Chad Basin

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Chad Basin
Dust storm over the Chad Basin on November 18, 2004 Source: NASA
Shari-Logone river system

The Chad Basin , also called Lake Chad Basin , is a low-lying plain in central and west Africa that gradually rises from the center in all directions . The Chad Basin region is managed as GIWA Region No. 43 by the Department of Global International Water Assessment, or GIWA, affiliated with the United Nations Environment Program , or UNEP for short .

The Chad Basin extends between the 6th and 24th degrees north and between the 8th and 24th degrees east. It covers an area of ​​around 2.434 million km², which corresponds to around 8% of the total area of ​​the African continent , and is one of the largest endorheic basins on earth . Due to its location in the northern center of Africa, its natural spaces are characterized by very different types of landscapes and vegetation. About half of the basin (the north) is occupied by the Ténéré , Erg du Bilma and Erg du Djourab deserts . In the middle part of the basin, the desert merges into the semi-arid vegetation zones of the Sahel zone with its typical thorn bush and dry savannah . In the catchment areas of the rivers Shari , Logone and Komadugu Yobe , large, internationally significant flood savannas extend. Gallery forests developed along the rivers and in the southern part of the basin there are also the humid savannas of Sudan with their typical dry forests .

The best-known geophysical element of the Chad Basin is Lake Chad , which has determined the development of people, flora and fauna in this region for thousands of years . As a water reservoir between the desert and savannah, Lake Chad has always attracted numerous immigrants, researchers and adventurers. The annual fluctuation of the water level, the extent of the floodplains and the flooding of the tributaries that trigger these cyclical changes opened up opportunities for the development of cultures and peoples, but also offered a place of refuge and protection. The Chad Basin served as a crossroads for both ruling dynasties and bourgeoisie, making it a region in which new political formations could develop that radiate beyond this region. At the same time, the region always formed a natural border that prevented trade and interaction.

Regardless of its important role in the development of the cultural history of North, West and Central Africa, social science, unlike the natural sciences, discovered the Chad Basin relatively late as a rich and promising field of research.

geography

The Chad Basin is surrounded in the south by the north equatorial sill, which is up to 1,420 meters high and extends to the continental dividing point between the Nile , Congo and Shari in the up to 1,330 meter high Bongo massif . In the east it extends up to the 3088 meter high Djebel Marra in Darfur , in the northeast of the basin the Ennedi massif rises to 1450 meters. In the north of the valley , in the volcanic mountains of the Tibesti, at 3415 meters ( Emi Koussi ), the highest point in the Central Sahara and the Djado plateau are located . The border in the northwest is marked by the Tassili n'Ajjer , the highest mountain Jebel Azao at 2,158 meters, in Algeria and the Aïr Mountains in Niger . In the southwest of the Chad Basin, the belly plateau , the Biu plateau and the Mandara mountains mark the geographical boundary.

In the north-eastern center is the Bodélé Depression , it is also the deepest point of the Chad Basin - about 155 meters above sea level - and is one of the most abundant natural sources of dust on earth. The constant trade winds from this region mobilize up to 700,000 tons of fine dust per year into the stratosphere , which then moves west across the Atlantic and contributes significantly to the fertilization of the Amazon rainforest . Lake Chad in the southwestern center is 275 meters above sea level. The large flood savannahs in the Logone Plain / Toupouri Depression , Massenya Plain , Aouk and Salamat Plains in Chad, Grand Yaeres in the Cameroon / Chad border region and the Hadejia stretch along the great river systems over an area of ​​90,000 to 100,000 km² -Nguru Wetlands in Nigeria. Migratory birds in the northern hemisphere use these wet savannahs as resting and wintering areas on their migratory routes into tropical Africa.

The lowest notch in the ring of watersheds surrounding the Chad Basin and thus the overflow threshold for the runoff from the prehistoric mega-Chad was about 325 meters above sea level southwest of the town of Bongor on the Logone . At that time, the excess lake water from the Chad basin spilled over the Mayo Kébbi into the Benue and Niger and thus reached the Atlantic .

Territorial division

A total of eight African countries have a share in the Chad Basin . The demarcation between them follows the division of the region from the colonial times, whereby tribal areas, such as that of the Tuareg , are distributed over several states. These are the following states: Chad occupies the center with 1.123 million km², Niger has the second largest share in the west with 674,800 km², the southern peripheral areas are divided by the states of Nigeria with 179,300 km², Cameroon with 47,700 km² and the Central African Republic with 216,000 km², on the eastern edge there are 97,700 km² in Sudan and on the northern edge approx. 5,100 km² belong to Libya and 91,000 km² to Algeria .

Lake Chad Basin Commission

→ Main article: Lake Chad Basin Commission

The Lake Chad Basin Commission was founded on May 22, 1964 with its headquarters in Fort Lamy, now N'Djamena . The founding states of this commission were Cameroon, Niger, Nigeria and Chad. The Lake Chad Commission currently has six member countries: Chad, the Central African Republic, Cameroon, Nigeria, Niger and, since April 2007, Libya. Sudan has only had observer status since 1994 and Algeria has no activities. The Commission is responsible for regulating and monitoring the use of water and other natural resources within the hydroactive areas of the Chad Basin. The commission has a subdivision of the Basin Committee For Strategic Planning (BCSP). This coordinates the local activities of the member countries.

The Lake Chad Basin Commission controls and monitors the hydroactive regions in the Chad Basin and describes them as “conventional” basins. This conventional basin was approx. 427,500 km² in size when it was founded in 1964. The definition states that it excludes areas that do not have an effective hydrological contribution to the water balance of the conventional basin. This mainly affects the northern regions of the basin. The control commission's territory was later expanded to include the hydroactive regions in northern Nigeria, southern Chad and northern Central African Republic. The current area of ​​the conventional basin covers approx. 967,000 km².

geology

The largest areas of the Chad Basin are covered by Quaternary sands. Below the sand layer, at a depth of around 75 m, there are clays that were formed in the Pliocene and have an average thickness of around 280 m. Under this layer of clay there is another 30-meter-thick layer of sand that was formed in the lower Pliocene. Below this layer are the layers of the actual Pliocene aquifer that carry the groundwater. Sandstone formations, known as the Continental Terminal and formed in the tertiary era, with a thickness of around 150 m appear underneath . Below this layer lies the lowest aquifer , known as the Continental Hamadien and formed in the Cretaceous period .

Groundwater reservoir

The groundwater reservoirs in the Chad Basin are mainly composed of a series of deposits. These sediments give rise to the four aquifers: the upper Quaternary-phreatic aquifer, the lower Pliocene aquifer, the Continental Terminal and the Continental Hamadien. Studies suggest that these groundwater reservoirs are fed by seeping surface water. For this reason, they are very sensitive to changes in climatic conditions and, above all, to changes in the surface runoff regime.

The quality of the groundwater of the Quaternary-phreatic aquifer is suitable for the consumption of the local population and livestock. The lower Pliocene groundwater reservoir is around 250 m deep, with an average thickness of 60 m. The capacity of the lower Pliocene aquifer is unknown, but it is mainly used in the Nigerian part of the basin. The extraction from this aquifer is estimated at around 3 million m³ per year.

The Continental Terminal groundwater reservoir is essentially an alternation of sandstone and clay. The deepest aquifer in the region is the Continental Hamadien. This is an important aquifer that extends to several other West African regions about which very little information is available.

In general, the active hydrographic basin is estimated to be approximately 967,000 km². The Nubian sandstone groundwater reservoir is located on the northern and northeastern border of the basin and the Iullemeden groundwater reservoir is on the western border .

Emergence

The Chad Basin was formed by extensional tectonic forces during the Cretaceous Period . The geological and geomorphological development of the basin was accompanied by a slow and "cold" expansion of the subsidence zone, due to the formation of the West and Central African rift system . As a result, a regional hydrological sink was created, known as the Artesian Chad Basin. The Chad Basin is part of a large meridional zone of subsidence that extends from the Gulf of Gabes in the north to the Karoo plain.

population

The total population was determined in 2003 with approx. 39 million inhabitants and is made up of over 70 peoples or ethnic groups. Around 22 million people live in Nigeria - this corresponds to around 59% of the total population - around 8 million in Chad, around 3 million in Sudan, around 2 million in Niger, around 2 million in Cameroon. and the Central African Republic about 1 million people. The areas in Algeria and Libya are considered uninhabited and are only occasionally visited by nomads .

The population density is very unevenly distributed: While the northern regions have a population density of 0 to 1 inhabitant / km², this increases in the southwestern regions of Nigeria to 500 inhabitants / km². The most populous region around Kano is to be found in Nigeria, on the east and south banks of Lake Chad. However, specific data collection is very difficult as states often suffer from political instabilities.

Archeology and written sources on the Chad Basin

Skull of the Sahelanthropus tchadensis
Title page of the English edition of Leo Africanus' Cosmography. London 1600

In 2001 a 6 to 7 million year old fossil was found in the site TM 266 near Borkou , which was named Sahelanthropus tchadensis . Its discoverers described it as possibly the oldest member of the human family tree discovered to date after separation from the chimpanzees , that is, as a close relative of the earliest common ancestors of the hominini . In 1995 a 3 to 3.5 million year old lower jaw was discovered at the northern Chadian site KT 12 , which was assigned to the new species Australopithecus bahrelghazali .

The settlement of the Chad Basin has always been determined by the change in pluvial and interpluvial times. Only archaeological finds from the age of Chad could prove this settlement. These include the grave fields of the Gobero archaeological site in the western Chad basin, which were discovered in two epochs from 7700 to 6200 BC. BC and 5200 to 2500 years BC Could be determined.

Another find is an approx. 8,000 year old canoe that was found on the banks of the Komadugu-Yobe river system; it is one of the oldest boats in human history.

The oldest more developed culture was located in the southwestern Chad Basin and was called the Gajiganna culture . The finds unearthed simple clay figures of people and animals from around 500 BC. Fortified settlements could be proven. It existed from approx. 1800 to approx. 400 BC. The most important archaeological site of this culture is Zilum . He was from around 400 BC. It was replaced by an iron-processing culture, as proven at the Mdaga excavation site . However, whether there was a technology transfer from the Middle East is highly controversial, as the smelting technology is similar to that of the neighboring Nok culture .

Further reports on the Chad basin are handed down by Claudius Ptolemy , who mentions an empire of Agisymba in the 2nd century, although it is still disputed where it was located, since this report does not contain any location information, only vague information about high, nameless mountains Speech is.

Archaeological traces in the Chad Basin can only be found again from the 6th century AD with the development of the Sao culture and its excavation sites southeast of Lake Chad.

The first European source about the Chad Basin is Leo Africanus , who toured the region in 1513 and reports from a land of Shary and the Lake of Gaoga. Further sources can be found in the book L'Universale Fabrica, written by Giovanni Lorenzo Anania , who reports on a Rio Negro (Niger) and the lake Lago di Sauo south of the Sahara. This work appeared in several volumes between 1571 and 1592 and served as a source for numerous cartographers of the time.

Since the geography of inner Africa was almost unknown until the 19th century, these are the only sources about the region from this period. The first modern reports come from the German Friedrich Konrad Hornemann , who traveled to the region in 1800 on behalf of the British; Further reports come from Denham , Clapperton and Oudney from 1841. The most famous travelers in the region were Heinrich Barth , Adolf Overweg , Gustav Nachtigal and the French Henri Carbou , who systematically used the dialect of the Chadian-Arabic language in the Waddai region explored.

climate

The climate in the Chad basin according to Köppen-Geiger

The types of climate in the Chad Basin are divided by vollaridem climate in the north, characterized by deserts , through semi-arid climate in the zone of the Sahel to the semi-humid climate in the area south of Lake Chad and vollhumidem air in the mountainous regions of Nigeria, Cameroon and the Central African Republic.

The Chad Basin lies in the zone of the Innertropical Convergence Zone , or ITCZ for short , which extends from latitude 15 ° north to 15 ° south. The seasonal shift of this convergence zone results in a separation into rainy and dry seasons for the region. Rainfall generally falls from April to October in the south and July to September in the northern part of the basin. During this time the region is under the influence of the south-west monsoons . In general, the precipitation is most abundant from July to September. The average amount of precipitation in the Chad Basin is very unevenly distributed due to the climatic conditions. The southwest averages 1,600 mm per year, while the north averages less than 150 mm per year. The evaporation rate is very high at 2300 mm / year.

The effect of the southwest monsoon based on the average monthly flow of the river Shari measured at the hydrological station of N'Djamena (in m³ / s)
(Calculated with data from a period of 58 years, 1933-91)

In the dry season from November to March , the Chad Basin is influenced by the north-east trade winds from the Sahara. These are called harmattan .

In July, the average daytime temperatures in the entire area of ​​the Chad Basin are around 30 degrees Celsius, in the northern regions they reach 35 to 40 degrees Celsius.

The regions in the Chad Basin have repeatedly experienced the absence of the south-west monsoons in the past . This led to the great dry seasons of 1972-74 and 1983-84 with the well-known famine for the population in the affected areas.

Evaporation potential

The evaporation potential is generally very high in the Chad Basin and peaks in April and May when the humidity saturation deficit is high. It is reduced in July and August with the arrival of the West African monsoons. This is followed by a brief rise in September and October and then falling to a minimum in December and January when air temperatures reach the region's annual minimum. The mean annual evaporation rate increases to the north by approx. 60 mm per degree of latitude in the areas south of the Chad Basin. In general, the evaporation potential varies between 1,500 and 1,800 mm per year over the area in northeastern Nigeria. It rises to 2,300 mm / year in the northeast of Lake Chad and to 6,000 mm / year in the desert lowlands in the northeastern part of the basin.

The West African monsoon

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

Research by the West African Monsoon Multidisciplinary Analysis Project (AMMA) has shown that the inflow of cold water into the Guinean Gulf at the beginning of the monsoon season plays a crucial role in this system. Similar to the meteorological conditions in the Mediterranean or the Indian Ocean, water temperatures are considered a key factor in the variability and the retreat of monsoon precipitation in autumn. The annual cycle of the sea surface temperature in the Gulf of Guinea is asymmetrical, with a rapid cooling from the highest water temperatures in April to the lowest water temperatures in August and a gradual increase in the water temperature until next April. The precipitation over West Africa and the Chad Basin is essentially characterized by the approach of air masses , which leads to a horizontal movement of the air over the marine boundary layer to the various temperature anomalies over West and Central Africa, through which the development of the high air pressure at sea level and the ground wind favored an anomaly in the secondary intra-tropical convergence . The investigations also showed that the seasonal changes in solar radiation control the seasonal changes and lead to a net increase in the amount of energy in the column of the atmosphere. This surplus of energy leads to a horizontal energy export through which the thermal circulation of the humid air masses is stimulated to a collection of thermally charged air humidity in the area of ​​the ITCZ. This process modulates the productivity of the precipitation inland.

The variability of the WAM over the past few decades is not really clear. On the one hand, there is an increase in water temperatures in the Gulf of Guinea, but also a change in the temporal and spatial sequence of the triggering mechanisms of the monsoon. A change in the ITCZ ​​cannot be ruled out either, but studies on this are still lacking. However, the results of these changes are measurable: The Isoheyte lines migrated about 200 km to the south in the last 50 years, which led to a significant decrease in the amount of rain in the Chad Basin.

Paleoclimate

Of the climate history of the Chad Basin , only the age of the younger Quaternary has been adequately researched. The effects of the frequent alternation of warm, humid pluvial and desert interpluvial times on the relief have, however, been insufficiently researched due to the lack of radiometric age determinations and the lack of preserved datable traces as well as the erasure of older relief states.

There is evidence of an old dune zone, called Erg Ancien , which extended beyond today's 800 mm isohyete line and points to an extremely arid climate up to around 40,000 years ago. This was followed by a wetter phase from 40,000 to 20,000 years ago. This humid phase was followed by an extreme dry period, called ogolia and kanemia , which lasted until 12,000 years ago. Dune advances, called Erg Recent , have been documented up to the current 500 mm isohyete line. Years before about 10,000 known wet period began, even Tschadien mentioned, which was separated by a drying phase before 7500 to 7000 years. From 9,000 to 5,000 years ago there were two phases in which Lake Chad was much larger than it is today. The Paleochad Sea also covered the north of today's Republic of Chad. The lake borders can be demonstrated by dark brown sediments that were deposited in the former bank area. Nowadays they are still a few decimeters thick.

Interrupted by a brief humid phase from 3500-2500 years ago - including the formation of shallow lakes and swamp lakes - there has been an increase in aridity with slight fluctuations to this day. In the Sahara, but also partly in the Sahel, these led to a remobilization of the sand dunes to this day.

Climate carousel for the past 1,000 years

The climate of the last 1,000 years in the Chad Basin has oscillated between arid and semi-arid in the Sahel zone and semi-arid and humid in the zone of the Sudan landscape. This change took place in different time scales, with the oscillation occurring in ever shorter time scales from around 1700 AD. Written sources about the Chad Basin are only available from the period from around 900 AD. The country description of Kanem-Bornu in Arabic records also made it possible to draw conclusions about the climatic conditions.

By evaluating the written Arabic sources and core drilling carried out on and in Lake Chad, it was possible to determine that the climate in the Sahel zone was semi-arid to semi-humid with a reduced potential for evaporation up to approx. 1150 AD. In the zone of the greater Sudan landscape , humid climatic conditions prevailed until this time. At that time Lake Chad had a size of approx. 36,000 km², the lake level was approx. 286 meters above sea level.

This was followed by a period of time up to approx. 1300 AD in which an increasing aridity was noticeable. After a short recovery phase, up to around 1380 AD, this change culminated around 1450 AD when the southern lake basin of Lake Chad dried up. Written sources report a severe drought during this period, which lasted until around 1480 AD.

By 1520 AD, the climate in the Chad Basin recovered and rainfall increased. Then the climate changed back to an arid climate trend. Written sources report the great famine Bu Ihagbana from 1541 to 1562 AD and from 1563 to 1568 of the Zima Azadu famine . The climatic conditions recovered until approx. 1610 AD. This became evident through the expansion of Lake Chad. This covered a surface of approx. 36,000 km² until approx. 1700 AD. However, during the same period, written sources report several prolonged periods of drought and famine. A dry spell was recorded in the years 1639–43, the Dala Dama famine reported from 1644 to 1680 , and another dry spell was recorded in the area of ​​today's Borno state from 1681 to 1684.

Accordingly, reports of southern migration in the dry phases and northern migration of the population in the wetter phases have been reported from these periods. In the middle of the 17th century the Kreda tribe of the Tubbu people reported that they emigrated completely and permanently from the Borkou region to the hills of Kanem .

As mentioned at the beginning, the oscillation of the climatic conditions increased from around 1700 AD: Lake Chad rarely reached the 284 meter mark. In some extreme years, the lake's water level was so low that the Grand Barrier divided the lake, as in the decade of the 1830s, from 1901 to 1915 and from 1973. The Grand Barrier dries up from a surface level of the lake of 280 meters.

Several droughts and famines are recorded in the decade from 1720 to 1730. From 1738 to 1756 sources report the great drought in the southern Chad basin. The arid phases in the Sahel zone become longer and longer from this point in time and accordingly the change from semi-humid to humid climatic phases in the large Sudan landscape takes place in ever shorter time scales, with the duration of the semi-humid phases increasing steadily and from 1900 onwards only by semi-humid climatic conditions can be spoken.

Written sources report several dry periods from 1790 to 1810. This pattern was repeated in 1828–39, with several famines recorded in the latter period. At the beginning of the colonial period, from 1898, English colonial authorities reported a great drought in northeastern Nigeria, which lasted until 1915. A great famine was recorded by the French colonial authorities in 1940-49. The climate then stabilized until the mid-1960s to a semi-arid climate in the Sahel zone.

From the mid-1960s on, one can only speak of an arid climate in the Sahel zone. The corresponding consequences were the great drought periods 1969–74 and 1983–87, each of which went down in history as the great drought and famine . Lake Chad as a climate indicator decreased its size from 23,000 km² (1962/63) to approx. 1,100 km² in 1994. This was followed by a slight increase in size to 1,350 km² by 2001. Since then, the size of the lake has stabilized at this level. Heavy rains will occur repeatedly in a few years, but most of them led to new hunger crises, such as in southern Niger in 2005 and in the western Sahel region in 2010.

Waters

Catchment area of ​​the Komadougou Yobe

There are two large river systems in the Chad Basin, that of the Shari - Logone and that of the Komadougou Yobe , as well as some smaller rivers and wadis . In this large region there is a large number of inland lakes, of which Lake Chad, Lake Nguru and Lake Fitri are the best known and have a supraregional importance. Numerous lakes in the region are also protected areas under the Ramsar Convention , such as Lake Maladumba . But also the lakes in the north of the Chad Basin such as the Mare de Zoui offer flora and fauna unique habitats for survival in the arid climate of the Sahara. The lakes in the south of the basin are mainly by fishing for the local population of meaning as the Bomboro Lake and Mamoun Lake . Lakes like Fianga Lake are unique in that it lies on a watershed and drains into two different river systems. Little is known about the seasonal Mare de Tizi .

Rivers

The Shari-Logone river system has a catchment area of ​​approx. 650,000 km², which extends from the Adamaua highlands to the Darfur region in Sudan. The river system is influenced by the tropical climate in the highlands of the north equatorial threshold and has a single flood season, which partially floods the Yaeres wetlands in the Waza plain from August to November. The average flow rate from this river system into Lake Chad is given as 37.8 km³ / year.

The rivers Yedseram and Ngadda , which also head towards Lake Chad, have their source in the Adamaua highlands , but have not reached it since the dry spells of the 1960s and 80s. The upper reaches of the Yedseram and Ngadda flow through the 130 km² Sambisa swamps and thus form a river system, as the Ngadda receives a significant proportion of its annual runoff from the Yedseram.

The in Mandara Mountains springing El Beid is the most water-rich Nigerian river in the region. It receives a significant part of its annual runoff from the drying Yaeres in the south of Lake Chad. Its course forms the border between Cameroon and Nigeria until it reaches the former shoreline of Lake Chad for more than 400 km.

The catchment area of ​​the Komadougou Yobe has a size of 148,000 km² and extends to the area of Kano , headwaters of the Hadejia , and the belly plateau , headwaters of the Jama'are , in Nigeria. The areas behind the confluence of the two source rivers are known as the Hadejia-Nguru wetlands and have a maximum extension of 6,000 km², starting at the end of August with the onset of the flood season. The Komadougou Yobe no longer reaches the open waters of Lake Chad and flows into an inland delta with no runoff about 120 km from its current coastline .

Wadis

In the north and east of the Chad Basin, there are only a few wadis that temporarily or seasonally carry surface water. Mention should be made of Wadi Kaya, which comes from Darfur. The Wadi Bahr Azoum , which also rises from Darfur , seasonally forms part of the Shari-Logone river system. The Wadi Tafassassed coming from the Tassili n'Ajjer reaches the northern edge of the Ténéré desert .

In the region of the Tibesti Mountains, wadis are called Enneri. Five large Enneris flow north to the Sarir Tibesti region in Libya, whereby the amount of water runoff depends on the productivity of the rainfall. In 1954, a water runoff rate of 453 m³ / s was measured at the Enneri Bardargué. This tide peak was followed by four years with an average discharge rate of 5 m³ / s and in 1963 it reached three tide peaks with 4, 9 and 32 m³ / s. The Enneri Touaoul, Tegaham, Enneri Mi and Enneri Ké, which are sometimes filled with water, drain to the south and irrigate the surrounding desert areas. The Touaoul and the Ké flow together in the south of the Tibesti and form the Enneri Miski, which flows into the Borkou plain.

The wadis that arise from the Ennedi massif are regionally referred to as quadi . They form an extensive drainage system that extends to the Wadai highlands around the city of Abéché . The largest quadi is the Batha - it reaches Lake Fitri in the west .

The Wadi Bahr el-Ghazal , which extends to the region around the Safi oasis, is also known regionally under the name Soro. It reaches the eastern foothills of Lake Chad. It is not a wadi in the traditional sense that feeds water into the lake, but rather an overflow canal of Lake Chad. The Bahr el-Ghazal is flooded when the level of Lake Chad reaches 286 meters above sea level.

In the west of the basin lies the valley of the Dilia, also called Dilia de Lagané . In the age of Chad, the Dilia de Lagané continuously supplied water to Lake Chad, today the Dilia de Lagané only carries water when there is heavy rainfall in the southern Termit massif , which no longer reaches Lake Chad.

Lake Chad

Lake Chad in 1994

The Lake Chad is the largest lake in the Chad Basin and has a long history behind it, which can be characterized with the words "from the mega Chad Lake Chad small". It reached its greatest extent in Chad , about 10,000 to 5,000 years ago, and covered an area of ​​about 350,000 km². This can be seen in the sedimentation areas and the beach walls that are still visible today .

The size of Lake Chad has constantly changed up to the present day. In 1962/63 it still covered almost 23,000 km², but by 1985 it had shrunk to around 3,000 km². The shrinking of the lake in modern times is related to two factors: On the one hand, the average annual rainfall has decreased by around a quarter since the 1960s, and on the other hand, water abstraction for agricultural projects at the tributaries has increased steadily. 90% of its water volume is supplied to the lake by the river system of the Logone-Shari, only 10% by local precipitation and the Nigerian rivers, which are also deprived of water due to increasing agricultural use. The water level has its annual low in July, then rises slowly in the rainy season and reaches its high in December.

Fitri lake

Lake Fitri is located at the coordinates 12 ° 41'-13 ° 00'N / 17 ° 24'-17 ° 38'E, about 250 km east of Lake Chad. It is popularly known as the little brother of Lake Chad, with which it was connected until 5,000 years ago. It covers an area of ​​300 km² with a maximum extension of 35 × 20 km with an orientation from northwest to southeast. It is part of a 1,950 km² biosphere zone. Lake Fitri is classified in the freshwater Sahel Lake category and has a low salinity. It is fed with fresh water by seasonal rainfall and the inflow of the Batha , which flows for 3-4 months . In contrast to Lake Chad, the Fitri is one of the few Sahel waters that have not undergone a hydrological change from large-scale irrigation systems, although it has dried up several times in the past, such as in 1901, 1973 and during the particularly severe drought in 1984 -1985.

Iro lake

Iro lake

The Iro Lake is a small lake, 15 km long and up to 7 km wide and is located at 10 ° 05'N / 19 ° 25'E, about 5 km north of the Bahr Salamat , with which it is more or less continuously at Flood is connected. When the water level is low, it is approx. 387 m above sea level. M. and then has an area of ​​almost 100 km². There is a continuous flood plain between the lake and the river, but the northern shores of the lake are not flooded extensively. The lake is lined with dense, herbaceous bank vegetation.

The lakes in the Kanem region

Several permanent, smaller lakes are located directly to the east of Lake Chad in the Erg Kanem dune area, where the water table reaches the surface and forms these lakes in the hollows between the dunes. In the past pluvial periods they were part of Lake Chad and clays were deposited on the lake bed. The three Djikare lakes are the closest to Lake Chad. The largest, Lake Bodou , is about 71 km northwest of Bol and 11 km inland from the coast of the "normal" Lake Chad. It has an area of ​​40 ha and a maximum depth of 2 m. Its water is very saline due to the high rate of evaporation. The two Moilo lakes are located approx. 31 km northeast of Bol and each cover areas of approx. 60 ha and depths of approx. 2 m. The Rombou Lake is located about 70 km northeast of Bol. It covers an area of ​​15 hectares and is about 1 meter deep. Direct precipitation over the lakes is less than 300 mm per year and the sunshine duration reaches an average of 3000 hours / year, while the potential evaporation is around 2300 mm per year. These lakes are surrounded by lush vegetation.

Ounianga Lakes

In the southeast of the Tibesti Mountains on the edge of the Mega Chad Basin lies the area of ​​the Ounianga Lakes , which lie on a NW-SE axis. This area is covered by a sandstone structure. At its feet are a series of permanent salt lakes about 402 m above sea level. These lakes owe their existence to the fact that water from an underground aquifer reaches the surface and emerges in depressions between sand dunes.

The most important lakes are at Ounianga Kebir (19 ° 05'N / 20 ° 31'E). The largest lake is the Joa lake (345 m above sea level) with an area of ​​370 ha and a maximum depth of 25 m. The Uma , Mioji and Forodom lakes are in the immediate vicinity . A second group of lakes is located about 50 km to the east at the Ounianga Serir oasis (18 ° 55'N / 21 ° 51'E). Ten lakes lie parallel to each other in a rough, rugged landscape. These are the lakes Melekoui, Dierke, Ardiou, Teli, Abrome, Hogou, Diara, Tarem, Tibichei and Bokou . The Teli Lake is the largest and covers an area of ​​approx. 70 hectares with a maximum depth of 10 m. The lakes are aligned on a north-east-south-west axis, their long axes are parallel to the prevailing wind direction.

Lake at Ounianga Serir

Vegetation zones

The Chad Basin can be divided into nine different vegetation zones. These offer a wide variety of habitats for a wide variety of animal and plant species . There are extensive deserts , thorn bush savannas , savannas , rivers , lakes , wetlands and extensive mountain regions with a diverse flora and fauna . In the Chad Basin, all large African animal species such as hyenas , lions , elephants , hippos , cheetahs , crocodiles and ostriches can be found . The Lake Chad and its tributaries and its wetlands makes a unique ecosystem caused by global significance. This not only offers native animal species a habitat, but also serves migratory birds from the northern hemisphere as a place to rest and hibernate on their migration routes. In addition, this extensive ecosystem offers effective protection against the further spread of the deserts.

Sahara vegetation zone

The surface of the Sahara vegetation zone in the Chad Basin is characterized by extensive deserts with sand dunes - called Erg , Chech or Raoui -, large stone and rock deserts with their uncultivated plateaus, called Hamadas , large gravel areas, called Reg , dry river beds, wadis and large, flat ones Salt beds. Rainfall in these areas can be less than 25 mm per year. The annual average temperatures are around 25 degrees Celsius and can rise to over 50 degrees Celsius in the summer months.

The flora in these areas is very species-poor and includes around 500 plant species, of which around 162 are endemic to the Sahara. They grow mainly in the wadis, oases , ranges of hills, depressions and individual rivulets over groundwater-bearing areas.

The fauna in the Sahara is much richer in species than previously assumed. Mostly insects and arthropods are seen , but a few mammals and reptiles are also found in this region. Bird species in the Sahara are the Alaemon alaudipes and the desert sparrow ( Passer simplex ).

Tibesti-Djebel-Uweinat mountain desert vegetation zone

The mountainous region of the Tibesti belongs to the category of arid desert climates . The annual rainfall is given as less than 600 mm per year due to its height, but there is little or no soils that can absorb and store this moisture, as they are classified as aridisole desert soils . The known maximum temperatures are around 30 ° Celsius in the lowlands and around 20 ° Celsius in the high areas of the mountains. In the winter months, however, it falls to around 12 ° C in the lowlands and 9 ° Celsius in the high areas.

The vegetation in the mountains of the Tibesti varies with the altitude and the gradient. In the south-western mountain slopes that are wadis Enneri Tegaham, Enneri Mi and Enneri Ké leading surface water at greater precipitation and the growth of trees such as the hyphaene ( Hyphaene thebaica ), the toothbrush tree ( Salvadora persica ), tamarisk ( Tamarix articulata ), the faidherbia albida ( Acacia albida ) and other tropical plants made possible by Abutilon , Hibiscus and Tephrosia .

In the higher elevations of the mountains the endemic Ficus teloukat grows on the south and south- west slopes, the Myrtus nivellei on the western slopes and Tamarix gallica nilotica on the northern slopes .

Larger mammals in the mountains include the Dorcas gazelle ( Gazella dorcas ), the barbary sheep ( Ammotragus lervia ) and the cheetah ( Acinonyx jubatus ). Populations of smaller mammals include the rock hyrax ( Procavia capensis ), the kaphase ( Lepus capensis ) and the spiny mouse ( Acomys spp.).

Western Sahara mountain desert vegetation zone

Aïr Mountains photographed from Gemini 6

This vegetation zone of the Chad Basin is determined by the topography of the Tassili n'Ajjer and Aïr mountains. The climate of this region is described as hot and dry in the summer months and cold and dry in the winter months. The annual rainfall is given as 150 mm. Temperatures reach 30 ° C in the lowlands and 12 to 18 ° C in the higher elevations of the mountains, where ground frosts also occur and snow can fall in the cold winter months. In the mountains, Gueltas can be found in narrow gorges that permanently carry water and, thanks to their low evaporation rate, ensure a survival for flora and fauna in these otherwise barren mountains. In the oases of the Aïr there is also an extensive garden restaurant.

The flora in this vegetation zone is determined by the nature of the surface of the area. In the plains there are extensive regs , hammadas and numerous wadis around which the vegetation is grouped. In the higher altitudes, the vegetation changes into a Sahara mountain vegetation with rare and largely endemic plants and tree species, some of which are relics of the humid past of the Sahara region. This mainly affects the Duprey cypress, the tarout (Cupressus depreziana) , the wild olive (Olea lapperrini) and the myrtle (Myrtus nivellei) .

The fauna of this vegetation zone is very diverse, so populations of the Dorcas gazelle (Gazella dorcas) and the Damagazelle (Gazella dama) live on the plateaus of the mountains. Migratory birds from Europe use this region as a resting and wintering area. There are also numerous reptiles such as the slender blind snake (Telescopus obtusus) or the white-bellied sand rattle otter (Echis leucogaster) . Amphibians such as the green toad (Bufo viridis) can also be found in this region.

South Sahara grass and shrub savannah

The vegetation zone of the South Sahara grass and shrub savannah is a dry savannah , at the same time a borderland and a transit zone between the Sahara and the Sahel acacia savannah . It is 100 to 200 km wide. The rainfall here is more abundant than in the Sahara and amounts to between 100 and 200 mm per year.

The flora in the north of this region is determined by seasonal grass savannahs , which can grow in summer, favored by the rainfall from July to September. They consist mainly of the love grasses ( Eragrostis ), Aristida and the dune grass ( Stipagrostis ). These grass savannahs are interspersed with herbs and shrubs such as the tribulus , heliotropium and pulicharia . The umbrella acacia and the Acacia ehrenbergiana grow mainly in the wadis and areas with aquiferous layers in this ecoregion . Millets ( Panicum turgidum ) also grow in the south of this region .

In this region, in addition to the live ostrich ( Struthio camelus ) and larger mammals such as the Addax ( Addax nasomaculatus ), the dunes gazelle ( Gazella leptoceros ), the Dama Gazelle ( Gazella dama ), the striped hyena ( hyaena ), the cheetah ( Acinonyx jubatus ) and the African wild dog ( Lycaon pictus ).

Sahel acacia savanna

male masked shrike

The vegetation zone of the Sahel-acacia savannah is a dry and thorn-shrub savannah . It connects to the South Sahara grass and shrub savannah and covers most of the Chad Basin . The topography in this ecoregion is generally flat, with no major elevations or mountains. The amount of precipitation varies between 200 mm in the northern area and 600 mm per year in the southern area of ​​the region. The monthly maximum temperatures fluctuate between 33 and 36 ° Celsius, the lowest temperatures are 18 to 21 ° C in the cooler months. The young and thin crust of the soil has no visible stratification and corresponds to the Entisol soils of the USDA soil classification. They cover most of this region. In the northern part they alternate with Aridisol soils, surface water is only available seasonally in the rainy season.

The flora in this region is a largely tree-covered savannah, which is interspersed with thorny bushes. The grassy landscape is dominated by the short, annual sweet grasses Aristida mutabil , Chloris prieurii and Cenchrus biflorus .

A large number of endemic animal species live in this ecoregion. Among the birds, the rust lark ( Mirafra rufa ), the masked shrike ( Lanius nubicus ) and the Sudan bag tit ( Anthoscopus punctifrons ) are endemic to this region. At the beginning of the 20th century there were large populations of elephants, the West African giraffe ( Giraffa camelopardalis peralta ) and ostriches in this region . However, these were heavily hunted, so that significant stocks could only survive in national parks and other protected zones. The saber antelope ( Oryx dammah ), which once appeared in large populations, is now believed to be extinct.

Lake Chad flood savannahs

The Lake Chad flood savannah lies in the zone of Lake Chad and the adjacent floodplains of its tributaries. The floodplains and wetlands in these areas cover an area of ​​approximately 2.5 million hectares and are of great importance far beyond the Chad Basin. The vegetation zone consists of a variety of surface shapes, then small island groups, large wetlands, find sedge -Savannen and large open water areas in the area of Lake Chad and permanent grass savannas and seasonal savannah as the Yaéré. The term "Sudd", which is used in this region, describes a permanent floodplain.

Lake Chad is divided into a northern and southern lake basin. The northern lake basin has an approximate depth of 6 meters and is currently (2011) only seasonally flooded with water from the Komagoudou Yobe. The southern lake basin has a depth of 2 to 3 meters and is currently only covered with a permanently open water surface in the core area of ​​the tributary of the Shari.

The flora in this vegetation zone of the southern lake basin is determined by large areas that are covered with real papyrus ( Cyperus papyrus ), Phragmites mauritianus , Vossia cuspidata and other marsh plants. The water lettuce ( Pistia stratiotes ) swims on the open water surfaces of the lake and covers a large area of ​​the lake. In the area of ​​the northern lake basin, the reed ( Phragmites australis ) and the cattail Typha domingensis dominate the vegetation.

The waters of Lake Chad are described as tropical waters with a low salinity , rich in phytoplankton and a large variety of algae and fish . More than 1,000 different species of algae and more than 140 species of fish have been counted in open waters.

Seasonally, in the rainy season, so-called Yaéré grass savannahs grow in the southern bank region. These are dominated by the Echinochloa pyramidalis , Vetiveria nigritana , Oryza longistaminata and Hyparrhenia rufa . The Yaéré vegetation dies in the dry season. The so-called Karal or Firki tree savannas grow in the more humid zones of the Yaéré. The tree population is dominated by the Seyal acacia ( Acacia seyal ) on the hills and the Acacia nilotica in the depressions. The plant surface in this tree savannah is formed by herbs and grasses 2 to 3 meters high, such as Caperonia palustris , Echinochloa colona , Hibiscus asper , Hygrophila auriculata and Schoenfeldia gracilis .

Western Sudan savannah

male bushbuck

The Western Sudan savannah is a wet savannah and covers the southwestern areas of the Chad Basin in the states of Nigeria and Niger. It is a lowland without major elevations, which is separated from the eastern Sudan savannah by the Mandara Mountains in the highlands of Cameroon. Temperatures reach 35 to 40 ° C in summer and 15 to 20 ° C in winter. The annual rainfall in this region ranges from 600 mm per year in the north to 1600 mm per year in the southern areas of this ecoregion. The soils are moderately fertile and are subject to lateritic weathering.

The flora in this vegetation zone is characterized by loosened and extensive forests, which are interspersed with bush forests and undergrowth with long-stemmed grasses and broad-leaved herbs. Gallery forests spread along the rivers .

A large number of different animal species live in the Western Sudan savannah, many of which are endemic to this savannah landscape. Larger populations of the bushbuck ( Tragelaphus scriptus ), the warthog ( Phacochoerus africanus ), the Ethiopian vervet monkey ( Chlorocebus aethiops ), the steppe monitor ( Varanus exanthematicus ), the anubis baboon ( Papio anubis ) and the mantled baboon ( Papio hamadryas ) live here. The once large populations of African mammals such as the elephant only survive in protected areas.

Eastern Sudan savanna

African wild dog

The Eastern Sudan savannah is a dry savannah and spreads in the south of Chad and in the north-west of the Central African Republic. Its topography is characterized by a pronounced flat land without major elevations. Its climate is characterized by a division into dry and rainy seasons. The highest temperatures are 30 to 33 ° C and the lowest are 18 to 21 ° C. The annual rainfall ranges from 600 mm in the north to 1,000 mm in the southern part. The soil quality according to USDA soil classification ranges from Entisol - via Ultisol - to Alfisol soils .

The flora in this vegetation zone is similar to that of the Western Sudan Savannah with its loosened and extensive forests, which are also interspersed with scrub forests and undergrowth of long-stemmed grasses and broad-leaved herbs. However, it differs in that most of the trees shed their leaves in the dry season and the grass surfaces wither. The trees are dominated by the Anogeissus leiocarpus , the Kigelia aethiopica and the Seyal acacia ( Acacia seyal ).

The fauna in this vegetation zone is characterized by a large number of intact populations of larger African mammal groups. In contrast to the Western Sudan savannah , the number of endemic animal species is low: only one mouse species, the Mus goundae , and two reptile species, the beak- nosed snake Rhamphiophis maradiensis and the Panaspis wilsoni , are endemic. Large mammals can be found in free-living populations of the African elephant ( Loxodonta africana ), the African wild dog ( Lycaon pictus ), the lion ( Panthera leo ) and the cheetah ( Acinonyx jubatus ).

Northern Congo forest savanna vegetation zone

Bongo antelope

This vegetation zone includes the northern areas of the North Equatorial Sill in the Central African Republic (CAR) and the highlands in Cameroon and its classification corresponds to that of a wet savannah .

It is a narrow transit zone between the Congolese rainforest areas and the Sudan / Sahel grass savannahs. The northern Congo forest savannah vegetation zone forms the northernmost forest savannah landscape on the African continent with a large number of different ecosystems. The annual rainfall ranges from 1,200 to 1,600 mm. In the rainy season the temperatures reach 31 to 34 ° C and in the dry season the minimum temperatures are 13 to 18 ° C. The soils in the CAR are described as non-weathering Entisol soils and in Cameroon as Oxisol to Ultisol soils due to their mountainous location .

The flora in this vegetation zone is determined by its character as a transit zone between the Sahel and the rainforest. The tree population is dominated by the genus Isoberlinia .

The fauna is very species-rich and is characterized by moderate biodiversity. Large populations of the African elephant ( Loxodonta africana ), the black rhinoceros ( Diceros bicornis ), the giant eland ( Taurotragus derbianus ) and in the eastern sector of the bongo ( Tragelaphus eurycerus ) are found in this zone .

literature

Web links

Individual evidence

  1. ↑ Height information at OpenCycleMap
  2. ↑ Leblanc et al .: Reconstruction of megalake Chad using shuttle radar topographic mission data . Palaeogeography, palaeoclimatology, palaeoecology 239, 2006, pp. 16-27 ISSN  0031-0182 1872-616X
  3. ↑ Chad Basin National Park . ( Memento of October 2, 2013 in the Internet Archive ) Nigeria Park Service (English)
  4. ↑ The Annotated Ramsar List: Nigeria (English)

Coordinates: 18 °  N , 19 °  E