I'm sure you've all noticed by now that it can rain quite a bit in-game. But in terms of practicality, where does all that rain go? Surely it can't just all evaporate or get absorbed into the stone! Like in the real world, that rain has to go some place. In theory, there would also be at least some kind of gradient on the ground and mountains as well. Together, this would cause the rain to go someplace.
For instance, if the player excavated a mountain, the water could flow into the excavated areas if the grading wasn't altered or pumps weren't set up. Or the player could excavate certain areas to create ponds or ditches to direct the water somewhere, e.g. to create arable land from sand. If there was a huge rainstorm, low-lying rooms and outdoor areas could flood for a time which would have to be remedied for farming areas. After all, before you can have a town or productive land, you need proper drainage.
For instance, if the player excavated a mountain, the water could flow into the excavated areas if the grading wasn't altered or pumps weren't set up. Or the player could excavate certain areas to create ponds or ditches to direct the water somewhere, e.g. to create arable land from sand. If there was a huge rainstorm, low-lying rooms and outdoor areas could flood for a time which would have to be remedied for farming areas. After all, before you can have a town or productive land, you need proper drainage.