The climate zone of the Atacama Desert is BWk, a cold desert climate in the Köppen classification.
The code begins with B, identifying a dry climate. W means desert conditions, where potential evaporation greatly exceeds precipitation. The final letter, k, indicates that the average annual temperature is below 18°C, distinguishing a cold desert from a hot desert classified as BWh.
The Atacama is among the driest places on Earth, especially across parts of northern Chile. Its extreme aridity results from several factors working together: the cold Humboldt Current limits evaporation along the Pacific coast, the Andes block moist air from the east, and descending air associated with the subtropical high-pressure belt suppresses rainfall.
A common mix-up is to assume every desert has a hot climate. Unlike the Sahara, the Atacama often has mild temperatures because of its coastal setting and elevation. In unusually wet years, some parts of the desert can also experience spectacular flowering events.