I have a problem I have been noodling for my fantasy world. I have a plot point where a powerful magic artifact is used, and part of the effect is climate change in one region of the continent to become desert. In my original map sketch, this was going to happen by having part of the continent break off (i.e. ultra-rapid tectonic movement), but after learning more about how to make believable fantasy world climates, I can’t make this work. Any help brainstorming would be helpful.

Things I really want to keep: - some habitable region of the continent becomes desert after this event - event has some dramatic effect geologically, but open to different options than continental break up. - must be some other habitable/farmable, ideally temperate climate zone on the continent that remains habitable/farmable.