Health Insurance
Heat Wave Season in Major Metros Triples Between 1960s and 2020s
Summer’s approaching, and many Americans look forward to warmer weather. However, as temperatures continue to rise across the globe, Americans are feeling the heat more than ever.
In fact, heat wave season has more than tripled between the 1960s and 2020s — and heat-related deaths have jumped 857.5% between 1986 and 2022.
In addition to detailing our findings, we’ll cover expert tips on health insurance and reducing exposure to extreme heat — and when to seek help.
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Key findings
- Heat wave season in the major metros has more than tripled since the 1960s. The average length of heat wave season across 50 of the most populous metros jumped from 23.75 days a year in the 1960s to 72.68 in the 2020s. In the same period, these major metros went from an average of 2.17 heat waves a year to 6.14.
- Across the 50 large metros measured, San Juan, Puerto Rico, saw the biggest jump in heat waves between 1961 and 2021. Here, the average number of heat waves increased by 14.25 in this period. Tampa, Fla., saw the average number of heat waves jump by 9.64, while New Orleans saw the average rise by 9.06.
- Bronx County, N.Y., has the highest percentage of residents socially vulnerable to extreme heat. Here, 45.4% of residents have at least three factors that would make them vulnerable in an extreme heat event. It’s followed by Hidalgo County, Texas (37.7%), and Kings County, N.Y. (36.0%).
- By state, Mississippi is the most socially at risk, with 30.8% of residents vulnerable to extreme heat. It’s followed by New Mexico (29.3%) and New York (28.4%).
- Heat-related deaths have increased by 857.5% between 1986 (when records began) and 2022 (the latest year of data available). In 2022, there were 383 heat-related deaths, up from 40 in 1986.
How is social vulnerability measured?
Researchers utilized U.S. Census Bureau Community Resilience Estimates data to determine the percentage of residents with at least three social vulnerabilities in the event of extreme heat. The risk factors are:
- Having financial hardship (an income-to-poverty ratio less than 130% or spending greater than 50% for housing/rental costs)
- Being a single- or zero-caregiver household (only one or no individuals ages 18 to 64 living in the household)
- Having poor housing quality
- Having a communication barrier (either with limited English speaking or no one older than 16 with a high school diploma in the household)
- Not having a full-time, year-round employed individual in the household
- Having a significant disability
- Not having health insurance coverage
- Being 65 or older
- Not having vehicle access or using commute methods that increase exposure
- Not having internet access
Heat wave season triples in major metros
Hotter days may be on the horizon. Between the 1960s and 2020s (ending in 2021 — the latest data available), the average length of heat wave season across 50 of the most populous metros more than tripled, jumping from 23.75 days a year to 72.68.
Climate change certainly plays an outsized role here. The rate of warming per decade since 1982 is more than three times as fast as the rate of warming per decade since 1850, according to a Climate.gov study. Additionally, the 10 warmest years on record have occurred between 2014 and 2023 — the two decades with the highest average length of heat wave season by a wide margin.
Heat wave changes over time across 50 of the largest metros
Decade | Frequency (average number of heat waves per year) | Duration (average length of individual heat waves, by days) | Season (average length of annual heat wave season, by days) | Intensity (average temperature above local threshold during eat waves, Fahrenheit) |
|---|---|---|---|---|
| 1960s | 2.17 | 3.00 | 23.75 | 1.95 |
| 1970s | 2.84 | 3.21 | 33.97 | 2.06 |
| 1980s | 3.22 | 3.30 | 38.81 | 2.15 |
| 1990s | 3.96 | 3.47 | 47.51 | 2.25 |
| 2000s | 4.67 | 3.65 | 53.50 | 2.30 |
| 2010s | 5.96 | 4.04 | 68.52 | 2.36 |
| 2020s | 6.14 | 4.03 | 72.68 | 2.32 |
Source: ValuePenguin analysis of Environmental Protection Agency (EPA) data.
Heat wave seasons aren’t only getting longer — heat waves are growing in frequency. Across these major metros, the average number of heat waves per year nearly tripled from 2.17 in the 1960s to 6.14 in the 2020s.
According to ValuePenguin health insurance expert Divya Sangameshwar, this increase will significantly impact Americans’ health.
"When we’re exposed to extreme heat, it can compromise our body’s ability to regulate temperature, leading to cascading and worsening illnesses, including heat cramps, heat exhaustion, heatstroke and hyperthermia," she says. "Heat waves have also been associated with an increased risk of aggression, which can result in crime and violence."
In fact, a 2023 Center for American Progress report estimates that the U.S. will spend over $1 billion on health care due to extreme heat each summer — and the most vulnerable populations are at risk.
"The risks of extreme heat are greatest among populations disproportionately exposed to heat with limited or no resources to prepare or protect themselves," Sangameshwar says. "They include low-income Americans, minorities, people 65 and older or people exposed to heat by working and living in places with inadequate protection against the heat. Among these populations, hospitalizations and even deaths from heat can occur rapidly."
(We’ll get deeper into heat vulnerability later.)
San Juan, Puerto Rico, sees biggest jump in heat waves
Not all parts of the U.S. have been affected equally by rising temperatures. Diving deeper into the 50 metros measured, San Juan, Puerto Rico, saw the biggest jump in the number of heat waves during the period analyzed, increasing by 14.25. San Juan also saw the biggest change in the length of heat wave season, jumping 134.68 days — one of just three metros in the triple digits.
This is largely because Puerto Rico, like all Caribbean islands, is particularly vulnerable to climate change due to its more delicate ecological systems.
Tampa, Fla., followed, with the average number of heat waves jumping by 9.64 and heat wave season increasing by 92.34 days. Meanwhile, New Orleans saw the number of heat waves rise by an average of 9.06 and the length of heat wave season increased by 102.58 days.
As coastal metros with traditionally warmer summers, it may not be surprising that these cities rank second and third. According to a study published on Nature.com, coastal cities can be more vulnerable to heat waves — particularly those with tropical climates.
Metros with biggest increase in number of heat waves between 1961 and 2021
Rank | Metro | Change in average number of heat waves per year | Change in average length of individual heat waves, by days | Change in average length of annual heat wave season, by days |
|---|---|---|---|---|
| 1 | San Juan, PR | 14.25 | 1.37 | 134.68 |
| 2 | Tampa, FL | 9.64 | 2.04 | 92.34 |
| 3 | New Orleans, LA | 9.06 | 4.13 | 102.58 |
Source: ValuePenguin analysis of EPA data.
Conversely, just four of the metros analyzed saw roughly the same number of heat waves a year in 2021 as in 1961. These include San Diego and Los Angeles — coastal metros with traditionally temperate summers — and Rochester, N.Y.
Jacksonville, Fla., is an exception here. Despite being a coastal metro with traditionally hot summers, it still saw roughly the same number of yearly heat waves.
Full rankings
Metros with biggest increase/decrease in number of heat waves between 1961 and 202
Rank | Metro | Change in average number of heat waves per year | Change in average length of individual heat waves, by days | Change in average length of annual heat wave season, by days |
|---|---|---|---|---|
| 1 | San Juan, PR | 14.25 | 1.37 | 134.68 |
| 2 | Tampa, FL | 9.64 | 2.04 | 92.34 |
| 3 | New Orleans, LA | 9.06 | 4.13 | 102.58 |
| 4 | Miami, FL | 8.85 | 1.43 | 82.25 |
| 5 | Austin, TX | 6.94 | 1.36 | 62.36 |
| 6 | San Francisco, CA | 6.79 | 2.90 | 111.43 |
| 7 | Atlanta GA | 6.21 | 2.24 | 85.37 |
| 8 | Norfolk, VA | 5.92 | 1.71 | 75.32 |
| 9 | Detroit, MI | 5.76 | 1.14 | 54.77 |
| 10 | Las Vegas, NV | 5.75 | 2.98 | 61.15 |
| 11 | Honolulu, HI | 5.62 | 1.78 | 47.82 |
| 12 | Birmingham, AL | 5.53 | 2.50 | 67.46 |
Source: ValuePenguin analysis of EPA data.
Bronx County, N.Y., has most socially vulnerable population
Heat waves can massively impact a person’s health — particularly those who may not be able to escape the heat due to economic or other factors. That’s known as social vulnerability — some places have a higher percentage of social vulnerability than others. (See the box below our key findings for a more in-depth definition of social vulnerability.)
By county, Bronx County, N.Y., has the highest percentage of residents at risk of extreme heat, with 45.4% having at least three risk factors. That’s followed by Hidalgo County, Texas (37.7%), and Kings County, N.Y. (36.0%).
Poverty rates likely play a role here. All three counties have poverty rates far above the national rate of 11.5%. The poverty rate in Bronx County is 27.6%, while the poverty rate is 27.4% in Hidalgo County and 19.8% in Kings County.
3 counties with the highest percentage of residents socially vulnerable to extreme heat
Rank | County | % of individuals with at least 3 risk factors present | % of individuals with no risk factors present |
|---|---|---|---|
| 1 | Bronx County, NY | 45.4% | 10.3% |
| 2 | Hidalgo County, TX | 37.7% | 16.5% |
| 3 | Kings County, NY | 36.0% | 13.6% |
Source: ValuePenguin analysis of U.S. Census Bureau Community Resilience Estimates data.
According to Sangameshwar, access is the biggest risk factor for these populations.
"Access to air-conditioned housing, health insurance, affordable health care, transportation or jobs that are indoors or that offer protection against extreme heat play a huge role in vulnerability," she says.
Notably, Miami — which ranked fourth among the metros with the biggest jump in the number of heat waves per year — also has a significantly vulnerable population. In Miami-Dade County, 31.3% of the population had at least three risk factors for extreme heat, seventh overall.
Looking more broadly by state, Mississippi had the most socially at-risk population, at 30.8%. New Mexico (29.3%) and New York (28.4%) rounded out the top three. Once again, poverty likely plays a role here. In Mississippi, 19.1% of the population is in poverty, while that rate is 17.6% in New Mexico and 14.3% in New York.
Full rankings
100 counties with the highest percentage of residents socially vulnerable to extreme heat
Rank | County | % of individuals with at least 3 risk factors present | % of individuals with no risk factors present |
|---|---|---|---|
| 1 | Bronx County, NY | 45.4% | 10.3% |
| 2 | Hidalgo County, TX | 37.7% | 16.5% |
| 3 | Kings County, NY | 36.0% | 13.6% |
| 4 | New York County, NY | 34.9% | 11.6% |
| 5 | Queens County, NY | 33.9% | 14.7% |
| 6 | Philadelphia County, PA | 33.4% | 19.8% |
| 7 | Miami-Dade County, FL | 31.3% | 21.1% |
| 8 | El Paso County, TX | 31.0% | 22.0% |
| 9 | Essex County, NJ | 30.6% | 22.7% |
| 10 | Hudson County, NJ | 30.0% | 17.1% |
| 11 | Kern County, CA | 29.7% | 22.0% |
| 12 | Fresno County, CA | 29.1% | 21.7% |
Source: ValuePenguin analysis of Census Bureau Community Resilience Estimates data.
States with the highest/lowest percentage of residents socially vulnerable to extreme heat
Rank | State | % of individuals with at least 3 risk factors present | % of individuals with no risk factors present |
|---|---|---|---|
| 1 | Mississippi | 30.8% | 26.6% |
| 2 | New Mexico | 29.3% | 23.8% |
| 3 | New York | 28.4% | 25.7% |
| 4 | Arkansas | 27.8% | 27.9% |
| 5 | Alabama | 27.7% | 30.2% |
| 5 | Louisiana | 27.7% | 28.3% |
| 7 | West Virginia | 27.0% | 30.7% |
| 8 | Florida | 26.6% | 27.7% |
| 9 | Kentucky | 26.0% | 32.1% |
| 10 | Oklahoma | 25.9% | 28.8% |
| 11 | South Carolina | 25.8% | 30.7% |
| 11 | Texas | 25.8% | 28.4% |
Source: ValuePenguin analysis of Census Bureau Community Resilience Estimates data.
Heat deaths jump 857.5% between 1986 and 2022
As heat waves rise and exposure risk increases, the chances of a heat-related injury or death will naturally rise. Between 1986 and 2022 (the full period for which data was available), heat-related deaths increased by 857.5%, jumping from 40 to 383.
The biggest jump occurred in 1995, with a 3,420.7% increase in heat-related deaths. That’s largely due to a historic heat wave across the Midwest and many East Coast cities in July 1995. Following that, 2005 saw a 2,533.3% increase in heat-related deaths, again due to an oppressive July heat wave, this time in the western U.S.
Change in heat-related deaths by year
Year | Heat-related deaths | % change |
|---|---|---|
| 1986 | 40 | N/A |
| 1987 | 38 | -5.0% |
| 1988 | 41 | 7.9% |
| 1989 | 6 | -85.4% |
| 1990 | 32 | 433.3% |
| 1991 | 36 | 12.5% |
| 1992 | 8 | -77.8% |
| 1993 | 20 | 150.0% |
| 1994 | 29 | 45.0% |
| 1995 | 1,021 | 3,420.7% |
| 1996 | 36 | -96.5% |
| 1997 | 81 | 125.0% |
Source: ValuePenguin analysis of National Weather Service (NWS) data.
"The increase in heat-related deaths isn’t surprising, but it’s alarming and should be seen as one of the many impacts of worsening climate change," Sangameshwar says. In fact, a global temperature increase of 2 degrees Celsius by midcentury could lead to a 370% increase in heat-related deaths worldwide, according to a report published by The Lancet.
Combating extreme heat: Top expert tips
As temperatures start rising again this summer, protecting yourself against the heat is more crucial than ever. Sangameshwar offers the following advice:
- If you’re part of the socially vulnerable population, look into assistance programs. Funds from the Low Income Home Energy Assistance Program (LIHEAP) can help pay for home energy bills, AC unit repairs or replacements and more.
- If you’re a Medicaid recipient, know your emergency costs are covered. "Medicaid recipients should know the costs of their emergency room visits or urgent care visits to treat heat-related injuries are covered," she says. "The uninsured shouldn’t avoid seeking care either, as many hospitals have charity programs that can assist with paying for treatment."
- Whatever your income level, educate yourself on extreme heat and how it can impact you or your family. "Make sure you have enough clean drinking water and stay hydrated," Sangameshwar says. "Water is best. Avoid sugary or alcoholic beverages during a heat wave, as they can accelerate dehydration and worsen your heat injury. Additionally, prepare your home for the hot season by checking and fixing your air conditioning and air filters, identifying local cooling centers near your home in case you need a place to cool down and having plenty of lightweight cooling clothing to wear."
Methodology
ValuePenguin researchers analyzed Environmental Protection Agency heat wave data by frequency, duration, season and intensity from the 1960s through 2020s (ending in 2021). We ranked 50 major metros and the states according to the frequency change between 1961 and 2021.
We also analyzed U.S. Census Bureau Community Resilience Estimates data to determine the counties and states most socially vulnerable to extreme heat events. Specifically, we analyzed 2019 (the latest available) data on the percentage of residents with at least three social vulnerabilities in the event of extreme heat.
Finally, researchers analyzed National Weather Service data on heat-related deaths between 1986 and 2022 (the latest available).