We’ve been saying it for years: the highest-returning investment your city can make in its neighborhoods is planting street trees. But the importance of the shade and cooling they provide goes far beyond the financial bottom line.

NPR, in conjunction with the University of Maryland's Howard Center for Investigative Journalism, has produced a fascinating new series about the effects of urban heat on physical and mental health.

One theme that runs throughout the series is how inequitable the impact of extreme heat can be. Different neighborhoods in the same city can vary in temperature by ten degrees or more. And, perhaps not surprisingly, the hottest neighborhoods tend to be the poorest. NPR looked at the 97 most populous American cities, drawing in part on income data from the U.S. Census Bureau and thermal satellite images from NASA and the U.S. Geological Survey. The results: "In more than three-quarters of those cities, we found that where it's hotter, it also tends to be poorer."

Photo via Wikimedia Commons.

Photo via Wikimedia Commons.

Again and again, the people experiencing the extra heat were often “a city's most vulnerable: the poorest and, our data show, disproportionately people of color. And living day after day in an environment that's literally hotter isn't just uncomfortable, it can have dire and sometimes deadly health consequences…" Higher temperatures lead to a spike in heart attacks and exacerbate existing conditions, including respiratory conditions like asthma, many of which the poor are already more vulnerable to.

Cities tend to be warmer than their surroundings rural areas and some city neighborhoods can be warmer than other neighborhoods, even those close by. This is a phenomenon  known as the urban heat island. The causes of heat islands will be well-known to readers of Strong Towns. They include, but are not limited to, the proliferation of asphalt and concrete — materials used to build roads and vast parking lots — as well as the removal of the green spaces (grass, trees, etc.) that would otherwise help cool cities. Low-income neighborhoods tend to have less green cover, as in Louisville, where wealthier areas have double the trees that their poorer neighbors enjoy.

We write often about the value of street trees here at Strong Towns. Street trees reduce greenhouse gases, increase property values, and increase safety for pedestrians and drivers. They frame our streets and make our places more comfortable and beautiful to live in. They also improve air quality and, as the NPR series demonstrates, help keep us cool. The benefits of trees to cities are so profound that, back in 2017, the Nature Conservancy went as far as to recommend funding trees as public health infrastructure.

Check out the NPR series. Then let us know in the comments below what steps your community has taken — or the steps you wish were being taken — to help mitigate the effects of extreme heat. Is planting and maintaining street trees part of that strategy?

Cover photo via NASA.