The Lake Chad Basin
The climate of the Lake Chad Basin is tropical comprising four climate zones, which match the different types of isohyets. The basin belongs to the sahelian zone in which the monsoon rainfall decreases from the south to the north (less than 100 mm of rainfall in the north of Chad, Libya and Algeria– to 1, 500 mm per year in the south of the basin, in the south of Chad and in the Central African Republic. The climate of the Lake Chad Basin is classified in four sub-types (from the north to the south):
- The Saharan climate is characterised by less than 100 mm of rainfall per year;
- The sahelian-saharan climate with an average annual rainfall between 100 mm and 400 mm ;
- The sahelian-sudanese climate , more wet with an average annual rainfall between 400 mm and 600 mm ;
- The sudanese-guinean climate with an average annual rainfall between 600 mm and 1, 500 mm.
The temperature deviation is very important as the temperature decreases during the rainy season and in the evenings during the dry season. The dry season usually last 8 months. The rainfall is reduced and covers few days.
The rainfall deviations are important within the geographical regions which face limited rainy days and the punctual and local fluctuations of the duration of the dry season. The relative humidity is fairly low and varies with the altitude.
The potential evaporation is higher than the rainfall. This is likely to justify the water deficit in some parts of the basin.
The climate features of the Lake Chad Basin: duration of the sunlighting, air humidity, temperature, evapotranspiration and rainfall are influenced by the seasonal movement of the Convergence Inter-tropical Belt (ZITC). This highlights the influence of the humid maritime equatorial air masses (Easterlies) and the dry continental tropical air masses (Harmattan). The climate situation of the 70s to 80s (exceptionally dry periods) illustrates the migration of the ZITC towards the south of the basin. The wet years up to the 60s indicate the longer rainy season thanks to the ascent of the ZITC towards the north.
Due to the movement of the ZITC, the position of the isohyets of each region can be displaced on 300 km towards the south or the north of the basin. Likewise, the monthly rainfall graphs can be modified in such a way that any change of the annual rainfall is attributed to an increase or decrease of the rainy months. Features of the climate in each LCBC member country.
In Chad, the average annual rainfall is 322 mm/year. This figure is just a sample as the quantity of rainfall varies too much from one area to another one due to frequent droughts. Chad is an inland country which comprises three major agro-climate zones from the north to the south with a huge variety of the distribution of the natural resources such as water, land and biomass. This includes the following:
- The Saharan zone with the rainfall which is lower than 300 mm/year in the border of the desert in the north while the rainfall is not constant in the zone. This zone covers close to 47 % of the country.
- The sahelian zone where the rainfall is between 300 and 600 mm/year in the centre of the country. It covers close to 28 % of the country.
- The Sudanese zone which is characterised by the rainfall which is higher than 600 mm/year (at times 1, 200 mm in the south). This zone covers 25% of the country.
The maximum rainfall is recorded in July/August. There are two seasons for the sahelian and Sudanese zones:
- The rainy season from June to September;
- The dry season from October to May.
The evapotranspiration covers 3, 000 mm in some regions. The average monthly temperatures vary from one month to another one. The relevant values are 28°C, 42°C during the daylight and 14°C in the evening. In the north of the country, the temperatures vary from 13°C to 29°C in January and 25°C to 44°C in May. In the south, the temperatures range between 15°C and 34°C in January and between 23°C and 35°C in May.
The Central African Republic
In the Central African Republic, the climate is wet tropical in the south and dry in the north (Lake Chad Basin), with a dry season (November to April) and the rainy season (from May to October). There are four agro-ecological zones of which three are located in the Lake Chad basin:
- The forest or equatorial zone located in the south-west, which is the extension of the equatorial zone of the Congo basin. The rainfall is abundant (1, 500 to 1, 800 mm/year) and the vegetation is luxuriant. This zone hosts perennial crops: coffee, cocoa, palm trees, banana, plantain, etc;
- Towards the north, the sudanese-guinean zone or humid tropical in the centre with an annual rainfall between 1, 100 and 1, 500 mm. The food crops are farmed in this zone (cassava, yam, etc.);
- The sudanese-sahelian zone towards the north with the rainfall level, which ranges between 800 and 1,100 mm ;
- The sahelian zone which is characterised by the instability of the rainfall and the frequent droughts.
The average temperature ranges between 25°C and 26°C and the relative humidity is 80% in Bangui as opposed to 57% in Birao, a city located within the basin.
Cameroon has three major climate zones:
- The sudanese-sahelian zone goes beyond the 10° north latitude. It is characterised by the dry season, which covers seven to nine months and the rainfall is not abundant and varies from 900 to 300 mm/year from the south to the north. The vegetation varies from one area to another one. There is the equatorial forest which covers 40% of the country in the south and there is the savannah and the steppe in the north. The average annual temperature is above 28°C in the Far North region ; it is lower in the Adamawa region except the Mounts Mandara which are fresher and the area of Garoua, which is warmer.
- The Sudanese zone covers 7° to 10° of the north latitude. The dry season lasts between five and six months. The average temperature is 22°C, and 1,000 mm of rainfall are recorded on a yearly basis.
- The equatorial zone covers 2° to 6° of north latitude and is characterised by the abundant rainfall of which the annual average is 2, 000 mm. The average temperature is around 25°C.
Cameroon records a huge quantity of rainfall. The average annual height of the rainfall was close to 1, 600 mm these past ten years but this is not regular in the whole country. In the north, the minimum temperature is recorded in December-January and the maximum temperature level is recorded in March-April. In the south, the minima temperatures are recorded during the period July-September. The potential evapotranspiration varies from 2, 200 mm/year in the Far North region and 1, 200 mm/year in the southern part of the country.
Niger has a sahelian climate which is characterised by the long dry season, which lasts between eight and ten months (October to May), a short dry season which lasts three or four months (June to September) and an important variation of the number of rainy days from the north to the south where the annual rainfall is between less than 100 mm and 700-800 mm, thus dividing the country in four climate zones:
- The Saharan zone (65% of the country) with the rainfall, which is lower than 100 mm/year. The average temperature is 35°C and the climate is desert;
- The sahelian-saharan zone (12.2% of the country) with the annual rainfall, which ranges between 100 and 300 mm. The climate is sub-desert;
- The sahelian-sudanese zone (12.9% of the country) with the sahelian area in the north where the annual rainfall vary from 300 to 600 mm and the Sudanese area in the south;
- The Sudanese zone (0.9% of the country) receives more than 600 mm/year.
The sahelian domain is characterised by the shrubs in the north and the variety of trees in the south. The Sudanese area comprises the vegetation of savannah which has a stratum of herbaceous dominated by the graminaceous and a forest stratum containing the shrubs and the trees. During the past decades, the recurrent droughts caused the desert encroachment which evolved from 66 to 77 % of its size. The key feature is the shrinkage of the Niger River by Niamey in 1985. The annual average temperature is 29°C and the highest ETP is 2, 114 mm/year at Tillabéry, higher than the rainfall except in August.
In Nigeria, the climate is subarid in the north and wet in the south except for a very wet strip located along the cost with the average rainfall of more than 2, 000 mm / year, where the rainfall is abundant and the rainfall regime is characterised by various dry and rainy seasons. The rainfall is abundant from June to September. The lack of the total annual of rainfall is an issue in the northern regions of the country. However, in most of the other regions, the major issues include the distribution of the rainfall in the time and space and its low frequency. The average annual rainfall is estimated at 1, 150 mm; or close to 1, 000 mm in the centre of the country and 500 mm in the north east. The average annual evaporation (bac) is 2, 450 mm in the south east, 2, 620 mm in the centre and 5,220 mm in the north of the country, notably in the basin.
In Libya, the climate conditions are influenced by the Meditteranean sea at the north and the Saharan desert in the south, this causes an abrupt transition. The following major climate divisions can be established:
- The Mediterranean coastal strip with the dry summer and the wet winter ;
- The mountains of Natusah Jabal Akhdar and Jabal which have a plateau climate with abundant rainfall, low temperatures during the winter, including the snow fall;
- Towards the south in the country in the sub-desert and desert zone: the climate conditions are paramount with the extreme temperatures and major variations of the daily temperatures. The rainfall is scarce and reduces gradually up to zero.
The annual rainfall level is low with 93% of land , which receive less than 100 mm / year of rainfall. The major rainfalls are recorded in the northern part of Tripoli (Jabal Nafusah and Jifarah ) and in the northern part of Benghazi (Jabal al Akhdar). These two regions are those where the average annual rainfall, which varies between 250-300 mm is vital as it supports the rainfed agriculture. The rainfall is recorded during the winter and varies from one region to another one and from one year to another one. The average annual rainfall for the whole country is 26 mm.
Sudan has a sub-inland tropical climate, which is characterised by the desert climate in the north marked by the summer rainfall and the equatorial climate in the south. The annual average rainfall is 416 mm, but this figure is between 25 mm in the dry north and more than 1, 600 mm in the rain forests of the south. The country can be divided in three zones based on the rainfall regime:
- The annual rainfall in the Far north of Sudan varies from 200 mm in the centre of the country by the north to 25 mm by the border with Egypt. The rainy season only lasts 2-3 months. The rainfall is generally noticed by isolated down pours, which vary in the time and space. The variation coefficient of the rainfall in the far north could reach 100%.
- In the centre of the country, the annual rainfall does not exceed 700 mm. It only covers four months, from July to October. The average annual rainfall of that region ranges between 300-500 mm. The rainfed agriculture in Sudan is mainly practised during that period. As the variation coefficient of the annual rainfall is close to 30% and the dry season covers eight months, the size of the farmland and the productivity vary from one year to another one.
- In the south of the country where the annual rainfall is 700 mm and can reach 1, 600 mm, the region is dominated by the vast wetlands of which some are infested by harmful insects to both the human beings and the stocks.
The average temperatures vary from 30 º C to 40 º C in the summer and 10 º C to 25 º C in the winter. The annual ETP varies from 3, 000 mm in the north to 1,700 mm in the far south. Most of the agricultural activities are concentrated in the centre of the country, mostly in the dry savannah crossed by the Blue Nile and the Atbara River. The farming season of the region is close to four months. The major hindrance is not the agricultural potential but the short rainy season combined with the irregular distribution of the rainfall during the farming season.