Turn your eyes to the Pacific coast of Chile or the edge of Africa, and you’ll see something that defies common sense: vast deserts hugging the ocean.

Why does parched land sit beside what should be a source of rain?

Scientists point to a quartet of climatic and geographic forces that shape these coastal deserts.

Coastal deserts often sit between 20 and 40 degrees latitude.

Air Circulation Zones

The sky’s engine begins at the equator. Warm air rises, loses moisture as rain in tropical regions, and travels toward the subtropics. There it sinks, creating high-pressure belts that suppress cloud formation.

This pattern leaves huge bands of land dry between about 20° and 40° latitude in both hemispheres.

That explains why deserts are common in these latitudes, even next to oceans. According to Live Science, this atmospheric circulation drives dry air down along the subtropical coasts. Coastal deserts like the Nascent Atacama and Namib lie within these zones.

Subtropical high-pressure systems suppress cloud formation.

Cold Currents, Little Rain

Water is key to rain—but only warm water.

Cold ocean currents running parallel to western continents cool the air above them. Cold air holds less moisture, and clouds struggle to form.

As the authoritative World Atlas explains, that chilled air dumps most of its moisture back into the sea before it reaches land. The result? Little to no rainfall along the adjacent shore.

This same principle is reinforced in climate science texts: upwelling cold water stabilizes the atmosphere and inhibits rainfall, even as fog drifts inland.

Rain Shadows and Mountain Barriers

Mountains can also seal a region off from moisture.

Prevailing winds laden with humidity are forced upward when they hit a high range. As the air rises, it cools and releases its water on the windward side. By the time it descends toward the coast, it is bone-dry.

The Andes Mountains are a stark example. Winds blow moist air from the Amazon basin westward, where the mountains wring out moisture before it ever reaches Chile’s coastal plains. As Live Science reports, this “rain shadow” leaves the Atacama extraordinarily dry.

Deserts are defined by lack of precipitation, not temperature.

Fog: Moisture in Disguise

Deserts next to oceans aren’t always devoid of water in every form. Eastern Atlantic winds cross the cold Benguela Current and bring thick fog inland along Namibia’s coast. While rain is rare, the moisture in fog supports specialized life.

Different But Not Typical

Most deserts earn their title from the absence of rain, not heat. Coastal deserts are no exception — they are dry because weather systems never release moisture there.

What they do offer are cooler temperatures and unusual ecosystems sustained by breezes off the water rather than rainfall.

In places like the Atacama and Namib, proximity to the sea is a trick of climate, not a blessing.