Extreme Heat
Extreme heat can be defined in two ways: It’s considered a period of two to three days above 90 degrees Fahrenheit (U.S. Homeland Security) or summertime temperatures that are much hotter and/or more humid than average (CDC). Across Tennessee, an extreme heat temperature varies depending on geography, since a particular location’s average temperature at a given time of year may be different than another’s.
Extreme heat can be measure in multiple ways. One way to measure extreme heat is the Wet Bulb Globe Temperature (WBGT). WBGT is a
measure of the extreme heat in direct sunlight, which accounts for:
temperature, humidity, wind speed, sun angle and cloud cover (solar radiation).
Another way to measure extreme heat is by using the heat index. The heat index, also known as the apparent temperature, is what the temperature feels like to the human body when relative humidity is combined with the air temperature. As humidity rises, sweat will not evaporate as quickly, and the body will not release heat efficiently.
Wet Bulb Globe Temperature and heat index differ as the wet bulb globe temperature takes into consideration temperature and humidity and is calculated for shady areas.
In either measure, extreme heat is especially dangerous when high temperatures are paired with humidity. This can lead to heat-related illness or death in extreme cases. In fact, extreme heat is one of the leading causes of weather-related deaths.
Effects of Extreme Heat
While extreme heat affects all Tennesseans, some groups are more vulnerable than others: such as those with chronic health conditions and outdoor workers. Factors such as the inability to control body temperature or respond to heat due to medication(s) and working long hours in the heat make them more susceptible to experiencing heat-related illness.
Additionally, extreme heat impacts the environment around us. Long-lasting high temperatures can contribute to respiratory issues due to the buildup of air pollutants. This is especially concerning for Tennesseans with asthma or COPD.
Extreme heat also creates urban heat islands. Urban heat islands are areas where buildings, roads, and other infrastructure are highly concentrated, and trees are scarce. Due to the lack of greenery, these structures absorb and re-emit the heat creating "islands" with higher temperatures than other areas.
Quick Facts About Extreme Heat
- 2023 was the hottest year on record across the globe.
- Each year, at least 2,000 emergency department visits in Tennessee can be attributed to extreme heat and heat-related illnesses; in 2023, there were over 4,000 emergency department visits related to heat.
Extreme Heat Data and Tools
Each summer throughout Tennessee, extreme heat creates a burden amongst all, whether we are working in the heat or trying to enjoy a nice day at the pool. This is why we track that! To view data about extreme heat days in our state, please browse our available datasets and observe how our summers are heating up! To track extreme heat in real-time, please browse the tools below and stay cool in your area!
National Integrated Heat Health Information System (NIHHS) Tool
The National Integrated Heat Health Information System (NIHHS) tool is used to look at multiple aspects of extreme heat. Using this tool, you can view the current heat conditions, the 7-day heat risk in your area, and extreme heat estimates in 2050 all in one place!
CDC's Heat and Health Tracker
The Heat and Health Index (HHI) is a national tool that incorporates historical temperature, heat-related illness, and community characteristics data at the ZIP code level to identify areas most likely to experience negative health outcomes from heat and help communities prepare for heat in a changing climate. Each ZIP code has a single ranking for the overall HHI and rankings for individual components so that users can make informed decisions to prepare for and prevent the negative health impacts from heat in their communities.
National Weather Service (NWS) HeatRisk Tool
The NWS HeatRisk is an experimental color-numeric-based index that forecasts the risk of heat-related impacts to occur over a 24-hour period. HeatRisk takes into consideration:
- How unusual the heat is for the time of the year
- The duration of the heat including both daytime and nighttime temperatures
- If those temperatures pose an elevated risk of heat-related impacts based on data from the CDC
Additional Resources
If you'd like to learn more about extreme heat and its effects, please visit some of the links below!