Did a quick search on it and found none. So, why not a really bogging rain in some scenes? Even flooding that could fill up bunkers. Even if possible, when submerged some organic actors could lose health, rather rapidly. I am no ModWiz atleast yet so I post this here.

What you are asking for here is dynamc water, which is impossible (well it is, prove me wrong if it isn't!).

There you go.

Buy it from the crafts tab, the more you add to the scene the stronger it will rain.
It doesn't do anything except coming down from the sky and lagging your CC. Oh, and it drives the AI mad, like, makes them go Parkinsons.

Full credit goes to TLB because this is just Coming Of God with everything except the rain removed (I did add a custom module icon though...).