Osamu Kashimura, a Tokyo University of Agriculture professor, examines the effectiveness of the heat-blocking pavement on Aug. 8 in Saitama. (Yusuke Saito)

A proposed measure to lower the surface temperatures of roads along the Tokyo Olympic marathon course could conversely increase the risk of heatstroke, according to a study.

The central government and the Tokyo metropolitan government plan to cover a 20-kilometer stretch along the route with a special heat-blocking agent by the 2020 Games to reflect infrared rays and rein in surface temperature increases.

But a team including Osamu Kashimura, an environmental physiology professor at the Tokyo University of Agriculture, discovered that the temperature and the wet bulb globe temperature (WBGT), an indicator to show heatstroke risks, rise at certain heights above the anti-heat pavement.

"The heat-blocking pavement, which reflects heat on its surface, could increase the risk of heatstroke on sunny days with strong sunlight at more than 30 degrees,” said Kashimura.

The findings will be presented at an upcoming academic conference.

Kashimura and his colleagues conducted a research this summer, which showed the temperature and the WBGT at specific heights increased owing to the pavement, although the road surface temperature dropped 10 degrees compared with asphalt.

In a study carried out in the morning of Aug. 8 in Saitama Prefecture, the air 50 centimeters above the pavement measured 39.4 degrees, 2.2 degrees higher than asphalt. The WBGT was also 1.3 degrees higher at 33 degrees.

The research results contradict the earlier findings of the central government.

The government has conducted experiments on multiple occasions to examine the effectiveness of the heat-blocking pavement since four years ago and found that the road surface temperature can be lowered 10 degrees compared with asphalt.

It also quoted a former Olympian as saying the pavement is obviously cooler.

“Its performance was best in temperatures on the bottom of feet to the air around the face,” the runner said.

According to government officials, no significant difference in the heatstroke risk indicator was reported between the pavement and asphalt.