There are a lot of different types of terrain I could theoretically discuss, but since I don’t want to spend too long on that general topic at one time, let’s close out the month with deserts, and come back to this again later.
Starting again with the foundations: where do you find deserts? It depends on how they’re formed. The “horse latitudes” between 30 and 35 degrees north or south are responsible for many of the deserts you think of when you hear the word — the Sahara, the Kalahari, the deserts of the Middle East and the southwestern United States, and so forth — because the behavior of the prevailing winds there creates frequently dry and sunny weather. I mentioned rain shadows before; a severe one can create a desert or at least a semi-arid region on the leeward side of a mountain range. The interior of a large continent is a good candidate for aridity, simply because the region is far from any major sources of water, such that air masses have long since lost the moisture they picked up previously. But coastal deserts like the Atacama are also possible; these are found where the ocean waters are cold and therefore contribute less moisture, and are often helped along by mountains.
You also find deserts in books. But oh man, they are so often written by people who have apparently never been in one. Toss in some vague descriptions of scorching heat and sand dunes, add a camel or two for color, nod toward the idea that water is precious, and you’re done, right?
Not so much.
First of all, let’s bear in mind that deserts are not necessarily hot. What are the two largest deserts on Earth? Antarctica, followed by the Arctic. A desert is defined scientifically by its scant precipitation, and less formally by its dearth of vegetation; by either metric, both of those qualify in spades. In fact, it’s only logical that our polar regions should be arid, because air that cold is incapable of carrying very much moisture. If you read a story about a polar explorer getting buried in a massive snowfall, that writer probably hasn’t done their research — though it’s quite possible for existing snow to blow around in a ground blizzard, and to pile up in dunes much like the sand-based ones we associate with the word “desert.”
Sand isn’t a required feature of hot deserts, though. In fact, though sand and extensive seas of dunes (known as ergs) are fairly common in Central Asian deserts, making up a little less than half of their total area, that’s almost non-existent in North American deserts, which are instead quite rocky. If there are large stony outcroppings, erosion from either wind or water can leave you with fascinating formations: Monument Valley in the United States is an incredibly well-known example, having been featured in countless film Westerns.
It also isn’t necessarily the case that a desert is barren. In many cases the limited precipitation falls in a clear seasonal pattern, rather than being evenly distributed across the year, and when the rains arrive, the desert springs to life. It doesn’t transform into Ireland, of course, but plants that were dry and scrubby put out their fresh new growth, and places you would have sworn had no plant life at all may suddenly be carpeted in flowers. Residents of such areas take advantage of this, gathering and preserving food for the dry season, fattening up their herds on the water-rich pasturage, and so on. And even when the rains don’t fall, life persists in all kinds of ingenious ways.
The part about water being scarce is true, though. If there isn’t some major river like the Nile nearby, your characters are going to need to be careful, making sure they know how to find water and rationing what they have until they reach the next supply. Depending on the politics of the area, water sources may be controlled by different groups, and it’s possible to exhaust a tiny spring and have to wait a long time for it to refill. Bathing in a tub full of water is probably Right Out; Islamic law even makes an allowance for “washing” yourself with sand before praying, if water is too scarce to spend on ritual ablutions.
One of the keys to survival is knowing how to get your hydration from organisms that are better at it than you are. Camels can extract moisture from plants inedible to humans, so if you travel with a string of milch camels, you can graze them and then drink their milk. Cactus fruit can also help you out — but beware the cartoons that lead you to believe there are reservoirs of potable water inside the plant itself. The liquid you get from most species is loaded with toxins that will actually make things worse for you.
Sandstorms are a real danger if you’re in an area of extensive sand, and in general wind erosion is going to be a constant factor, because of all the particulate matter blown around. But water can also be a threat: if the ground is dry, and then seasonal precipitation shows up in the form of a thunderstorm, a large percentage of that is going to become runoff rather than soaking into the ground, creating flash floods. When one of those slams through a gully or slot canyon, it can kill you in no time flat. (This can strike even if you aren’t being rained on directly, if the storm is happening at higher elevation, and the runoff comes downhill.)
And don’t forget about sunburn! Not only do you have to worry about the sun beating down on you from above, but also the light reflecting up from the sand or stone. In a hot desert it may be tempting to strip down to minimal clothing, but unless you’re blessed with abundant melanin, you’re going to wind up regretting that. (We aren’t just talking reddened skin, either. A severe sunburn can produce blisters, fainting, and more.) Loose robes have the advantage of full coverage while also allowing for more air circulation inside than tight-fitting shirts and trousers. You may also need to protect your eyes from the constant brightness or wind-borne dust; eye problems are very common in desert-dwelling populations.
So in the end, deserts make for good storytelling, because they pose such dramatic challenges to the traveler, and constrain the societies living there in ways that are deeply unfamiliar to your average temperate-zone-dwelling reader. But as with so many things, do your research: once you know what kind of desert you’re talking about, read up on the cultures that have adapted to such a place, whether that’s the Bedouin or the Hopi or the Uyghurs. Everything from their foodways to their governmental structure will teach you things about how people survive in that terrain, and help you set your tale in something more specific than a basic cartoon desert.