-induced danger.

From an infrastructure perspective, using materials that reflect sunlight when constructing roofs, streets, and sidewalks help lower the risk of heat-trapping.

“More cities are incorporating green roofs and more trees in a city area, so those things will help,” Spaccio said.

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