The Heat Is On: Observations and Trends of Heat Stress Metrics during Florida Summers

Abstract

Abstract Extreme heat is annually the deadliest weather hazard in the United States and is strongly amplified by climate change. In Florida, summer heat waves have increased in frequency and duration, exacerbating negative human health impacts on a state with a substantial older population and industries (e.g., agriculture) that require frequent outdoor work. However, the combined impacts of temperature and humidity (heat stress) have not been previously investigated. For eight Florida cities, this study constructs summer climatologies and trend analyses (1950–2020) of two heat stress metrics: heat index (HI) and wet-bulb globe temperature (WBGT). While both incorporate temperature and humidity, WBGT also includes wind and solar radiation and is a more comprehensive measure of heat stress on the human body. With minor exceptions, results show increases in average summer daily maximum, mean, and minimum HI and WBGT throughout Florida. Daily minimum HI and WBGT exhibit statistically significant increases at all eight stations, emphasizing a hazardous rise in nighttime heat stress. Corresponding to other recent studies, HI and WBGT increases are largest in coastal subtropical locations in central and southern Florida (i.e., Daytona Beach, Tampa, Miami, and Key West) but exhibit no conclusive relationship with urbanization changes. Danger (103°–124°F; 39.4°–51.1°C) HI and high (>88°F; 31.1°C) WBGT summer days exhibit significant frequency increases across the state. Especially at coastal locations in the Florida Peninsula and Keys, danger HI and high WBGT days now account for >20% of total summer days, emphasizing a substantial escalation in heat stress, particularly since 2000. Significance Statement Extreme heat is the deadliest U.S. weather hazard. Although Florida is known for its warm and humid climate, it is not immune from heat stress (combined temperature and humidity) impacts on human health, particularly given its older population and prevalence of outdoor (e.g., agriculture) work. We analyze summer trends in two heat stress metrics at eight Florida cities since 1950. Results show that heat stress is increasing significantly, particularly at coastal locations in central and southern Florida and at night. The number of dangerous heat stress days per summer is also increasing across Florida, especially since 2000. Our analysis emphasizes that despite some acclimation, Florida is still susceptible to a serious escalation in extreme heat as the climate warms.