I would assume there is good data to back it up as depression rates tend to trend in this way way as well. With that said, alcoholism in Germany is still worse than with US states at the same light levels. Also if you take a peek at lists of alcoholism Lists of alcoholism there are both dark and sunny countries in favorable and unfavorable places. So I'm not sure it can be a sole factor in drinking rates but likely a contributing factor.

You could probably back this up by looking at the alcoholism rates in Scandinavia (especially Norway and Sweden)

Scandinavia had their own prohibition and still to this day have a strict 18/21+ drinking age with booze only being sold during very specific hours (and never on Sundays or religious holidays), with anything above I think 12% only available at the government run bottle shop