National Heat Awareness Day

Facts About National Heat Awareness Day

Heat Is the Deadliest Weather Hazard in the United States

Across decades of records, extreme heat kills more people in the United States each year than any other kind of weather, including hurricanes, tornadoes, floods, or lightning.

The National Weather Service notes that major heat waves, such as the 1980 central U.S. event that caused more than 1,250 deaths and the 1995 Chicago heat wave with over 700 deaths, illustrate how quickly mortality rises when high temperatures persist for days without relief.

Nighttime Heat Is Rising Faster and Increases Health Risks

Climate assessments show that in many regions of the United States, minimum nighttime temperatures are rising faster than daytime highs.

Hot nights prevent the body from cooling down, which increases strain on the heart and can worsen chronic conditions like cardiovascular and respiratory disease, especially among older adults and people without air conditioning.

The Fifth National Climate Assessment reports that the frequency of warm nights has increased markedly since the mid‑20th century and is projected to continue climbing as the climate warms.

Humidity Makes “Feels Like” Temperatures Much More Dangerous

The National Weather Service’s heat index combines air temperature with relative humidity to estimate how hot it actually feels to the human body.

High humidity slows the evaporation of sweat, which is the body’s main cooling mechanism, so a temperature of 92°F with 65 percent humidity can stress the body like an air temperature near 100°F.

As a result, the same thermometer reading can be relatively safe in dry conditions but hazardous when the air is moist.

Urban Heat Islands Can Be Over 10°F Hotter Than Nearby Areas

Cities tend to run significantly hotter than surrounding rural regions because pavement, dark roofs, and concrete absorb and store heat while trees and vegetation are often sparse.

The U.S. Environmental Protection Agency reports that on a hot summer afternoon, urban air temperatures can be 1 to 7°F higher than nearby rural areas, and urban surfaces like asphalt can exceed rural surface temperatures by as much as 27°F.

These “urban heat islands” particularly endanger residents in neighborhoods with fewer trees and more impervious surfaces.

Structural Racism Shapes Who Dies From Extreme Heat

Research by New York City’s health department found that an estimated 525 New Yorkers die each year from heat-related causes, and that Black residents have about twice the heat-stress death rate of white residents.

The report links these disparities to structural racism, including historical housing discrimination that left many Black communities with fewer trees, less green space, and poorer-quality housing that is harder to cool, as well as unequal access to air conditioning.

Outdoor Workers Face Elevated Heat Illness Risk on the Job

Construction crews, farmworkers, delivery drivers, and other outdoor workers are at higher risk of heat exhaustion and heat stroke because they often perform strenuous tasks in the sun for hours at a time.

Federal occupational health agencies highlight that physical exertion intensifies heat stress, especially when workers are not acclimatized to heat, lack shaded rest breaks, or have limited access to cool drinking water.

These conditions can turn otherwise manageable temperatures into life-threatening exposures.

Extreme Heat Drives Hundreds of Thousands of Medical Visits

Analyses of hospital and emergency department data indicate that spikes in temperature translate quickly into health care demand.

One national study estimated that extreme heat event days in the United States are associated with nearly 235,000 emergency department visits and more than 56,000 hospital admissions each year, for problems ranging from dehydration and heat stroke to heart, kidney, and respiratory complications triggered or worsened by heat.