How Deserts Are Formed

Tap a cause to see how it creates a desert.

Subtropical High Pressure

Around 30 degrees latitude, descending dry air associated with the subtropical high pressure belt suppresses rainfall, forming some of the world's largest deserts, such as the Sahara.

Rain Shadow Effect

When moist air is forced to rise over a mountain range, it cools and releases its moisture as rain on the windward side, leaving the air dry by the time it descends on the leeward side, creating a desert in the mountain's "shadow."

Continental Interior (Distance from Ocean)

Regions located deep in the interior of large continents, far from any ocean, receive little moisture from sea air by the time it travels that distance, resulting in dry conditions.

Cold Ocean Currents

Along some coastlines, cold ocean currents cool the air above them, reducing its capacity to hold moisture and suppressing rainfall on the adjacent coast, forming coastal deserts like the Atacama.

Polar Deserts

Polar regions can also be classified as deserts because, despite the presence of ice, the extremely cold air holds very little moisture, resulting in very low actual precipitation.

Deserts are defined by low precipitation, not just heat

A common misconception is that all deserts are hot — in reality, a desert is defined by very low annual precipitation (generally under about 250 mm), which is why polar regions with almost no snowfall can technically be classified as deserts despite freezing temperatures.

Frequently Asked Questions

Can a desert exist right next to a mountain range in a generally wet climate?

Yes — this is exactly what the rain shadow effect describes, where one side of a mountain range can be lush and rainy while the other side, just a short distance away, remains extremely dry.

Are deserts always sandy?

No — many deserts are rocky or covered in gravel rather than sand, and sand dunes, while iconic, actually cover only a relatively small portion of the world's total desert area.