The Sahara - SpeedyLook encyclopedia

Geographical limits

; According to botanical criteria for Cap-Rey (1953)

in North: limit of maturity of the palm trees - date palms
in the South: southern limit of the Had ( Cornucala monacantha ) a Chenopodiaceae or northern limit of the Cram-cram ( Cencrus biflorus ) a Poaceae sahélienne.

; According to climatic criteria

in North the Isohyetal of the 100 mm
in the South a limit fuzzier than one can base on the Isohyète of the 150 mm knowing than the rains strongly vary from one year to another.

Climate

the northern fringe of the Sahara is subjected to a mode of winter rains in which the Mediterranean disturbances arrive attenuated.
the southern fringe is subjected to a mode of irregular rains of summer which occur only when the intertropical face of convergence goes up rather far towards north or when tropical depressions are rather strong.
Between the two, the central Sahara is subjected to an extremely arid mode marked by the establishment of the continental Alizé or Harmattan. Only the tops of the Hoggar and the Tibesti are sprinkled.
Enfin the Atlantic coastal area bathed by the cold current of the the Canaries is subjected to the breezes of sea and some phenomena of fogs.

Precipitations

They are characterized by their weakness and their extreme variability (from 1 to 100 mm). It can happen that they are violent and devastating. It only rains very seldom in this part of Africa. In the Libyan south they occur at a 25 years intervals.

Cattle grazing a last square of thorn-bush in a athmosphère of end of the world… Image of yesterday and today. With the the Sahel, the attempts to stop the advance of the desert remain vain. Grounds are lost each year, out of the decimated herds, the famine still kills… To be defended against the desert, the whole world should be mobilized.

Sunning

3103 hours of Sunning to the the Western Sahara (Dakhla).
3686 hours of sunning in the Ténéré (Bilma) or in the Hoggar (Tamanrasset).
3723 hours of sunning in the libyque desert (Kufrah).

Temperature of the air and water content

The maximum temperatures in the hottest areas exceed 50°C. Moreover the highest temperature recorded in the Sahara was of 58°c in Libya with Aziziyah. In June, with Bilma in Ténéré the average of the maxima is of 43°C, with Tamanrasset of 35°C, the hottest month with Dakhla is August with maxima of 27°C.

The average minima are in January of 7°C with Bilma of 4°C with Tamanrasset but of 13°C with Dakhla.

The water content of the air is very weak, except on the Atlantic edge. In the Ténéré the minima (with 13:00) are lower than 20% and the maxima (in the small hour) are lower than 43% except in August (29% and 56%). Consequently, potential evaporation is considerable and it is reinforced by the action of the winds.

Wind

The most constant wind on the central part and west of the Sahara is the Harmattan, trade wind continental which blows of the North-East. It is reinforced with the Anticyclone and produces the sand winds then. In the north of the Sahara can be established other winds in connection with the Mediterranean depressions of winter like the Khamsin in Egypt. With the south, gusts of wind of dust are associated with the tropical Tornade S of August.

Animals of the desert

It is the night that the desert becomes animated. There, in the middle of the dunes and the rocks, a life in tiny majority - it belongs especially to the world of the insects - leaves its torpor. Each one then seeks to be nourished. Because if the majority of the animal species of desert spaces do not need to drink to survive, they must absolutely recover the invaluable liquid in the flesh of their prey.

Camel X, Dromedary S and Chèvre S is of course the animals which come us to mind but those are pets by the man. The camel was always the favorite animal of the nomads, because of its well-known qualities of sobriety, endurance and speed. In the Sahara, one meets only dromedaries.
the yellow scorpion with broad tail is as well known for us. It can be 10 cm long. Its puncture is mortal in the majority of the cases.
the monitor gray, of an irascible naturalness, sinks deliberately on the enemy.
the viper of sands equipped with a head punt and triangular, hides in sand thanks to gyratory movements of the trunk.

the fennec also called sand fox lives everywhere in the Sahara. The fennec spends the day to the shelter in its burrow. The night, it drives out insects and rodents. To avoid any useless physical exercise in the localization of its preys, it has a hearing extrèmement developed.

the daman of rock is a host of the reliefs.

the Autruche became rare because it is driven out.

the Addax, large antelope white, is a threatened species (especially because of hunting). Adapted to the desert, there can remain months without drinking, even a whole year.

the gazelles dorcas do without drinking. They are satisfied with the water extracted the foliage which they consume.

the Saharan Guépard lives in Niger, Mali and Chad. There remain about it only a few hundreds. Very emotive, avoiding any human presence, the cheetah flees the sun from April at October. He then seeks the shelter of shrubs such as balanites and acacias.

the ants reaping-machines work hard - spring with the autumn - to pile up various seeds in their anthills. Located between 25 and 40 cm of the surface of the ground, their reserves are for a long time known by the wandering people, which, in period of famine, do not hesitate to adapt them to survive.

the ganga with the characteristic to nest very far from the oases. To water brooded, the male does not hesitate to cover long distances to find a water point. It stores water in its plumage particularly absorbent and returns near its chicks.

There exists of course of other animals in the desert (of the birds in particular), but the animals referred to above are most representative of the Sahara.

Natural environments

Ergs

The erg S are the large solid masses of dunes, they occupy approximately 20% of the surface of the Sahara.

Regs

The regs, so called to serir in the oriental parties of the desert, are extents punts, stony and gravelly and constitute the most frequent landscape of the Sahara. Large the regs is particularly inhospitable. One can quote the reg. of Tanezrouft, it serir Libyan or the reg. of Ténéré which occupy each hundred of thousands of km ². They can also occupy the top of the plates.

Dayas

The dayas are basins of limited extension, at the bottom in general argillaceous in which the surface water can accumulate. An alternation of flood and wind erosion can explain their formation. They are sometimes of karstic origin on the plates. They constitute perennial zones of vegetation. One especially meets them in the north of the Sahara.

Sebkhas

With the difference of the preceding ones, the sebkhas form temporary saline marshes. Water can come from the streaming or temporary sources. Largest, the Chott el-Jérid, covers 5000 km ². Some are exploited in the form of saltworks since the 16th century as with Taoudeni with the Mali.!!

Hamadas

The hamadas are tabular rock plates limited by cliffs. They are of origin Sédimentaire, generally Calcaire. When they are covered with sandstone, they are named tassilis (for example: Tassili of Ajjer in Algeria). In general surface shows naked rock, smoothed by the wind erosion.

Djebels

The term djebel indicates all the other reliefs that they are more important hills or mountainous solid masses.

The most important solid masses are:

the Tibesti (area of the Borkou-Ennedi-Tibesti) made of a volcanic solid mass emerging from a thick sedimentary tablecloth resting on the crystalline base. It culminates to 3415 m (Emi Koussi).
the Hoggar is another imposing volcanic solid mass. It culminates to 2918 Mr.
the Aïr is less low the tops is more tabular but culminates all the same with 2022 Mr.
the Adrar of Ifhoras in the south of Hoggar in is a crystalline prolongation and metamorphic which culminates to 890 Mr.
the Ennedi (area of the Borkou-Ennedi-Tibesti) is a solid mass sandy in the south-east of the Tibesti and reached 1282 Mr.

Oases

The Saharan Oases, natural environment and anthropic, occupy only one thousandths of the surface of the Sahara. They are located sometimes on the bed of rivers coming to lose itself in the desert or with the producing foot of solid masses of the sources or directly to tops of ground water the levelling or not very deep.

Guelta

This term indicates temporary water levels or not without visible flow. It can be ponds in the beds of the wadis, or the natural cisterns in the rock. One meets them in the situations protected from a too great exposure to the sun in the mountainous solid masses, that of the Ennedi or in the Adrar of Ifoghas to the Mali.

Foggaras

The Foggara S, are underground works big length allowing the water conveyance in some Oasis, since the mountainous plates or solid masses. This ancestral technique was born in what today is the Iran, under the name of Qanat.

Wadis

The Oued S are rivers to temporary visible flow. The majority of time they are dry, in-depth durable pockets of water can persist, gueltas can be supplied with a resurgence. Violent risings can sometimes occur especially in the mountainous solid masses. The upstream part is born from the gathering of channels from streaming, the median part forms a broad bed and whose limits are sometimes difficult to recognize in plain and the downstream part can be divided into several arms on a wide cone of alluvia. It is along the wadis that one observes the only a little dense formations raised in the Sahara.

Ténéré

The deserted Ténéré, or “ of the deserts ” is the central part of the Sahara which extends in Niger. The term comes from the tamacheq, the language of the Touaregs and means simply “deserted”.

White desert

The white desert, also called Désert Libyque extends to the west from the the Nile, over a width of approximately 800km. It owes its name with the presence of Calcaire which gives by places the white color.

Precipitations are there very weak (approximately 5mm per annum).

Current populations and cultures

Among the current populations of the Sahara, one can note:

the Tuaregs, people of nomads, with the number estimated at a million. Fabric Vêtus traditionally of color indigo blue which fades on the skin, they were also called the “ blue men ” or the “ lords of the desert ” by the Western travellers.
the Saharaoui S.
the Moor S.
Per tens of thousands, the nomads are folded up in front of the dryness. Never again they will make the traditional circuit of the pastures to the liking of the seasons, because more the least graminaceous one will not push on their burned grounds. They move back until the accesses of the cities, plant their tents there and come to enlarge the rows of the population of these Bidonville S of a new kind, everywhere in rapid extension.
In an area of the north of the Senegal, there was formerly a forest of Tamari S and out of Acacia S. the dryness killed it. The peasants started by tearing off the sheets of the trees to nourish their cattle. They now collect the deadwood and the brushwood to feed their fires. When they uproot the remainders of the trunks, plus nothing the ground will not retain. The turning into a desert will be total.

The prehistory of the Sahara

One can find in the Sahara of many traces of a prehistoric human activity (tools, potteries, and cave paintings).

The climate of the Sahara underwent climate changes during prehistory:

In the oasis of Bilma (Niger), of the glaucous craters of Saline S is the vestiges of the seas which covered the Sahara 100 million years ago.
There is approximately 40 000 years, there exist big lakes in the Sahara, then populated seminomads
There is 18 000 years, the Sahara was hyperaride.
Towards 12 000 years before our time, its south-Eastern limit had gone back to height of the Tropique of Cancer.
Towards 10 500 years before our time, it is its south-Western limit which had gone up, desert surface being then half less than the current one.
radoucissement of the climate of this écorégion continued to remain moderate to the 8.500 year old neighborhoods before our time. The Sahara was then marshy, cover of steppe and savanna.
Although the warming had started, the Sahara was still wet around 6.500 years before our time.
This desert acquired the current arid climate towards 3 000 years before our time but one can speak about true desert only since 3 000 years, before it was a green vastness, populated hunters and wild animals.

Random links:

Legislative National Assembly (French revolution) | Dano (department) | Abbadon the Plague | Castle of Pez | Thjálfi