The Atacama Desert, located in northern Chile along the Pacific coast of South America, is renowned for its unique and challenging climate. Spanning approximately 1,600 kilometers (1,000 miles), this desert plateau is a subject of scientific interest due to its distinct conditions and extreme aridity.
Hallmarks of Extreme Aridity
The Atacama Desert’s climate is defined by its profound aridity, making it the driest non-polar desert in the world. Many areas receive incredibly low average annual rainfall, often just a few millimeters. For example, the city of Arica, on its northern edge, records only about 0.76 millimeters (0.03 inches) annually, making it the driest inhabited place on Earth. Some central weather stations have gone for years without recorded rainfall, and studies suggest some riverbeds have been dry for 120,000 years. This “hyper-arid” classification reflects regions that have experienced extreme dryness for millions of years, with some areas potentially not receiving significant rain for over four centuries.
Temperature Dynamics
The Atacama Desert experiences significant diurnal temperature variations. Clear skies and dry air allow for intense solar radiation during the day, leading to warm conditions, while heat rapidly escapes at night, resulting in cold temperatures. For instance, in San Pedro de Atacama, daytime highs can reach 25-27°C (77-81°F), but nights can cool to 4-16°C (39-61°F), with sub-zero temperatures possible at higher altitudes. Despite these daily swings, seasonal temperature changes are relatively stable. The cold Pacific Ocean current moderates coastal temperatures, preventing the intense heat often associated with other desert environments.
The Role of Fog
Despite its overall dryness, coastal areas of the Atacama Desert benefit from a unique moisture source: fog, locally known as “camanchaca.” This dense marine fog forms when warm air over land interacts with cold ocean currents, creating cloud banks that move inland. While camanchaca droplets are too fine to produce rain, they provide a vital water supply for adapted plants, such as cacti and lichens. Human communities have developed fog-collection systems, utilizing polyolefin netting to capture these microscopic water droplets, providing water for daily use and even for brewing. This phenomenon sustains localized ecosystems and human settlements.
Geographic and Atmospheric Influences
The extreme climate of the Atacama Desert results from a combination of geographic and atmospheric factors. To the east, the Andes Mountains create a “rain shadow” effect, blocking moisture-laden air from the Amazon basin. As air ascends the eastern slopes, it cools and releases moisture as precipitation, leaving dry air to descend on the Atacama’s western side.
Along the Pacific coast, the cold, northward-flowing Humboldt Current (also known as the Peru Current) plays a crucial role. This current cools the air above the ocean, inhibiting evaporation and cloud formation, preventing precipitation over the coastal desert.
A persistent high-pressure system, the South Pacific Anticyclone, also contributes to the aridity. This anticyclone creates stable atmospheric conditions that suppress rain-producing clouds and push dry, subsiding air over the region. The combination of the Andes rain shadow, the Humboldt Current’s influence, and the South Pacific Anticyclone collectively traps the Atacama Desert in a state of extreme dryness.