Visiting China in August: Where will it be tolerable and where will it be unbearably hot?

I'm currently planning a trip to China in early August (for 5 weeks). I'm worried about the heat. I know that it will be hot everywhere, but are there some regions that are hotter than others? Or some places that have some shade or more breeze? Or any places with water or lakes to cool off? Or some mountain towns to retreat to for a few days? Any help or advice would be great. Thank you.