The overall climate of the Atacama Desert, located primarily in northern Chile, is defined by its status as the driest non-polar desert on Earth. This vast plateau stretches approximately 1,600 kilometers along the Pacific coast of South America, west of the Andes Mountains. The conditions here are so extreme that certain areas have been used by scientists as an analog for the Martian environment. This unique climate is a result of large-scale geographic and oceanic forces that combine to eliminate nearly all sources of moisture. The climate is characterized by an extreme lack of precipitation, a distinct coastal microclimate, and dramatic daily temperature variations.
Defining the Hyper-Aridity
The defining feature of the Atacama’s climate is its profound hyper-aridity, placing it among the most water-stressed regions globally. The average annual precipitation across the central core of the desert is often less than 2 millimeters per year. In some locations, such as near the abandoned Yungay mining town, annual rainfall averages only 1 to 3 millimeters, with some weather stations never having recorded rain.
This extreme lack of moisture suggests that some parts of the Atacama may have gone without significant rainfall for centuries. The extreme dryness creates an environment where humidity levels often remain near zero throughout the year. This consistent scarcity of water is the central factor shaping the desert’s geology and biology.
Geographic Mechanisms Driving Dryness
The Atacama’s hyper-aridity is maintained by a combination of two major geographic and oceanic influences. The first factor is the powerful rain shadow effect created by the Andes Mountains to the east. These high elevations intercept moisture-laden air masses traveling west, forcing the air to rise and shed its moisture as precipitation on the eastern slopes.
By the time the air descends over the Atacama plateau, it is hot and dry, effectively blocking any significant moisture from the east. The second mechanism is the influence of the cold, north-flowing Humboldt Current in the Pacific Ocean. This cold water cools the air directly above it, leading to a constant temperature inversion that stabilizes the atmosphere.
The cold air layer is prevented from rising high enough to condense and form rain-producing clouds. This process inhibits the formation of large-scale weather systems capable of delivering rainfall to the coast and interior.
Temperature Extremes and Daily Variation
The Atacama Desert is dominated by a high diurnal temperature range, meaning a dramatic fluctuation between day and night temperatures. The clear, dry air and high elevation allow intense solar radiation to heat the ground, with daytime highs often reaching 27°C (81°F) or more. The lack of atmospheric moisture means that heat rapidly dissipates after sunset, leading to a steep drop in temperature. Nighttime lows frequently dip toward or below freezing, particularly at higher elevations, resulting in daily temperature swings often exceeding 17°C (30°F).
The Unique Coastal Microclimate
While the interior is defined by extreme dryness, the Pacific coast features a distinct microclimate. This coastal strip experiences regular marine fog known locally as Camanchaca. This fog results from the cold Humboldt Current cooling the air, trapping a layer of moisture near the surface during the night and morning hours. This limited moisture provides the primary water source for unique ecosystems along the coastal hills, supporting specialized flora like lichens and certain cacti. Strategically placed fog collectors are often used by local communities to harvest this moisture for domestic and agricultural use.