CR 58:183-191 (2013)  -  DOI: https://doi.org/10.3354/cr01199

ABSTRACT: Extreme heat poses a serious health threat, particularly for people like athletes, soldiers, and workers engaged in outdoor physical activity. For athletes, the American College of Sports Medicine (ACSM) specifies environmental risk categories based on the wet bulb globe temperature (WBGT). We examined the present and future frequency of days that exceed the most extreme ACSM risk category (>32.3°C), when training and practice activities should cease. Using a physically based model, the WBGT was computed for present (1991-2005) climate conditions using standard weather observations and for future (2041-2070) climate conditions using an ensemble of regional climate model output. Results indicate diverse spatial patterns of exceedance across the US in the present-day climate, ranging from <5 d yr^-1 in northern portions of the country to >50 d yr^-1 across portions of the southeastern US and southern Arizona. Under a warming climate, the frequency of days unsuitable for practice sessions according to current ACSM guidelines increases considerably, ranging from 15 to >30 d yr^-1 in broad swaths of the country. Further, our temporal analysis revealed an expansion in the threat for extreme heat through the day ranging from late morning through early evening, although early mornings remain one of the safest periods to avoid heat exposure. Various adaptation strategies such as shifting practice times and developing heat acclimatization plans may be useful in mitigating the impacts of more frequent oppressive days on training sessions.

KEY WORDS: Climate change · Wet bulb globe temperature · Heat illness · Sports · United States