Look at a world map of deserts and a pattern jumps out. The Sahara, the Arabian Desert, the deserts of the American Southwest, the Kalahari, and the great dry interior of Australia all sit at roughly the same distance from the equator, somewhere near 30 degrees north or south. That is not a coincidence. Deserts are some of the most predictable features on Earth, and once you understand the handful of forces that create them, you can almost guess where the next dry zone will be before you find it on the map.
The 30-Degree Rule
The single biggest reason deserts exist is the way air moves around the planet. Near the equator, intense sunshine heats the surface and drives warm, moist air upward. As that air rises it cools, dumps its moisture as tropical rain, and then spreads out toward the poles high in the atmosphere. By the time it has traveled to about 30 degrees latitude, it has lost almost all its water and begun to sink back toward the surface. Sinking air warms and dries as it descends, which suppresses cloud formation and rainfall. This loop is called the Hadley circulation, and the belt of descending dry air it creates is why so many deserts line up along the subtropics.
Rain Shadows: When Mountains Steal the Water
Mountains create deserts too. When moist air is forced up and over a mountain range, it cools and releases its rain on the windward slope. By the time it crests the ridge and sinks down the far side, it is wrung dry. The result is a rain shadow, a band of arid land in the lee of the mountains. The deserts east of the Sierra Nevada and the Cascades in North America, much of the dry Patagonian steppe behind the Andes, and the parched Tibetan Plateau behind the Himalaya all owe their dryness to ranges that block the incoming weather.
Too Far From the Sea
Oceans are the source of nearly all the moisture in the air, so the deeper you go into the interior of a large continent, the less water reaches you. This effect, sometimes called continentality, helps explain the great dry hearts of Asia and Australia. By the time ocean air has crossed thousands of kilometres of land, most of its moisture has already fallen as rain. Central Asia's deserts, far from any coast and ringed by mountains, are dry for both reasons at once.
Cold Currents and the Coastal Deserts
Some of the driest places on Earth sit right next to the ocean, which seems to break the rule, until you look at the water temperature. Cold ocean currents chill the air above them, and cold air holds very little moisture and rarely rises enough to form rain. Instead it produces fog. The Atacama Desert along the coast of Chile and Peru, widely regarded as the driest non-polar place on the planet, and the Namib Desert of southwestern Africa both hug coastlines cooled by powerful cold currents. They get fog rolling in off the sea but almost no actual rainfall.
The Deserts That Aren't Hot
It is worth remembering that a desert is defined by how little precipitation it receives, not by how hot it is. Plenty of deserts are cold. The Gobi in Mongolia and northern China freezes hard in winter. And the largest desert on Earth is not the Sahara at all, it is Antarctica, a continent that receives so little snowfall that its interior qualifies as a polar desert. Defining deserts by dryness rather than heat is the key to understanding why they show up in such different climates.
How to Spot a Desert From Above
From satellite imagery, deserts are some of the easiest landscapes to identify. Look for large expanses with almost no green, sharp colour shifts where irrigation suddenly meets bare ground, long unbroken dune fields, and dry riverbeds that branch like veins but carry no water. The boundary between the Nile's green ribbon and the surrounding Sahara is one of the most dramatic edges anywhere on Earth, a hard line between life and emptiness drawn entirely by the availability of water.
Once you start reading the planet this way, dry landscapes stop looking random. You begin to notice the latitude, the mountains upwind, the distance to the nearest coast. Want to put it to the test? Fire up a round of EarthGuessr, drop into an unfamiliar dusty scene, and see whether you can reason your way to the right part of the world before the answer appears.