Well in my case i take a lot of water on my summer hikes and very little on my winter ones. And i don't take as much clothes for the summer. But the biggest difference you can do is time your hiking hours. If you start at 5-6 O'Clock in the morning in summer, than there is a good chance, that you will get high enough to avoid the extreme heat. You just need to have a lot of water and some sun protection. But our summers aren't nearly as hot as the ones in Arizona i believe. Especially in the mountains, the temperatures are usually around 25-30°C. But can reach to 40 in the valleys.