Many athletes, amateur and professional alike, compete in and train for outdoor running events every year, and even more participate in outdoor sports in general. Many major sport events such as the Summer Olympic and Paralympic Games and World Championships take place in summer and mostly in the Northern Hemisphere. Therefore, athletes are often at risk of sustaining heat illnesses during heat extremes, which are exacerbated by climate change.1

Heat illnesses describe a group of pathologies ranging from relatively minor to very severe symptoms such as potentially fatal exertional heat stroke.2 3 The risk for heat illnesses increases with high air temperature, high solar radiation, high humidity, low wind speed and strenuous exercise requiring continuous muscle work.4 There are different strategies to prepare athletes for exercising in the heat, and thus reduce the risk for heat illnesses including acclimatisation, acclimation, hydration and cooling strategies.5 However, to properly implement those strategies, the forecasting of the environmental conditions prior to the event is paramount, but the timing of the forecasting depends on the strategy to be implemented.

Anticipation of the expected temperature can be done by the consultation of a location’s climate data from recent decades.6 The latest International Olympic Committee consensus statement on sport events in the heat recommends that bidding cities provide retrospective weather data for the 10 previous years and proactively measure environmental conditions at the respective competition venues.5 However, the variability of weather superimposed …