Of course, certain parts of Thanalan also experience so much rain these days that I'd be hesitant to call it a desert at all.
That still looks pretty healthy for a desert, though? Compare that to bits of Mojave National Park.
This isn't really on SE, it's pretty standard fantasy convention that desert and swamp = corrupted and bad since you can make them pretty hostile to the lead character. However the native plant and wildlife feel about it is never really considered.
It'd be cool if they'd open up some of the unfinished areas of the map and have flash floods there, maybe a bit like the CT rising waters mechanic.
It might be better compared to the African savannah or Australian outback than to a stereotypical desert.
It is certainly still a drier environment by comparison.
I don't see what's the confusion with Thanalan, it's overall climate seems perfectly in line with a Group B region (Arid to semi-arid) on the Koppen scale. The more healthy areas are simply steppes as opposed to actual deserts. If anything, it would make scientifically less sense if ALL of Thanalan were desert.
WHM storyline spoiler:
Early on in the storyline, Raya-O-Senna preaches to you to never give in to anger, as White Magic is supposed to be used against such negative emotions. Yet not only does her brother have no qualms against voicing his contempt at the idea of a common adventurer participating in the cleansing ritual, but during the quest where you discover A-Towa-Cant's grave has been robbed, Raya actually becomes the very type of person she describes as the antithesis of WHMs - she gets extremely angry, and even threatens physical violence against her Moogle minions if they don't help her find the culprit.
If Gridania's treatment of others matched its preaching of peace and harmony, it would be my favorite city-state. Unfortunately for the Padjal and the Elezen, it doesn't.
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I grew up in Southern Arizona, which is part of the Great Sonoran Desert. Parts of it are pretty lush, in comparison to what you've posted there from the Mojave. I don't find the Thanalan scenery to be at all out of scale with the deserts with which I am familiar. Now, the rain in Camp Moistbone... that is out of scale, unless the climate is changing there. But if the climate is changing, perhaps all the quest and leve texts describing how people there would kill for a drink of water needs to be revised?