Heat Wave Map: See where Americans face the most extreme heat risk

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It was mid-July and that summer had already become a top contender for the hottest in recorded Texas history. There were three dozen in San Antonio, which would normally experience triple-digit heat for about three days through July. Houston, Waco and Austin also saw temperatures 5 to 8 degrees above normal. The state was on fire and Texans were using a record amount of electricity to keep cool.

New calculations suggest this record-breaking Texas summer could look normal by mid-century.

Across much of the United States, millions of people are expected to experience more frequent and prolonged exposure to extreme temperatures—a threat that will only increase as climate change worsens. The new data, released Monday by the nonprofit First Street Foundation, calculates the heat risk each property in the contiguous United States faces over the next 30 years, the length of a typical mortgage, and provides some of the most detailed estimates nationwide. It uses the heat index, a measure of how hot it feels outside by factoring in temperature and humidity.

An analysis of the group’s data by The Washington Post found that today’s climate conditions have caused an estimated 46 percent of Americans to endure at least three consecutive days of hotter than 100 degrees each year. In the next 30 years, that will increase to 63 percent of the population.

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Days with a heat index above 100°F in 2053


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Nowhere is the danger more widespread than in the South, where global warming is expected to deliver an average of 20 extra days of triple-digit heat per year. In some southern states like Texas and Florida, residents have seen over 70 consecutive days when the heat index exceeded 100 degrees Fahrenheit.

“We’re talking about taking the already hot summer and stretching it out by months,” said Jaime González, director of the Houston Healthy Cities program for the Nature Conservancy in Texas. “It’s going to lead to all sorts of disruptions to everyday life.”

This data comes as more Americans are moving to some of the hottest parts of the United States. For more than a decade, census data has shown that Sun Belt states like Arizona, Texas and Florida are attracting new residents, while the Northeast and Midwest are not.

The larger pattern identified by the First Street model suggests that people living in the South are likely to face some of the most dramatic changes over the next few decades. A previous analysis found that the southern half of the country also faces the greatest risk of wildfires.

First Street’s lot-level heat stress analysis is based on a combination of high-resolution measurements of surface temperature data, tree cover, impervious surfaces – such as pavement and asphalt – and proximity to water. It incorporates global climate models from the United Nations Intergovernmental Panel on Climate Change and is based on a moderate scenario in which global greenhouse gas emissions peak around 2040 and then slowly decline. If countries act faster or don’t take climate-friendly action, the outcome could change.


areas with at least three

consecutive days of

dangerous heat

percent of the population

Living in areas exposed

dangerous heat

Arizona, Colorado, Idaho,

Mont., Nev., NM,

Utah, Wyoming.

Del., Fla., Ga., Md.,

NC, SC, Va., W.Va.

Iowa, Kan., Minnesota,

Mo., ND, Neb.,

SD

Fig., Ind., Mich.,

Ohio, Wis.

Conn., Mass.,

Maine, New Hampshire,

RI, vt

Areas with at least three consecutive

days from dangerous heat

percent of the population living there

exposed areas dangerous heat

Arizona, Colorado, Idaho, Nevada,

Mont., NM, Utah, Wyo.

Del., Fla., Ga., Md.,

NC, SC, Va., W.Va.

Iowa, Kan., Minnesota, Mo.,

ND, Neb., SD

Fig., Ind., Mich.,

Ohio, Wis.

Conn., Mass., Maine,

NH, RI, Vt.

areas with min

three consecutive days of

dangerous heat

percent of the population living there

exposed areas dangerous heat

Arizona, Colorado, Idaho, Mont.,

Nev., NM, Utah, Wyo.

Del., Fla., Ga., Md., NC,

SC, Virginia, W.Va.

Iowa, Kan., Minnesota, Mo.,

ND, Neb., SD

Illinois, Ind., Mich., Ohio, Wis.

Conn., Mass., Maine,

NH, RI, Vt.

The analysis found that Florida’s Miami-Dade County is likely to experience the most extreme changes. While the county records a heat index of over 100 degrees on about 50 days, there will likely be 91 brat days through 2053.

“We know that we have a heat problem here. This is exactly what we were expecting,” said Jane Gilbert, Miami-Dade Chief Heat Officer.

Unlike the West and Midwest, which have been scorched by extreme heat waves this year, South Florida faces months of chronic high heat, Gilbert said. This drives up energy costs, putting outdoor workers, the homeless and those who cannot afford to air-condition their homes all day at risk. The county has designated May 1 through October 31 as the official heat season and launched an awareness campaign targeting neighborhoods with the highest rates of heat-related hospital admissions.

Gilbert said property-level heat projections could help county officials advocate for more tree planting and painted roofs, which reduce the need for air conditioning.

“When it’s really good modeling, it’s extremely valuable to help us develop policies that require cooling,” she said.

Florida leads the states that will see the largest increase in days with a heat index above 100 degrees. But residents throughout the Gulf Coast and Southeast Atlantic are also likely to face more weeks of dangerous heat due to muggy summer conditions, low elevation and the warm waters of the Gulf of Mexico.

Even harsher temperatures are expected to hit a portion of the country stretching from northern Texas and Louisiana to Illinois and Indiana. While the central United States is not typically thought to bear the brunt of the summer heat, First Street analysis found that ten million more people living in that region are likely to experience a heat index above 125 degrees by mid-century will. The group calls this area a “belt of extreme heat.”

This part of the country lies between the Appalachian Mountains and the Rocky Mountains and “almost forms a bowl that draws moisture into the area, which pushes up those ‘perceived’ temperatures,” said Jeremy Porter, First Street’s chief research officer.


By mid-century, the number of counties experiencing at least one day with a 125°C heat index will increase from 50 to more than 1,000.

days with extreme

Dangerous heat in 2053

Heat index ≥125°F

By mid-century, the number of counties experiencing at least one day with a 125°C heat index will increase from 50 to more than 1,000.

days with extreme

dangerous heat in 2053

Heat index ≥125°F

By mid-century, the number of counties experiencing at least one day with a 125°C heat index will increase from 50 to more than 1,000.

days with extreme

dangerous heat in 2053

Heat index ≥125°F

By mid-century, the number of counties experiencing at least one day with a 125°C heat index will increase from 50 to more than 1,000.

days with extremely

dangerous heat in 2053

Heat index ≥125°F

According to the National Weather Service, a heat index of 125 degrees — which the agency classifies as an “extreme danger” day — makes heat stroke “very likely.” And while there’s no set temperature threshold at which roads, bridges and trains fail or water pipes rupture, recent examples show that it doesn’t take a 125-degree day to overwhelm essential infrastructure.

Unequal risk

Heat is the weather-related killer in the United States. But like other effects of climate change, it is felt unevenly. The poor, the elderly, very young children and those with certain chronic conditions are most at risk.

Treeless neighborhoods full of buildings, parking lots, and paved streets absorb and retain more heat than areas with tree-lined streets and parks. Scientists call this the urban heat island effect. Across the country, this pattern is unfolding in city after city, concentrating the heat in most of the low-income Black and Latino neighborhoods that decades ago were labeled risky investments.

Today, about 67 percent of black-majority neighborhoods in the United States are experiencing a dangerous heat wave, defined as more than three consecutive days with a heat index above 100 degrees. But that will increase to 82 percent in 30 years, leaving a population that is already more vulnerable to heat significantly more exposed.

The Post also found that 71 percent of the country’s poorest neighborhoods are likely to endure intense heat by mid-century.

Extreme heat also makes the work more dangerous. Today, around 3.8 million people work outdoors and are experiencing at least one severe heatwave. In 30 years, that number will increase by almost 30 percent to 4.9 million.

In the Houston borough of Gulfton, a shift to more days of dangerous temperatures and humidity would expose the area’s 45,000 residents — many of them immigrants from Afghanistan, Syria and Central America — to unbearable heat. The neighborhood has a park and few trees. Two years ago, when Houston officials worked with scientists and volunteers to map the heat island effect, they found that parts of Gulfton were 17 degrees hotter in the afternoon than the coolest neighborhood they had measured.

González said that until recently, talks about climate change in Houston have been dominated by flooding and sea-level rise. The devastation caused by Hurricane Harvey in 2017 forced the city to face the likelihood of increasing storms. Now this summer’s record-breaking heat is forcing another shift in focus, he said.

“We’re getting a little preview of what it might be like if we don’t take more action,” González said.

About this story

The 2023 figures in the analysis reflect the current climate. They are estimates based on 2014-2020 averages, adjusted to include temperature and humidity projections from the United Nations Intergovernmental Panel on Climate Change global climate model ensemble. Population estimates are based on the 2020 American Community Survey 5-year census data. Regions and divisions were identified by the Census Bureau. Outdoor worker estimates are based on 2020 County Business Patterns and include the agriculture, construction and landscaping sectors.

Editing by Monica Ulmanu.

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