I live...in Japan and I lived, in Tokyo and there are no trees, basically only concrete, hence the inspiration for my comment.

I live in Japan too. Sure there's very few trees in cities and more would help, but at the same time it's so hot that I doubt this would make cities significantly more livable in summer. We're not talking about some moderate summer heat like 33C low humidity. It's 36C high humidity in the afternoon and getting higher with climate change. In summer, the outside during daytime is for going from some place with AC to some other place with AC. Some people have to work for long time outside and they need something significantly stronger than a few trees to protect their lives.

With that being said, I agree some more trees would be nice.