At 3 p.m., New York City is typically approaching its hottest time of the day. The city’s been steeping in late-afternoon sun for hours, heat building up between the densely packed buildings and lingering over the concrete sidewalks. The hum of window air conditioners hangs in the heavy air.

As temperatures climbed toward their peak on a sunny Saturday afternoon last month, Martin Stute and Aboud Ezzeddine were criss-crossing upper Manhattan from the air-conditioned comfort of Stute’s Kia Niro. Affixed to the passenger-side window, a small sensor was recording the outside temperature and humidity in real time as they zipped through the city streets.

Stute and Ezzeddine—an environmental science professor at Barnard College and a master’s student in public health at the City University of New York, respectively—were completing their second shift of the day as volunteers with a special urban heat-mapping project. A collaboration between nonprofit organization South Bronx Unite and Columbia University’s Earth Institute, sponsored by NOAA, the project aims to pinpoint which neighborhoods are hotter than others—and why.

Stute and Ezzeddine already had driven the same mapped route at 6 a.m. as the sun rose over the city, and they’d drive it once more at 7 p.m. Across upper Manhattan and the South Bronx, other volunteers were doing the same thing at the same time on different routes. The idea was to collect data from a variety of neighborhoods at the exact same time of day, so the temperatures could be easily compared.

The second shift had gotten off to a rocky start for Stute and Ezzeddine. The little instrument in the window was programmed to start collecting data automatically at exactly 3 p.m. At that time, a flashing green light on the sensor was supposed to stop blinking and hold steady, indicating that it was ready to go.

Several minutes past the hour, however, the light was still flashing. Idling in the shade at the corner of 101st St. and West End Avenue, Stute and Ezzeddine peered at the sensor through the window and debated what to do. It had worked just fine during the first shift.

The setback didn’t last long, though. After a quick call to a project organizer who offered some time-honored advice—“Maybe try turning it off and turning it back on?”—the little green light finally stopped blinking. They were off.

Columbia and South Bronx Unite’s collaboration is one of a number of heat-mapping projects sponsored by NOAA this year. There are others happening in San Francisco, San Diego, Atlanta, Kansas City and a handful of other cities across the country, including a separate project in Brooklyn.

‘There’s a lot of complexity’

It’s the fourth year in a row the agency has funded these kinds of projects as part of its U.S. Urban Heat Island Mapping Campaigns program. The sponsorship program is a collaboration with the National Integrated Heat Health Information Program and the analytics firm CAPA Strategies, which specializes in climate data.

The program provides the sensors and helps project organizers map out their routes. Later, CAPA processes the data collected by the sensors and integrates it with satellite maps so communities can visualize which areas are hotter than others. The maps can help project organizers figure out what aspects of the urban environment might be contributing to the higher heat.

“There’s a lot of complexity around how temperatures vary,” said Christian Braneon, a remote sensing specialist at NASA, director of the Environmental Justice and Climate Just Cities Network at Columbia University, and one of the project’s organizers. “It really has to do with the urban form.”

Everything from the height and density of a neighborhood’s buildings to the kinds of materials they’re made of can influence local temperatures. Denser neighborhoods with lots of dark surfaces tend to be warmer. Vegetation helps cool the local climate, whereas neighborhoods with fewer trees or parks may be exposed to more heat.

Studies show that differences in urban heat from one neighborhood to the next disproportionately affect some demographics. Lower-income people and people of color are more likely to live in hotter neighborhoods in cities across the United States (Climatewire, Dec. 10, 2020).

Studies also suggest that a long history of racist redlining—a practice in which lenders would refuse mortgages and loans to areas with large minority populations—has contributed to the disparities in urban design that make some neighborhoods hotter than others. While redlining was outlawed in 1968, its legacy has persisted decades later. Research suggests that formerly redlined neighborhoods are still warmer than their non-redlined counterparts (Climatewire, Jan. 21, 2020).

These are critical public health issues. Heat is the biggest weather-related killer in the United States. Hundreds of people die of heat-related illnesses across the country each year.

‘Anytime somebody hurts, we all hurt’

This summer has been particularly extreme. Experts estimate that hundreds of people died during the record-breaking Pacific Northwest heat wave last month alone. Scientists warn that these kinds of extreme heat events are growing more frequent and more intense as the climate warms.

Neighborhoods that are already warmer than their surroundings may be more vulnerable when heat waves strike. Lower access to air conditioning in lower-income neighborhoods makes the danger even greater. These issues are compounded by other challenges that members of these communities may face, including unequal access to health care.

recent report from the New York City Department of Health and Mental Hygiene found that Black New Yorkers experience disproportionately high rates of death due to heat stress—about twice the death rate of white New Yorkers. Death rates also tended to be higher in neighborhoods with a greater percentage of residents living below the poverty line.

Braneon and other project organizers hope the heat-mapping project can help support interventions aimed at reducing these disparities—for instance, by advocating for more parks and green spaces in hotter neighborhoods.

“I like to actually think of this project as almost like a culmination of what we’ve been doing,” said Melissa Barber, co-founder of South Bronx Unite.

The organization tackles a variety of environmental justice issues, such as advocating for more green space and less community exposure to air pollution. One of the organization’s first campaigns was a fight to stop the grocery delivery service FreshDirect from relocating its diesel trucking operation to the South Bronx, in part because of concerns about its impact on local air pollution.

Urban heat, Barber said, is an issue that relates to all the organization’s priorities.

Urban heat is exacerbated by a lack of green space, and a combination of high temperatures and air pollution can worsen human health impacts. She said she hopes that data from the project will help bolster the organization’s case when it approaches elected officials about issues related to environmental justice in the South Bronx.

These issues are more pressing as climate change continues to drive temperatures skyward, she noted.

“Most of us think that we can actually ignore the issue, and that it doesn’t affect us—but it does,” she said. “Anytime somebody hurts, we all hurt.”

Reprinted from E&E News with permission from POLITICO, LLC. Copyright 2021. E&E News provides essential news for energy and environment professionals.