You might want to check for spider mites, which thrive in hot dry air. Mine had the same symptoms as yours during the summer and I realized that it was growing near the exhaust of my window AC. In fact, some of the vines began to fry and die back after the leaves turned yellowish and checking on the back of the leaves, I found the tell-tale sign of black dots left from the mites. Once I redirected the flow of the AC's hot air and sprayed the plant's leaves with "Mite beater" (by Bonide I believe), it helped alot and it is putting out new growth.

I think it's a foregone conclusion that where you live, it can get hot and dry, so not sure if you change that unless you can position the vine in a protected spot and perhaps give it some shade if it is in full sun.