Here we say "Pours like from a bucket" when in rains heavily
Some even say, that our country name derived from word "rain", as it rains quite often here. But official statistics, as I remember, doesn't even put us in top 100.
I think one or two swear words can describe every more or less extreme situation quite accurately. And since they are widely known and easy to use, many people use them. Of course, while using idioms you can be more original and inventive, so these expressions can't and won't be completely replaced by anything.