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 انكليزي DESERT

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تاريخ التسجيل : 19/01/2008

مُساهمةموضوع: انكليزي DESERT   السبت يناير 19, 2008 5:11 pm

desert
Contents


1. Terminology 3
2. Types of desert 4
3. Montane deserts 5
4. Rain shadow deserts 5
5. Flora and fauna 5
6. Vegetation 5
7. Water 6
8. Human life in deserts 6
9. References 6

Desert


Submitted
This article is about arid terrain. For other uses, see Desert (disambiguation).
For the act of abandoning or withdrawing support from an entity, see desertion.
Not to be confused with Dessert.


Erg Chebbi, Morocco


Saguaro's in the Sonoran Desert of Arizona


Body
Terminology
Deserts where vegetation cover is exceedingly sparse correspond to the 'hyperarid' regions of the earth, where rainfall is exceedingly rare and infrequent.



Types of desert


The Thar Desert near Jaisalmer, India


High desert in Eastern Oregon, United States


The Agasthiyamalai hills cut off Tirunelveli (India) from the monsoons, creating a rainshadow region
In 1953, Peveril Meigs divided desert regions on Earth into three categories according to the amount of precipitation they received. In this now widely accepted system, extremely arid lands have at least 12 consecutive months without rainfall, arid lands have less than 250 millimeters (10 in) of annual rainfall, and semiarid lands have a mean annual precipitation of between 250 and 500 millimeters (10-20 in). Arid and extremely arid lands are deserts, and semiarid grasslands are generally referred to as steppes.[1]
However, lack of rainfall alone can't provide an accurate description of what a desert is. For example, Phoenix, Arizona receives less than 250 millimeters (10 in) of precipitation per year, and is immediately recognized as being located in a desert. The North Slope of Alaska's Brooks Range also receives less than 250 millimeters (10 in) of precipitation per year, but is not generally recognized as a desert region. Deserts have moderate to cool winters and hot summers.



Montane deserts
Montane deserts are arid places with a very high altitude; the most prominent example is found north of the Himalaya especially in Laddakh region of Jammu and Kashmir (India), in parts of the Kunlun Mountains and the Tibetan Plateau. Many locations within this category have elevations exceeding 3,000 meters (10,000 ft) and the thermal regime can be hemiboreal. These places owe their profound aridity (the average annual precipitation is often less than 40 mm/1.5in) to being very far from the nearest available sources of moisture. Montane deserts are normally cold.
Rain shadow deserts
Rain shadow deserts form when tall mountain ranges block clouds from reaching areas in the direction the wind is going. 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.
Flora and fauna
Deserts have a reputation for supporting very little life, but in reality deserts often have high biodiversity, including animals that remain hidden during daylight hours to control body temperature or to limit moisture needs. Some fauna includes the kangaroo rat, coyote, jack rabbit, and many lizards. Some flora includes shrubs, Prickly Pears, and the Brittle bush.
Vegetation


Flora of Baja California Desert, Cataviña region, Mexico
Most desert plants are drought- or salt-tolerant, such as xerophytes. Some store water in their leaves, roots, and stems. Other desert plants have long taproots that penetrate to the water table if present, or have adapted to the weather by having wide-spreading roots to absorb water from a greater area of the ground. Another adaptation is the development of small, spiny leaves which shed less moisture than deciduous leaves with greater surface areas. The stems and leaves of some plants lower the surface velocity of sand-carrying winds and protect the ground from erosion. Even small fungi and microscopic plant organisms found on the soil surface (so-called cryptobiotic soil) can be a vital link in preventing erosion and providing support for other living organisms

Water


The shifting sands simulator at Questacon, Canberra
Rain does fall occasionally in deserts, and desert storms are often violent. A record 44 millimeters (1.7 in) of rain once fell within 3 hours in the Sahara. Large Saharan storms may deliver up to 1 millimeter per minute. Normally dry stream channels, called arroyos or wadis, can quickly fill after heavy rains, and flash floods make these channels dangerous.
Human life in deserts
A desert is a hostile, potentially deadly environment for unprepared humans. The high heat causes rapid loss of water due to sweating, which can result in dehydration and death within days. In addition, unprotected humans are also at risk from heatstroke and venomous animals. Despite this, some cultures have made deserts their home for thousands of years, including the Bedouin, Touareg and Puebloan people. Modern technology, including advanced irrigation systems, desalinization and air conditioning have made deserts much more hospitable. In the United States and Israel, desert farming has found extensive use.
Conclusion

In the end, you benefited from this report, which contains valuable information on the Sahara Desert and features

References
• From Wikipedia, the free encyclopedia
• Books features desert
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