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Millions of Americans are feeling the effects of this summer's heat waves, which scientists tell us are made worse by climate change. Extreme heat is most miserable and dangerous in cities, especially in the most developed areas of cities that lack trees and open space. That's according to a new analysis of temperature data in 44 U.S. cities, including Charlotte and Raleigh.
It's called the urban heat island effect. Climate news and research group Climate Central found that 41 million people in those 44 cities live in census tracts where summer temperatures average 8 degrees or more above the surrounding area.
Scientists with the group World Weather Attribution say heat waves like this past month's extreme heat in North America, Europe and China would not have happened without climate change caused by human activity such as burning fossil fuels.
The Climate Central analysis estimated an "urban heat island index" value for each census tract based on each area's land use, said Jen Brady, a senior data analyst at Climate Central.
"We're talking about elevated temperatures as a result of the in-place environment. …We're thinking about buildings, pavement and lack of things, like a lack of trees, lack of parks," Brady said.
This analysis is more detailed than other studies of the urban heat effect. But these figures are estimates, rather than actual temperatures. Brady compiled them by matching satellite maps of land use with research about how different land uses affect temperature.
The analysis shows that the hottest zones can be not only in downtown areas, but also in outlying areas, such as shopping centers or even parks with large bodies of water, Brady said.
In the Charlotte region, for example, about 9,000 people feel at least 9 degrees hotter than the area's baseline summer temperature. They're in two areas:
- Uptown Charlotte, with its dense grid of skyscrapers and office buildings.
- And an area south of Belmont, in Gaston County, that includes shopping centers, two public schools and sprawling residential neighborhoods.
Many other neighborhoods surrounding uptown average 8.5 degrees warmer than the area's baseline. So do scattered areas at the edges of the Charlotte area, from a dense area of warehouses and factories in South Charlotte, along South Tryon Street and Interstate 77, to the area north and west of Mountain Island Lake.
In Raleigh, downtown and areas just to the north and west registered as 8.5 degrees hotter. But the hottest area — 9 degrees higher — is an area north of Raleigh around Falls Lake.
That's because water has the same ability to reflect sunlight as pavement, Brady said.
In Raleigh and Charlotte, most census tracts that Climate Central examined are 6.5 to 9 degrees warmer than the cities' baseline temperatures on hot days. But parts of some U.S. cities are 10 degrees hotter — as in Washington, D.C., New York, Chicago and San Francisco.
About 80% of the U.S. population lives in cities, where heat can reach these extremes.
This data is important because it can help policymakers and planners identify areas with the highest heat-related health risks.
"Those (are) places that we should really be paying extra attention to because they're going to be even at higher risk for, unfortunately, heat-related deaths and illnesses," Brady said.
Last summer, North Carolina saw 3,739 emergency department visits for heat-related illness, according to the N.C. Department of Health and Human Services. About 60% of those visits were in the Piedmont region, where the state's largest cities are located.
Brady said the maps can also guide our responses to climate change. Potential solutions in these areas can include planting trees or using umbrellas for shade; adding parks; and using lighter pavement colors, which can be cooler.
Also, Brady said, "I think it really identifies areas where solutions need to be put in place. And unfortunately, it also identifies a lot of disparity that we noticed there."
Other studies have found that extreme heat tends to affect people of color and lower-income areas.
"It's very unusual for the highest income neighborhood in town to also be a heat island, or the most severe heat island," Brady said.
