Chad Water and Seasons
The national water net is essentially composed of two rivers: the Chari, 1,200 km long and emanates from the Central African territory; the Logone, 1,000 km springs in Cameroun. The two rivers form a confluence near the capital N’Djamena, and travel together for about 125 km before they cockle in the Lake Chad. Apart from Lake Chad, which is the principal lake, there is also the Fitri, Iro, Lere, Tikem, and the two Ounianga lakes. Oasis are scattered in the desert zone in the north.
On the other hand, Lake Chad receives water from other streams, of which the most important ones are: Halha, Bahr-El-Gazal, Bahr-Aouk, Malir-Keita, Mandoul, Pende. But these rivers and other streams are not capable to stop the vaporescence and reduction of Lake Chad, which was many centuries ago called “the paleo-Chadian sea”; millions of years ago this continental sea came from Bardai, but in just a matter of a few centuries it reduced, measuring only 25,000 square km in the 1960s. Today the ground-water table of Lake Chad is of merely 3,000 square km. However, it still constitutes Chad’s main water reservoir. Its volume is estimated to be 40 cubic meters on average, which represents 80 per cent of the waters of the Chari and the Logone.
The beginning of precipitation is announced by a humid wind coming from the south-west from April/May in the south, and May/June in N’Djamena in the north.
Rain season: in the south from May to October, in the centre from June to October, variable in the north from June to September.
Dry and cold season:
from October/November until February, sand wind (harmattan) blows in the north-east. The annual average temperature in the whole country is 20 degrees, with maximums between 30 and 35 degrees during the warm season, and minimums between 20 and 23 degrees. In N’Djamena (Sahel zone), the seasons are as following:
July to September: occasional thunderstorms and rain, followed by a slight decrease in temperature varying between 21 and 35 degrees; the level of humidity is increased.
October to mid-November: warm season without rain, but relatively humid
Mid-November to mid-March:
Dry season more or less cold, with very cool evenings and nights, in which the temperature declines to 8 degrees.
February and March: sand wind period (harmattan) End of March to June: very hot and dry season: the temperature decreases only rarely less than 35 degrees, and during the day she can rise to 46 degrees in the shadow.
Lake Chad is a large, shallow lake in Africa with fresh waters, which is rare for an endorheic lake, that is, where the waters do not join the ocean. Its economic role is very important, because it must provide water to more than 20 million people in the four neighboring countries: Chad, Cameroon, Niger and Nigeria.
The lake's hydrographic basin is theoretically 2,380,000 km², covering 7.8% of the continent, but the active basin is in fact only 967,000 km². The main contribution, 90%, comes from the Chari River and its tributary Logone, both from the mountains of the Central African Republic. The Komadougou Yobé, from Nigeria, is weakened by the presence of two dams which have reduced its flow from 7 km3 to 0.45 km3 per year. Although it participates only for 10% in the waters of the lake, it is the separation caused into two basins, north and south, which made the supply of the north precarious. The water loss downstream of the dams has also been compensated by increased uptake of wells.
Once one of the largest lakes in the world, the lake has shrunk considerably over the past four decades. In the 1960s, it covered an area of over 26,000 km². By 2000, it had fallen to less than 1,500 km². The rainfall deficit combined with greater use of lake and river water for irrigation - the basin's population has doubled in the meantime, and irrigation quadrupled between 1983 and 1994 - explain this decline. Its shallow depth, at most 7 meters, makes it fragile and very dependent on seasonal fluctuations. Navigation is now impossible.
Following the decline of the lake in the 1970s and 1980s, the new emerged lands, still wet, made it possible to undertake very productive crops, especially in the south of the lake, on the Chadian side. The irrigated land amounts to 135,000 ha, of which 100,000 ha are in Nigeria.
NASA funded a study on Lake Chad as part of its Earth observation system. The variations are followed by artificial satellite, in order to warn residents of the expected modifications. NASA, which has carried out a climate simulation study on the region, predicts the disappearance of the lake more or less soon.
During the postglacial periods, the Sahara enjoyed much milder climatic conditions than today and the actual desert was very small. The Sahara was mostly covered with Mediterranean-type wooded vegetation, particularly in the central massifs with around them numerous lakes and dry meadows, a situation favorable to game fauna.
Following the alternation of wet phases and dry periods, Lake Chad extends or retracts, but from 4000 BC. J. - C. until our days, the fall of water is fast, corresponding to the installation of aridity and the advance of the desert.
The variations of Lake Chad bear witness to many changes:.
The cause: increasingly rare rains, dramatic droughts (1973, 1984, 2008) and deforestation.
Paradox: while the lake is in the process of disappearing, its residents are opposed to its replenishment. The drying up has in fact exposed fertile land from which they derive a good income.
The climate around the lake is hot and dry, with highly variable rainfall - from 94 to 565 millimeters per year, 90% of which falls between June and September. The south shore is wetter than the north. Although evaporation is important, especially during the dry season, the salinity of the lake does not increase very much, the water with the highest salt content leaving the lake through the subsoil.
The salinity of the northern basin could increase if the water supply to the latter remains low, which could cause the disappearance of many plant and animal species, increasing erosion thereafter. Fishing, which has already fallen from 243,000 tonnes in 1970-1977 to 56,000 tonnes in 1986-1989, could decline further, depriving local residents of a substantial income while the northern states of Cameroon and Nigeria are already among the poorest in their respective countries. The scarcity of drinking water could finally increase the cases of diarrhea, cholera and typhoid fever. However, the prospect of a classification of Lake Chad as a world heritage could allow the implementation of a preservation policy by all the riparian countries.
Water transfer project from the Congo Basin
To save Lake Chad, an old project resurfaced at the beginning of the 21st century, that of Transaqua. This is an inter-basin water transfer project, departing from certain tributaries of the Congo River to Lake Chad, through a gigantic canal that would use the Chari River valley.
The project of the 1990s
The original project formalized in the early 1990s planned to block the courses of several important rivers in the northeast of the Democratic Republic of the Congo by means of regulating dams, and to subtract part of their flows to bring them towards a artificial lake built on the Oubangui upstream of Bangui. From there a channel would lead these waters to the watershed between the Congo basins and the Chari basin, at an altitude of about 600 meters. Once crossed this threshold, the flows would be routed, still by canal, in the bed of the Chari, and would end up supplying Lake Chad and its entire region.
The whole would also constitute an important international waterway.
The volume of withdrawal foreseen in this first project was of the order of 100 billion cubic meters of water annually, that is to say about 3 150 cubic meters per second.
The work planned to block the tributaries of the Oubangui, Aruwimi, Lindi and Lowa, all right-wing tributaries of the Congo in the north-eastern quarter of Congo-Kinshasa and the south of the Central African Republic.
The total length of the canal would have been around 2,400 kilometers, about half of which in the Chari basin.
Current status of the project
Two different projects are currently on the table, both providing for the transfer of part of the waters of the Ubangi through a 1350 km canal.
It should be noted that first of all it was necessary to convince the Democratic Republic of the Congo and the Republic of the Congo to accept the project, the watercourse to be diverted (the Ubangi) having its source in the Democratic Republic of the Congo and then forming a border. with the Central African Republic then with the Republic of Congo. The agreement of the two countries has been in place since 2005.
In March 2008, Nigeria, Niger and Chad agreed to go ahead and finance studies to transfer part of the waters of the Oubangui.
The feasibility study requires significant resources and Nigeria, the region's oil and financial power, is ready to allocate five million dollars to it. The other four member countries of the LCBC (Lake Chad Basin Commission), namely Cameroon, the Central African Republic, Niger and Chad, will together contribute a sixth million. Studies are due to start in 2009.