August 12, 2017 9:59 am JST

Welcome to Tokyo, Olympians; try to stay in the shade

2020 host counting on trees and a special resin to keep things cool

A worker takes his pruners to a tree along a street in Tokyo's Chiyoda Ward.

TOKYO -- If you live in the Japanese capital, please step outside for a moment. No, sorry, never mind. Don't do that; it's too hot. And you probably already have an appreciation for what officials are trying to do -- cool things down for the 2020 Olympics.

The idea is to protect athletes and spectators alike from the sticky, energy-sapping heat that wallops Tokyo in the summer. Metropolitan officials seem to be concentrating on keeping surface temperatures down.

One way they are doing this is by allowing roadside trees to grow to a size large enough that their crowns cast enough shade to keep street surfaces from overheating.

Athletes have suffered dehydration and heatstroke at past Olympics and world championship events. The 2020 Games will be held from July 24 to Aug. 9 -- the thick of the Tokyo summer.

This helps to explain why on a blazing late July day workers were trimming the trees that line Sotobori Street in Tokyo's Kanda district. They were not involved in typical pruning. Rather, they were trying to trim the branches to a uniform length so that they can get on with the job of growing out their foliage forming a single, shade-casting canopy.

In fiscal 2016, the metropolitan government surveyed trees along 45km worth of roads, some of which will be used for the marathon and others near sites where Olympic venues will be.

It selected some 2,000 trees for the special pruning, about 70% of the total.

One plan is to grow oriental planes along Yasukuni Street in Tokyo's Chiyoda Ward so that their shade-throwing girth measures 6.5 meter and they stand 12 meter tall. A typical oriental plane found on the street now measures around 2.7 meter in width and 8.6 meter in height. They have a three-year deadline to get up to Olympic snuff.

A test conducted by the Japanese government found that when the shade of a tree covers a road that would otherwise have the sun beating down on it, the surface temperature can fall by up to 7 C.

According to a senior metro government official, this heat-relief measure is not temporary. "We will keep the shade after the Olympics," the official said, "and create an environment where pedestrians can stay cool."

Roads themselves are also having work done to them. The metropolitan government last summer conducted a survey and found that surface temperatures in Tokyo's Nihombashi district can rise up to 60 C on days when the temperature reaches into the 30s.

So the Tokyo metro government as well as authorities from waterfront communities have been coating asphalt, a voracious heat trap, with resins capable of reflecting heat from sunlight.

The measure is expected to reduce surface temperatures by up to 8 C.

According to Tetsuo Yai, a professor of urban engineering at the Tokyo Institute of Technology, because roads in Tokyo are surrounded by skyscrapers, their surface temperatures can easily rise since the heat from the cars that drive over them -- as well as that from office building air conditioners -- has nowhere to go.

This effect adds to the humidity that Japanese summers are known for.

"During the Olympics, foreigners who are not acclimated to Japan's muggy summer days will be visiting," Yai said. "Local governments should bolster measures so that [athletes and spectators] can either safely take part in or watch the events."

(Nikkei)

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