I don't know what to say, I guess it's because of lack of sunlight. Drinking is linked with depression, but so are many other things such as compulsive eating. My question is why do the start drinking instead of doing something else. I believe all of us had in their lives some down periods, but it doesn't make us alcoholics.
Alcohol probably takes effect quicker too. Dark, cold and rainy seem to have higher rates of depression also.