Across Japan, the oppressive gloom of the rainy season is giving way to the country’s infamously hot summer, with its temperatures in the mid- to high 30s and its smothering humidity.

This combination of heat and humidity can be dangerous: In July 2018, a heat wave struck the country, with temperatures exceeding 40 degrees Celsius leaving more than 130 people dead due to heatstroke and more than 54,000 rushed to the hospital.

In summer 2019, more than 75,000 people required emergency care for heatstroke across the country, with 118 deaths from June to September. And in 2020, almost 65,000 people sought emergency care for heat-related issues, with 112 of them dying.

It is the same heat that athletes will have to compete in at the Olympics.

Heat has been an Olympics-related concern for Japan before. When Tokyo first hosted the Summer Games in 1964, the entire event was shifted to October in acknowledgement of the city’s sweltering summer temperatures.

Due to global warming, the city has only become hotter in the 57 years since those games. According to the Environment Ministry, Tokyo’s annual average temperature has increased by 2 C since the mid 1960s, and the number of days exceeding 35 C each year has risen from just one in 1964 to 12 each in 2018, 2019 and 2020. Japanese weather agency Weathernews forecasts that this summer will be hotter than average, with temperature spikes in late July and late August across the Kanto region.

People receive ice packs to cool off during a beach volleyball test event for the Tokyo Olympics at Shiokaze Park in the capital in July 2019. | AFP-JIJI
People receive ice packs to cool off during a beach volleyball test event for the Tokyo Olympics at Shiokaze Park in the capital in July 2019. | AFP-JIJI

Makoto Yokohari, an advisor to the Tokyo Organising Committee, told Reuters that the combination of high summer temperatures and humidity could be a “nightmare.”

“When it comes to heat stress or heatstroke, the problem is not only the temperature but also the humidity as well,” Yokohari said. “When you can combine these two … Tokyo is the worst (games) in history.”

In anticipation of the heat, organizers have moved the Olympic marathon and race walks north to Sapporo, where temperatures are typically much lower than those of the capital during summer.

These athletes should be considered fortunate since many won’t be lucky enough to escape the heat. The Olympic cycling road race is one event that is likely to be particularly brutal. Though sections of the course will approach 1,500 meters above sea level — altitudes that should be significantly cooler — the 234-kilometer men’s course will force athletes to climb a punishing 4,865 meters uphill over the race. The race begins at 11 a.m., during the hottest part of the day, and is expected to last five to six hours.

Excessive heat has multiple negative effects on the human body. According to the Rings of Fire report by the British Association for Sustainable Sport (BASIS), overheating can affect muscle and cardiovascular functions, which is made worse if athletes become dehydrated at the same time. In the worst case scenarios, excessive heat can lead to heatstroke, organ failure and death.

Increases in body temperature can also impact cognitive function and reduce the ability of people to perform the complex tasks required of high-level athletes. This could be particularly problematic in a sport such as tennis, which requires intense physical and mental stamina from individual athletes over the course of a multihour game.

Novak Djokovic, who won the 2021 Wimbledon men’s singles title on Sunday, urged Tokyo Olympics organizers in 2019 to factor the heat into their scheduling, saying, “With heat, it is going to be very, very tough for players and for fans, for anybody who is in the stadium.”

Runners jog on a sidewalk around the Imperial Palace during a heat wave in Tokyo last August. | AFP-JIJI
Runners jog on a sidewalk around the Imperial Palace during a heat wave in Tokyo last August. | AFP-JIJI

Although heatstroke among fans will no longer be an issue at most venues, following last week’s announcement of a largely spectatorless games, it is still a risk for everyone else attending the games, from athletes and officials to horses, which will compete alongside their riders in the outdoor equestrian events.

Five-time World Champion and three-time Paralympic medalist para dressage rider Rixt van der Horst told the writers of the BASIS report, “(A) horse is more difficult to cool down than a human and therefore the horse needs help to cool down sooner than we as humans. The horse heats up faster than a human and because of its large (muscle) mass also loses its heat less easily.”

As the Earth continues to warm, excessive heat is likely to become an issue for more and more athletic competitions. In early August 2020, Paris, which will host the 2024 Games, experienced its worst heat wave in more than a century. Los Angeles, which will host the 2028 Olympics, suffered from record-setting forest fires, which burned through 4 million hectares of California, in summer 2020.

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