High temperatures trigger a flood of heat alerts in Japan


June 30, 2022

TOKYO – As the rainy season comes to an abrupt end this summer in region after region, the “heat stroke alert” system set up last year by the Ministry of the Environment and the Japan Meteorological Agency is already join the game.

The system aims to raise awareness of the risks of heat-related illnesses, using the long-established “heat stress index” which is based not only on temperature, but also on factors such as humidity, exposure to direct sunlight and the force of the wind.

Each prefecture issues a heatstroke alert on days when the Heat Stress Index, also known as the Wet Bulb Temperature Index (WBGT), is expected to exceed 33. On Monday, a total of 28 alerts were issued This year.

The highest level of the Heat Stress Index starts at 31 – which usually occurs when the temperature exceeds 35°C – resulting in a ‘danger’ warning. At this level, people are advised to be vigilant even in their daily activities.

A reading of 28 (“serious warning”) on the scale often precedes an increase in the number of people with heat stroke requiring transport to a hospital.

In July 2018, the temperature reached 41.1°C in Kumagaya City, Saitama Prefecture, the highest temperature ever recorded in Japan. The municipal administration informs the population of the issuance of an alert through loudspeaker announcements, e-mail and other means. Faxes are sent to households whose residents are hearing impaired.

Moreover, he goes so far as to make rounds in the city by garbage collection trucks and fire trucks, announcing through loudspeakers to refrain from going outside.

In Funabashi, Chiba Prefecture, on heatstroke alert days, the city allows people to cancel reservations for city-run sports fields or gymnasiums for that day. For example, reserving a city-run tennis court at Hoten Park costs ¥990 for two hours, and in principle, there are no refunds for last-minute cancellations. But this is canceled during an alert.

The cities of Niigata and Tama in western Tokyo are among those with similar arrangements.

Unconfirmed effects

It’s still unclear how effective the Heat Stroke Alert has been in opening people’s eyes to the risks associated with extreme heat.

Last year, when the system was first introduced, alerts were announced a total of 607 times between June and September, according to the Ministry of the Environment. During this period, the number of people requiring an ambulance due to heatstroke stood at 46,251, according to the Fire and Disaster Management Agency of the Ministry of Home Affairs and Communications.

While the ambulance figure was the lowest since 2015, an official from the Meteorological Agency pointed out: “Last summer, temperatures in August were lower than usual in western Japan. So we can’t say what effect the alert had [on reducing the number].”

Last year in Tokyo, alerts were issued over seven days in July and August. The number of heatstroke ambulance calls ranged from 60 to 170 a day, showing that there were more on days when there was an alert.

Masaji Ono, a visiting scholar at the National Institute for Environmental Studies, said: “Given that people refrained from going out during the pandemic, it is difficult to determine how many have increased their vigilance due to the alert. We do not have enough data to assess the effect.

The Department of the Environment provides a service that notifies people of heat stroke alerts and the Heat Stress Index via email or social media, but only around 150,000 people have signed up for it through the country. “The reality is that there are still few people using it,” an official said. “We hope more people will sign up.”

Growing interest

In the meantime, the alert system seems to have led to an increase in awareness and interest in the heat stress index.

Tokyo’s Chiyoda Ward distributed index measurement materials to its elementary and middle schools, kindergartens and other institutions this year. Schools and establishments are encouraged to make daily records, on which they base decisions such as whether or not to cancel sports club activities.

At Kojimachi Junior High School, teachers and school officials measure the index before physical education classes and sports club activities.

“Using the index as a guide, I try to find [with the best approach]like changing the intensity of the workout or moving it indoors where air conditioners are available,” said a 32-year-old teacher who coaches the school’s athletics club.

From July, the municipal government of Minami-Uonuma, Niigata Prefecture, plans to set up a heat stress index measuring device at the entrance of Ohara Sports Park, which is often used by students for summer training camps.

Kyoto Electronics Manufacturing Co. saw its orders for heat stress index measuring equipment double from 2017.

“With the implementation of the heat stroke alert, I think it’s clear that there are more people who want to understand the risks using the heat stress index,” said an official from the Kyoto-based company.


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