For anyone else who was also wondering how three African savanna animals could die of mainland Japan levels of heat:

Hideaki Karaki, professor of veterinary medicine at the University of Tokyo, told local media that high humidity makes it difficult for lions to regulate their body temperatures.

He explains that instead of sweating, lions take deep breaths to expel moisture from their airways. When the moisture evaporates, body temperature drops.

But the lions’ body temperatures could not drop sufficiently in high humidity, he says.

Another factor could be the sudden spike in temperature in mid-July, leaving the animals insufficient time to acclimatise to the heat, Karaki adds.

Sounds like torture

That’s not good. Japan, fix that.