Here's why:

* Location: The Atacama Desert stretches along the Pacific coast of Chile and Peru.

* Rain Shadow Effect: The Andes Mountains block moisture-laden winds from the east, creating a rain shadow effect over the Atacama.

* Cold Ocean Currents: The cold Humboldt Current along the coast further inhibits rainfall by cooling the air and reducing its capacity to hold moisture.

The Atacama Desert is considered the driest non-polar desert on Earth, with some areas receiving less than 0.004 inches of rain per year.