What is the difference between desert and desertification ?

What is a desert ?

A desert is a landscape form or region that receives very little precipitation.

Deserts can be defined as areas that receive an average annual precipitation of less than 250 mm, or as areas in which more water is lost than falls as precipitation.

World desert's map. Distribution of non-polar arid land. Source: USGS.

There are different types of deserts:

Low-latitude (sub-tropical) deserts
- resulting from global air circulation pattern ↓ ↑
  
  The warm tropics form a belt around the equator where the tropical heat generates rising, unstable air. As it climbs, the air condenses the moisture evaporated from the warm tropical seas and forests, and produces the heavy downpours that characterize the wet tropics. As it moves away from the equator at high altitudes, the air cools again and eventually starts descending towards the midlatitudes, some 3000 km away from the equator both north and south. The air masses heat in their descent and, having lost their moisture during their tropical ascent, they become extremely dry.
- characterized by little rain, high evaporation, clear skies
- Australia, Sahara and Southern Africa deserts
Continental deserts
- occur on high plateaus in the continental interior ↓ ↑
  
  Most of the water in the atmosphere is ultimately derived from evaporation from the seas. The land closer to the sea often receives a larger share of this ocean derived water and, as air moves inland, it gets depleted of moisture and precipitation drops. Regions lying deep within a continent may become deserts simply because air currents reaching them have already traversed vast land distances and lost most of the moisture they originally carried.
- characterized by warm summers, cold winters
- Gobi and Taklimakan deserts (East Asia), central Australia desert, Great Basin (North America), Monte desert (South America)
Coastal deserts
- occur near coastal upwelling of deep ocean waters ↓ ↑
  
  In the coasts neighbouring oceanic upwellings, typical coastal deserts tend to develop, forming some of the driest ecosystems on Earth. The upwelling of deep cold seawater, driven by ocean coastal currents, induce very dry inland conditions. This type of desert can be seen on the western seaboard sections of the African and American continents.
- characterized by little rain, extreme dryness, evening fog
- Atacama desert (Chile), Namib desert (West Africa), Baja California desert (USA), Atlantic coastal desert of Morocco
Rain shadow deserts
- occur inland from coastal mountain ranges ↓ ↑
  
  Deserts occur on the leeward sides of mountain ranges that are deprived of ocean generated moisture.
- characterized by little rain, high evaporation, clear skies
- Sierra Nevada, Cascades, Himalayas, Andes mountains
Polar deserts
- result from descending cold dry air and are often associated with lots of snow and ice
- Greenland, Antartica

Do you know which are the 2 world's largest deserts ? ↓

And which are the 2 oldest deserts ? ↓

The Namib Desert. Photo: Julien Fauqueur.

What is desertification ?

Desertification is the degradation of drylands in terms of their productivity. This global problem results from human activities and climatic variations.

Dryland areas cover 40% of the world's land surface and are the most at risk of turning into deserts.

Current desertification is taking place worldwide much faster than historically, and usually arises from the demands of increased populations that settle on the land in order to grow crops and graze animals.