Deserts are regions where evaporation exceeds precipitation.
- There are mainly two types – hot like the hot deserts of the Saharan type and temperate as are the mid-latitude deserts like the Gobi.
- They include the biggest Sahara Desert (3.5 million square miles), Great Australian Desert, Arabian Desert, Iranian Desert, Thar Desert, Kalahari and Namib Deserts.
- In North America, the desert extends from Mexico into U.S.A. and is called by different names at different places, e.g. the Mohave, Sonoran, Californian and Mexican Deserts.
- In South America, the Atacama or Peruvian Desert is the driest of all deserts with less than 2 cm of rainfall annually.
- The temperate deserts are rainless because of either continentality or rain- shadow effect. [Gobi desert is formed due to continentality and Patagonian desert due to rain-shadow effect]
- Amongst the mid-latitude deserts, many are found on plateau and are at a considerable distance from the sea. These are Ladakh, The Kyzyl Kum, Turkestan, Taklimakan and Gobi deserts of Central Asia, drier portions of the Great Basin Desert of the western United States and Patagonian Deserts of Argentina etc.
- The Patagonian Desert is more due to its rain-shadow position on the leeward side of the lofty Andes than to continentality.
Rainfall (Both Hot and Cold deserts)
- Deserts, whether hot or mid-latitude have an annual precipitation of less than 25 cm.
Temperature of Hot deserts
- There is no cold season in the hot deserts and the average summer temperature is high around 30°C.
- The highest temperature recorded is 57.77° C in 1922 at A1 Azizia, Libya.
- The predominant vegetation of both hot and mid-latitude deserts is xerophytic or drought-resistant.
- This includes the cacti, thorny bushes, long-rooted wiry grasses and scattered dwarf acacias.
- Trees are rare except where there is abundant ground water to support clusters of date palms.
- Most desert shrubs have long roots and are well spaced out to gather moisture, and search for ground water. Plants have few or no leaves and the foliage is either waxy, leathery, hairy or needle-shaped to reduce the loss of water through transpiration.
The seeds of many species of grasses and herbs have thick, tough skins to protect them while they lie dormant.
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