 Why was there fear for the wind shifting around the Hairy People?
Here at least the air was thick enough to support life, and somewhere nearby the outlaws who smuggled their precious contraband water into the water-starved domes of North Mars lay hidden. And the barrier became a jumbled mass of roughly-dressed stone slabs, from whose earth-filled crevices sprouted green life. So slowly was the spinner dropping that the blackened desolation of the other hemisphere came sliding up beneath his boots. This mysterious world that floated above the cavern floor might be their headquarters. A hundred paces away Rolf made the dark shapes of armed warriors as they filed downward from the Barrier into the blackened desolation of the desert half of Lomihi. "They cross the Barrier from the fertile plains of Nyd to raid the Hairy People.
 The wind would spread the scent of the Earthmen and cause an attack
 They wind would block the mind reading abilties of the Hairy People.  The wind would cause explosions.  The wind would spread the hair from the Hairy People and block vision.  The wind would spread the scent of the Earthmen and cause an attack