It presents the argument well, although to me it feels a bit deterministic as well as influenced a bit by colonialist thought. But it does seem undeniable that the environment was affected by the Arabs in ways it would have not have been otherwise.
But what about rainfall? Disregarding historic degredation, changing the amount of moisture in the atmosphere would affect how people use the nearby land. And that's something that making a few lakes in the Sahara, especially one as big as the Qattara Sea has been proposed to be, will do.
Also, what about any interplay between the Qattara Sea (or more distantly, the Sahara Sea of Tunisia/Algeria) and the Aswan Dam? Egypt would love any way to reduce evaporation of water in the Nile Basin to increase the amount used for irrigation.