Deserts and desertification

In short: Deserts are areas with very little precipitation (below about 250 mm a year). Not all are hot: Antarctica and the Arctic also count as cold deserts. About a third of the land area is arid.

In more detail: Deserts arise mainly in zones of descending air (the tropics), in the rain shadow of mountains or far from the sea.

In detail

• Sahara: The largest hot desert at about 9 million km², nearly as big as the USA.
• Sand desert is the exception: Only about a fifth of deserts consist of sand dunes, the rest of rock and gravel.
• Temperatures: Extremely hot by day, cold at night because clear air radiates heat away quickly.
• Life: Cacti, camels and fennec foxes are adapted to dryness.
• Oases: Water from springs or groundwater allows settlement and farming.
• Desertification: Overuse, deforestation and climate change turn land into steppe (klimazonen-der-erde, klimawandel-grundlagen).