From the high-pressure belts, about 30° N. and 30° S., the trade winds blow towards the low-pressure belt round the Equator. As they are flowing from cooler to warmer regions they become warmer as they proceed, and tend to absorb rather than deposit moisture. Thus they are dry winds. For this reason, a desert belt is found around the tropics on the western sides of the continents.
Seven major tropical deserts are:
(1) the Sahara is the biggest desert of the world. It stretches 3500 miles from the Atlantic ocean to the Red sea and 1200 miles from Sudan to Mediterranean sea and Atlas Mountains. Niger, Mauritania, Mali, Chad, Sudan, Morocco, Tunisia, Algeria, Libya, Egypt, Ethiopia, Somalia, Eritrea etc. are all contained in this vast and sterile desert.
(2) Desert of south-west Asia which contains in it almost all of the Arab peninsula excluding Yemen and Oman, Southern Israel, Jordan, Iraq, Iran and most of the parts of central and southern Syria.
(3) The Desert, which contains in it the middle and lower parts of Indus Valley in Pakistan and western portion of Rajasthan in India.
(4) Australian Desert which is the biggest in the southern hemisphere and covers about 40% area of Australia,
(5) Kalahari of South Africa
(6) Akatama Desert in South America covering coastal regions of Peru and some part of the Northern Chile,
(7) Sonoran Desert which includes lower California North-west coast of the Mexican Mainland.
Temperatures of tropical deserts are highest on the earth and the rainfall is the lowest. Noon temperature is 105° to 110°F. The highest shade temperature ever recorded was 136.4°F at Azizia in Sahara.
Precipitation is low and is erratic in nature. Annual rainfall are less than 10 inches. In Sahara averages are not more than five inches. Coastal areas of Atacama and Kalahari have dense mists because incoming airs are chilled by the cool currents.
Sources of water supply in the desert regions are not many. Rivers play very important role in this respect. The Nile has changed the desert land of Egypt into a fertile and rich cultivated area producing long staple cotton. Irrigation has helped a lot in Iraq. Tigris and Euphrates supply water and their combined channel known as Shettal Arab flowing above Basra 120 miles to the Persian Gulf. Indus river crosses the Thar Desert and supports very large irrigation work.
Sahara type Desert
Deserts have xerophytes, which adjust themselves to harsh dry climatic environments. Normally everywhere in the desert thorn bushes, misquite and sege brush etc. are the species of vegetation found. Desert fox and a specie of antelope are found in Sahara. Birds are few in number. Camel is used in African and Asian deserts. Soils are sandy with saline deposits on the surface caused by evaporation. Thorny scrub and bushes, which are drought resistant, occur in patches here and there. In the oases, date palm and other trees may be grown and small areas may also be cultivated. The primitive Bushmen of Kalahari desert of South Africa and the Aborigines of Australia practice food gathering and hunting. The Bedouins of Arabia are nomadic herdsmen rearing camels, horses, sheep and goats. They live in tents and migrate from place to place in search of pastures for their animals.
In the river valleys passing through desert region and in scattered cases, agriculture has developed. There are permanent rural settlements and towns in the Nile Valley and delta. Modern irrigation methods have ensured adequate water supply. The Indus Valley in Pakistan and the Imperial Valley in California are other examples of large tracts of settled agriculture. Small mining settlements are found in some of the deserts. The discovery of vast resources of petroleum and their mining in the recent decades have resulted in rapid economic development in Kuwait, Saudi Arabia, Iran and Iraq.
The Middle East only produces oil and has three-fourths of worlds proved reserves. Petro - dollars are the result of oil deposits. Deposits of nitrates in Chile have helped it in the improvement of economy.
Oil refining is significant in the Middle East. Sugar refining, cotton ginning and cement manufacturing are some of the occupations of Egypt. Damascus, Syria, Bagdad, Iraq and Tombouctou in Mali, Karachi in Pakistan. Alexandria, and Suez in Egypt, Dakar in Senegal, Lima in Peru and San Diego in California and Basra of Iraq, Cairo, Mecca, Phoenix etc. are principal cities of desert of natural region.
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