TOKYO >> Summer heat readings are expected to reach excessive levels at some of the venues for the 2020 Tokyo Olympic and Paralympic Games, posing a danger to athletes and spectators.

The Environment Ministry took temperature readings at 14 venues for the games from mid-July to mid-September in 2017.

According to the temperature readings, four venues, including the new National Stadium in Shinjuku Ward, Tokyo, and Saitama Stadium in Saitama, had at least 25 days of dangerously high levels.

The central and Tokyo metropolitan governments and the Tokyo Organizing Committee of the Olympic and Paralympic Games plan to step up measures to cope with the heat, with athletes and spectators expected to endure intense heat during the period.

The Tokyo Games will run from July 24 through Aug. 9, and the Paralympics from Aug. 25 through Sept. 6.

The ministry selected the 14 venues and set observation equipment outdoors at the venues from July 11 through Sept. 15 last year to measure the WBGT index.

The wet bulb globe temperature monitoring system, which was invented in the 1950s in the United States, measures heat based on temperature, humidity and direct sunlight.

The Japan Sports Association divides guidelines for exercise into several categories based on the index. According to the association, it is “generally safe” to do exercise when the index is below 21; “caution” is needed at 21 or above but below 25; “warning” is given at 25 or above but below 28; “severe warning” is given at 28 or above but below 31; and the association suggests not engaging in exercise if the index rises to 31 or above.

Of the 14 venues, an index reaching 31 or above was recorded at Kasumigaseki Country Club in Kawagoe, Saitama Prefecture, for 27 days; new National Stadium in Tokyo and Tokyo Stadium in Chofu, Tokyo, for 26 days; and Saitama Stadium for 25 days. The index reached at least 31 once every three days or so.

Index 31 or above is classified the most dangerous level of the five-level scale set by the Japan Sports Association. The association suggests that all exercise should be stopped.

A study committee of experts has started discussing how to deal with the heat for players, spectators and volunteers.

There are concerns over possible heatstroke for runners at the Tokyo Olympic marathon.

Authorities have already started working on constructing pavements with a surface that curbs temperature increases and planting roadside trees to provide shade. They are also considering making the starting time earlier than the initially scheduled 7:30 a.m.

The new National Stadium is designed to take in natural air flows so heat and humidity are not retained inside the stadium.

Osaka International University Prof. Yoshimitsu Inoue, who specializes in thermal physiology, said special consideration is needed for the elderly, children and foreigners who are not used to Japan’s summer heat. “Even if all possible measures are taken, there may be no perfect protective measure. But we should make the best efforts as a host country,” he said.