Deserts of the world

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A desert is a barren area of land that receives almost no rainfall and consequently living conditions are hostile for plant and animal life. In deserts the average precipitation is less than 250 mm per year. Deserts are the region of moisture deficit i.e. they lose more moisture than they receive.  In deserts more water is lost by evaporation and transpiration than falls by precipitation. Deserts constitute about one third (33%) of the Earth's land surface. The largest desert on Earth is Antarctica. Normally vegetation in desert area is sparse or nonexistent. Antarctica is the largest desert on earth.

Classification of deserts :

  • Hot deserts
  • Cold deserts
  • Montane deserts
  • Rain shadow deserts

Hot deserts Hot deserts are mainly located in subtropical region. They can be covered by sand, rock, salt lakes, stony hills and even mountains. Hot deserts are hot in the day and chilly at night.  The temperature in the daytime can reach 50 °C or higher in the summer, and dip to 0 °C or lower at night time in the winter. The largest hot desert of the world is the Sahara in North Africa.The Sahara is also the hottest desert in the world. Sahara  is almost as large as Europe or the United States. The driest hot desert in the world is the Atacama Desert in South America . It got no rain  for 401 years, between 1570 and 1971.

Cold deserts : Cold deserts are the deserts that are covered with snow or ice. Cold deserts are mainly found close to the poles. That is why they are also called polar deserts.  An ice cap can be a cold desert that remains below freezing year-round.  Antarctica is the world's largest cold desert.

Montane desertsMontane deserts are maily located at very high altitudes (example- Ladakh, Tibet). These areas have very low humidity because they are at large distance  from the nearest available source of water.

Rain shadow desert

Rain shadow deserts Rain shadow deserts are formed when a tall mountain ranges block clouds from reaching areas in the direction of the wind.  As the air moves over the mountains, it cools and moisture condenses, causing precipitation on the windward side. Moisture almost never reaches the leeward side of the mountain, resulting in a desert. When that air reaches the leeward side, the air is dry, because it has already lost the majority of its moisture. The air then warms, expands, and blows across the desert. The warm air takes with it any remaining small amounts of moisture in the desert.

Features Of Desert

Vegetation in the deserts :

Plants face severe challenges in the desert area which includes - how to obtain enough water, how to avoid being eaten and how to reproduce but they face all these challenges in a unique way :

Process of  Photosynthesis

 

 

 

 

 

Photosynthesis is essential for the growth of plant but it  can only take place during the day as energy from the sun is required, but during the day, many deserts become very hot so opening the stomata to allow in the carbon dioxide necessary for the process causes evapotranspiration, and conservation of water is a top priority for desert vegetation so plants have resolved this problem by adopting crassulacean acid metabolism, allowing them to open their stomata during the night to allow CO2 to enter, and close them during the day.

  • When rain falls, the water is rapidly absorbed by the shallow roots and retained to allow them to survive until the next downpour, which may be months or years away.
  • The giant saguaro cacti of the Sonoran Desert (Arizona,USA) grows to about 15m height . they grow slowly but live up to 200 years, providing nests for birds and serving as desert trees.
  • Some desert plants produce seed that lie dormant in the soil until sparked into growth by rainfall but ones the rain falls such plants grow rapidly nd may flower and set seed within weeks, aiming to complete their development before the last vestige of water dries up. 

Rainfall in the deserts

Their is occasional rainfall in the desert which is with great violence. The deserts have dry stream channels known as arroyos or wadis meandering across its surface which can fill up quickly and cause dangerous flash floods. Some deserts are crossed by exotic rivers sourced in mountain ranges or other high rainfall areas beyond their borders. The River Nile, the Colorado River and the Yellow River do this, losing much of their water through evaporation as they pass through the desert and raising groundwater levels nearby. There may also be underground sources of water in deserts in the form of springs, aquifers, underground rivers or lakes.  Example of  desert lake - Great Salt Lake (Utah,USA)

Mineral resources in the deserts :

  • The Atacama Desert (Chile) is abundant in saline minerals. Sodium nitrate for fertilisers and explosives has been mined from the Atacama since the middle of the 19th century. The Great Basin Desert (USA) has been extensively used to mine borates, which are used in the manufacture of glass
  • Evaporation enriches mineral accumulation in desert lakes, including gypsum, salts (including sodium nitrate and sodium chloride)  and borates. The minerals formed in these evaporite deposits depend on the composition and temperature of the saline waters at the time of deposition.
  • Many petroleum productive areas on Earth are found in arid and semiarid regions of Africa and the Middle East, although the oil fields were originally formed in shallow marine environments.
Largest deserts of the world
Rank Desert Area
1 Antarctic Desert (Antarctica)     14,200,000 km square
2 Arctic Desert (Arctic)     13,900,000 km square
3 Sahara Desert (Africa)   9,100,000 km square
4 Arabian Desert (Middle East)    2,600,000 km square
5 Gobi Desert (Asia)    1,300,000 km square
6 Patagonian Desert (South America) 670,000 km square
7 Great Victoria Desert (Australia)    647,000 km square
8 Kalahari Desert (Africa)   570,000 km square
9 Great Basin Desert (North America)  490,000 km square
10 Syrian Desert (Middle East) 490,000 km square

Nowadays many successful solar power plants are being built in deserts because they have low amount of cloud cover . The solar power plants in Mojave Desert have a combined capacity of 354 megawatts (MW) making them the largest solar power installation in the world.

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