Chad Basin

The Chad Basin, also known as the Lake Chad Basin, is a large lowland area in north-central Africa. In all directions from the center of this area the elevation changes are gentle. The Chad Basin is an endorheic (closed) basin - its water does not flow into any ocean. It has a long history of human settlement, and for a long time was an important crossroads for the Trans-Saharan trade from north to south and west to east in Africa. The first known developed civilization in the northern area of the Chad Basin was that of the Garamantes during the Roman Empire; the second was the Sao civilization in the 6th century, located south of Lake Chad.

The most significant feature inside the basin is Lake Chad. The lake has been known outside Africa since the Middle Ages. However, despite the region's important role in the development of cultures and history in northern and central Africa, social scientists have recently discovered that it is a rich and promising area for ​​research. In 17th century maps, the lake was designated as Borno Lake and was a mystery to Western scientists. The next reports about this area came from the German Heinrich Barth in the middle of the 19th century. He was the first to report rock art in the northern mountainous areas of the basin. This was the first time that Western scientists had heard of a wet paleoclimate in the Sahara desert and the Chad Basin.

The existence of Lake Chad has contributed to the development of peoples, flora, and fauna in this region for many thousands of years. As a source of water between the desert and the savannah, the region has attracted many immigrants, explorers, and adventurers. The annual fluctuation of the lake's water level, and the floods which are associated with this cyclical change, opened opportunities for the development of cultures and nations as well as a place of refuge and protection. The Chad Basin served as a region in which ruling dynasties could develop new political formations with momentum that carried them far beyond this region. However, at the same time, the region was a natural barrier that prevented greater trade and interaction.

Geography

The Chad Basin extends between 6°N and 24°N latitude, and between 8°E and 24°E longitude. It covers an area of approximately 2.434 million km², equivalent to 8% of the total area of the African continent.

The Chad Basin is surrounded by high mountain ranges which rise up to the highland of the North Equatorial Plateau (known in some countries as the Asande Barrier). This plateau includes parts of the Adamawa Plateau in the west and the Bongo Massif in the east.

In the east, the Chad Basin extends to the 3088 m high Jebel Marra in Darfur. In the northeast, the basin -- known as the Ennedi Plateau -- rises to 1450 m. In the north of the basin the volcanic mountains of Tibesti are located, with 3415 meter high Emi Koussi being the highest point of the central Sahara; to the west lies the Djado Plateau. The border in the northwest is marked by the mountains of Tassili n'Ajjer in Algeria, the highest peak being Jebel Azao at 2158 meters. The western boundary is formed by the Aïr Mountains and the Termit Massif in Niger. In the southwestern Chad Basin the Jos Plateau, the Biu Plateau and the Mandara Mountains mark the geographical boundary. In the center of the Chad Basin is the Bodélé Depression, which is also the deepest part of the basin, about 155 meters above sea level. Lake Chad is 275 meters above sea level.

Countries in the Chad Basin

The Basin is shared among the countries of Republic of Chad, Niger, Nigeria, Cameroon, Central African Republic (CAR), Algeria, Libya, and Sudan. The biggest part of the basin lies in Chad, around 1,123 million km² covering the center. The western part, 674,000 km², is in Niger. In the north and northwest 91,000 km² are in Algeria and 5,100 km² in Libya. In the southwest there are 179,000 km² in Nigeria and 47,400 km² in Cameroon. The southern part of the basin, 216,000 km², is in the territory of the Central African Republic, and the eastern part, 97,700 km², is in the Islamic Republic of Sudan.

Population of the Chad Basin

Presently (2011), more than 30 million inhabitants, including migrants from various African countries, live in the Chad Basin where they draw the essence of their livelihood through activities like fishing, agriculture and animal husbandry. The Population in the Chad Basin had in 2001 a growth rate of 2.72% per year and some administrations expect that in 2020 there will be more than 50 million people living in the basin. The areas in Algeria and Libya are unoccupied.

Lake Chad Basin Commission

The Lake Chad Basin Commission (LCBC) was created on 22 May 1964 and is headquartered in Fort Lamy, now N'Djamena. It was founded by Cameroon, Niger, Nigeria and Chad. The LCBC now has six country members: Chad, Central African Republic, Cameroon, Nigeria, Niger, and since April 2007, Libya. Sudan has an observer status. The commission is responsible for regulating and monitoring the use of water and other natural resources within the Lake Chad Basin. One of its sub-divisions, the Basin Committee for Strategic Planning (BCSP), coordinates local activities among the member states.

The LCBC controls and monitors the hydroactive regions in the Chad Basin and the so-called conventional basin. The initial conventional basin consisted of approximately 427,500 km² of the total area of the Chad basin in 1964. This definition excludes most of the terminal depression consisting of desert that provides little or no effective hydrological contribution to the conventional basin. This was subsequently expanded to include additional watersheds in northern Nigeria, southern Chad, and northern Central African Republic, with a current total area of 967,000 km².

Geology

The Central African Shear Zone and Rift systems around the Chad Basin

The Chad Basin was formed by extensional tectonic forces during the Cretaceous period with the geological and geomorphological development of the basin being conditioned by the slow and ‘cool’ rifting of the Mesozoic-Tertiary rift system in Central and West Africa. The rift system developed primarily in the Early Cretaceous, during the opening of the South Atlantic and a regional NE-SW extension. This tectonic movement of the lithosphere formed a regional hydrological sink known as the Chad Artesian Sub-Basin and Chari-Logone Artesian Sub-Basin. The greater Chad Basin is part of the major meridional zone of depressions extending from the Gulf of Gabes in the north of Africa to the Karoo aquifer in the south.

Most of the basin is covered by Quaternary sands. Below the sands, at about 75 m depth, are clays of the Pliocene with a mean thickness of approximately 280 m. Further down, a layer of sand about 30 m thick is encountered that belong to the Lower Pliocene. These sands give place to the real Pliocene aquifer, as the clays are generally considered to be impermeable. Further down, sandstones of the Continental Terminal appear; they formed in the Tertiary period and are about 150 m thick. The deepest known rock formation is the Continental Hamadien, formed in the Cretaceous period. It also consists of sandstone.

The basement of the Tibesti region is Precambrian schist, overlaid with Palaeozoic sandstones, all capped by Tertiary and Pleistocene outpourings of basalt.

Undifferentiated granites and gneisses are found in the eastern part of the basin. Lower Paleozoic sandstone sequences are found on the border to the Kufra Basin in the northeast, close to the border to Libya and Sudan. They are overlaid by Nubian sandstones in the area of the Ennedi and Erdi Plateau.

Aquifers

The four aquifers in the Chad Basin are composed of a series of sediment deposits and include the Upper Quaternary phreatic aquifer, the Lower Pliocene, the Continental Terminal and the Continental Hamadien. Investigations suggest the main recharge to the aquifers is from surface water bodies. They are very sensitive to climate changes and especially to open water surface runoff regimes.

The groundwater quality of the Quaternary phreatic aquifer is suitable for domestic consumption by the local population and livestock. The Lower Pliocene Aquifer, found at depths of about 250 m with an average thickness of 60 m, is an artesian aquifer intensively used in the Nigerian part of the basin. The reserves of the Lower Pliocene Aquifer are unknown; exploration of this aquifer has led to estimates of about 3 million m³ per year. The Continental Terminal aquifer is essentially an alternation of sandstone and clay. The deepest aquifer is the Continental Hamadien. This is an important aquifer in some West African regions, but very little reliable information is available about it.

In general, the area of the active hydrographic basin covers about 967,000 km²; toward the north and northeastern borders of the basin lie the Nubian Sandstone Aquifer System and the Iullemeden Aquifer System is at the western border.

Climate

The types of climate in the Chad Basin is very varied: hyperarid climate in the northern areas, characterized by the deserts, semiarid climate in the zone of the Sahel and subhumid climate further south in the area of Lake Chad, with humid subtropical climate in the mountainous regions of Nigeria, Cameroon and the Central African Republic.

The Basin is principally located in the transition zone between the Sahara desert over Sahel and Sudan to the rainforest areas in the Congo Basin. Rainfall is a very important factor to conditioning the hydrology and the climate in this region. The Chad Basin is under the influence of the Inter-Tropical Convergence Zone (ITCZ), which oscillates seasonally between about 15° N and 15° S latitude. In the north of the basin is also high pressure zone and prevents the sahara from rainfall. Except during the Boreal winter when occasionally cold air descends from the north, its the dry Harmattan winds. Rain only occurs over the region after the ITCZ has moved past this area towards the north. From April to October, rainfall occurs but is generally heaviest in August, corresponding with the maximum northward extent of the ITCZ, followed by July and then September. About 90% of the rain falls from June to September. Its the time of wet south west Passat winds, also known as West African Monsoon System. In the last decade, the Isohyet-lines have moved somewhat southwards, as the high pressure system over the Sahara has extend southwards. This movement of the ITCZ is corresponding to the movement of North Atlantic oscillation and responsibly of drought periods in the last century. Since the 1960s the annual rainfall has decreased by as much as 25% in some regions of the basin. For example, on the dry northeast side of Lake Chad, at the town of Bol, rainfall from 1954 to 1972 ranged from 125 to 565 mm per year and averaging 315 mm. In general the annual rainfall over the Chad Basin is characterized by a sharp meridional gradient, varying from 1200–1600 mm at the southern edge to 50–100 mm at the northern edge. The variability of the position and intensity of rain-belt over the Chad Basin is dominated by the West African monsoon (WAM) and is very important for the region’s rain-fed agriculture, water resources, health, and climatically sensitive natural environments. The socio-economic and environmental shocks resulting from the dramatic decline in rainfall since the mid-1960s have produced widespread human misery and environmental degradation. Some of the countries in the Basin generate 80% of their gross national product from agriculture activities.

Evapotranspiration potential

The evapotranspiration potential (ETP) is high and peaks in April and May, when the saturation deficit is high, and falls during July and August as the saturation deficit reduces. There is a brief rise during September and October as the saturation deficit increases once more, falling to a minimum in December and January, when air temperatures are at a minimum in the region. Mean annual ETP increases northwards by about 60 mm per degree of latitude. In general, the ETP varies over the area from 1,500 - 1,800 mm year in northeastern Nigeria to 2,300mm northeast of Lake Chad to 6,000 mm in desert lowlands in the northeastern part of the basin.

West African monsoon system

The West African monsoon (WAM) is a coupled atmosphere-ocean-land system characterized by summer rainfall over the continent and winter drought. The processes that couple the land, ocean, and atmosphere involve multiple interacting space- and time-scales.

Investigations by the African Monsoon Multidisciplinary Analyses project (AMMA) have shown that the formation of cold water in the Guinean Gulf plays a determining role in the monsoon onset. Similarly, meteorological conditions in the Mediterranean Sea or in the Indian Ocean are key factors in the variability and the retreat of the monsoon. The annual cycle of the sea surface temperature (SST) in the Gulf of Guinea is asymmetrical with a rapid cooling from the highest SST in April to the lowest SST in August, and a gradual increase up to the next April. West African rainfall, including the Chad Basin, is significantly influenced by SST through the advection of marine boundary layer temperature anomalies over Africa which cause sea level pressure and surface wind convergence anomalies. They study also showed that seasonal changes in insolation control the seasonal changes in the net budget of energy input in the atmospheric column, which is balanced by horizontal energy export in the thermally direct circulation associated with convection in the ITCZ. This modulates the moisture advection inland and controls the rainfall production over West Africa.

Reasons for the variability of the WAM over the last decades are not clear; there has been an abrupt ITCZ shift. Further investigation is needed.

Climate history

Little is known about the climactic history of the Chad Basin. Only the younger age of the Quaternary period has been sufficiently explored, since the prevailing transformation of landscapes and the beginning of hull surface fragmentation in the Early Quaternary period has been newly recognized as leading to river valleys. The effects of frequent changes of humid Pluvial and desert-like Interpluvial times on the relief, however, have been adequately investigated despite the absence of radiometric age determinations, a lack of datable preserved traces, and the extinction of older relief states.

One can prove the existence of an older dune zone, called Erg Ancien, that extended over the current 800 mm isohyet-line and suggests an extremely arid climate 40,000 years ago. This was followed by a wetter period of years 40,000 to 20,000 years ago. This humid period was followed by an extreme drought, called the Ogolien and the Kanemi, which lasted until 12 000 years ago. At that time the dune advanced; it is called Erg Recent and extended up to today's 500 mm the isohyet line. About 10,000 years ago the well known period of humid climate began in the Sahara area, also called Tschadien; it ended with a dry period from 7500–7000 years ago. From 9,000 to 5,000 years ago there were two phases in which Lake Chad had a much greater extent than today. This lake, also named Megalake Chad or Paläochad, covered an area of approximately 350,000 km² with a constant elevation of 325 m above the current sea level. The historical sea borders can be identified by the dark brown sediments deposited in the former shore area; they are now a few tens of centimeters thick.

A short humid phase 3500–2500 years ago, demonstrated by shallow lakes and large wetland areas, ended in an increase in aridity with minor fluctuations. This resulted in the Sahara as we know it, but also started the remobilization of sand dunes in the Sahel, a process continuing to the present day.

River Systems

Komadugu Yobe River basin

The Chad Basin has two major river systems, the Chari-Logone-Riversystem and the Komadugu Yobe Riversystem. There has formed a wide Floodplains and Wetlands foremost in the south and western part of the basin. From the highland of the Adamawa Plateau and Mandara Mountains flow also the EL Beid River, the Ngadda River and the Yedseram River in the southern sea basin of Lake Chad.

Komadugu Yobe

The Komadugu-Yobe sub-system has a basin area of 148 000 km²,85.000 km² in Nigeria and 43.000 km² in Niger, but contributes less than 2.5% of the total riverine inflow into Lake Chad basin. In present times the River Doesn't reach the open water surface of the lake. The Komadugu-Yobe River is formed by various tributaries, the main tribuary is the Hadejia River which flows from the area around Kano, the particular is the Jama'are River and flows from Jos Plataeu. The two River forms the Hadejia-Nguru wetlands and join in the near of Gashua and now designated as Komadugu Yobe River. These River is also temporary supplied by the Misau River, also known as Komadugu Gana, which flows from the north of Bauchi and joins the Komadugu-Yobe 120 km from historical seashore of Lake Chad. The annual rainfall is very different in this sub-basin area. In the north, in Niger, falls only 200 mm/m² per year, in the area of Hadejia-Nguru wetlands is up to 500mm/m² and on Jos Plateau up to 1.600 mm/m².

Chari-Logone

The Chari Logone catchment Area

The Chari-Logone sub-system has a basin area of approximately 650.000 km² and extents from Dafur in Sudan to the Adamawa Plateau in Cameroon. The Chari River himself extends 1.400 km in length. The parts of the sub-system lying in Central African Republic (CAR) constitutes the headwater region. The Ouham in CAR, becoming the Bahr Sara in Chad, is the main tributary of the Chari River with its confluence located at Manda, downstream of Sarh. Its contribution was estimated to be twice that of the Bahr Aouk, despite having a smaller catchment area. The Bahr Aouk drains the entire northeastern part of CAR and together with its tributaries, is a true floodplain river. The Bamingui and Bangoran rivers drain the northern part of CAR and form the transition between the northeast and the more populated northwestern areas. All rivers in the CAR parts of the Basin have their main flow during and following the rainy season from July to September. The Logone River forms the border between Cameroon and Chad until N’Djamena where it flows together with the Chari River northwards to the Lake Chad. The Chari and Logone rivers have a tropical regime with a single flood occurring at the end of the rainy season, which lasts from August to November and feeds the extensive Waza-Logone floodplains in northern Cameroon.

Yedseram River

The Yedseram River, also known as Mbuli River, has a catchment area of 16,320 km². The source of the river is in the Mandara Mountains, about 250 km south of Lake Chad. About 30 km west of Bama, south of the Gombole Forest Reserve, the Yedseram is joined by the Ngadda River in a large swamp (Sambissa) covering about 130 km², where the main water courses are not defined.

Ngadda River

The Ngadda River has a catchment area of 14,400 km². It drains into several lakes and swamps in its north westerly flow, before it is dispersed in the low flow zone of the old Lake Chad bed. The Ngadda River does not, therefore, succeed in maintaining a definite course to the lake.

EL Beid River

The El Beid River, locally known as the Ebeji, forms a long part of the border between Nigeria and the Cameroon for more as 400 km. The River has a catchment area of approximately 22,640 km². This stream flows most of the year, beginning in June or July and ending in the following May. Peak discharge occurs in November or December, when the Yaeres floodplain dry up. The El-Beid is by far the water richest Nigerian river flowing into Lake Chad. The El Beid has three main sources of water: direct runoff from the Mandara Mountains, flood overspill from the Logone River into Yaeres and relatively small overspills from the Serbewel River.

Wadis

In the north and east of the Chad Basin, there are only a few wadis, the temporary or seasonal water run from the mountains into the lowlands. In the region of Darfur lie the valley of Wadi Kaya. Also springing in the Darfur the Wadi Bahr Azoum and seasonal forms a part of the Chari-Logone river system. From the Tassili n'Ajjer range coming from the Wadi Tafassassed and reached the northern edge of the Ténéré desert.

In the region of the Tibesti Mountains the Wadis are known as Enneri. Five major Enneris flow north into the Sarir-Tibesti region in Libya, where the water runoff is dependent on the yield of precipitation. So at Enneri Bardargué were a water discharge rate of 453m ³/s, recorded in 1954. This flood peak was followed by 4 years with an average discharge rate of 5 m³/s and in 1963 he obtained three flood peaks with 4, 9 and 32 m³/s. After raining in the mountains temporarily filled with water the Enneri Touaoul, Tegaham, Enneri Wed, Enneri Ké and flow in the surrounding desert areas. The Touaoul and Ké join in the south of the Tibesti and form the Enneri Miski that does to flow into the Borkou plain. The Enneri`s of the Tibesti Mountains forms impressed Gorges and support flora and fauna in this desertlike area.

The Wadi `s of the Ennedi- and Ouaddaï massif are designated as regional Ouadi or called only by name. They form an extensive drainage system ranging from Ennedi Highlands to the region around the town of Abeche. The largest is the Batha, Ouadi Achim and -Enné. The Batha River reaches in the west the Lake Fitri.

In the region around the Lake Chad springing in the near of the oasis Safi the Wadi Bahr-el-Ghazal and regionally known as Soro. He reached the eastern edge of Lake Chad.

In the western part of the Basin lie the Dilia or Dillia de Lagané. Is a wide valley and extend 200 km in north-western direction from Nguigmi, at the edge of the former extent of Lake Chad, to the southern end of the Termit Massif. The valley is possible created by tectonic forces and forms a depression, which historically carried water to Lake Chad during periods when the climate was wetter.

The Lakes of the Chad Basin

Lake Chad

Lake Chad is the largest lake in the Chad Basin and has a long history . It can described "from Mega-Lake Chad to the small Lake Chad". It reached the greatest extension in age of the Tschadien, in age of 10,000 to 5,000 years in the past and covered an area of ​​approximately 350,000 km².

The size of Lake Chad has changed constantly until to the present day. In 1962/63 he included almost 23,000 km², he shrank 1985 to 3,000 km² and in the new century the lake size is falls under 2,000 km².

The shrinkage of the lake in the modern age is related by two factors: the first is the average annual rainfall has decreased since the sixties, about 25%. The second is the abstraction of water for agricultural projects on the tributaries increased steadily. 90% of the amount of water supplied to the lake from the river system of Logone-Chari, only 10% of local rainfall and the Nigerian rivers, which will also be withdrawn by the increasing use of agricultural water. The water level has its annual low point in July, then slowly rises during the rainy season and reached the peak in December.

Lake Fitri

Lake Fitri is located in Chad and has a surface area of 300 km² and during the dry season is part of a large biosphere reserve covering 1,950 km². It is normally a freshwater Sahelian lake, fed by seasonal rainfall and runoff from the seasonal Batha River. Unlike Lake Chad, it is one of the few Sahelian water bodies that has not experienced large-scale hydrological change, although it became desiccated during the 1984-1985 severe drought.

Lake Iro

Lake Iro is a small lake, 15 km long and up to 7 km wide, is situated (10°05'N/19°25'E) some 5 km north of the Bahr Salamat, with which it is more or less continuous at high water. It is 387 m asl at low water and then has an area approaching 10 000 ha. A floodplain is continuous between the lake and the river, but the northern lakeshore is not extensively flooded. The lake is fringed by dense herbaceous vegetation.

Lakes in the Kanem Region

Several small permanent lakes occur saisonal the region in the east of Lake Chad, in the Dune Area of Kanem Region, where the water table reaches the surface in the troughs between dunes. In previous more pluvial times the area has been a part of Lake Chad and clays have been deposited in the inter-dune troughs where the lakes now occur. The three Djikare Lakes are situated closest to Lake Chad. The largest is Lake Bodou and is located 71 km NW of Bol and 11 km inland from the shore line of "normal" lake Chad. It cover an area of 40 ha and a maximum depth of 2 m. The water of this lake is more saline. The two Moilo Lakes are located 31 km northeast of Bol, and cover areas of about 60 ha and depths close to 2 m. Lake Rombou is located 70 km NE of Bol. It cover an area up to 15 ha and is in maximum 1m deep. Direct precipitation over the lakes is less than 300 mm/yr and insolation averages 3000 hrs/yr, while the evaporation potential is over 2200 mm/m² and year. All of these lakes are fringed by lush green vegetation. In those lakes with a low bicarbonate content in the water.

The Ounianga Lakes

In the north east of the Chad Basin and southeast of the Tibesti Mountains is located the Ounianga Lakes (18°44'-18°05'N/20°31'-21°51'E)oriented from Northwest to southeast.

This is a sandstone structure area and the lakes owe there exitence the fact, that a groundwater aquifer reaches the surface in valleys between the sand dunes and ridges. In gerneral this lakes are at all permanent and dividet in two groups. The first group of lakes are at Ounianga Kebir (19°05 'N/20°31 'E), the largest lake is the Lake Joa (345m asl) and cover an area of 370 ha and a maximum depth of 25 m, and there are 3 smaller lakes close by, known as Lakes Uma, Mioji and Forodom. The second group of lakes 50 km east and cover an Area near by the Ounianga Serir (18°55'N/21 °51'E). Here ten lakes lie in rough parallel; these are the lakes of Melekoui, Dierke, Ardiou, Teli, Abrome, Hogou, Diara, Tarem, Tibichei and Bokou. Lake Teli is the largest, covering an area of 70 ha, with a maximum depth of 10 m at an evelation near by 360 m asl. The lakes are a unique habitat in the Sahara dessert and have conserved the genetic heritage of the Sahara’s humid past over more than 3000 years of hyperaridity.

Lake close to Ounianga Serir

Mare De Zoui

The Mare De Zoui is locatet by the Coordinates 21°20'N/17°05'E and is a small permanent lake on the northern flank of the Tibesti Mountains. The lake cover an area of few hectares, the nearst town is Bardai 10 km south and is situated in the valley of the Enneri Bardaquè. The narrow lake is supplied by springs at the head of the gorge. After rain it overflows and a small stream cascades and trickles down the gorge through small marshy patches and pools.

Vegetation Belts and ecological regions

The Lake Chad Basin contains a variety of habitats, including deserts, shrub steppes, savannahs, forests, lakes, wetlands and mountains. About half of the basin area (the north) is occupied by the Ténéré Desert, Erg du Bilma and Erg du Djourab. To the south of the desert in the belt of Sahel-zone is occupied by thorny scrub savannas and dry savannah. Along the rivers Chari, Logone and Komadougou Yobe find flooding savannas and riparian forests and dry forests in the far south. Along the major river systems are in widespread flooding large wetland areas Sategui-Deressia-, Massénya floodplains in Chad, Grand Yaeres in the border region Cameroon/Chad and Hadejia-Nguru wetlands in Nigeria.

Sahara Desert

The surface of the desert ranges from large areas of sand dunes, they called Erg, Chech or Raoui. The stone plateaus called Hamadas, gravel plains called Reg, dry riverbeds called Wadi in Libyia, Enneri in Tibesti/Djado region, Qued in Algeria and Ouadi in eastern Chad. The term Adrar means a single standing Mount in this Area and is used in Niger and Algeria. Salt flats can be found in depressions. Vast underground aquifers underlie large areas of the region, on some points reach the Aquifer system the surface, forms Oases and support the people, animals and plants to survife in this hyperarid Area.

The annual rainfall is below 25 mm and mean annual temperatures are around 25°C. In the hottest months, temperatures can rise over 50°C, and temperatures can fall below freezing in the winter.

The flora of the Sahara Desert is very poor and estimated to include only 500 species. As many as 162 of the plant species are endemic to the Sahara. The vegetation of the region shows strictly Sahara-Arabian affinities and exceptional adaptations to aridity. The vegetation occupied smal areas in wadis, channels, runnels, depressions and hill slopes.

The fauna of the central Sahara is richer than earlier believed. Arthropods are dominated, especially ants. Among the Sahara-Sindian biome avifauna are Greater hoopoe-lark (Alaemon alaudipes) and Desert sparrow (Passer simplex).

South Saharan Steppe and Woodlands

The South Saharan steppe and woodlands is a transition zone from the Sahara to the Sahel-region and is only 100 or 200 km wide. The vegetation belt oriented on the rainfall Isohyte-lines of 100 to 200 mm per year. In the southern portion of this ecoregion the temperatures are between 26°C and 30°C.

The vegetation in the northern area are characterised by summer grassland pasture composed of the grasses Eragrostis, Aristida, and Stipagrostis spp. with the Herbs Tribulus, Heliotropium and Pulicharia. Woody species include Acacia tortilis and Acacia ehrenbergiana, which mainly grow along the dry river beds and stand alone or in smal groups of trees.

The Fauna include small and scattered groups of Animals, the important species are included the Addax (Addax nasomaculatus), Slender-horned gazelle (Gazella leptoceros), Dama gazelle (Gazella dama), Striped hyena (Hyaena hyaena), Cheetah (Acinonyx jubatus), African wild dog (Lycaon pictus), and the Ostrich (Struthio camelus).

Tibesti-Jebel Uweinat Montane Xeric Woodlands

The Tibesti-Jebel Uweinat montane xeric woodlands is made up of two isolated montane areas in the central and the eastern part of the Sahara Desert. The Tibesti Mountains is located in the northern part of the basin and the Jebel Uweinat is located on the border of Egypt, Libyia and Sudan outside of the basin. Annual average rainfall in the surrounding Sahara Desert is under 100 mm/m² and reached in the higher mountain area up to 600 mm/m² and year. The mean maximum temperature is approximately 30°C in the lowlands and falls to 20°C in the higher elevations. Mean minimum temperatures are 12°C in the lowlands, but fall to 9°C over most of the ecoregion and are as low as 0°C at the highest elevations during the winter months.

The Tibesti mountain vegetation varies according to elevation and slope. Large Enneri valleys penetrate the mountain areas in all directions and supporting tree species such as the Doum palm (Hyphaene thebaica), Salvadora persica, Tamarix articulata and Acacia albida, and other tropical herbs in the genera Abutilon, Hibiscus and Tephrosia.

The Saharamontane vegetation of the higher elevations supports a few endemic plants like the Ficus teloukat, which grows on the south and southwestern slopes, Myrtus nivellei on the western slopes, and Tamarix gallica nilotica on the wetter northern slopes. Some tropical and Mediterranean plant species are a relict of the wetter climate in the past and seen throughout this ecoregion, including Palms, Hibiscus sp. and Rhynchosia sp.

This vegetation supports populations of several important Saharan large mammals including the Dorcas gazelle (Gazella dorcas), Barbary sheep (Ammotragus lervia) and the cheetah (Acinonyx jubatus).

West Saharan Montane Xeric Woodlands

The West Saharan montane xeric woodlands is a ecoregion in the mountain areas of the Aïr and the Tassili n'Ajjer on the north west border of the Basin. Climatically, it is cold and dry in the winter and hot and dry in the summer season. Rainfall is variable, but averages less than 150 mm per year, with most falling at higher elevations. The mean maximum temperature reaches 30°C at the lower elevations and 18 to 12°C at the highest elevations, whereas the mean minimum temperatures are as low as 3°C at the highest elevations.

This ecoregion supports an interesting relict flora, with Mediterranean, Sudano-Deccan and Saharo-Sindien affinities and contains a number of endemic and rare species. The most notable of these is the Tarout (Cupressus depreziana), Wild olive (Olea lapperrini) and myrtle (Myrtus nivellei), all of which are relict Saharan-Mediterranean species.

The plateaus that comprise this ecoregion are biologically important, and function as one of the last refuges for some species. These include populations of globally threatened antelope, such as Dorcas gazelle (Gazella dorcas) and Dama gazelle (Gazella dama). Migratory birds use this ecoregion as a rest area because of the year round water and cooler temperatures. Many reptiles are also present including the snakes Telescopus obtusus and Echis leucogaster. Amphibians include the European green toad (Bufo viridis).

Sahelian Acacia Savannah

West African Giraffe

The Sahelian Acacia Savannah is the largest vegetation belt inside the Basin and encompasses the floodsavannas around Lake Chad. This type of savanna is symbolic around the planet for the Sahel. The topography is mainly flat and the climate is tropical hot and divided in two season. The geographic borders of the vegetation belt oriented on the 200 mm Isoheyt line in north and 600 mm Isohyete line in south. The soils of the vegetation belt are mainly Entisols, with some Aridisols, and most are sandy and highly permeable, so that permanent surface water is rare. The monthly mean maximum temperatures vary from 33 to 36°C and monthly mean minimum temperatures are between 18 to 21°C.

Wooded grassland is widespread on sandy soils in the southern part, with many thorny shrubs and small trees including several Ziziphus species. Grass cover is continuous but often dominated by short annual species such as Aristida mutabil, Chloris prieurii and Cenchrus biflorus. In the northern part, short grasslands grow on deep, sandy soils, with widely dispersed shrubs. Most plant species are widespread and fairly common. There are a number of endemic plants such as the Indigofera sengalenisis and Panicum laetum.

This part of the Basin hosts several endemic animals, mainly small rodents adapted to arid climate conditions. Three bird species are considered near-endemic: the Rusty lark (Mirafra rufa), the Masked shrike (Lanius nubicus) and the Sennar penduline-tit (Anthoscopus punctifrons). For reptiles, endemism is more pronounced, with 10 species regarded as strictly endemic in this area.

Prior to the 20th century vast herds of ungulates and other large animals, including elephant, giraffe and ostrich were found in this ecoregion. Most of the large populations have been reduced to scattered remnants due to unregulated hunting with modern firearms. The Scimitar-horned oryx(Oryx dammah) is presumed to be extinct in this area. Other species are only found in a handful of protected areas e.g. the West African Giraffe (Giraffa camelopardus peralta) are only found in Niger. In Nigeria the African elephant near to extinct only survived in the Chad Basin National Park. The pronounced dry season signals a significant migration of fauna within the ecoregion. This includes the annual passage of large numbers of migrant birds on the Afrotropical-Palaearctic flyway.

West Sudanian Savannah

the West Sudanian Savannah

The West Sudanian savannah is mainly a flat area and the climate is tropical hot and strongly seasonal. The highest average daily temperatures vary from 35 to 40°C whilst the lowest average daily temperatures are between 15 and 20°C. Mean annual precipitation ranges up to 1600 mm in the south, but declines to 600 mm per year on the northern border with the Sahelian Acacia Savannah. The rainfall in this northern region of the ecoregion is close to 600 mm. The Mandara Plateau, in northwest Nigeria and northern Cameroon, separates the West and East Sudanian savannahs. Soil fertility is relatively low in the heavily weathered lateritic soils.

The vegetation consists of woodland with a understory of long grasses, shrubs, and herbs. The northern portion hosts mainly grasslands dominated by numerous short grasses. Shrubland is scattered in patches throughout the ecoregion. Riparian forests occur along many waterways and small areas of adaphic vegetation such as grassy floodplains, or Fadamas are found in the Komadugu-Yobe Basin.

This typ of savanna supports a relatively rich fauna, including a number of endemic species. Common large animals are Bushbuck (Tragelaphus scriptus), Warthog (Phacochoerus africanus), Vervet monkey (Chlorocebus aethiops), Baboons (Papio hamadryas papio and P.h. anubis) and Savannah monitor lizard (Varanus exanthematicus). Most large mammals have been heavily hunted and many species only survive sparsely, mainly in protected areas. The pronounced dry season signals a migration of fauna within the ecoregion. This includes the annual passage of migrant birds on the Afrotropical-Palaearctic flyway.

East Sudanian Savannah

East Sudanian Savannah

The East Sudanian Savannah is mainly a flat area, with a climate that is tropical and highly seasonal. Average high temperatures range from 30 to 33°C and lows fall between 18 to 21°C. Annual rainfall is as high as 1000 mm in the south. During the rainy season, which lasts from April to October, large areas of southern Chad and northern Central African Republic become totally flooded and inaccessible. During the dry season, however, most of the trees lose their leaves, and the grasses dry up and may burn. The soils are mainly ultisols and alfisols in the south and entisols in the north.

The vegetation is undifferentiated woodland with trees that are mainly deciduous in the dry season, with an understory of grasses, shrubs and herbs. Typical trees in the Lake Chad Basin sector of this ecoregion include Anogeissus leiocarpus, Kigelia aethiopica, Acacia seyal and species of Combretum and Terminalia.

The East Sudanian Savannah ecoregion closely resembles the West Sudanian Savannah in habitat structure and species composition. The two ecoregions differ somewhat in terms of their species assemblages and the degree to which the habitat and mammal assemblages are intact. The Eastern Sudanian Savannah has low rates of faunal endemism. For example there is only one endemic mammal (a mouse, Mus goundae) and two strictly endemic reptiles (Rhamphiophis maradiensis and Panaspis wilsoni). Threatened mammal species include large herds of African elephant (Loxodonta africana) in Chad and Central African Republic and African wild dog (Lycaon pictus), Cheetah (Acinonyx jubatus) and Lion (Panthera leo).

Northern Congolian Forest-Savannah Mosaic

The western Bongo

The Northern Congolian Forest-Savannah Mosaic is a narrow transition zone marked by an abrupt habitat discontinuity between the extensive Congolian rainforests and Sudanian/Sahelian grasslands. It contains the northernmost savannah woodlands in Africa. The forest savannah mosaics with their characteristically diverse habitat complexes, support a high proportion of ecotonal habitats, which have high species richness and are possible loci of tropical differentiation and speciation. This ecoregion lies in the tropical savannah climate zone. Mean annual precipitation ranges locally from about 1200 mm to 1600 mm per year. This ecoregion experiences small seasonal temperature fluctuations, with rainy season mean daily maximum temperatures of 31 to 34°C and dry season mean daily minimum temperatures of 13 to 18°C. The Chad Basin proportion of this ecoregion consists of western CAR, which is underlain by relatively new and unweathered entisols, and central Cameroon, which consists of a mixture of oxisols and ultisols, highly weathered soils that often contain a fragipan.

Vegetation common either to the Sudanian or Congolian provinces characterises much of the region. In the relatively arid corners in the northeast Cameroon and northwest portion of the ecoregion, the transitional Isoberlinia spp. dominated Sudanian woodlands and wooded savannahs characterise the flora where cultivation has not drastically altered the system.

The savannah sub-species of African Bush Elephant (Loxodonta africana africana) occupies the savannah woodlands where it denudes trees and suppresses sapling growth, effectively creating a more fire-prone system. The ecoregion provides a unique set of habitats and resources that supports moderate levels of diversity, including many species with broad distributions in tropical Africa. The Red-flanked Duiker (Cephalophus rufilatis) inhabits forest patches within the savannah matrix across the Guineo-Congolian/Sudanian transition zone. Widespread mammals in these savannah forest mosaics include the Black rhinoceros (Diceros bicornis longipes) now however restricted to a few individuals remaining in Cameroon, Giant eland (Taurotragus derbianus) and in the eastern sector, Bongo (Tragelaphus eurycerus).

References

• "Boundaries of Lake Chad Region" UNEP Publikation 8,41 MB PDF Format English
• Lars Wirkus, Volker Böge: Afrikas internationale Flüsse und Seen. S. 54. (PDF; 1,38 MB) German version
• Gerhard Meier-Hilbert: Tschad: Historische, politische, geographische und ökonomische Strukturen eines der ärmstes Länder der Welt. (PDF; 105 kB) German version
• T.M. Hess : The impact of climatic variability over the period 1961-1990 on the soil water balance of upland soils in the North East Arid Zone of Nigeria 1,54 MB PDF Format
• Serge JANICOT, Jean philippe LAFORE, Chris THORNCROFT: The West African Monsoon System
• Ramsar Information about Chad [1] 172 kb PDF
• Stefan Kröpelin : The Saharan lakes of Ounianga Serir –a unique hydrological system 1,33 Mb PDF format
• S. Kröpelin, D. Verschuren, A.-M. Lézine, H. Eggermont, C. Cocquyt, P. Francus, J.-P. Cazet, M. Fagot, B. Rumes, J. M. Russell, F. Darius, D. J. Conley, M. Schuster, H. von Suchodoletz, D. R. Engstrom: Climate-Driven Ecosystem Succession in the Sahara: The Past 6000 Years 892 kb PDF format published in Science Magazin Mai 2008 Volume 320, Issue 5877
• Dr. Hassan Haruna Bdliya and Dr. Martin Bloxom: TRANSBOUNDARY DIAGNOSTIC ANALYSIS OF THE Lake Chad Basin 1,96 MB PDF Format
• Federal Institute of Geosciences and Natural Resources: LAKE CHAD SUSTAINABLE WATER MANAGEMENT 4,07 MB PDF Format
• HIGH-LEVEL CONFERENCE ON WATER FOR AGRICULTURE AND ENERGY IN AFRICA: THE CHALLENGES OF CLIMATE CHANGE @ 2008
• Tibesti-Jebel Uweinat montane xeric woodlands on WWF
• Sahara desert on WWF Website
• West Saharan Montane Xeric Woodlands on WWF Website
• The Sahel Acacia Savanna on WWF Website
• West Sudanian savanna on WWF website
• East Sudanian savanna on WWF Website
• Northern Congolian Forest-Savannah Mosaic on WWF Website
• Chad country information Birdlife International 2,20 MB PDF Format
• Niger country informations Birdlife international 496 kb PDF Format
• Nigeria country information on birdlife International 2,7 Mb Pdf format
• Central African Republic country informations on Birdlife International 432 kb PDF format

External links

• Lake Chad Basin Project
• Philip Mulholland (University of Lancaster, UK): West African Monsoon crosses the Sahara desert (August 2007)
• Ancient lakes of the Sahara
• historical maps of Africa