The high temperatures and humidity of Tokyo summers are causing concern ahead of the next Summer Olympics to be held from July 24 to Aug. 9, 2020, with experts warning that national and local government countermeasures to beat the heat may be insufficient.
"Once foreign athletes learn how hot Japanese summers are during the Olympic period, isn't it possible they will begin dropping out one by one?" asks one expert.
University of Tokyo professor Makoto Yokohari has been comparing Tokyo's weather trends with the temperatures of host cities of the Summer Games over the last 30 years.
"Tokyo summers are both very hot and humid. Compared with past host cities, the atmospheric conditions are the absolute worst, and this will take quite a toll on the human body," he warns.
The biggest worry is the marathon event. A team of researchers from Tokyo Metropolitan University and Saga University measured the mean radiant temperature (MRT) at about 1.2 meters from the ground at six locations -- places with almost no shade and those where many spectators are expected to gather -- along the marathon's planned course. The MRT takes into account the strength of sun exposure and the heat reflected off of the ground and surrounding buildings, thus giving a more realistic idea of the temperature athletes and spectators will actually experience than just the air temperature.
If the sky is clear on the day of the marathon, at the start time of 7:30 a.m., the temperature is expected to average approximately 33 degrees Celsius at the six locations, and top 37 degrees Celsius toward the end of the race at 9:30 a.m. However, at 5:30 a.m. the average temperature is only 27 degrees. The national and metropolitan governments proposed heat countermeasures such as improving the pavement, but the results of the research have shown that moving up the start time is far more effective in the fight against the heat.
"The earlier the marathon starts, the better," says Tokyo Metropolitan University assistant professor Eiko Kumakura. "Blocking sunlight in places with no shade and other measures are also necessary."
Heatstroke is also a worry for other events. Toin University of Yokohama professor Akio Hoshi and his research team calculated the Wet Bulb Globe Temperature (WBGT), which like MRT, uses the atmospheric data of air temperature, humidity and solar radiation, for the Tokyo metropolitan area for the period of the games over the last 10 years. WBGT is a heat index measured in degrees Celsius specifically used to set the temperature at which heatstroke is likely to occur.
The Ministry of the Environment sets a WBGT of over 31 degrees as a "dangerous" level and recommends that all exercise at that temperature be ceased in principle. However, according to the research team, the WBGT of the Tokyo area has been rising 0.4 degrees per year, and will surpass 34 degrees by 2020, well above the ministry's advised limit.
Additionally, when the team estimated the daylight hours during the games from 50 years of past atmospheric data, they concluded that 13 out of the 17 days of the Olympics will have clear skies. Unobstructed sunlight further increases the risk of heatstroke.
Not only the athletes, but the large numbers of the elderly and children expected to visit the games as spectators and the many volunteers under the hot sun are also at risk. Even for indoor events, the sudden temperature difference when leaving an air-conditioned venue for the outdoors may make athletes, spectators and volunteers ill.
"It's impossible to even estimate the number of people who may end up suffering from heatstroke during the Tokyo Olympics," says Hoshi.