Sahara Desert (ecoregion)The Sahara Desert ecoregion, as defined by the World Wide Fund for Nature(WWF), includes the hyper-arid center of the Sahara, between 18° and 30° N.]

It is one of several desert and xeric shrublandecoregions that cover the northern portion of the African continent.

The Sahara Desert is the world's largest hot desert, located in North Africa. It stretches from the Red Sea to the Atlantic Ocean. The vast desert encompasses

several ecologically distinct regions. The Sahara Desert ecoregion covers an area of 4,619,260 km2 (1,783,510 sq mi) in the hot, hyper-arid center of the

Sahara, surrounded on the north, south, east, and west by desert ecoregions with higher rainfall and more vegetation.

The North Saharan steppe and woodland secretions lies to the north and west, bordering the Mediterranean climate regions of Africa's Mediterranean and

North Atlantic coasts. The North Saharan steppe and woodlands receives more regular winter rainfall than the Sahara Desert ecoregion. The South Saharan

steppe and woodlands ecoregion lies to the south, between the Sahara Desert ecoregion and the Sahel grasslands. The South Saharan steppe and woodlands

receives most of its annual rainfall during the summer. The Red Sea coastal desert lies in the coastal strip between the Sahara Desert ecoregion and the

Red Sea.

Libya

An oasis in the Ahaggar Mountains. Oases support some life forms in extremely arid

deserts.

Some mountain ranges rise up from the desert and receive more rainfall and cooler temperatures. These Saharan

mountains are home to two distinct ecoregions; the West Saharan montane xeric woodlands in the Ahaggar, Tassili n'Ajjer, Air, and other ranges in the western and central

Sahara Desert, and the Tibesti-Jebel Uweinat montane xeric woodlands in the Tibesti and Jebel Uweinat of the eastern

Sahara. The surface of the desert ranges from large areas of sand dunes (erg), to stone plateaus (Hamada's), gravel plains (reg), dry valleys (wadis), and salt flats. The only permanent

river that crosses the ecoregion is the Nile River, which originates in central Africa and empties northwards into the

Mediterranean Sea. Some areas encompass vast underground aquifers resulting in oases, while other regions severely lack

water reserves.

The Sahara is a harsh environment with extreme conditions. It is the world's largest subtropical hot desert and the world's hottest desert .The Sahara has mainly a subtropical hot desert ( BWh) with long, prolonged, extremely hot to scorching summers while the winters stay short, brief, extremely warm to truly very hot. The climate of this desert is also characterized by a perpetual clear sky, fair weather and

by very low, and even almost non-existent rainfall but the precipitation is also very irregular and sporadic. Although the Sahara is located under the tropic of caner in the most part, this climate is said

to be subtropical due to the subtropical high pressure belt, which is mainly responsible of the hot desert climate. The northern fringe of the Great Desert receives very low winter rainfall, where low

pressure systems associated with the polar front arrive as being very weak and very attenuated. The southern fringe of the Great Desert receives summer irregular rainfall but relatively low which can only occur when the Intertropical convergence Zone moves up far enough northerly or when the

tropical low pressure systems are strong enough to cause precipitation. In both cases, the climate is very arid and the rainfall only occur on a few days per year. Between the two parts, the central Sahara

has an extremely arid climate, with the influence of the continental trade wind. The western coastal desert zone bask under the cool ocean current, the canary current which is responsible of a higher clouds and fog formation. According to the dryness of the air, the climate of the Sahara can not be

extreme, since any place where visible and invisible cloud cover as well as the water vapor contained within the atmosphere don't act as temperature regulator, the day between sunlight and ground in order to reduce the roasting, and the night between the Earth surface and space in order to reduce

cooling process by sending the absorbed infrared radiation of contracted heat during the day towards the sky, any place having that feature will be characterized by large temperature variations and

therefore by an extreme climate. The climates of the Sahara possess relatively high diurnal temprature ranges (between days and nights), and in some rare cases, brutal temperatures variations due to the

extremely dry and pure air as well as the clarity of the desert skies. The presence of slow but constant winds make the dryness and the aridity of the Sahara even worse, by enabling a greater evaporation.

The Sahara Desert features a hot desert climate (Köppen climate classification BWh). The Sahara Desert is one of the driest and hottest regions of the world, with a mean

temperature sometimes over 30 °C (86 °F) and the averages high temperatures in summer are over 40 °C (104 °F) and can even soar to 47 °C (116.6 °F) and often for

over 3 months. In desert rocky mountains such as the Tibesti in Chad or the Hoggar in Algeria, averages highs in summer are slightly moderated by the high elevation and are

between 35 °C (95 °F) and 42 °C (107.6 °F) towards 1,000 m (3,280 ft) or 1,500 m (4,921 ft) height. Daily variations may also be extreme: a swing from 37.5 to −0.5 °C

(100 to 31 °F) has been observed, but are rather around 15 °C (27 °F) and 20 °C (36 °F). Precipitation in the Sahara Desert is extremely low and very scarce throughout the

year as the whole desert generally receives less than 100 mm (3,93 in) of rain per year except on the northernmost and southernmost edge as well as in the highest desert mountains and more than half of the desert area is hyper-arid and virtually rainless, with an average annual precipitation below 50 mm (1,97 in) and many consecutive

years may pass without any rainfall in hyper-arid places. The south of the Sahara Desert, along the boundary with the hot semi-arid climate (BSh) of the Sahel, receives most of his annual rainfall during the highest-sun months (summer) when the Inter-Tropical Convergence Zone moves up from the south while. Wind and sand storms

occur as soon as early spring. Local inhabitants protect themselves from the heat and the sun as well as the dry air, the high diurnal temperature ranges and the sometimes

dusty or sandy winds by covering their heads, such as the cheche worn by Tuareg.

HumidityThe relative humidity of the air is generally extremely low to very low during summer and very

low to low during winter, knowing the relative humidity of the air directly depends of the air temperature. The region's low relative humidity rarely exceeds 30% and is often in the 4% to 5%

range.[30] The northern Sahara is more favorised, with a humidity between 20% and 35% in summer and 35% and 55% during winter. We have sometimes recorded some extremely low

absolute relative humidity values, like in Tamanrasset, Algeria where the humidity dropped at an extreme of 2% during summer at several occasions. The Nigerian desert is the part of the Sahara which has the least water vapor amount in the air : the air is even drier than other parts and the

annual verage relative humidity is lower than 20% and even reaches 15% in some areas of the Ténéré. For example, the annual average relative humidity is 26.2% in Aswan, Egypt; 29.9%

in Luxor, Egypt; 28.8% inKhartoum, Sudan; 28.6% in Wadi Halfa, Sudan; 25.1% in Dongola, Sudan; 22.8% in Faya-Largeau, Chad; 15.3% in Bilma, Niger; 19.6% in Agadez, Niger; 27.6%

in Atar, Mauritania; 33.7% in Bir Moghrein, Mauritania; 29.3% in Kufra, Libya; 33.9% inSebha, Libya; 33.8% in Ghadames, Libya; 27.3% in In Salah, Algeria; 22.3% in Tamanrasset, Algeria. In order to compare,Paris has an annual average relative humidity of 78.1%. It's also because of

the excessively dry air that the diurnal temperature variations can be high. The only exceptions to the hygrometric regime of the Great Desert are the coastal areas or the desert zones close to a water source, such as lakes or rivers. According to the ones of the temperatures, some diurnal variations of the relative humidity occur : the hygrometric degree is the lowest at about 3 p.m.

and is the highest at about 6 a.m., during the sunrise.

http://en.wikipedia.org/wiki/Aeolian_processes

The Sahara covers large parts of Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Western Sahara, Sudan and Tunisia,

extends over 9 million square kilometres (3,500,000 sq mi) and it covers about 1⁄4 of the African continent. If all areas with a mean annual

precipitation of less than 250 mm were included, the Sahara desert would be over 11 million square kilometres (4,200,000 sq mi) in area. It is one of three distinct physiographic provinces of the African massive

physiographic division.The desert landforms of the Sahara are shaped by wind or by extremely rare rainfall and include sand dunes and dune fields or sand seas (erg),

stone plateaus (Hamada), gravel plains (reg), dry valleys (wadi), dry lakes (oued) and salt flats (shatt or chott).Unusual landforms include the

Richet Structure in Mauritania.Several deeply dissected mountains and mountain ranges, many

volcanic, rise from the desert, including the Air Mountains, Ahaggar Mountains, Saharan Atlas, Tibesti Mountains, Adrar des Iforas, and the

Red Sea hills. The highest peak in the Sahara is Emi Koussi, a shield volcano in the Tibesti range of northern Chad.

Most of the rivers and streams in the Sahara are seasonal or intermittent, the chief exception being the Nile River, which crosses the desert from its origins in

central Africa to empty into the Mediterranean. Underground aquiferssometimes reach the surface, forming oases, including the Bahariya, Ghardaïa,

Timimoun, Kufra, and Siwa.The central part of the Sahara is hyperarid, with little, to no vegetation. The

northern and southern reaches of the desert, along with the highlands, have areas of sparse grassland and desert shrub, with trees and taller shrubs in

wadis where moisture collects. In the central, hyperarid part, there is many subdivisions of the great desert such as the Tanezrouft, the Ténéré, the Libyan

Desert, the Eastern Desert, the Nubian Desert and others. These absolute desert regions are characterized by their extreme aridity, and some years can

pass without any rainfall.To the north, the Sahara reaches to the Mediterranean Sea in Egypt and portions of Libya, but in Cyrenaica and the Maghreb, the Sahara borders

Mediterranean forest, woodland, and scrub ecoregions of northern Africa, which have a Mediterranean climate characterized by a winter rainy season.

According to the botanical criteria of Frank Whiteland geographer Robert Capot-Rey.

To the south, the Sahara is bounded by the Sahel, a belt of dry Tropical Savanna with a summer rainy

season that extends across Africa from east to west. The southern limit of the Sahara is indicated botanically by the southern limit of conalaka

moanakantha(a drought-tolerant member of the, or northern limit of Chenchrus, a grass typical of the Sahel. According to climatic criteria, the southern

limit of the Sahara corresponds to the 150 mm (5.9 in) isohyets of annual precipitation (this is a long-term

average, since precipitation varies annually).

WildlifeThe Sahara's environment requires that the wildlife adapt to hyper-arid conditions, fierce winds, intense heat and wide temperature swings. In the heart of the Sahara, for instance, most mammals are relatively small, which helps to minimize water loss. They often meet their water needs from their diets. They take refuge in burrows during the day, hunting and foraging primarily at night, when temperatures are lower. They have developed anatomical adaptations such as the fennec fox's large ears, which help dissipate heat, and its hairy soles, which protect its feet.Altogether, the Sahara hosts some 70 species of mammals, 90 species of resident birds, 100 species of reptiles, and numerous species of arthropods (invertebrates that have jointed limbs, segmented bodies and external skeletons). The animals include, for a few examples, Barbary sheep, Oryx, Anubis baboon, spotted hyena, dama gazelle ,common jackal and sand fox; the birds--ostriches, secretary birds, Nubian bustards and various raptors; the reptiles--cobras, chameleons, skinks, various lizards and (where there is sufficient water) crocodiles; and the arthropods--numerous ants, scarab beetles and the "deaths talker" scorpion. The wildlife is concentrated primarily along the less severe northern and southern margins and near desert water sources.

Perhaps the Sahara's most famous animal is the dromedary camel, domesticated for thousands of years and long used by the desert nomads. Relying on its fat-filled hump and other physiological adaptations, the dromedary can travel for days with no food or water; with its large thick lips, it can feed on thorny plants, salt-laden vegetation and dry grasses; with its thick footpads, it can negotiate rocky and sandy terrain; with its slit nostrils and heavy eyebrows and lashes, it can protect its nose and eyes from punishing sandstorms; and when given water, it can consume more than 30 gallons in a matter of minutes, preparing for more hot dry days

Seeds sprout quickly after a rain and attempt to completetheir growing cycle before the soil dries out.

Ruins of a mosque, its minaret still standing prominently. Located in the Atlas Mountains, at the northern edge of the Sahara, the ruins date back to the early days of Islam in North Africa.

People and CulturesAccording to estimates, the Sahara's entire population probably equals less than two million people, including those who live in permanent communities near water sources, those who move from place to place with the seasons, and those who follow the ancient trade routes as permanent nomads. Most have Berber and/or Arabic roots. The Berbers, speaking several dialects of the Berber language, appeared on the scene at the dawn of the Sahara's history. The Arabs, speaking Arabic, a Semitic language that originated in Arabia, appeared on the scene thousands of years ago. Most of the Sahara's population follows the Islamic religion, introduced in the seventh century AD.

The Sahara's history is written in terms of primitive hunting and gathering, nomadic trade, agricultural development, early communities, conquest, sophisticated civilizations, monumental architecture, dynasty, exploration, colonization and war. It bears the stamp, not only of the Berbers and early Arabs, but also of Egyptians, Nubians, Phoenicians, Greeks and Romans. In more recent centuries, it experienced the imprint of Ottoman, Spanish, Italian, French and English colonialism. In the nineteenth century, it heard the whisper of Roman Catholicism. During World War II, it suffered fierce and destructive battles between the Germans and the Allies. In the middle of the last century, its countries cast off their colonial yokes and found freedom.

WondersThe Sahara, with its natural and cultural wonders, offers the tourist a rich travel experience. For a few examples, you can:Explore dune fields, oases, the Nile and Niger rivers and even the most barren areas, (for instance, the Tanezrouft Basin--the Land of Terror).See exotic wildlife such as the Barbary sheep, Oryx, hyena, jackal and sand fox as well as various birds and reptiles.Join hiking and camel treks, recalling ancient nomadic trading caravans.Visit stunning monuments to the human story in the Sahara, for instance, the standing ruins of ancient cultures and the edifices of more recent cultures.Enjoy the rich fare of ancient, but still lively, bazaars and marketplaces.If you have not traveled in the Sahara and you are not familiar with the local conventions and standards, you should consult a travel agent, who should provide the information you will need for a rewarding trip.

Interesting FactsThe ancient Egyptians held the scarab beetle in reverence because the insect's newborn seemed to appear spontaneously, as if by magic. (In fact, newborn hatched from a ball of animal dung, where the female beetle had laid her eggs.)Berber as well as Arab nomads took their caravans of camels across the Sahara, trading in goods such as cloth, desert salt, gold and slaves.The narrow strip of desert land along the Atlantic coast sustains various lichens, succulents and shrubs. The organisms take their moisture from fogs produced by the cool Canary Current, which parallels the coast, just offshore.The crescent dunes, driven by the wind, may travel several yards in the course of a year.The Sahara, with 3.5 million square miles, is the largest "hot" desert in the world; however, the Antarctica, with 5.4 million square miles, is the largest desert. (While the Sahara receives an average of but few inches of precipitation per year, the Antarctica receives only slightly more.)