This is how hotter urban sprawl makes US cities feel

Nearly 34 million people in 65 U.S. cities – roughly one in 10 Americans – live in a place where the built environment makes temperatures at least 8 degrees Fahrenheit warmer than they would be without urban sprawl. This is in line with a new to study by the non-profit organization Climate Central, which mapped the impact of a phenomenon called the urban heat island effect in major US cities.

Dark, paved surfaces with little vegetation tend to absorb heat. Hot exhaust from heavy traffic and industrial facilities can also make some neighborhoods hotter than others. This is how the urban heat island effect can make heat waves even worse for some communities. In the US, a history of segregation and Red line which resulted in chronic underinvestment in many colored neighborhoods also created heat islands in cities.

It’s a problem that often goes unnoticed because a typical weather forecast for a city doesn’t pick up on these hyperlocal nuances. To get a better picture of how heat affects a city from neighborhood to neighborhood, Climate Central documented the urban heat island effect down to a more granular level.

“When you look across the country, this is everywhere. This is not a big city problem. This is a huge development problem. And it can happen anywhere,” says Jennifer Brady, senior data analyst and research manager at Climate Central.

Brady and his team examined 37,094 census groups across the US. A single block group can house between 600 and 3,000 residents, an even smaller range than a census tract. “The more details that can be obtained, the more accurate the estimates will be, because what we are seeing is type of soil cover,” says Brady.

They compared maps of these census block groups to an existing map National Land Cover Database to assess what the makeup of the neighborhood was – whether it was full of tall or low buildings or any tree cover.

They used methods previously published in Daily Scientific Reports to estimate how much these factors can heat or cool a neighborhood. This allowed them to calculate an urban heat island index (UHI) for each block group, a measure of how much hotter these areas are due to the appearance of the built environment.

The average per capita UHI index for all locations studied was 8 degrees Fahrenheit, but some places may feel even hotter. You can explore Climate Central interactive map online to see how this works nationally and at the census block group level in each city.

In New York City, for example, the average per capita ICU index reached 9.7 degrees – meaning that the way many neighborhoods were built makes them feel about 10 degrees warmer than they would without the same expansion. urban. New York’s top weather observation station is located in Central Park, where tree cover and vegetation can have a cooling effect in comparison. In 2021, On the edge explored New York City with thermal cameras and also found large differences in temperatures from neighborhood to neighborhood.

The good news is that we know how to undo the urban heat island effect. Simple measures like painting roofs and other surfaces lighter colors, planting trees and making roofs greener can help neighborhoods cool down. This could make an even bigger difference in the future as climate changes makes hot flashes more frequent and intense.

“It’s very easy to go out and say, ‘Oh, this area is warmer.’ But I think the logic behind it is very explicit: Why is it hotter?” Brady says. “I think this leads to your solution.”