Adam Clarke on Isaiah 21:1

The desert of the sea - This plainly means Babylon, which is the subject of the prophecy. The country about Babylon, and especially below it towards the sea, was a great flat morass, overflowed by the Euphrates and Tigris. It became habitable by being drained by the many canals that were made in it.

Herodotus, lib. 1:184, says that "Semiramis confined the Euphrates within its channel by raising great dams against it; for before it overflowed the whole country like a sea." And Abydenus, (quoting Megasthenes, apud Euseb. Praep. Evang. 9:41), speaking of the building of Babylon by Nebuchadonosor, says, "it is reported that all this part was covered with water and was called the sea; and that Belus drew off the waters, conveying them into proper receptacles, and surrounded Babylon with a wall." When the Euphrates was turned out of its channel by Cyrus, it was suffered still to drown the neighboring country; and, the Persian government, which did not favor the place, taking no care to remedy this inconvenience, it became in time a great barren morassy desert, which event the title of the prophecy may perhaps intimate. Such it was originally; such it became after the taking of the city by Cyrus; and such it continues to this day.

As whirlwinds in the south "Like the southern tempests" - The most vehement storms to which Judea was subject came from the desert country to the south of it. "Out of the south cometh the whirlwind," Job 37:9. "And there came a great wind from the wilderness, and smote the four corners of the house," Job 1:19. For the situation of Idumea, the country (as I suppose) of Job, see Lam 4:21 compared with Job 1:1, was the same in this respect with that of Judea: - "And Jehovah shall appear over them,

And his arrow shall go forth as the lightning;

And the Lord Jehovah shall sound the trumpet;

And shall march in the whirlwinds of the south." Zac 9:14.