by
J.P. Lamagat
Chargé de Recherches ORSTOM
Chef de Mission Hydrologique ORSTOM au Mali
Since 1968, the climatic conditions of the West African Sahel (see definitions of climatic zones, section 2.1) have deteriorated and it is only during the 1974 rainy season that a condition close to normal is prevailing again in West Africa.
That condition has been featured by a general shortage of rain in the West African Sahel. This shortage has been increasing from 1971 to 1973 inclusive.
At the beginning of 1974 the condition was particularly disastrous (extremely low water level in the Senegal and Niger Rivers - Lake Chad becoming droughty) and hydrologists and climatologists were asked many questions among which two were more frequent:
the series of generalized shortage 1971–73, does it feature a change of climate inside the West African Sahel?
did periods of return to normality exist for the series of shortage years? If they do, is it possible to forecast them at long term and make provisions to face them?
When writing the present report, the author has got only little information on the 1974 rains (except some information from Mali). It seems that the 1974 rainy season will be excessive over the whole zone. It may be the same for the flow of rivers (at Koulikoro the maximum exceeded the normal by 10 percent approximately).
The rain shortage recorded in the Senegal, Niger Rivers and Lake Chad Basins have been such during the period considered that the introduction of a parameter other than the yearly height of rain seems to be useless.
In fact, it seems that whatever can be the distribution in the time of the rains if the rain shortage is over 40 percent the short-fall in the agricultural production is equal at least to this shortage, and can aim at 100 percent due to a bad distribution.
The proposed analysis will bear on the shortage of yearly rain height and on the flow of the main rivers of the zone.
Hydrologists used to classify the climates and corresponding zones according to the average height of the average yearly rains, as follows:
sub-desert climate (rain lower than 100 mm)
Sahelian climate (between 100 and 600 mm approximately)
pure tropical climate (between 600 and 1 200 mm)
tropical transitory climate (over 1 200 mm).
In spite of the fact that great rivers (Senegal, Niger, Chari) take their rise under transitory tropical climate, the analysis will not include this climate in which the drought has never been severe.
The term Sahel will be used in general with a wide meaning when there will be no reference to a determined climatic zone.
The three first quoted climates are featured by a rainy season quite homogeneous from July to September with some storms in May and mainly in June.
In chart No. 1 it is stated that the yearly average 100–500 and 1 000 mm isohyetal lines have generally an east-west direction which is due mainly to the displacement of the anticyclones of the Azores, Saint Helena and the Inter-Tropical Front (ITF).
Within the zones under consideration rainfalls are rather well known in the time and in the space due to the national weather network pooled in the ASECNA (Association for the Security of Aerial Navigation). The author has selected the reference pluviometric stations according to the following features:
quality of the measurements.
The pluviometric data quoted in this analysis came from the ORSTOM files. The recordings correspond to originals for which biases have not been corrected. The trends of the actual drought can be unscrambled in spite of the fact that in some stations the last years' records seem to be slightly optimistic.
There are solid data for the rivers, the basins of which are under examination (Table I).
Data are more scarce for the Sahelian zone due to a lack of recordings in 1971–72–73, or a lack of control of the stations because of insecurity. Only few usable data are available. Table I gives the stations retained due to their location and the value of the recordings. There is not any permanent station in the sub-desert zone.
Chart No. 2 shows the main hydrometric stations in West Africa (French-speaking countries).
This inventory of the recent drought is based on:
an arrangement in increasing order of the annual rainfall at the reference station;
evaluation of the deficit D of the module Q of the rivers compared with the average module Qm expressed in percentage such as 
(the excess being 
;
numerical values recapitulated in Tables II (rain) and III (flow).
In general, the actual period is considered as beginning in 1968; 1967 was definitely over the average; It should be noticed that certain regions received little rain as early as 1965, these regions being at the limit of the Sahelian and Saharan zones:
Agades received 97 mm only in 1966 (median 150 mm)
Kabara-Timbuktu 125 mm in 1965 and 89 mm in 1966 (minimum observed at this station where the average is 210 mm).
Senegal and Mauritania suffer more than the others:
Dakar 259 mm (median 500 mm).
The Senegal River: module 426 m3/s at Bakel (deficit of 45 percent).
Niger River at Koulikoro deficit 10 percent only, as well as the western part of the Upper Volta.
The eastern part of the Upper Volta and Niger River suffer heavily:
the Goulbi of Maradi at Madarounfa (2.45 m3/s - deficit 59 percent).
The situation is better in the eastern part of the Sahelian zone:
Logone, module slightly in excess.
Practically no drought except in sub-desert zone or nearby:
at Gao 186 mm (median 260 mm)
Normal year in the Senegal Basin.
The Niger River in excess (module 2 060 m3/s + 34 percent at Koulikoro).
Central part of the zone (Upper Volta - west of Niger River) situation normal (Volta, Sirba), or in excess (Gorouol, Maggia).
Eastern part of the zone, very variable situation: Goulbi of Maradi, Chari, Komadougou - deficit.
Logone in excess (module 493 m3/s, + 26 percent at Moundou).
Drought is expanding but it is irregular, e.g., in Mauritania: Nema 202 mm, less than in 1972, Kiffa in excess of 447 mm (median 550 mm).
The whole zone north of the isohyetal line 150 mm suffers:
Kaolack: 477 mm (median 780 mm).
Deficit of the Senegal Basin, Bakel module - 28 percent, maximal flow 3 425 m3/s (median 4 600 m3/s), flow at its lowest 1 m3/s approximately.
Deficit of the Niger River, at Koulikoro module - 28 percent. North of the Upper Volta and West of the Niger, well marked deficits.
In the eastern part the deficits decrease and there are even excesses in the Logone River.
Deficits are less drastic but the drought is general; in the Sahelian zone some stations only record an excess.
| Senegal Basin: | Bakel, deficit of the module 22 percent (595 m3/s); maximal flow close to the median (4 330 m3/s); flow at normal low water level (2.5 m3/s). |
| Niger Basin: | Koulikoro: module slightly longer than in 1970 (1 270 m3/s instead of 1 110 m3/s, deficit 18 percent), downstream Niamey 800 m3/s module is inferior to the 1970's one (1 080 m3/s). Goudebo at Yakouta, deficit 63 percent, 0.6 m3/s module. Deficit is between 20 and 40 percent for the rivers east of the Niger River. |
| Chad Basin: | Chari module at N'Djamena is 993 m3/s (deficit 22.5 percent). Minimal flow 105 m3/s when the average minimal flow is 163 m3/s. Logone module at Moundou is 308 m3/s, deficit 21 percent. Flow at low water 19 m3/s (average 29.3 m3/s). |
Drought is becoming more severe, all the rainfall recording stations show deficits, some records are reached:
| Mauritania: | Boghe: 112 mm, median 310 mm Kiffa: 119 mm, median 350 mm. |
| Senegal: | Dakar: 117 mm, median 500 mm. |
In the other countries there are frequencies to non-overpassing corresponding to return periods of at least 50 years.
Drought is becoming more drastically severe. Accurate measurements have been taken.
Table IV shows the following results in the hydrological stations:
maximal flow of 1972 compared with the average of maximal flows and its frequency of non-overpassing
annual average flow of 1972 compared with the average of the modules and its frequency of non-overpassing
minimal flow at low water of 1972 compared with the average of minimal flows at low water and its frequency of non-overpassing.
Some records are reached: Senegal River at Bakel has a 264 m3/s module, the smallest value recorded since 1903 (frequency about one hundred years). Maximal flow 1 430 m3/s comes just after 1913 (1 040 m3/s). Minimum low water level flow is 0.25 m3/s when the average is 2.3 m3/s.
Severe situations in the Niger River too, the modules have frequencies between 0.05 and 0.15, low water flow is very small: 16 m3/s at Koulikoro (frequency over 100 years). At Niamey it is more serious: 2.5 m3/s for a minimal average flow of 75.6 m3/s, module is 647 m3/s where the average is 1 010 m3/s (periodicity 20 years).
The rivers of the Sahelian zone: Maggia, Sirba, Gorouol, Goulbi of Maradi are much in deficit (periodicity almost over 10 years).
In the eastern part of the zone the situation is catastrophic, periodicity is 100 years
at N'Djamena the Chari River module is 578 m3/s (average 1 280 m3/s), low water flow is 48 m3/s (average 163 m3/s)
the module of the Logone at Moundou is 215 m3/s (average 390 m3/s) and flow at low water 12 m3/s (average 29.3 m3/s).
The same conclusions are reached for the maximal flow.
Water level of Lake Chad is recorded with regularity at Bol since 1953. From 1964 there is a yearly lowering of the water level of 0.30 m between successive maxima, that means now a total decrease of about 3.00 m of the level since 1964. That lowering has been the reason why the Great Barrier is exposed and the southern basin was isolated in May 1973.
The situation is far from improving, there is a deficit at all the stations and very often periodicity is over ten years. In most stations the deficit is greater than in 1972. New peaks are recorded:
Dedougou: 649 mm (median 980 mm), frequency 100 years.
In Mauritania the deficit is less than in 1972 but the periodicity is over 5 or 10 years.
In Senegal, it is almost the same except in the upper basin of Gambia.
In Mali the situation becomes more serious mainly in the Sahel where frequencies are in the range of 100 years at Timbuktu, Gao, Mopti, Nioro, Segou, Koulikoro. The upper basin is not so badly affected: the deficit at Bamako is 17 percent only.
In the central part of the zone the situation is unchanged, sometimes deficits are more important than in 1972.
In the eastern part a similar situation is observed: N'Djamena and Moissala have a greater deficit than in 1972.
At Bakel the Senegal River has a maximal flow overpassing the one of 1972 (2 500 m3/s instead of 1 430 m3/s) but it is well in deficit, its module follows the maximum: 367 m3/s instead of 264 in 1972 with an interannual average of 764 m3/s, which means a deficit of 52 percent in volume. For the first time the river has no water at Bakel, during about fifteen days.
The Niger River has a maximal flow larger than in 1972: 4 140 m3/s instead of 3 680 m3/s but the module is much lower: 903 m3/s instead of 1 080 m3/s where the average module is 1 540 m3/s, with a deficit of 41 percent in volume. Flow at low water is almost the same as in 1972: 16 m3/s.
At Niamey the flow at low water level is exceptional, 600 l/s have been recorded of which 250 l/s were taken by the city, the average flow at low water level is 75 m3/s.
The Chari River shows the same trend as the Niger: maximal flow larger than in 1972 (2 130 against 1 430 m3/s and almost equal module, 577 against 578 m3/s).
Influence is weaker on the Logone: maximal flow 1 660 m3/s against 966 in 1972 and 258 m3/s against 213 m3/s. The deficit is still important: 32 percent in 1973, 45 percent in 1972.
The flood of the Chari River once more was very small and the volume brought by the flood (18.5.109 m3) is very small compared with the average intake (about 40.109 m3).
Table II shows all the interesting values of rainfall. The results of a statistical analysis of the annual rainfall heights at 54 stations of West Africa are tabulated. The last 10 stations are not included in the zones studied here but are listed for comparison purposes.
In Table II, from left to right there are:
height 1971–72–73 and corresponding frequencies.
Table I shows the selected stations, the area of the basins, the periods of recording and the number of years.
Table III shows the development of the average flows of some rivers of interest to us. The table includes:
years 1968 to 1972: corresponding module and deficit or excess.
Table IV gives the most complete results for the year 1972:
frequency of the 1972 minimal flow.
In Table V the average modules of the Niger at Koulikoro and of the Senegal at Bakel during different dry periods are compared:
| ● | 3 year average: | 1912–14 | 5 year average: | 1940–44 |
| 1942–44 | 1910–14 | |||
| 1970–72 | 1968–72. |
Data referring to 1973 are not included in the tables because complete information was not available. The known data are in sections 3.7.2
The lake basin begins at Ke Macina up to the level of Timbuktu. An average year the Niger flood covers 50 000 km2 during about three months.
Up to now there is no precise study of the flooded areas in terms of the strength of the flood of the Niger and Bani.
The “Project SAPHYR” or “Research on the causes of anomalies of the Niger floods” beginning at the end of 1974 will up-date the question through the utilization of photographs transmitted by the satellite ERTS (NASA). This study conducted jointly by ORSTOM (Hydrology), BDPA (interpretation of photographs) should lead to a better knowledge of the hydraulic mechanisms ruling the breaking of the forces of the Niger floods through its internal delta.
During the 1972 and 1973 rainy seasons the floods were non-existent. The only part located in the angle formed by Diakka and Niger was reached by the waters, the force of the flood not being broken yet but the duration of the flood did not exceed two weeks.
When examining the heights of maximal flows classified at the stations of the Niger at Diakka, it appears that there is overflow when the frequencies of maximal heights are at least higher 0.25–0.30 to the “non-overpassing”. In 1972 and in 1973 the floods did stay below that barrier.
Tanda and Kabara Lakes downstream Mopti and Debo Lake have not received water for three years and they are dry; in December 1973 even the bottoms of ponds had disappeared.
In mid-December 1972 there was only one place flooded in the lake basin, the triangle Diafarabe, Tenenkou, Ouro Modi. There was not any overflow in the zone of Lake Debo and downstream.
On the right bank of the Niger downstream Mopti the lakes were poorly supplied. In December 1973 the Goundam channel supplying these lakes was already deflooding and the flow stopped at the beginning of January. In July 1974 the level of Lake Faguibine would be the lowest known.
The Lake Chad is an endorphic basin and the changes of level are the result of a balance between the intake on one side and the losses through evaporation and infiltration on the other part.
The total input during an average year is 50 000 million m3, distributed as follows:
direct tributaries: El Beid, Yedseram and Komadougou 8–10 percent.
The annual fluctuations of the lake each follow the variations of the Chari with a certain delay: it is minimum in July and maximum in December to January.
Since 1964 there is a continuous lowering of the water level which becomes more severe from 1968, the supply of the six last years being in deficit. Two maps of the lake, by A. Chouret (Figures 3 and 4) show the open waters beginning of 1968 and middle of 1973, that is to say almost at the extreme of the recent drought period.
After the maximum level of 1968 due to the 1967 flood, lowering of the level increases, the intake of the four years 1968 to 1971 being smaller than the average Chari supply estimated to 40 billion m3 with an annual average deficit of 8 billion m3. In 1971 at the minimum the area of the lake was 19 000 km2 only instead of 23 500 in a normal period.
After the 1971 flood in deficit, the lowering of the water level began abruptly as soon as January 1972 and affects more particularly the southern basin. At the minimum water level of 1972, a coastal strip 5 to 20 km wide from Chari delta westbound to Baga Kawa is exposed. Eastbound the delta, water which was nearby the Hadjer el Hamis rocks in 1971 withdrew at some kilometres from these.
After the 1972 flood which supplied 17.5 billion m3 only to the lake (100 year frequency) there is no rise of the level - never observed before. This is explained by the inversion of the winds beginning of October (harmattan replacing the monsoon) producing a rocking motion of the water from north-east toward south-west.
In April–May 1973 the lake was below the critical level corresponding to exposition of the shallows of the southern basin. Waters are withdrawing at a lesser degree at the ends of the branches of the south-eastern and eastern archipelago.
The Great Barrier is exposed at the level of Baga Kawa in June. The northern basin cut off water supply has a decreasing area and the total open waters of the lake fall to 8 000 km2 about, that is to say one third of the 1964 area. The stocked volumes are 28 billion m3 only instead of 105 in 1964.
In 1973 the flood of the Chari is 2 130 m3/s instead of 1 430 m3/s in 1972. The volume of water supplied to the lake is slightly higher, only 18.5 billion m3 instead of 17.5. In December 1973 the water level of the lake in the northern basin was lower by 1 m to the one of the previous year.
Levels measured in 1973 are lowest ever recorded but it seems that the lake had smaller depths and areas (Tilho). However, as the Chari supplies have been definitely weak it is to be feared that the drying up of the northern basin practically not supplied by the southern basin be increased and that 1974 the level of the whole lake be lower.
Concerning the floods along the Chari and Logone Rivers, it can be noticed:
The Yaérés - flood plains - of North Cameroon have not received flood water in 1972. El Beid and Ba-Illi (effluents) had no water. There was no overflowing between Chari and Logone Rivers.
In spite of the fact that the flood of Logone in 1973 was a little higher than that of 1972, there was not any important overflow. El Beid had no water. In August some rainfalls were stagnant in the Yaérés. Ba-Illi had a weak flow due to rainfalls only.
Senegal is always in deficit since 1968. The flood zones are located downstream Bakel. Little information only is available on the importance of the flood along the valley. Since 1971 it does not seem that any noticeable overflow of the river has happened. In 1970 there was a 28 percent deficit for the module; the statistics of the Agriculture Services indicate an area of 31 000 ha approximately, for culture; with a deficit of 22 percent in 1971 the surface becomes 47 500 ha. In 1972 the deficit jumps to 66 percent and there is not possibility of cultivation, that means no overflow; in 1973 where the deficit is almost the same there was no overflow either. The river did stay in its main channel.
1 Verbal information by P. Chaperon, Chief, ORSTOM Hydrological Service, Senegal
ROCHE M. - 1973 - “Les incidences climatiques et hydrologiques de la sécheresse” in Techniques et Développement no 10, Nov. Déc. 1973, pp. 4–15 -
ROCHE M. - 1973 - “Note sur la sécheresse actuelle en AFRIQUE de l'Ouest” in “Report of the 1973 Symposium Drought in Africa” LONDON -
RODIER J.A., ROCHE M. - 1973 - “La sécheresse actuelle en AFRIQUE Tropicale - Quelques données hydrologiques” in Bulletin des Sciences Hydrologiques vol. XVIII, no 4, pp. 411–418 -
CHOURET A. et al. - 1974 - “Les effets de la sécheresse actuelle on AFRIQUE sur le niveau du lac TCHAD” - Cah. ORSTOM, sér. Hydrol., vol. XI, no 1, 1974, pp. 35–45 -
SIRCOULON J. - 1974 - “Les données climatiques et hydrologiques de la sécheresse en AFRIQUE de l'Ouest sahélienne” à publier par “Secretariat for International Ecology” SWEDEN (S.I.E.S.) -
Documentation ORSTOM extraite des banques de données hydrologiques et pluviométriques.
| Station | Area of the basin (km2) | Recording period | Number of recorded years |
| Senegal at Bakel | 218 000 | 1904–1972 | 68 |
| Niger at Koulikoko | 120 000 | 1907–1972 | 66 |
| Niger at Niamey | 700 000 | 1929–1972 | 36 |
| Black Volta at Nwokuy | 15 000 | 1954–1972 | 15 |
| Gorouol at Dolbel | 7 500 | 1961–1972 | 12 |
| Sirba at Garbekourou | 38 750 | 1956–1972 | 14 |
| Maggia at Tsernaoua | 2 525 | 1954–1972 | 17 |
| Goulbi of Maradi at Madarounfa | 5 400 | 1956–1972 | 15 |
| Komadougou at Gueskerou | 120 000 | 1957–1972 | 15 |
| Chari at N'Djamena | 600 000 | 1933–1972 | 37 |
| Logone at Moundou | 33 970 | 1935–1972 | 30 |
Table II
Rainfall features of the main droughts within the different climatic zones
| Stations | Country | Median mm | No. of years | 1913 ? | Minimum | 1913 | 1971 | 1972 | 1973 | |||||
| Height mm | Year | Height mm | Frequency | Height mm | Frequency | Height mm | Frequency | Height mm | Frequ | |||||
| SUB-DESERT CLIMATE | ||||||||||||||
| Faya Largeau | Tehad | 12 | 37 | non | 0 | 35–40–70 | - | - | 18 | 0 57 | 0 4 | 0 10 | 12 | 0 50 |
| Bilma | Niger | 15 | 49 | non | 1 | 40–41 | - | - | 2 | 0 05 | 20 | 0 63 | 0 5 | 0 01 |
| Fada | Tchad | 70 | 40 | non | 0 | 1972 | - | - | 10 | 0 06 | 0 | 0 01 | 8 | 0 04 |
| SAHELIAN CLIMATE | ||||||||||||||
| Agadès | Niger | 150 | 51 | non | 40 | 1970 | - | - | 93 | 0 11 | 74 | 0 05 | 76 | 0 07 |
| Nguigmi | Niger | 190 | 49 | non | 41 | 1928 | - | - | 125 | 0 20 | 69 | 0 05 | 85 | 0 07 |
| Tombouctou-Kabara | Mali | 210 | 60 | oui | 89 | 1966 | 142 | 0 16 | 202 | 0 50 | 107 | 0 04 | 105 | 0 04 |
| Gao | Mali | 260 | 54 | non | 60 | 1931 | - | - | 175 | 0 20 | 163 | 0 14 | 144 | 0 07 |
| Nema | Mauritanie | 280 | 48 | non | 167 | 1928 | - | - | 238 | 0 18 | 250 | 0 29 | 220 | 0 15 |
| Bol | Tchad | 290 | 39 | oui | 46 | 1913 | 46 | (0 01) | 204 | 0 14 | 62 | (0 02) | 152 | 0 12 |
| Boghe | Mauritanie | 310 | 55 | non | 112 | 1972 | - | - | 146 | 0 03 | 112 | 0 01 | 213 | 0 14 |
| Saint-Louis | Sénégal | 330 | 70 | oui | 144 | 1914 | 150 | 0 01 | 177 | 0 08 | 152 | 0 02 | 190 | 0 11 |
| Kiffa | Mauritanie | 350 | 51 | non | 119 | 1972 | - | - | 164 | 0 09 | 119 | 0 01 | 176 | 0 15 |
| Kaedi | Mauritanie | 400 | 50 | non | 120 | 1920 | - | - | 267 | 0 20 | 129 | 0 03 | 218 | 0 09 |
| Tahoua | Niger | 400 | 52 | non | 209 | 1942 | - | - | 267 | 0 07 | 267 | 0 07 | 245 | 0 06 |
| Louga | Sénégal | 420 | 51 | non | 156 | 1972 | - | - | 300 | 0 21 | 156 | 0 01 | 290 | 0 21 |
| Abéché | Tchad | 420 | 39 | non | 307 | 1970 | - | - | 340 | 0 12 | 313 | 0 04 | 188 | 0 01 |
| Zinder | Niger | 490 | 67 | oui | 215 | 1912 | 229 | 0 02 | 352 | 0 11 | 303 | 0 07 | 298 | 0 06 |
| Yang Yang | Sénégal | 500 | 53 | non | 156 | 1972 | - | - | 378 | 0 20 | 156 | 0 01 | 228 | 0 05 |
| Bakel | Sénégal | 500 | 56 | non | 357 | 1954 | - | - | 541 | 0 67 | 394 | 0 17 | 396 | 0 20 |
| Dori | Hte-Volta | 520 | 51 | non | 244 | 1926 | - | - | 427 | 0 15 | 472 | 0 31 | 394 | 0 09 |
| Mopti | Mali | 530 | 51 | non | 360 | 1947 | - | - | 493 | 0 39 | 390 | 0 11 | 326 | 0 01 |
| Bandiagara | Mali | 580 | 53 | non | 315 | 1938 | - | - | 417 | 0 09 | 442 | 0 13 | 526 | 0 33 |
| Niamey | Niger | 580 | 67 | oui | (290) | 1915 | 337 | 0 04 | 370 | 0 08 | 412 | 0 13 | 395 | 0 11 |
| Nioro du Sahel | Mali | 600 | 48 | non | 310 | 1921 | - | - | 341 | 0 03 | 440 | 0 12 | 360 | 0 07 |
| PURE TROPICAL CLIMATE | ||||||||||||||
| Dakar | Sénégal | 500 | 76 | oui | 117 | 1972 | 310 | 0 06 | 367 | 0 12 | 117 | 0 01 | 287 | 0 05 |
| N'Djamena | Tchad | 620 | 50 | oui | 306 | 1913 | 306 | 0 01 | 423 | 0 07 | 618 | 0 41 | 315 | 0 03 |
| Kaya | Hte-Volta | 670 | 54 | non | 479 | 1970 | - | - | 688 | 0 52 | 582 | 0 18 | 759 | 0 68 |
| Kidira | Sénégal | 680 | 50 | non | 385 | 1968 | - | - | 552 | 0 15 | 623 | 0 28 | 410 | 0 03 |
| Kayes | Mali | 690 | 67 | non | 361 | 1898 | - | - | 596 | 0 23 | 485 | 0 04 | 529 | 0 11 |
| Segou | Mali | 710 | 55 | oui | 456 | 1949 | 708 | 0 50 | 510 | 0 05 | 531 | 0 08 | 505 | 0 05 |
| Ouahi-Gouya | Hte-Volta | 720 | 52 | non | 413 | 1947 | - | - | 481 | 0 03 | 502 | 0 05 | 477 | 0 03 |
| Kaolack | Sénégal | 780 | 55 | non | 477 | 1970 | - | - | 850 | 0 62 | 480 | 0 03 | 440 | 0 01 |
| Fatick | Sénégal | 800 | 54 | non | 298 | 1972 | - | - | 803 | 0 50 | 298 | 0 01 | 394 | 0 05 |
| Ouagadougou | Hte-Volta | 810 | 72 | oui | 408 | 1913 | 408 | 0 01 | 717 | 0 27 | 966 | 0 85 | 746 | 0 35 |
| Fada N'Gourma | Hte-Volta | 870 | 53 | non | 569 | 1944 | - | - | 739 | 0 18 | 840 | 0 44 | 730 | 0 14 |
| Koulikoro-Niénébale | Mali | 890 | 51 | oui | 556 | 1972 | 646 | 0 03 | 685 | 0 09 | 556 | 0 01 | 612 | 0 03 |
| Tambacounda | Sénégal | 900 | 53 | non | 476 | 1931 | - | - | 988 | 0 70 | 632 | 0 01 | 718 | 0 20 |
| Dedougou | Hte-Volta | 980 | 51 | non | 670 | 1972 | - | - | 789 | 0 11 | 670 | 0 01 | 649 | 0 01 |
| Léo | Hte-Volta | 1010 | 52 | non | 647 | 1926 | - | - | 1152 | 0 76 | 827 | 0 13 | 748 | 0 07 |
| Bamako | Mali | 1040 | 51 | non | 728 | 1972 | - | - | 1038 | 0 50 | 728 | 0 01 | 868 | 0 23 |
| Bobo-Dioulasso | Hte-Volta | 1110 | 62 | oui | 694 | 1921 | 980 | 0 27 | 964 | 0 22 | 894 | 0 16 | 889 | 0 15 |
| Maïssala | Tchad | 1130 | 36 | non | 900 | 1941 | - | - | 1061 | 0 30 | 1142 | 0 57 | 1026 | 0 24 |
| Kédougou | Sénégal | 1300 | 51 | non | 839 | 1932 | - | - | 1179 | 0 33 | 972 | 0 07 | 1211 | 0 40 |
| Sedhiou | Sénégal | 1350 | 67 | oui | 808 | 1905 | 914 | 0 07 | 1032 | 0 14 | 846 | 0 04 | 1018 | 0 14 |
| TRANSITORY TROPICAL CONDITIONS AND EQUATORIAL TREND | ||||||||||||||
| Bouna | Côte-d'Iv. | 1080 | 54 | non | 350? | 1920 | - | - | 1081 | 0 50 | 936 | 0 25 | 1102 | 0 51 |
| Bouaké | Côte-d'Iv. | 1160 | 60 | oui | 580 | 1919 | 741 | 0 03 | 1268 | 0 67 | 1284 | 0 70 | 928 | 0 18 |
| Guoua | Hte-Volta | 1210 | 58 | oui | 823 | 1947 | 1684? | 0 89 | 1083 | 0 31 | 874 | 0 06 | 981 | 0 16 |
| Bougouni | Mali | 1300 | 53 | non | 805 | 1947 | - | - | 1104 | 0 28 | 908 | 0 07 | 843 | 0 03 |
| Abengourou | Côte-d'Iv. | 1360 | 54 | non | 852 | 1946 | - | - | 908 | 0 03 | 1242 | 0 39 | 1482 | 0 68 |
| Daloa | Côte-d'Iv. | 1410 | 52 | non | 1120 | 1932 | - | - | 1720 | 0 85 | 1283 | 0 34 | 1265 | 0 32 |
| Korkogo | Côte-d'Iv. | 1420 | 48 | oui | 811 | 1961 | 2738? | maxi obs. | 1151 | 0 16 | 994 | 0 10 | 1194 | 0 20 |
| Gagnea | Côte-d'Iv. | 1460 | 51 | non | 899 | 1925 | - | - | 1505 | 0 53 | 1260 | 0 23 | 1441 | 0 48 |
| Boundiali | Côte-d'Iv. | 1510 | 47 | non | 1022 | 1946 | - | - | 1975 | 0 89 | 2058 | 0 92 | 1804 | 0 82 |
| Grand | Côte-d'Iv. | 2050 | 61 | oui | (1470) | 1918 | 2477 | 0 87 | 1637 | 0 17 | 1686 | 0 22 | - | - |
Table III
Evolution of average flow of some African rivers since 1968
| River | Station | Average module (m3/s) | 1968 | 1969 | 1970 | 1971 | 1972 | |||||
| Module m3/s | Deficit or excess % | Module m3/s | Deficit or excess % | Module m3/s | Deficit or Excess % | Module m3/s | Deficit or Excess % | Module m3/s | Deficit or Excess % | |||
| Senegal | BAKEL | 764 | 426 | - 45 | 753 | - 2 | 553 | - 28 | 595 | - 22 | 264 | - 66 |
| Niger | KOULIKORO | 1540 | 1390 | - 10 | 2060 | + 34 | 1110 | - 28 | 1270 | - 18 | 1080 | - 30 |
| Volta Noire | NWOKUY | 36 4 | 35 7 | - 2 | 34 8 | - 5 | ? | ? | 26 8 | - 26 | 17 2 | - 58 |
| Gorouol | DOLBEL | 8 05 | 4 44 | - 45 | 10 9 | + 35 | 7 45 | - 7 | 6 22 | - 23 | 5 62 | - 30 |
| Sirba | GARBEKOUROU | 20 6 | 2 88 | - 86 | 18 5 | - 6 | 10 9 | - 45 | 14 1 | - 29 | 5 96 | - 70 |
| Maggia | TSERNAOUA | 1 34 | 0 44 | - 66 | 1 72 | + 33 | 2 31 | + 79 | 0 78 | - 40 | 0 88 | - 32 |
| Goulbi de Maradi | MADAROUNFA | 6 01 | 2 45 | - 59 | 3 92 | - 35 | 10 8 | + 79 | 4 97 | - 17 | 2 65 | - 56 |
| Komadougou | GUESKEROU | 14 3 | 12 2 | - 15 | 12 3 | - 14 | 14 3 | 0 | 12 1 | - 16 | 7 83 | - 46 |
| Chari | NDJAMENA | 1280 | 1040 | - 19 | 1060 | - 17 | 1180 | - 8 | 993 | - 23 | 578 | - 55 |
| Logone | MOUNDOU | 390 | 401 | + 3 | 493 | + 26 | 430 | + 10 | 308 | - 21 | 215 | - 45 |
Table IV
Hydrological situation of the year 1972
| River | Station | Average maximal flow (m3/s) | Maximal flow 1972 | Frequency | Average annual module (m3/s) | Module 1972 (m3/s) | Frequency | Average minimal flow (m3/s) | Minimal flow 1972 (m3/s) | Frequency |
| Sénégal | BAKEL | 4770 | 1430 | 0 02 | 764 | 264 | ≤0 01 | 2 3 | 0 25 | 0.02 |
| Niger | KOULIKORO | 6260 | 3680 | 0 02 | 1540 | 1080 | 0 15 | 46 3 | 16 0 | <0 01 |
| Niger | NIAMEY | 1860 | 1550 | 0 06 | 1010 | 647 | <0 05 | 75 6 | 2 50 | <0 01 |
| Volta Noire | NWOKUY | 105 | 48 9 | 0 04 | 36 4 | 17 2 | 0 04 | 5 90 | 3 50 | <0 10 |
| Sirba | GARBEKOUROU | 198 | 124 | 0 50 | 20 6 | 5 96 | 0 20 | 0 | 0 | |
| Maggia | TSERNAOUA | 36 0 | 40 0 | 0 65 | 1 34 | 0 88 | 0 40 | 0 | 0 | |
| Komadougou | GUESKEROU | 33 2 | 26 3 | 0 02 | 14 3 | 7 83 | 0 03 | 0 | 0 | |
| Chari | NDJAMENA | 3540 | 1430 | 0 01 | 1280 | 578 | 0 02 | 163 | 48 0 | 0 02 |
| Logone | MOUNDOU | 2110 | 996 | <0 02 | 390 | 215 | 0 03 | 29 3 | 12 0 | 0 04 |
Table V
| Module | Period | Module | Period | Module | Period | |
| Average modules (m3/s) in three consecutive years | ||||||
| Senegal at Bakel | 427 | 40–42 | 435 | 12–14 | 471 | 71–72 |
| Niger at Koulikoro | 1015 | 12–14 | 1060 | 42–44 | 1150 | 70–72 |
| Average modules (m3/s) in five consecutive years | ||||||
| Senegal at Bakel | 455 | 40–44 | 486 | 10–14 | 518 | 68–72 |
| Niger at Koulikoro | 1120 | 40–44 | 1150 | 11–15 | 1380 | 68–72 |
One can notice from Table V that the recent drought in the West African Sahel has not been quite as severe as the drought of the years 1910 to 1914 or 1940 to 1944 on a three or five year scale. Nevertheless, at an annual scale, 1972 or 1973 seem to have been absolute records at the level of annual supply and mainly low water levels. This is illustrated by the absence of water of the Senegal River at Bakel and the collapse of low water level of the Niger downstream the lake basin.
Fig: 3
Fig: 4
