Three deserts
Sahara, Atacama and Antarctica
Three places that are all called deserts, in sources we checked, and that are not the same kind of dry.
The Sahara
The Sahara of Africa is the world's largest desert, in USGS wording. USGS The Sahara of North Africa has experienced temperatures as high as 57 degrees C, and is a trade wind desert. USGS A record 44 millimeters of rain once fell within 3 hours in the Sahara. USGS
Which desert is the largest?
USGS calls the Sahara of Africa "the world's largest desert" in its types essay (a non-polar framing in that sentence). The British Antarctic Survey says "Antarctica is a desert," with snowfall equivalent to only 150mm of annual rain. We report both wordings. We do not call Antarctica the world's largest desert, because none of the sources we checked for this site use that phrase.
The Atacama
A coastal desert, the Atacama of South America, is the Earth's driest desert, according to USGS. USGS In the Atacama, measurable rainfall of 1 millimeter or more may occur as infrequently as once every 5-20 years. USGS The Andes mountain chain causes a rain shadow effect that results in minimal precipitation in the Atacama region of Chile. NASA The Atacama Desert is widely recognized as one of the driest places on Earth. NASA Some areas of the Atacama are touched by rain only four times a century. NASA Other areas have never received rainfall for as long as records have been kept. NASA Uyuni is the world's largest salt flat and spans about 9,600 square kilometers (3,700 square miles). NASA
How often does it rain in the Atacama?
USGS says that in the Atacama, measurable rainfall of 1 millimeter or more may occur as infrequently as once every 5-20 years. NASA Earth Observatory says some areas of the Atacama are touched by rain only four times a century, and other areas have never received rainfall for as long as records have been kept. Those are different statements about different places and timescales, so we keep both.
Antarctica
Antarctica is a desert. British Antarctic Survey Snowfall is equivalent to only 150mm of annual rain. British Antarctic Survey By comparison, Britain is 6 to 7 times wetter with about 1050mm annual rainfall. British Antarctic Survey Antarctica is the coldest, highest, driest and windiest continent on Earth. British Antarctic Survey Antarctica is a rocky continent capped by an ice sheet up to 4.8km thick. British Antarctic Survey Only about 0.4% of the surface of Antarctica is free of snow and ice. British Antarctic Survey The world record for lowest temperature, -89 degrees C, was recorded at Vostok Antarctic station. British Antarctic Survey The ice sheet contains approximately 90% of the world's total surface fresh water. British Antarctic Survey
We do not use a figure of “nearly 14,000 km²” for the area of Antarctica. That number appears on the British Antarctic Survey factsheet we checked, but it is not a credible area for the continent, so it is not cited here.