Story at a glance

  • Researchers analyze city temperatures in relation to outer regions to gauge the effects of urban planning on hot temperatures.
  • Cities with tall buildings, low greenery and faltering sidewalks and roadways tend to have hotter temperatures.
  • These components trap heat inside city limits, exacerbating already climbing temperatures.

As sweltering conditions break records across cities in the Pacific Northwest and wildfires rage, a new study looks at how modern urban design is far less heat resistant than residents may know.

Focusing on what are called “urban heat islands,” the report was published by the research group Climate Central and analyzes the infrastructure in some of the U.S.’s major cities that contribute to exceedingly hot conditions inside the city limits.

Between the effects of anthropomorphic climate change and these specific design features, many metropolitan areas exhibit temperatures hotter than their surrounding regions.

The main factors contributing to dangerously hot temperatures include a given city’s albedo, percentage of plants and greenery, population density, as well as the average building height and the average width of streets.


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A city’s albedo is the percentage of light — in this case, sunlight — reflected by a surface. A lower albedo implies a surface, such as concrete on sidewalks and asphalt on roads, is absorbing more heat, which then warms that surface and contributes to higher temperatures.

More trees and plants in a city can contribute to both cooling shade and carbon sinks, which remove heating carbon dioxide from the atmosphere.

Measuring multiple cities by these metrics, the top five U.S. cities with the hottest temperature relative to areas just outside the urban parameters include New Orleans; Newark, N.J.; New York City; Houston; and San Francisco.


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Tall buildings in each of these cities contribute to a high index score. Population density and impermeable, hot surfaces also contributed largely to these high scores.

“Urban heat islands are local—caused by development and the increase of impermeable surfaces and loss of vegetation in cities, impacting the local microclimate,” the report explains. “While humans are creating new urban heat islands, this does not explain the warming trends that scientists have been recording. We see evidence of warming across the planet, including in the oceans where urbanization is not a factor and in weather stations in rural areas.”

Many of the solutions include infrastructure repairs, like whitewashing roads and sidewalks to help them absorb less heat. Planting more trees and investing in urban forestry and agriculture is also a key investment in bringing down temperatures.

Shorter-term solutions to reducing heat-related fatalities include helping vulnerable city residents pay energy bills and having cooling centers that are publicly accessible.

Part of President Biden’s expansive infrastructure bill calls for helping cities become more heat resilient.


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Published on Jul 14, 2021