Weather, Geography, and the Calamity

[Enkidoh]

Further adding to Professor Moose's excellent explanation about pre-Calamity Thanalan, there was a quest in version 1.0 which stated that Thanalan was originally forested like the Black Shroud an inderterminable time in the past, but had gradually become arid until it was the semi-desert savannah seen in 1.0 (and the even more arid version it is now).

Hence there was a sincere attempt in Ul'dah by ecologically-minded souls (one of whom was fittingly from Gridania) to try and make Thanalan green again by planting trees, efforts that were constantly being frustrated by vermin eating the sproutlings (specifically, dodos, hence the player was tasked to kill the vermin as part of the quest.). I haven't seen this information stated anywhere in ARR though, so whether it is still canon I am unsure.

EDIT: the 1.0 quest in question was called 'An Inconvenient Dodo' and the entirety of the quest dialogue is recited below:

U'bokhn: "Parched much? How's about a cold beverage to slake that adventurer's thirrrrst?"
U'bokhn: "What is it then? You think I enjoy this? Doling out drinks to passersby? It ain't the most glamorous work, I grant you that. But it's got to be done-for the sake of the Desert Shade."
U'bokhn: "Never heard of the Desert Shade have you? See, there? You have only proved my point. Well, I'll enlighten you. It is a group of concerned souls fighting for the ecology of Ul'dah. We do what we can to stop these arid lands becoming even drier."
U'bokhn: "I hail from Gridania, myself. I couldn't believe me own peepers first time I laid eyes on Ul'dah. Never knew there to be landscapes without the merest trace o'green."
U'bokhn: "Willing to wager you didn't know this whole area used to be forests, either, did you? Aye, well it was. It pains me heart to think of all them trees and shrubs and whatnot, slowly drying up and dying."
U'bokhn: "And look at this hellish-hot, barren wasteland left in the wake of it all."
U'bokhn: "That's why I gathered together all those who felt like I did, and founded the Desert Shade. Even got sanctioned by the Botanists' Guild so as we could register guildleves and get you willing and able-bodied adventurers to help our cause."
U'bokhn: "Trouble is, on the rare occasions when we are able to get seeds to sprout in these fallow barrens, those damned stuffed dodos come along and gobble 'em up! It's enough to make you think Mother Nature don't know what's in her own best interest!"
U'bokhn: "The most recent success we've had is over by the Nanawa Mines. I'm asking every adventurer to kill me eight stuffed dodos. You look capable enough. What do you say?"
(after accepting)
U'bokhn: "I see there's a bit o' green in your heart! I'll mark the lands we fertilized on your map."
U'bokhn: "Hurry along now, and kill the vile little buggers before they polish off all of our sprouts!"
(Upon completion)
U'bokhn: "Parched much? How's about a cold beverage to slake-oh! It's you!"
U'bokhn: "Tell me, have you killed those winged vermin that have been eating our sprouts?"
U'bokhn: "Magnificent! May their blood feed the soil! Thanks to you, the Desert Shade's efforts won't be for naught!"
U'bokhn: "You've done Eorzea a great service. I thank you-and the land thanks you too. Here, take this."