Millions of people in these cities are exposed to more intense heat, new report shows

By Rachel Ramirez, CNN

(CNN) — The record-shattering heat this summer has been downright dangerous in some of the largest cities in the US. But for some, the oppressive temperatures were likely far higher — even within the same city limits.

A new analysis from Climate Central, a non-profit research group, found that urban development increased temperatures by at least 8 degrees Fahrenheit for a total of 41 million people who live in certain pockets of 44 US cities, making them much more vulnerable to higher cooling costs, heat-related illnesses, hospitalizations and even death.

“Population density alone makes cities hotter than other environments, because so much of our everyday activities, including cooling our homes and workplaces, generate heat,” Jen Brady, a senior data analyst at Climate Central who designed and led the research, told CNN.

“But even when cities and neighborhoods have similar population densities, development patterns and materials allow some to get much hotter than others.”

Extreme heat has gripped the country’s southern tier from Southern California to Florida since June. And Phoenix, one of the hardest-hit cities in this summer’s scorching heat, is in its fourth week in a row of high temperatures over 110 degrees, smashing a previous record of 18 straight days.

Phoenix is one of nine cities where at least 1 million people live in neighborhoods that climb 8 degrees higher than surrounding areas, the Climate Central analysis showed. More than 1.3 million residents in Phoenix are exposed to these higher temperatures.

The analysis also found even more intense urban hotspots where temperatures are at least 10 degrees Fahrenheit higher than the rest of the city. Nearly 3.8 million New Yorkers, for example — 41% of the city’s population — faced temperatures at least 10 degrees Fahrenheit hotter than the city’s official readings, Climate Central found.

These giant swings in temperature over short distances in cities, known as the urban heat island effect, make heat waves even worse. Areas blanketed with asphalt, buildings, industry and freeways tend to absorb the sun’s energy then radiate more heat, while areas with abundant green space — parks, rivers, and tree-lined streets — radiate less heat and provide shade.

For instance, only a few miles from Manhattan’s bustling Central Park, where luxury apartments, upscale shops, green spaces and trees neatly line the neighborhood streets and provide cooling for residents, Harlem experiences severe heat vulnerability due to nearby freeways and lack of green spaces.

Urban heat islands can be deadly when temperatures spike. Extreme heat kills more Americans than any other weather-related disaster, according to data tracked by the National Weather Service — and climate change is making these extreme heat events more intense and frequent.

“This analysis shows that planting rooftop gardens or trees at street level can make a difference, so can using lighter, more reflective surfaces for sidewalks and streets when it’s time to repave them,” Brady said.

In Los Angeles, where much of the city’s land surface is heat-trapping black asphalt, and more than 3.2 million residents are exposed to the 8-degree temperature increase, city officials have installed California’s first white, reflective road coatings in some areas.

In New York, an $106 million initiative aim to coat roofs with white reflective paint, while in Chicago, local green roof initiatives are taking place.

“The way neighborhoods are built plays a huge role in how much additional summer heat their residents are exposed to, but many can be changed to reduce their urban heat island effect,” Brady said.

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