The 'scenario' is based on a simple yet unproven assumption that a warmer globe means a drier climate in specific localized regions. Yet there is no proof of this or a validated model for this.
We know what weather patterns form deserts, and what produces those weather patterns. Are you saying that we can't take a good guess at what will happen if we simply pour more energy into the existing weather patterns? I suspect that's something we're fairly good at.
With our inability to understand the feedback mechanisms in a warmer world that we've not yet witnessed, we might find that precipitation actually increases in some of these regions.
Yes, we might. But probably not. We've already had the opportunity to observe significant global warming, so our ability to make declarative statements about it is improving over time, and you're pretending that it itsn't.
I call general bullshit on the predictions that always say dry areas get dryer, wet areas get wetter, stormy regions get stormier. Its too simple an assumption in a complex system.
That's not the prediction. This is a prediction about one specific dry area. You know what's more suspicious than a prediction that a dry area will get dryer? Refusing to accept such a plausible prediction. They're making a quite believable claim (adding energy to a system will increase its extremes) and you are making the exceptional counterclaim. It is you with the responsibility of providing exceptional evidence.