The forecast called for sunny skies and highs in the low 80s – mild weather by summer standards in New York City. The shady trails of Sakura Park in Manhattan’s Morningside Heights neighborhood were windy and cool. But on the same block, the midday sun set on an exposed stretch of Riverside Drive, and heat radiated from the asphalt.
The exact phenomenon is what brought NASA remote sensing specialist Dr. Christian Braneon to the park on this midsummer day in late July, where he met with about two dozen New Yorkers who had volunteered to cover neighborhoods of Manhattan and the Bronx by car, measuring temperatures as they walked.
“We’re really feeling the city’s hot island right now,” Braneon said as he pulled the sign board into the shadows.
This day of temperature mapping was part of a nationwide effort by the National Oceanic and Atmospheric Administration to better understand the city’s heat islands: areas where dense buildings, lots of concrete and a little wood cover make life feel extra hot in the summer. Advocacy group South Bronx Unite as well as researchers from Columbia University’s Earth Institute coordinated Bronx and Manhattan branches of the project.
“A temperature that we actually know is like 70-something or 80-something, or maybe even 90 degrees, we will feel it several degrees higher,” said Dr. Melissa Barber, founder of South Bronx Unite and organizer of this mapping project.
Urban heat islands will become even more dangerous as temperatures continue to climb globally and new residents flock to cities. A global study published this month covering 13,000 urban areas found that urban residents’ exposure to life-threatening heat and humidity has tripled since the 1980s. This change was partly due to the fact that the population growth in the cities put more people in the crosshairs with rising temperatures. And the New York City Panel on Climate Change predicts that by 2050, the city will experience about twice as many days above 90 degrees Fahrenheit as in the 2020s.
This year’s scorching summer sent close to 650 people to emergency rooms in New York, more than the average toll for the four summers before. And extreme heat is killing more New Yorkers than any other form of severe weather, according to a 2017 report prepared by Mayor Bill de Blasio’s office. But it affects some neighborhoods more than others.
Studies show that poorer neighborhoods and areas with more residents in color experience warmer temperatures in the summer. Barber says it’s because these places tend to be densely built — with lots of asphalt and few shade trees.
“We have been neglected in terms of many of the structures and infrastructures that need to be in place to buffer heat,” she said.
These differences can be dangerous for people who are vulnerable to extreme heat, such as children and older adults and people working outside. A city report found that heat stress has killed an average of about 10 New Yorkers each year between 2010 and 2019. Black New Yorkers died with twice as many of their white neighbors.
“People in areas that are more vulnerable to heat risks are also less likely to have access to health care,” says Dr. Liv Yoon, co-organizer and postdoctoral researcher at the Earth Institute. “It’s not random.”
The temperature maps worked in pairs, driving pre-planned routes through the city with white plastic temperature sensors hanging out of their cars’ passenger windows. The sensors fired every second, capturing block-by-block differences in heat and humidity.
Some volunteers heard about the project through climate advocacy groups; others were captured by family members. At least two were former taxi drivers and put their deep knowledge of the streets to use in a new way. They all had first-hand experience of brutal summers in New York City.
“I came from Africa, so I expected it,” Fatou Diop, one of the volunteers, said of the heat as she drove through traffic at noon with the sensor looking out of her car window. “But it was so hot I thought, ‘What is this?'”
“Sometimes up here in Harlem, it’s like stagnant air,” added co-pilot Liz McMillan, who led Diop through the turns on the pre-planned route. “You get all the heat that comes from the concrete. All the heat comes from the ground. All the heat jumps off the buildings. ”
Project organizers say they will analyze the results and put the maps online. Researchers like Braneon will overlay them with other data to better understand how infrastructure affects our experience of heat.
South Bronx Unite and other groups can use these cards to advocate for heat-bursting infrastructure projects such as parks, accessible waterfront fronts, and refrigeration centers — especially in neglected areas that are mostly inhabited by residents of color.
“If we use some of that data, we can promote the idea that we can also enjoy things like a waterfront,” Barber said. “We too can enjoy things like greenspace. So if this can be one of the ways we start moving forward with the idea of equity, let’s do it. ”