hot weather and weight gain

Question
I believe that I found out the reason for my periodic weight gains. I was born in Russia where I lived till 17 yrs old, where the temperature stays relatively cold throughout a year. I have been living in USA, Europe and Argentina. Every summer during the hot weather I gain up to 20 pounds of extra weight (although I keep staying active and eat lighter diet). The rest of the year when temperatures are cooler I get plenty of exercise in the gym or outdoors (skiing) as well as maintain healthy eating; therefore I usually loose in an average 5-10 pounds.

Why my body tends not to burn calories during summers?
Is there a trick with changing a diet? (when its hot in addition to drinking lots of plain water I generally eat lots of waterbased meals: cereal with milk, popsickles, watermelon, salads, as a source of protein yogurt, cottage cheese, low fat cheese, eggs, fish.
I know that you might recommend me to stay away from hot climate so I could maintain lifestyle of winter seasons but I need to find a different option please.
I appreciate any of your recommendations.  

Answer
It's hard to say exactly what is going on with your weight gain in the summer because I don't know the portion-size that you're eating or the amount of exercise that you're doing.  

It could be that you actually exercise less vigorously although you still stay active.  For example, skiing burns many more calories than a walk on the beach.  

In addition, some of the water-based foods that you listed are high in sugar or fat.  Popsicles and watermelon are high in sugar and yogurt, milk, and cottage cheese are high in fat.  

You might want to try more vegetables and fruit during the summer and add more strenuous workouts like weight training.

Thanks for your question, Elena.  I hope that my answer has given you some help.

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