I love the rain, why rainy weather would give me a debuff? :)
Yeah, you love the rain, but try to do some work in it, for example having to gather herbs in the thick woods or building your house while in a rainstorm.
Not going to be easy that's for sure. Also, if you have like 20-30kg of armor on you and you are soaking wet, you should walk/run slower.
Of course, these are theories, and we have to keep in mind that we are building a high fantasy game :)