America’s most severe summer heat risks are heavily concentrated across the South, where persistent high temperatures overlap with vulnerable populations, outdoor employment and a disproportionate share of child hot-car deaths.
An analysis by Texas Law Dog found that all 10 states with the highest scores in its national Heat-Danger Index are located in the South or Sun Belt.
Florida ranked No. 1 with a score of 84.5, followed almost immediately by Arizona at 84.4 and Louisiana at 84.0. Texas ranked fourth with a score of 81.7, while Mississippi completed the five states facing the greatest combined summer heat danger.
The ranking arrives against a backdrop of increasingly frequent U.S. heat waves. Federal environmental data show that large American cities experience roughly three times as many heat waves as they did during the 1960s, while the heat-wave season has expanded by more than a month.
The consequences can range from heat illness and workplace injuries to vehicle failures and preventable deaths involving children trapped inside cars.
Florida Edges Arizona for the Highest Overall Heat Risk
Florida and Arizona were separated by only one-tenth of a point in the Texas Law Dog ranking, but the two states reached the top for different reasons.
Florida’s risk profile was shaped heavily by persistent overnight heat, with average summer minimum temperatures reaching 73.8°F.
Arizona, meanwhile, experienced the country’s most extreme daytime conditions. The state averaged a summer maximum temperature of 95.7°F, and its grid cells recorded an average of 33.5 days at or above 100°F.
Arizona also averaged 6.2 days at or above 110°F, the highest figure included in the analysis.
Texas recorded another notable result. Although it placed fourth overall, the state had the highest five-year average summer maximum temperature in the country, at 95.2°F from 2021 through 2025.
Rank | State | Overall Heat-Danger Score |
| 1 | Florida | 84.5|
| 2 | Arizona | 84.4 |
| 3 | Louisiana | 84.0 |
| 4 | Texas | 81.7 |
|5 | Mississippi |
| 6 | Arkansas |
| 7 | Oklahoma |
| 8 | Alabama |
| 9 | South Carolina |
| 10 | Georgia |
The concentration of Southern states reflects both geography and the way Texas Law Dog constructed the ranking. Four separate measures of temperature make up 80% of the final score, while population vulnerability accounts for the remaining 20%.
Warmer Nights Are Becoming an Increasing Part of the Heat Problem
Daytime temperature records often draw the most attention, but nighttime heat has become an increasingly important component of summer risk.
NOAA reported that 12 states recorded their warmest average July minimum temperatures in 2025, including several states across the Southeast and Mid-Atlantic.
The average temperature across the contiguous United States during July 2025 reached 75.4°F, which was 1.8°F above the 20th-century average.
Federal climate indicators also show that unusually warm summer nights have increased more rapidly than unusually hot summer days in recent decades.
Persistent nighttime warmth can be especially consequential because homes without adequate air conditioning and people who spend long periods outdoors may have fewer opportunities to recover from heat accumulated during the day.
Texas Law Dog gave nighttime temperatures 20% of the weight in its final ranking, making them the second-largest single temperature component after daytime heat.
Heat Waves Are Now Far More Common in Major Cities
The increase in extreme heat is also visible in the frequency and length of heat waves.
EPA data tracking major American cities show that the average city experienced approximately two heat waves annually during the 1960s.
That figure has climbed to approximately six per year during the 2010s and 2020s.
The typical heat-wave season is now about 46 days longer than it was during the 1960s, while individual heat waves in major urban areas have recently lasted around four days on average.
Cities monitored in the federal data include Dallas, Miami, Phoenix, Chicago, Boston, Memphis and Seattle.
That expanding exposure increases the number of days on which vulnerable people may face dangerous conditions, particularly when high humidity pushes the apparent temperature well beyond the reading on a thermometer.
Child Hot-Car Deaths Are Concentrated in High-Heat States
The state ranking also shows a strong overlap between extreme heat exposure and child deaths inside vehicles.
Of the 1,038 child hot-car deaths recorded nationally between 1998 and 2025, 531 occurred in the 10 states ranking highest on the Texas Law Dog heat index.
That represents 51.2% of all recorded deaths during the period.
The highest-risk states recorded the following totals:
| State | Child Hot-Car Deaths |
| Texas | 155 |
| Florid | 115 |
| Arizona | 46 |
| Georgia | 43 |
| Louisiana | 39|
| Alabama | 34 |
| Oklahoma | 31 |
| South Carolina | 25 |
| Mississippi | 23 |
| Arkansas | 20 |
Texas alone accounted for 155 deaths, by far the largest number among the 10 highest-risk states.
The contrast becomes even more pronounced after adjusting for the number of children living in each state.
The 10 highest-ranked heat states averaged 33.7 hot-car deaths per 1 million children age 14 and younger between 1998 and 2025. The 10 states at the bottom of the heat ranking averaged only 8 deaths per million children.
That means the population-adjusted rate was slightly more than four times as high among the states experiencing the greatest heat risk.
National Highway Traffic Safety Administration data show that 31 children died of vehicular heatstroke in 2025. NHTSA reports that more than 1,000 children have died in hot vehicles over the past quarter-century.
Emergency Departments See the Health Effects of Extreme Heat
Extreme temperatures also produce a measurable impact on hospitals.
CDC researchers documented 119,605 emergency department visits for heat-related illness in 2023, with the overwhelming majority occurring during the warmer months.
A total of 92% of those visits occurred between May and September.
July and August were particularly severe.
During those two months, heat-related illness averaged 303 visits per 100,000 emergency department visits, more than triple the rate recorded during May, June and September.
Men recorded a rate of 271 heat-related visits per 100,000 emergency visits, compared with 104 among women. Adults ages 18 to 64 were also among the groups experiencing particularly high rates.
Those patterns are significant because working-age adults may face heat both at home and on the job.
Outdoor Workers Face Elevated Exposure
For millions of workers, avoiding extreme temperatures is not always an option.
Construction crews, agricultural workers, landscapers, maintenance workers and other outdoor employees can spend hours performing physically demanding work during the hottest part of the day.
Federal data incorporated into Texas Law Dog’s analysis recorded 48 occupational deaths involving heat in 2024.
Of those fatalities:
– 40 occurred outdoors
– 24 involved construction workers
Longer-term federal records have documented more than 1,000 occupational heat deaths since the early 1990s, along with tens of thousands of cases serious enough to require employees to miss work.
Texas Law Dog’s analysis identified Arkansas, Oklahoma, Louisiana, Texas, Illinois and Arizona among the states with the highest documented construction-worker heat fatality rates.
Vulnerability Can Change a State’s Heat Risk
Not every state with a vulnerable population ranks among the hottest.
Texas Law Dog calculated a separate vulnerability component using the proportions of young children, older adults and people employed in outdoor or physically demanding occupations.
South Dakota received the highest vulnerability score, at 76.2, but ranked only 30th overall because its temperatures were considerably less severe than those found across the South and Southwest.
Several states stood out for individual population characteristics:
– Utah had the largest share of children younger than 5, at 6.5%.
– Maine had the largest older population, with nearly one-quarter of residents age 65 or older.
– Wyoming had the highest share of outdoor workers, at 14.4%.
Those figures show why temperature is only part of the equation. The same heat event may pose substantially different risks depending on the age, occupation and access to cooling among the people exposed.
Heat Protections Remain Uneven
The states experiencing the greatest heat do not necessarily have the broadest protections for people exposed to it.
At the time of the Texas Law Dog analysis, none of the 10 states with the highest Heat-Danger Index scores had a comprehensive statewide enforceable worker heat standard.
By comparison, California, Maryland, Minnesota, Nevada, Oregon and Washington had adopted broader heat rules, while Colorado maintained protections specifically covering agricultural workers.
California’s rules include requirements related to drinking water, shade, training and emergency procedures, with additional measures triggered as outdoor temperatures rise.
The difference between state exposure and state preparedness is significant because extreme heat can affect workers, children, older adults, drivers and emergency services simultaneously.
How Texas Law Dog Ranked the States
The Heat-Danger Index combined five measures:
| Measure | Share of Overall Score |
| Average summer maximum temperature, 2025 | 30% |
| Average summer minimum temperature, 2025 | 20% |
| Average summer maximum temperature, 2021-2025 | 20% |
| 2025 temperature anomaly | 10% |
| Population vulnerability| 20% |
Each variable was converted into a percentile score and then combined using those weights.
Additional measures, including the number of days reaching 90°F, 100°F and 110°F and historical child hot-car deaths, were used to provide context but did not determine the final rankings.
The resulting scores measure comparative heat danger, not the probability that an individual resident will become sick, suffer an injury or die.
Still, the broader patterns are difficult to miss.
The 10 states with the highest combined heat risk are all located across the South and Sun Belt, and those same states account for more than half of recorded child hot-car deaths since 1998.
At the same time, federal health data show more than 119,000 heat-related emergency department visits in a single year, while EPA data demonstrate that heat waves are becoming considerably more frequent and persistent.
The findings from Texas Law Dog therefore point to a summer hazard that extends beyond record-setting temperatures themselves. In the states experiencing the most severe conditions, extreme heat intersects with transportation, workplace exposure, child safety and public health, creating risks that can persist long after the hottest part of the day has passed.