In short
Facts at a glance
A shorter path through the same sourced claims. The full list, and the disagreements, live on the fact-check log.
What a desert is
Approximately one-third of the Earth's land surface is desert. USGS
USGS describes desert as arid land with meager rainfall that supports only sparse vegetation and a limited population of people and animals. USGS
Britannica describes a desert as any large, extremely dry area of land with sparse vegetation. Britannica
Desert environments are so dry that they support only extremely sparse vegetation; trees are usually absent. Britannica
Deserts are always dry. USGS
Deserts are natural laboratories in which to study the interactions of wind and sometimes water on the arid surfaces of planets. USGS
Rainfall categories
In 1953, Peveril Meigs divided desert regions on Earth into three categories according to the amount of precipitation they received. USGS
In Meigs's widely accepted system, extremely arid lands have at least 12 consecutive months without rainfall. USGS
Arid lands have less than 250 millimeters of annual rainfall. USGS
Semiarid lands have a mean annual precipitation of between 250 and 500 millimeters. USGS
Arid and extremely arid land are deserts, and semiarid grasslands generally are referred to as steppes. USGS
Why they form
Descending air north and south of the tropical zone produces almost permanent areas of high pressure across the subtropics. Met Office
This produces almost cloud-free skies virtually year-round, giving rise to deserts. Met Office
Desert climates are extremely dry, and their cloudless skies lead to large temperature swings. Met Office
Deserts have some of the hottest temperatures on Earth, but many will drop below freezing at night. Met Office
The trade winds in two belts on the equatorial sides of the Horse Latitudes heat up as they move toward the Equator. USGS
These dry winds dissipate cloud cover, allowing more sunlight to heat the land. USGS
Most of the major deserts of the world lie in areas crossed by the trade winds. USGS
Rain shadow deserts are formed because tall mountain ranges prevent moisture-rich clouds from reaching areas on the lee, or protected side, of the range. USGS
As air rises over the mountain, water is precipitated and the air loses its moisture content. USGS
Types
USGS classifies deserts by geographical location and dominant weather pattern as trade wind, midlatitude, rain shadow, coastal, monsoon, or polar deserts. USGS
Midlatitude deserts occur between 30 and 50 degrees north and south, poleward of the subtropical high-pressure zones. USGS
These midlatitude deserts are in interior drainage basins far from oceans and have a wide range of annual temperatures. USGS
Coastal deserts generally are found on the western edges of continents near the Tropics of Cancer and Capricorn. USGS
"Monsoon," derived from an Arabic word for "season," refers to a wind system with pronounced seasonal reversal. USGS
Crescent-shaped dunes are common in coastal deserts such as the Namib, Africa. USGS
The Sahara of North Africa has experienced temperatures as high as 57 degrees C, and is a trade wind desert. USGS
Sand, water and plants
Sand covers only about 20 percent of the Earth's deserts. USGS
Most of the sand is in sand sheets and sand seas: vast regions of undulating dunes. USGS
Nearly 50 percent of desert surfaces are plains where wind has exposed loose gravels. USGS
The remaining surfaces of arid lands include bedrock outcrops, desert soils, and fluvial deposits including alluvial fans, playas, desert lakes, and oases. USGS
Oases are vegetated areas moistened by springs, wells, or by irrigation. Many are artificial. USGS
Most desert plants are drought- or salt-tolerant. USGS
Some desert plants store water in their leaves, roots, and stems. Others have long tap roots that penetrate the water table. USGS
Deserts typically have a plant cover that is sparse but enormously diverse. USGS
The Sonoran Desert of the American Southwest has the most complex desert vegetation on Earth. USGS
Saguaro grow slowly but may live 200 years. USGS
When 9 years old, they are about 15 centimeters high. USGS
After about 75 years, the cacti are tall and develop their first branches. USGS
When fully grown, saguaro are 15 metres tall and weigh as much as 10 tons. USGS
Cold deserts have grasses and shrubs as dominant vegetation. USGS
Rain does fall occasionally in deserts, and desert storms are often violent. USGS
A record 44 millimeters of rain once fell within 3 hours in the Sahara. USGS
Normally dry stream channels, called arroyos or wadis, can quickly fill after heavy rains, and flash floods make these channels dangerous. USGS
More people drown in deserts than die of thirst. USGS
Though little rain falls in deserts, deserts receive runoff from ephemeral, or short-lived, streams fed by rain and snow from adjacent highlands. USGS
Although most deserts are in basins with closed, or interior drainage, a few deserts are crossed by 'exotic' rivers that derive their water from outside the desert. USGS
Places
The Sahara of Africa is the world's largest desert, in USGS wording. USGS
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
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
Polar and cold deserts
Polar deserts are given a mean annual precipitation less than 250 millimeters and a mean temperature during the warmest month of less than 10 degrees C. USGS
Polar deserts on the Earth cover nearly 5 million square kilometers and are mostly bedrock or gravel plains. USGS
According to some definitions, any environment almost completely free of plants is considered desert, including regions too cold to support vegetation, called "frigid deserts." Britannica
Other definitions apply the term only to hot and temperate deserts, a restriction followed in the Britannica account checked here. Britannica
Though normally associated with hot, sandy environments, cold deserts are also widespread. Met Office
The Gobi Desert of east Asia is one example, where annual average temperatures can be below 0 degrees C. Met Office
Whether hot or cold, deserts pose great challenges for the plants and animals that live there, which must adapt to extreme, prolonged water deficits. Met Office
United States
In the United States, three "hot deserts" receive precipitation in the summer months: the Mojave, Sonoran and Chihuahuan. USGS
One "cold desert" receives precipitation in the winter: the Great Basin. USGS
These US desert ecosystems receive less than 10 inches (250 mm) of annual precipitation. USGS
Far from desolate, the deserts support high levels of biodiversity, including iconic species such as Joshua trees. USGS
The Mojave Desert is among the hottest and driest of the North American drylands. USGS