Defined as a large expanse of land that is extremely dry, and consists of either no vegetation, or limited areas that are vegetated, deserts make up a significant part of the Earth’s landscape.

Over one-third of the Earth's land surface is desert and at least one desert is found on all of the continents, including the Tabernas Desert in Europe.

They are caused by a number of factors, which include permanent areas of high air pressure preventing rain from developing over an area, rain shadow effects, and even because an area of land is too far away from large water bodies to receive rain.

The variety of different factors also means that some deserts are drier than others, ranging from semi-arid expanses of land through to hyper-arid areas, some of which have not seen measurable rain for hundreds of years.

Also, although many deserts around the world are located in hot and dry locations, and often consist of sand or rocks, some also exist in cold polar regions.

The Atacama: The Driest Warm Desert on Earth

If we are looking at the driest warm desert in the world – one which is rocky, sunny and receives hot days all year round, then the driest one is the Atacama Desert.

Making up the central section of the west coast of South America, the Atacama runs from the plateau of the Andes Mountains, and borders the Pacific Ocean on its western side. With a total area of 40,541 square miles (105,000 km2), it occupies the northern quarter of Chile, and small parts of Argentina, Bolivia and Peru. It contains a spectacular landscape of rocky plains, barren hills and the large mountains of the Andes on its eastern side.

Vast salt flats cover parts of the desert, the largest of these being Salar de Uyuni in the Bolivian section of the Atacama. Natural saltwater pools accumulate within some of the salt flats, often from groundwater that has risen to the surface.

Excluding polar regions, the Atacama is the driest desert in the world. Although the average rainfall across the whole desert is around 0.6 inches (15 mm) per year, some places within the Atacama barely record 0.1 inches (2.5 mm) of rainfall a year.

The small city of Calama, located in the heart of the desert, is one of the driest cities in the world, with an average annual precipitation of only 0.2 inches (5 mm). In 2015, parts of the hyper-arid core received unexpected rainfall; this is estimated to have been the first rain to land on those areas for at least 500 years.

1. Rain shadow

2. Prevailing high air pressure

3. Cold Pacific Ocean current

Firstly, being located to the west of the Andes Mountains means that, when the prevailing south-easterly trade winds bring in moisture across the South American continent from the South Atlantic, they reach the Andes and rise. This results in the moisture condensing and falling on the eastern side of the Andes – very little of it reaches the Atacama side.

Secondly, constant high air pressure over the region prevents moisture from falling over the region, and means that any moisture is converted into water vapor, and so cannot condense into rain.

However, the last factor is due to the cold Humboldt Current – running northwards along much of South America’s western coast, the current brings cold water up from the southern Pacific region, fairly close to Antarctica. This means that any onshore wind is chilled, and so it cannot pick up any moisture from the Pacific.

These three factors merge to create a perfectly dry storm – an incredibly arid region of South America.

 The McMurdo Dry Valleys, Antartica: Driest Place on Earth

Although the Atacama is the driest warm desert on Earth that fits the definition of a warm, rocky and sunny desert, there is one place on Earth which is even drier – The McMurdo Dry Valleys in Antarctica, the driest place on Earth.

• Located around 2,000 miles (3,400 km) to the south of New Zealand, these valleys consist of a 1,850 square mile (4,800 km2) area that is completely barren of any ice or snow.

• Cold air holds less water vapor than warm air

  • Air at freezing temperature (32°F) holds 10 times less moisture than air at 100°F

  • Air at 32°F holds about 20 times less moisture than air at 130°F

  • Average temperature of the Mcmurdo Dry Valleys = -16°F/-27°C

• The McMurdo Dry Valleys have not seen rain for nearly 2 million years

Katabatic Winds: Antarctica

This is due to the presence of mountains to the south and west of the valleys, which cause katabatic winds to form.

This means that cold air is dragged down from the ice-covered region that overlooks the valleys, and in turn warms up. These strong katabatic winds cause any ice or snow that has slid or drifted into the dry valleys region to evaporate.

What are Katabatic Winds?

• Katabatic Winds = winds that blow down slopes that are cooled by radiation

  • Strong winds that are a climatic feature of Antarctica

  • Winds caused by cold denser air falling down the slope of the Antarctic continent

  • Katabatic Winds average 45-mph (72kph)

    • Katabatic winds have been recorded approaching 150-mph (241-kph)

Katabatic wind is a gravity flow maintained by the temperature/density difference of the air in the surface layer when compared with the free air temperature at the same altitude further down the slope.

Very little precipitation falls in the region. No rain has fallen in the region for nearly two million years, and snow falls are very little, with an average of 4 inches (10cm) falling in the valleys per year.

A combination of the aforementioned katabatic winds, overlooking mountains and incredibly cold temperatures prevents more measurable amounts of snow from falling, and the strong and dry winds prevent any rare meltwater from sinking far into the soil.

Therefore, although the Atacama Desert is drier in terms of annual precipitation levels being lower, the McMurdo Dry Valleys have been completely barren of any rainfall for a far longer time.

The McMurdo Dry Valleys, with a combined area of approximately 4800 km2, is the largest ice-free area in Antarctica. This region was discovered by members of Robert Falcon Scott’s party during their 1903 expedition to reach the South Pole.

bottom line

The Atacama is the driest non-polar desert in the world while the McMurdo Dry Valleys is the coldest polar desert on planet Earth. Both places are thought to resemble Mars and are both used as training grounds for astronauts.

Valentina is a guide for Pedal Chile and is our geology expert. Valentina has been in love with geology ever since she first saw Villarrica glowing in her native country of Chile. Valentina was born and raised in La Patagonia, which probably explains her affinity for adventuring. When Valentina isn’t crushing some poor dude’s soul, you can find her shredding down Rucapillán. Favorite season: Austral Summer

More articles from Pedal Chile

• Related article from Valentina: Country with the most active volcanoes

Sources and references

1. Cain, Fraser. “What Is the Driest Place on Earth?” Universe Today, 12 June 2008, www.universetoday.com/15031/driest-place-on-earth/.

2. California Academy of Sciences. “The Desert Biome.” Berkeley.edu, 2019, ucmp.berkeley.edu/exhibits/biomes/deserts.php.

3. Charlotte L. King, Andrew R. Millard, Darren R. Gröcke, Vivien G. Standen, Bernardo T. Arriaza, Siân E. Halcrow. “Marine resource reliance in the human populations of the Atacama Desert, northern Chile – A view from prehistory. ”Quaternary Science Reviews, Volume 182,2018, P. 163-174.

4. Clarke, Jonathan D.A. “Antiquity of Aridity in the Chilean Atacama Desert.” Geomorphology, vol. 73, no. 1-2, Jan. 2006, pp. 101–114, 10.1016/j.geomorph.2005.06.008.

5. Crits-Christoph, A., Robinson, C.K., Barnum, T. et al. Colonization patterns of soil microbial communities in the Atacama Desert. Microbiome 1, 28 (2013). https://doi.org/10.1186/2049-2618-1-28

6. Doran, Peter T. “Valley Floor Climate Observations from the McMurdo Dry Valleys, Antarctica, 1986–2000.” Journal of Geophysical Research, vol. 107, no. D24, 2002, 10.1029/2001jd002045.

7. Dreesens, Lisa, et al. “The Distribution and Identity of Edaphic Fungi in the McMurdo Dry Valleys.” Biology, vol. 3, no. 3, 30 July 2014, pp. 466–483, 10.3390/biology3030466.

8. Friedlander, Blaine. “For Arid, Mars-like Desert, Rain Brings Death.” Phys.org, 14 Nov. 2018, phys.org/news/2018-11-arid-mars-like-peruvian-death.html.

9. Juli Hennings, Juli, and Harry Lynch. “Exploring Earth’s Driest Deserts | EarthDate.” Www.earthdate.org, 2017, www.earthdate.org/exploring-earths-driest-deserts.

10. Nkem, Johnson N., et al. “Wind Dispersal of Soil Invertebrates in the McMurdo Dry Valleys, Antarctica.” Polar Biology, vol. 29, no. 4, 27 Sept. 2005, pp. 346–352, 10.1007/s00300-005-0061-x.

11. November 2013, Becky Oskin 01. “Antarctic Hills Haven’t Seen Water in 14 Million Years.” Livescience.com, 1 Nov. 2013, www.livescience.com/40890-antarctic-dry-valleys-no-water.html.

12. Nylen, Thomas H., et al. “Climatology of Katabatic Winds in the McMurdo Dry Valleys, Southern Victoria Land, Antarctica.” Journal of Geophysical Research: Atmospheres, vol. 109, no. D3, 14 Feb. 2004, p. n/a-n/a, 10.1029/2003jd003937.

13. Parish, Thomas R., and John J. Cassano. “The Role of Katabatic Winds on the Antarctic Surface Wind Regime.” Monthly Weather Review, vol. 131, no. 2, Feb. 2003, pp. 317–333, 2.0.co;2">10.1175/1520-0493(2003)131<0317:trokwo>2.0.co;2.

14. Speirs, Johanna C., et al. “Regional Climate Variability Driven by Foehn Winds in the McMurdo Dry Valleys, Antarctica.” International Journal of Climatology, vol. 33, no. 4, 4 Apr. 2012, pp. 945–958, 10.1002/joc.3481.