I am lucky enough to live in the Caribbean and play golf year-round. That also means that it is always warm and relatively humid year-round. My home course is a walking course and I recently analyzed my scores and discovered that my "blow-up" holes and mental errors were occuring later in the round when I would start to lose energy and focus. I found this article and the tips on nutrition and hydration are actually helping my game. Hope it helps in your game as well-
http://www.rcga.org/_uploads/documents/Greg%20Wells%20-%20Golf%20Nutrition.pdf