Driest desert

The Atacama Desert, stretching around 1,000 kilometres (600 miles) along the coast of Peru and Chile and covering an area of approximately 105,000 square kilometres (40,540 square miles), typically receives 10–15 millimetres (0.4–0.6 inches) of precipitation per year on average. Most of this comes in the form of condensation from coastal fog, referred to locally as camanchaca. In some areas of the Atacama, such as the towns of Arica and Quillagua in northern Chile, this plummets to as little as 0.76 millimetres (0.003 inches) and 0.5 millimetres (0.02 inches), respectively, of annual precipitation.

There are other areas of the Atacama, mainly in the hyper-arid core of the desert, that have no record of rainfall since observations began around 500 years ago. Officially the longest sustained dry period, according to the World Meteorological Organization, is 172 months in the Atacama town of Arica in northern Chile, which went from October 1903 to January 1918 without seeing a drop of rain.

The driest cold desert is the Antarctic Ice Sheet, which receives no more than 50 millimetres (1.9 inches) of water-equivalent precipitation per year, reducing to lower values farther inland in arid areas such as the McMurdo Dry Valleys.

By comparison, the Sahara Desert – the world's largest hot desert – receives 100–250 millimetres (4–10 inches) of precipitation on average annually.