Here in the Adelaide Hills where we've just lost 80+ homes and a friend in a huge bushfire, I decided I would run in the middle of the day in around 30degC. Huge mistake! I drank two glasses of water before leaving but very soon realised that I was dehydrated. I finished the 30mins but it just about knocked me over with exhaustion. I wasn't expecting that.
Presumably it was the increased temperature that had the impact. Oh, then there's the incline that I normally stay away from. Will search out flat terrain and stick to running in the cool of the mornings.