WBGT and the heat alert system in Japan

I was looking this up for myself, but I thought I'd share it as it might be useful to others too. I was curious about how and when they decide to issue a heat alert in Japan, because they've issued them for my area quite a lot in the last two weeks. I am also curious as to why so many schools, sports clubs and companies don't adhere to the warnings. I can't information online about the why for that, but here's what I learned about the heat alert system.

Japan's heat alert system is operated by the Japan Meteorological Agency (JMA) in conjunction with the Environment Ministry. There is a standard one and a "special" one. The latter was only introduced in 2024. They use the WBGT, an acronym I've been seeing on the television a lot lately, but I didn't know what it stood for. Evidently it stands for the Wet Bulb Globe Temperature (WBGT) , which is an index to assess heat stress and issue alerts.

Wet Bulb Globe Temperature (WBGT)

Wet Bulb is also a new term to me. According to Wikipedia the wet bulb temperature is " the lowest temperature that can be reached under current ambient conditions by the evaporation of water only."A wet-bulb temperature above 35°C is the point the human body can no longer effectively cool itself through sweating. However, some argue that in a humid country like Japan that temperature could be (should be?) 31°C.

But in Japan, they have decided on 33°C as the cut off point. Thus, when the WBGT is predicted to reach 33 or higher, a general "Heatstroke Alert" is issued. If the WBGT is forecast to exceed 35 at all observation points in a prefecture, a "Special Heatstroke Alert" is issued.  As far as I am aware, the Special Heatstroke Alert has not yet been issued, but the standard one has multiple times already. 

The government issued alert uses words like "Severe Warning, heavy exercise prohibited" and then you drive by a school where the kids are playing soccer or tennis outside. I wish they would enforce the advisories more strictly. Because heat stroke is a real and very dangerous threat in Japan every summer, but I think particularly this summer. Please stay safe and cool.