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“Developed areas such as roads, buildings, sidewalks and roofs soak up heat in the daytime hours and radiate that heat through the night and into the next day,” said USGS scientist Jon Dewitz at EROS, who is on the NLCD team. 

“This amplifies the heat index when combined with larger developed areas and longer heat cycles. NLCD’s impervious surface calculations are critical baseline metrics for calculating and understanding the amplified risk of heat stress to our urban and vulnerable populations,” Dewitz added.   

NLCD is the definitive U.S. database for categorizing the type of material that covers land across the country, from field and forest to pasture and pavement and other developed surfaces. Landsat satellite imagery serves as the basis for determining those categories. This information helps, in a vast number of ways, people who manage land and resources—and populations.

In the Heat and Health Index, people can type in their ZIP code or select an area on a map of the United States to find out how their community ranks with the rest of the country in percent vulnerability to the effects of heat. They can also learn how their community rates in four factors that influence the effects of heat. 

One of those factors is Natural and Built Environment. It focuses on characteristics of natural and manmade attributes that increase exposure or sensitivity to heat or reduce a person’s ability to cope with extreme heat. The NLCD data provides information on land cover, or the percentage of developed, water-resistant surfaces; and land use, or the percent of land used for development. 

“NLCD has provided calibrated percent impervious surface models since 2001. These models give a very accurate measurement of the amount of developed area for every 30-meter pixel,” Dewitz said. 

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The Heat and Health Index’s three other factors are: 

• Historical Heat and Health Burden, about the community’s previous experience with heat compared to the rest of the country.
• Sensitivity, which considers the community’s prevalence of six pre-existing conditions that can increase the risk of heat effects on people with those conditions.
• Sociodemographic, comparing that community to the rest of the country in social and demographic characteristics that increase exposure or sensitivity to heat or reduce a person’s ability to cope with extreme heat.

The Heat and Health Index tool is designed to help identify the areas most vulnerable to extreme heat and to help individuals and communities make informed decisions to prepare for and prevent negative health impacts from heat.