Beware the Light Box Effect — and Other Secrets of NYC's Microclimates

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Over the last two summers, teams of students fanned out across Manhattan carrying equipment that looked half high-tech, half dime-store. They carried expensive, hand-held devices in their hands connected to a supersensitive thermometer that hung off their backpacks. In order to keep the thermometers from being overly affected by the sunlight, however, they were covered by Styrofoam cups and mounted on pieces of cardboard wrapped in white paper.

The research was all part of a project to map and understand the city’s “microclimates”: how temperatures vary from one neighborhood to another depending on elevation, building type and other factors.

None of these elements make more than a few degree Fahrenheit difference by themselves. But Brian Vant-Hull, the research scientist at the City College of New York leading the project, said that understanding these minor variations could be a life or death issue.

“It turns out that mortality during a heat wave is a very sensitive function of temperature,” said Vant-Hull, who is also affiliated with the National Oceanographic and Atmospheric Administration. “Just a one or two degrees difference can make a significant impact from neighborhood to neighborhood.”

Heat can be deadly and some research suggests that the difference between 99 and 100 degrees Fahrenheit could translate into a difference of roughly 1.5 percent in the city’s mortality rate. The theory is, if 300 people die a year in heat-related deaths in New York City, getting people to slightly cooler locations, or increasing air-conditioning in chronically-warm neighborhoods, could save potentially dozens of lives.

Vant-Hull’s team has not completed crunching its data, much less published its findings, but so far has come up with some rules of thumb:

  • Streets lined with dark brownstones tend to be warmer than streets with lighter buildings.
  • Parts of Manhattan that are at low elevations, such as the Lower East Side and East Harlem, are warmer than those up on hills, such as the Upper East Side, by as much as 3 to 4 degrees on hot days.
  • Tall buildings along north-south avenues, such as in Midtown, create a “light box,” whereby sunlight is reflected down into the avenues and intensifies the warmth. The "light box effect” is especially pronounced at 1:30 p.m., because that’s when the sun shines most directly into the avenues.
  • East-west cross streets are as much as 1.5 degrees cooler because they are in the shade half the time. (Thank the north-south orientation of the Manhattan street grid for that.)