The desert air is not simply devoid of humidity. It is filled with palpable aridity.
In my first few experiences in Anza-Borrego Desert State Park, I made a surprising discovery about the nature of dryness. Of course, people who live in deserts or visit them more frequently than I do are thoroughly familiar with the phenomenon, and they probably don't even think of it as an odd thing.
But it is an odd thing.
It's funny how we humans can become so accustomed to the things we live with that we are completely unaware that other people who have never experienced them would consider them odd.
I once had the amusing experience of hearing my high school classmates in Georgia describe snow to me. They had seen snow only once in their lives, just a year before, and when they realized that I hadn't lived in that town during the snowstorm, they went to great lengths to tell me what it was like, until I reminded them that I had lived with snow every year of my then-brief life. Yes, when you make a snowball with your bare hands, it's so cold it feels like it's burning. Yes, it fills in all the high and low spots in a field so you can't even see where the gullies are. To my view, there was nothing weird about snow, but to these kids in Georgia, it was astonishing.
So, I'm sure, it must be with the aridity of a desert. People who live there would not even think to try to describe this, but it is a very weird phenomenon.
It's not just that the desert air is lacking in humidity. Even if you've never been to the desert, you know the difference between "humid" and "not humid." (Well, maybe not if you live in Seattle or Houston.) And you might imagine that the desert is just an extreme form of "not humid."
It isn't. It's much more than that.
The desert aridity is not just the lack of something, it is a presence of something: It is palpable aridity.
And this aridity is separate from heat. You can smell and feel this aridity even when it is quite cool.
I have a vivid memory of standing on a rocky ridge overlooking Yaqui Well early one morning. It was pleasantly cool, maybe in the mid 60s Fahrenheit, and there was not a breath of wind. As I took in the desiccated scenery glowing in the first blush of sunrise, a breeze stirred in the flats and slowly swept up the ridge. When it reached me, it didn't just blow past or sweep over me. It was not unpleasant, but it struck me. It drew moisture out of my skin and nose. It rolled over me. It infused me. It was palpable aridity.
People describe fog "so thick you could cut it with a knife." So, too, this aridity felt so substantial that I might take a piece of it out of that breeze and bring it home in my pocket.
I read an interesting article by International Space Station Science Officer Don Pettit, entitled "The Smell of Space." He describes a peculiar odor that clings briefly to spacesuits and tools after returning from spacewalks. I wonder whether the smell he calls "sweet" and "metallic" might be at least partly attributable to the same palpable aridity that I'm describing. (Certainly, the air in the space station carries other odors which Dr. Pettit had the good taste not to describe.)
Since I first observed it in the desert, I have come to recognize it in another, more ordinary circumstance. When I open the preheated oven to put in whatever I'm cooking, I feel a blast of hot, desiccated air. Everyone who has ever baked anything has felt this, but unless you have also felt the palpable aridity of the desert, you can not distinguish that the air from the oven exhibits two separate phenomena. One is great heat, and the other is aridity.
What does this palpable aridity do? It permeates your body, displacing the moisture.
In response, you need to drink water. A lot of water. More water than you think you need to drink.
The first time I spent a whole day in the desert, I brought as much water as I needed, but I did so by accident.
I had bought a six-pack of 1.5-liter bottles of water when I arrived for my annual Naval Reserve two weeks of active duty in San Diego. By Saturday morning, as I set off for a day exploring the desert, there were only two bottles left, so I stopped at a little store before I left the city. The little store only had gallon bottles of water. (This was a long time ago, before half-liter bottles of spring water became as ubiquitous as they are today.) I figured the two 1.5-liter bottles plus a gallon of water, and the two bottles of juice I was bringing for lunch, would be much more than I would need to drink, so I could use the "leftovers" in my barracks room the next week.
By the time I returned to my barracks that evening, there were no leftovers. I drank the two bottles of juice plus the entire gallon along with the two smaller bottles of water, and I was very, very glad I had it.
So, whenever you go out in the desert, even for just a mile walk around Cactus Loop Trail, figure on drinking twice as much water as you might in ordinary circumstances. Then bring twice as much as you figured.
Then when you smell and feel the palpable aridity of a desert breeze, it will be novel and it will be odd, and it will be vaguely pleasant. The same sensation without water would be the touch of death.