Tokyo landscape summer sun
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Check these websites daily for heatstroke warnings in Tokyo

The heat stress index is updated hourly

Tabea Greuner
Written by
Tabea Greuner

For a few days now, Tokyo has been hit by a massive heatwave, with daily temperatures exceeding 30 degrees Celsius. To help you avoid heatstroke, NHK World Japan provides this English website with information on the most recent heat stress index, also known as the Wet Bulb Globe Temperature (WBGT) index.

It calculates the temperature as well as the humidity and radiation levels and assess their negative impact on our human body’s heat balance. Thanks to the easy-to-understand graph, you can see the index at different times of the day, so you know when to stay in and when it’s okay to go out. There’s also a forecast for the next day to help you plan accordingly.

To find out if a heatstroke warning has been issued for your area, you can also check this website by the Ministry of Environment, which is updated hourly.

Heat stress index
Photo: Ministry of Environment – screenshot of the heat stress index

As seen in the image above, the heat stress index indicates the heatstroke alerts that have been issued and in which region. There are also recommendations on the kinds of activities that should be avoided at certain WBGT levels.

While Japan is known for its extremely hot and humid summer, the early end of this year’s rainy season has brought forth a massive heatwave. On Saturday June 25, central Tokyo recorded 35.4 degrees Celsius; any temperature above 35 degrees Celsius is considered extreme heat in Japan. This is the first time since records began in 1875 that such a high temperature was measured in the Tokyo metropolis.

For the past couple of days, the government has encouraged everyone in Greater Tokyo to reduce electricity consumption as demand increases due to the heat. Today, on June 29, the government called on people again to take energy-saving measures between 3pm and 8pm. This doesn’t mean to stop using air conditioning, but to turn off unnecessary lights and electronic devices that are not in use.

Make sure to stay hydrated and avoid going out between noon and early evening when the temperature is at its peak. In case you feel ill or see someone who may be suffering from heatstroke, check this website on how to act accordingly.

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