(i) Deserts are the regions of scanty rainfall (less than 25 cm or 10 inch of rainfall)
(ii) May be hot like Saharan Desert; Coastal dry deserts like Atacama & Temperate or the mid latitude deserts viz. Gobi.
(iii) Hot desert climates are typically found under the subtropical ridge.
(i) Unbroken sunshine for the whole year
(ii) stable descending air
(iii) high pressure aloft
(iv) These areas are located between 15-30 degrees south & north latitude, under the subtropical latitudes called the horse latitudes.
(v) Major hot deserts of the world include—
(a) Sahara Desert (Africa)
(b) Thar Desert (India)
(c) Libyan Desert (Africa)
(d) Mojave Desert (N-America)
(e) Kalahari Desert (Africa)
(f) Iranian Desert
(g) Arabian Deserts
(h) Hot desert drylands, like the Atacama of Chile, the Namib of southern Africa, and the western Australian desert, are the result of cold oceanic currents that divert rainladen air away from coastlines.
(vi) Among the mid-latitudes deserts, many are found on plateau & are at considerable distance from the sea - Cold Deserts:
(a) Gobi Desert
(b) Turkestan Desert
(c) Patagonian Desert
The hot deserts lie astride the horse latitudes or sub-tropical high pressure belts, where the air is descending, a condition least favorable for precipitation of any kind.
(i) Air descending leeward side from mountainous areas warms and dries by compression, little rainfall forms and aridity is the result for e.g. Patagonian desert due to rain shadow effect of Andes.
(i) Cold air present above such currents ensures less evaporation of moisture with scarse evaporation resulting in formation of mist & fog, but no clouds - hence no rain. Effect of cold Peruvian current makes Atacama the driest place of the earth.
(i) Central areas of continents are dry because they lie far away from the oceans & air moving over landmasses does not absorb large amounts of water vapour, required for precipitation.
(i) Deserts are some of the hottest spots on the earth & have high temperature throughout the year.
(ii) There is no cold season in hot deserts & average temperature is around 30 -35 degree Celsius.
(iii) Diurnal range of temperature is extremely high in deserts due to intense high temperature during the day & freezing cold nights.
(iv) Days are unbearably hot with highest temperature of 76 degree Celsius recorded in open barren sand and in shaded, well-ventilated areas.
(v) Al- Azizia in Libya has had a recorded high temperature of 58 degree Celsius.
(vi) An interesting variant of tropical and subtropical deserts are the so-called West Coast.
(vii) Desert areas found on the western coastal margins of the regions such as Atacama deserts of South America, and the Sahara -Moroccan part and Namib deserts of Africa.
(viii) These areas are much cooler than their latitude would suggest (monthly mean temperatures of only 15-21 degree Celsius.
(ix) The cooling results from airflow off adjacent coastal waters where upwelling of the ocean gives rise to cold currents.
(x) Deserts of this sort are subject to frequent fog and low-level clouds; yet they are extremely arid.
(i) Deserts cover more than l/5th of the Earth’s land, and they are found on every continent.
(ii) Despite the common conceptions of deserts as dry and hot, there are cold deserts as well.
(iii) The largest hot desert in the world, northern Africa’s Sahara, reaches temperatures of up to 122 degrees Fahrenheit (50 degrees Celsius) during the day.
(iv) But some deserts are always cold, like the Gobi desert in Asia and the desert on the continent of Antarctica.
(v) Simoom - Violent dust storms in deserts
(i) Desert animals have adapted ways to help them keep cool and use less water. Camels, for example, can go for days without food and water.
(ii) Many desert animals are nocturnal, coming out only when the brutal sun has descended to hunt, have long feet & secrets cone, waste.
(iii) Some animals, like the desert tortoise in the southwestern United States, spend much of their time underground.
(iv) Most desert birds are nomadic, crisscrossing the skies in search of food.
(v) Because of their very special adaptations, desert animals are extremely vulnerable to introduced predators and changes to their habitat.
Desert vegetation is an amazing example of adaptive power of plants and trees, which maiorly consists of scrub, herbs, weeds, roots & bulbs.
(i) The predominant vegetation of deserts is xerophyte or drought resistant which usually has special ways of storing and conserving water viz. Cacti
(ii) Trees are rare except where there is abundant of ground water to support clusters of date palms.
(iii) Absence of moisture retards the rate of decomposition hence desert soils are deficient in humus content along with high rate of evaporation making the soil saline.
(iv) Plants have few or no leaves & foliage is waxy, leathery or hairy / needle shaped to reduce the loss of water through transpiration.
(v) Thick bark & tough skins to protect them while they lie dormant from excessive evaporation
(vi) Develop an extended root system close to the surface to collect a lot of water during scant rainfall.
(vii) Develop a deep root system and reach groundwater.
(i) Stay many years dormant as a seed and when sufficient rain falls, and speed up your active life to a 3 week compressed cycle, producing leaves, flowers and new seeds in no time.
(ii) Poison your immediate neighbours, and reduce competition of even your own species.
(iii) Remain small, it saves surface through which water evaporates.
(iv) Get round, a more advantageous ratio volume/surface, and develop green cylindrical stems able to perform photosynthesis.
(v) Cut off your limbs, I mean, led some of your branches die in order to consume less of everything.
(i) Bushmen— Kalahari
(ii) Bindibu / Aborigins— Australia
(iii) Bedouin— Arabia
(iv) Tauregs— Sahara
(v) Mangols— Gobi (Cold Desert
(i) Diamond & Copper— Kalahari (Thirst land) Atacama
(ii) Caliche (Cemented gravels) i.e Sodium Nitrate fertilizer
(iii) Chuquicamata (Chile) = Largest copper town
(iv) Sahara & Arabia—Oil
(vii) Nevada— Copper