The game was already installed on my main drive when the problem happened. Plus, not every area was affected; in fact, in most areas it would run smoothly.
Viewing post in [RPG] GROVE: "Dark Places" (v0.308) comments
If you have a save from before you entered the desert, it might be an idea to go back to your room at the inn, interact with the journal there, and disable the game's UI effects for a while. Some of the desert ones can cause some machines to lag.
Other small things that might be relevant:
Make sure you're playing the most recent version of the game (v0.308)
Check your computer isn't in power-saving mode or anything else like that which could hamper performance
Playing the game windowed as opposed to full-screen can help slightly too.
Other than that... it might just be down to your computer's performance and specs, I'm afraid.