Regional Homeland Security Coordinating Committee

This site was created in cooperation with the Regional Homeland Security Coordinating Committee, and is supported by funding from the Department of Homeland Security.

 

Excessive Heat

Heat waves can be deadlyMany people do not realize how deadly a heat wave can be. In contrast to the visible, destructive, and violent nature of floods, hurricanes and tornadoes, heat waves are “silent killers.” More people die in an average year in Kansas City from heat-related conditions, than from all other weather types combined. According to the Center for Disease Control, an average of 350 people die from the effects of heat in the U.S. each year.

What is a heat wave?

A heat wave is a period of excessive heat lasting two days or more. High humidity, which often accompanies heat in the Midwest, can make the effects of heat even more harmful. While heat-related illness and death can occur due to exposure to intense heat in just one afternoon, heat stress on the body has a cumulative effect. Consequently, the longer a heat wave lasts, the greater the threat to public health.

The “heat-island” effect

Most heat-related deaths occur in cities. Brick and mortar buildings, asphalt streets, and tar roofs absorb daytime heat and slowly release it at night. Consequently, temperatures in urban areas can be warmer than rural areas by several degrees both day and night. This is commonly called the urban “heat-island” effect. In addition to the burden of heat, stagnant conditions often develop during heat waves, with pollutants increasing in concentration near the ground and contributing further to public health problems during heat waves.

Who is most vulnerable during a heat wave?

The elderly are most vulnerable to the dangers of heat, due to a diminished ability to perspire. Perspiration provides evaporation, which in turn provides cooling, so the elderly have a reduced capacity to release heat from the body.

In addition to the elderly, infants, young children, and people with chronic health problems (especially pre-existing heart disease) or disabilities are more vulnerable to the effects of heat waves. People who are not acclimated to hot weather, overexert themselves, are obese, or use alcohol or drugs are also at greater risk.

Measuring the combined effects of heat and humidity

The National Weather Service uses the Heat Index to compute the “apparent temperature,” which is a measure of how hot it feels to people at a certain combination of temperature and humidity. The greatest number of heat-induced illnesses and fatalities
from a heat wave usually peak two days after the maximum heat index values occurred.

The National Weather Service issues a Heat Advisory when a heat index of 105° will be reached for at least three hours, with little cooling expected overnight. A Heat Warning is issued if the heat index will reach 105° for three days or more, or if the heat index will reach 115° on a single day.

Heat Safety Tips