CDC Environmental Health Nexus Newsletter | DEHSP CDC

April 22, 2022 | Volume 9

Environmental Health Nexus (EH Nexus)

Environmental News Nexus

The Centers for Disease Control and Preventions (CDC) Environmental Health Nexus (EH Nexus) shares environmental health messages with the public and gives special attention to environmental justice concerns.

EH Nexus newsletters provide information about environmental health issues and promote actions to help save lives. The newsletters communicate how to reduce harm from many threats, including climate change, contaminated food and water, toxic environments, and inadequate systems and practices.

This issue covers the following topics to help you prepare for extreme heat:

  • U.S. Summers are Hot, and Cities are Getting Even Hotter
  • Extreme Heat can Take a Toll on Cities
  • Why do we Care About Urban Heat Islands?
  • Act Fast and Prepare Yourself for Extreme Heat
  • People at Increased Risk from Extreme Heat
  • What is Being Done to Address Extreme Heat and Urban Heat Islands?
  • Urban Heat Island Mapping Campaign
  • What are the Next Steps?
  • Additional Environmental Resources

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U.S. Summers are Hot, and Cities are Getting Even Hotter

Extreme heat events in the United States are expected to become more common, more severe, and longer lasting as our climate changes. The 4th National Climate Assessmentexternal icon[2] projects that U.S. heat waves will become more frequent and more intense.

As temperatures continue to rise, it is important that you identify steps that you can take now to prepare for an extreme heat event pdf icon[PDF 8.6 MB][3].

Extreme Heat can Take a Toll on Cities

We all expect it to be warm in the summer, but sometimes the heat can be severe or even dangerous. A series of unusually hot days is referred to as an extreme heat event.

Extreme heat conditions are defined as weather that is much hotter than average for a certain time and place and sometimes more humid, too. Extreme heat is not just annoying, it kills hundreds of U.S. residents every year and causes many more to become seriously ill.

Cities tend to get much warmer than their surrounding rural landscapes, particularly during the summer. This is known as the urban heat islandexternal icon[4] effect. This temperature difference occurs when the unshaded roads and buildings in cities gain heat during the day and radiate that heat into the surrounding air. As a result, highly developed urban areas can experience mid-afternoon temperatures that are 15F to 20F warmer than surrounding, vegetated areas.

Temperatures are usually cooler at night, giving your body some relief from hot daytime temperatures. But during an extreme heat event, which typically lasts more than one day, nighttime temperatures might stay too warm to allow your body to cool down, especially if you live in an urban heat island.

People who reside in lower income neighborhoods are affected more due to the lack of greenery and other cooling infrastructure that provide shade during the day. A nationwide studyexternal icon[5] found that neighborhoods exposed to historical redliningexternal icon[6], typically lack green spaces and suffer most from having urban heat islands. The study found that 94% of redlined areas, which remain mostly lower income communities of color, are exposed to higher temperatures than are non-redlined, affluent communities. Reducing harmful environmental exposures can improve population health and may contribute to decreases in health disparities.

This diagram represents how an urban heat island can increase local air temperatures by several degrees. Source: US EPA 2006

Why Do We Care About Urban Heat Islands?

Elevated temperatures with urban heat islands affect a communitys quality of life and can adversely affect natural and built environments. These adverse effects include the following:

  • Compromised human health and comfort
  • Increased risk for respiratory illnesses, heat exhaustion, heat stroke, and heat-related death
  • Increased energy consumption to air condition homes and buildings, which leads to increased emissions of air pollutants and heat-trapping gases


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