It's actually been rather explicit for a while now. The New Battlefronts Visual Guide had been the first to specifically mention that only "portions" of Mandalore were desert, and it was in those deserts that the pacifist New Mandalorians dwell. The Essential Guide to Warfare notes that "swathes" of the planet were transformed, fully introducing the Republic conflict that was responsible as the "Mandalorian Excision." Even the Atlas, though, acknowledges the events of the series while still continuing to relate Mandalore's terrain as forested and possessing seas, alongside desert regions. With all of the above having been Jason Fry's handiwork, it really seems as though he's really spearheaded the effort to take on the issue and restore Mandalore. I'm actually a bit more partial to the New Battlefronts and Warfare guides' phrasing over Shadow Conspiracy's, personally, since having "much of the planet" be desert is a bit, well...much, considering that much of Mandalore's northern hemisphere is supposed to be covered in veshok tree forests that stretch nearly to the ice capped pole. But it's all good when you consider it as a non-definitive bit of passing prose. Also, Spoiler: The Last Jedi spoiler as if to solidify the move of Mandalore back to its established "roots," The Last Jedi features the protagonist going to Keldabe and the more verdant areas of Mandalore over Sundari and the deserts.