How the desert kills

The Army survival manual (FM 21-76) warns that in extreme climates, especially arid ones, an average person can lose 2.5 to 3.5 liters of water per hour, and that under those conditions they might need 14 to 30 liters a day. Nobody carries that much while walking. That is why in the desert survival depends less on how much water you carry and more on how much you stop losing.

Heat works on three fronts at the same time:

• Direct sun: it heats your body from the outside.
• Hot ground: sand, rock, and asphalt in the sun are much hotter than the air. Sitting or lying on them heats you by contact.
• Dry air and wind: sweat evaporates so fast you do not notice it. You can be losing a lot of water without feeling wet.

Dehydration reduces your strength, your coordination, and your judgment, just when you need them most. Heat stroke can kill in hours. Learn the signs in chapter 7.