What does your world do with a season that no longer comes?
A festival timed to a flood that stopped flooding. A harvest song for a crop that no longer grows this far north. Climates drift over centuries, but the rituals built on them are stubborn and outlive their own reason. I keep coming back to the idea of a people still performing the shape of a season they have not actually lived through in generations, half memory and half instruction. Does your world ever notice the mismatch, or does the ritual quietly become about something else?