South America is home to some of the world’s most extreme arid regions, defined by low precipitation, typically receiving less than 250 millimeters of rain annually. These diverse biomes are shaped by powerful natural forces. Their formation is primarily driven by the barrier of the Andes Mountains and the cooling influence of cold ocean currents along the Pacific coast. This combination creates varied desert types, from hyper-arid coastal strips to vast, cold plateaus.
The Atacama Desert
The Atacama Desert, stretching across a long strip of land primarily in northern Chile and extending into southern Peru, holds the distinction of being the driest non-polar desert on Earth. In its core, precipitation can average less than 5 millimeters per year, with some areas historically recording no significant rainfall for centuries. This hyper-aridity results from a double rain shadow effect: the Andes Mountains block moisture from the Atlantic, and the lower Chilean Coast Range prevents Pacific moisture from moving inland.
A second major factor is the cold Humboldt Current, which flows north along the Pacific coast. This current cools the air above the ocean, creating a thermal inversion that generates thick coastal fog, locally called camanchaca. This atmospheric stability prevents the formation of rain-producing clouds, stabilizing the dry conditions. The remarkable dryness, high altitude, and minimal light pollution create atmospheric conditions ideal for astronomical observation, hosting major international observatories like the Atacama Large Millimeter Array (ALMA).
The Patagonian Desert
Located primarily within Argentina, the Patagonian Desert is recognized as the largest desert in the Americas. This expansive plateau is a cold winter desert, where average temperatures rarely exceed 12 degrees Celsius and frequent frosts occur. Its aridity is almost entirely due to the extreme rain shadow cast by the towering Andes Mountains to the west.
Moisture-laden winds from the Pacific Ocean are forced upward by the Andes, dropping precipitation on the western, Chilean side. By the time the air descends the eastern slopes into Patagonia, it is significantly drier, creating a vast, arid steppe characterized by gravel plains and scrubby vegetation. Strong, persistent westerly winds further increase evaporation and contribute to the region’s overall dry, cold climate.
The Sechura Desert
The Sechura Desert occupies a coastal strip along northwestern Peru, north of the Atacama. While less intensely dry than the Atacama, the Sechura is still a coastal desert where rainfall is scarce and unreliable. Its climate is moderated by the nearby ocean, but the upwelling of cold water suppresses rainfall in the same manner as further south.
The desert’s unique ecology is sustained by the frequent coastal fog, known locally as garúa. This moisture condenses on the hillsides and ridges, supporting isolated patches of vegetation known as lomas or fog oases. These ecosystems thrive on the fog’s moisture, allowing for the growth of unique plant species like carob trees and various herbs. The Sechura region also experiences occasional flooding events during strong El Niño years, which can temporarily transform the dry landscape with vast, shallow lakes.
Distinct Characteristics of South American Desert Life
Life in these deserts requires specialized biological and cultural adaptations. Flora across these regions, such as the Tillandsia airplants in the Atacama and cushion plants in Patagonia, have evolved to gather moisture directly from fog or dew rather than relying on soil water. Other plants utilize deep root systems, known as phreatophytes, to tap into underground water sources.
Animals have also developed unique mechanisms, such as the specialized kidneys of burrowing mammals and dietary reliance on sparse vegetation by grazing animals like guanacos and vicuñas. Human communities, including ancient indigenous groups, survived by developing sophisticated resource management techniques. In the Atacama, historical populations relied on underground water channels and agricultural methods that maximized the use of limited Andean meltwater. Modern settlements continue to use these scarce water resources for mining and agriculture, often employing technologies like fog nets to capture the camanchaca moisture.