I remeber watching a program or article about US cities in extreme cold, it may have been detrioit where buildings are linked together. Maybe this could be the answer for extreame heat, as you would not go outside as much.
Cities need more shade, more water fountains for example but I think it is doable to create a system where you can get around, solar panels on buildings could power air con for example or at least power fans to get air moving around more.