At the center of a map is a civilization that's under pressure from climate change. Originally, this civilization was situated around a Mediterranean-like sea. It began along the south shore of this sea, then spread. The idea is that those that live on the south shore see themselves as the "center" of the civilization--their genealogies are more glorious, their cities older, and so on. However, the south is in decline, in large part due to climate change, causing a lot of resentment towards the more prosperous north shore among these people. My original idea was that the south is becoming drier.
What I would really like to do instead, though, is to make the climate too wet. Just to be different. I'd like to flood some of the old cities, and make it difficult for them to farm in the areas that remain above water. I've read up on problems with tropical agriculture on Earth and so far have that increased rainfall would more quickly deplete the soil of nutrients and would force them to switch to crops that are not as productive. But this isn't quite as dire as I would like.
Would the soil become more acidic, like the soil in a lot of tropical areas on Earth, or is that acidity due to something besides just too much water?
And what could lead to this increase in wetness anyway? I have a vague idea of the weather pattern changing, forcing wet air that normally moved on to stop and dump there, but my understanding of is rather vague and I can't get a handle on it.
Ideas? Real-world examples to look at?
I've googled variations of climate change, increased precipitation, tropical agriculture, and so on.
ETA Thanks everyone! You've given me some neat ideas to consider.