“ The PCs are accosted in a major city containing at least one famous fortuneteller / prophet of the future. They are informed that their as-yet-unborn child will (insert terrible evil), and that, although they are very sorry, the PC must be executed to keep this from happening.”
“ The desert is a curse from the Water God upon the wicked people who live in the South.
Said people offended the Water God in some way, and so the Water God placed water-trappers, bizarre, water-sucking beings, in the soil, and within years, the wilderness became a desert.
Thus, the desert folk shamans have special powers that allow them to find water-trappers so that they can be dug up and their water harvested.”