There is no single universally correct answer unless the measurement criterion is specified, because the driest place can mean the lowest long term precipitation, the longest period without measurable rain, the driest non polar environment or the driest environment overall. The Atacama Desert in northern Chile is widely recognised as one of the driest places on Earth and is often described as the driest non polar desert.
Some parts of the Atacama receive only a few millimetres of precipitation per year, while some extremely arid areas can go for years without measurable rainfall. NASA describes the Atacama as one of the driest places on Earth and notes that some parts receive only a few millimetres of rain per decade. The McMurdo Dry Valleys of Antarctica are even more extreme in terms of cold desert dryness and receive exceptionally little precipitation, but they are polar environments. Consequently, saying that the Atacama is the driest place is most useful when the intended meaning is the driest non polar region or one of the driest generally inhabited and accessible terrestrial environments.
The Atacama is exceptionally dry because several geographical and atmospheric mechanisms operate together. The Andes Mountains create a powerful rain shadow that prevents much of the moisture originating east of the mountains from reaching the western desert. Moist air moving toward the Andes rises over the mountains, cools and loses water through precipitation, leaving relatively dry air on the western side. The Atacama is also influenced by the cold Humboldt Current along the Pacific coast.
Cold ocean water suppresses evaporation and tends to stabilise the lower atmosphere, reducing the development of deep convective clouds. In addition, persistent or frequent subtropical high pressure promotes descending air, which warms and dries as it sinks. These mechanisms combine with the deserts geographic position to suppress rainfall exceptionally effectively. The result is a hyperarid landscape where water is one of the strongest limiting factors for biological and geological processes.
The Atacama is not uniformly dry. It extends for a long distance along northern Chile and contains substantial variations in elevation, precipitation, fog, groundwater and local climate. Coastal areas can receive marine fog known locally in different contexts as camanchaca, providing limited moisture even when measurable rainfall is extremely scarce. Higher elevations can receive precipitation in forms that differ from the coastal desert, while some valleys and oases have access to groundwater or river water originating in the Andes.
The Salar de Atacama is an important example of a hyperarid basin containing salt flats and subsurface brines. NASA notes that some parts of the desert have no historical or current rainfall records and that the Salar de Atacama is considered one of the driest places on Earth. The existence of groundwater and occasional precipitation demonstrates that dryness does not mean absolute absence of water everywhere.
The McMurdo Dry Valleys provide an important alternative interpretation of the phrase driest place on Earth. They are a group of largely ice free valleys in Antarctica characterised by extremely low humidity, very little precipitation and an unusual absence of surface snow and ice compared with surrounding Antarctic terrain. NASA describes them as one of the driest and coldest deserts on Earth and an important analogue for Martian environments.
Their dryness results from extremely cold air, limited atmospheric moisture and powerful katabatic winds that descend from the Antarctic ice sheet and remove or prevent accumulation of snow. Because Antarctica is already extremely dry despite its enormous ice sheet, the Dry Valleys demonstrate that a landscape can contain massive quantities of frozen water nearby while its local surface environment remains exceptionally arid. They are therefore relevant when defining the global extreme of dryness, but they belong to a polar desert rather than the non polar desert category.
Extreme dryness has profound effects on landscapes and life. In the Atacama, sparse precipitation slows chemical weathering and biological activity, while intense solar radiation and large temperature changes can affect exposed rocks. Some surfaces remain remarkably stable for long periods because water driven erosion is limited. The environment has consequently become important for studying geological processes under arid conditions and for testing instruments designed to search for life on Mars.
NASA researchers have used the Atacama because some of its soils and microbial environments resemble aspects of the Martian surface. Life nevertheless exists in the Atacama, including microorganisms adapted to extreme water limitation. This is important because the desert demonstrates that extremely low precipitation does not automatically mean complete biological sterility. Water can enter through fog, rare rainfall, groundwater and atmospheric sources, and microbial communities can exploit very small amounts of available moisture.
Dryness is not identical to heat. The Atacama can be extremely dry while temperatures vary substantially with elevation, season and proximity to the Pacific. The McMurdo Dry Valleys are both extremely dry and extremely cold. Death Valley is hot and dry but is considerably wetter than the most hyperarid regions of the Atacama. This distinction matters because climate classification uses several independent variables, including precipitation, temperature and seasonal patterns.
A desert is generally defined by insufficient precipitation relative to potential evaporation rather than by high temperature alone. Polar deserts demonstrate that a place can qualify as a desert despite being permanently cold. The driest locations therefore cannot be identified simply by looking for the hottest deserts. Instead, long term precipitation, atmospheric moisture, evaporation, snow accumulation and local water balance must be considered.
Human life in hyperarid environments depends heavily on water imported from elsewhere or stored underground. Northern Chile has settlements and industrial operations that rely on rivers descending from the Andes, groundwater and increasingly desalinated seawater. Mining is economically important in the Atacama, including extraction of minerals from salt flats and other geological deposits. The extreme aridity can be advantageous for astronomical observatories because dry air and limited cloud cover improve observing conditions, particularly at high elevations. At the same time, water extraction can place pressure on fragile desert ecosystems and groundwater dependent habitats. Salt flats can contain specialised microorganisms and unique biological communities, while mining can alter water balances. Extreme dryness therefore has both practical advantages and environmental consequences.
The most precise answer is that the Atacama Desert is widely recognised as one of the driest places on Earth and the driest non polar desert, while the McMurdo Dry Valleys represent one of the strongest candidates when polar environments are included. Some Atacama locations receive only a few millimetres of precipitation per year or even less over longer periods, and some areas can go years without measurable rain.
The extraordinary dryness results from the combined effects of the Andes rain shadow, the cold Humboldt Current, persistent atmospheric subsidence and regional circulation patterns. The McMurdo Dry Valleys are different because their extreme dryness is produced within a polar environment by cold, low atmospheric moisture and katabatic winds. Thus, the phrase driest place has to be tied to a defined metric and geographical category rather than treated as an unambiguous single record.
