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Avenir du fleuve Niger

 | 
Jérome Marie
, 
Pierre Morand
, 
Hamady N’Djim

English Version

Introduction

Texte intégral

THE PLAN FOR THIS SYNTHESIS

1This review involved answering the six questions raised by the main public-sector agencies in charge of monitoring and administrating the Niger River in Mali (see appendix 1). As the questions spanned a very eclectic variety of issues, we decided against answering them one by one at first. Doing so would have entailed considerable needless repetition and neglected the fact that several of the questions (and hence answers) are indeed interdependent. So this report was based on the more integrated and reasonably linear approach detailed below.

2This introduction ends with a general background on the river and its environment. The following section provides an in-depth review of what scientists and experts know about the current situation and about trends unfurling in the river’s and its basin’s socio-ecosystem (SES). This firstly includes the “major motor variables” springing from general dynamics and “imposing themselves” on the system. Here, we will look at population increase and at the commensurate rise in food and energy requirements, and then at the climatic dynamics at work in this part of Africa. Next, we will describe the current situation and trends shaping the way in which this river’s resources (its water, as well as its surrounding areas and ecosystems) are used in Mali (the “river usage systems”). This chapter will include an overview of the schemes used for power generation, farming, fishing, livestock farming, household and industrial use of water, and navigation. We will review these usage systems in the light of their weight in the country’s economy, productivity, and their toll on this river’s water. Then we will review what the scientific community knows about the current situation and trends at work in the Niger River’s ecosystem from a broader perspective, covering surface and underground water availability and quality, geomorphological stability, soil fertility, vegetation and flora, fish population and wildlife. The last chapter in this section reviews the agencies administrating these resources, the instruments they use and the way in which they use them today.

3The third section uses the above information to provide a concise analysis of the issues – ranked as hazards, tensions and threats – facing agencies administrating the Niger River’s resources. These issues often arise because human factors and natural factors (i.e. requirements and impacts) clash. Several of the problems we will analyse in that light, as we will see, are closely correlated to the questions in the framework.

4The fourth (and last) section discusses a number of management instruments and choices that might better address the identified problems, while tackling environmental issues and allowing the people living around the Niger River in Mali to look forward to the future more serenely.

5The information in these four sections will address the six framework questions as comprehensively and as clearly as is possible. However, readers who are only interested in one of those six questions will find the answers using table 1.

OVERVIEW

Mali

6Mali is situated between latitudes 10°30 and 25°00, and longitudes 12°00 west and 4°00 east. This landlocked West African country spans 1,240,000 km2 across Saudi, Sahel and desert zones. The dry season there lasts 6 to 9 months. The short rainy season brings practically all of Mali’s rainfall. Its fairly uniform landscape encompasses plateaux and plains, with well-developed dune systems in the north and east. The Niger River winds southwest to northeast across the southern half of Mali.

7The Niger River in general, and the Middle Niger River in particular, played a considerable role in West Africa’s history. Djenne, one of the cities alongside it, was founded some 2,000 years ago. Under the Mali Empire (13th century), it played a prominent part in trans-Saharan trade between the day’s Arabic States and the Mediterranean. Its wealth came from gold, salt and slave trading, and its eminence crested between 1450 and 1650, during the Gao Empire’s apogee. The early 16th century, however, saw the gold trade shift to Portuguese bases in the Gulf of Guinea, and the Gao Empire’s ensuing downfall. Its capital fell to a Moroccan military campaign in 1591. The Middle Niger lost its central role on trans-Saharan trade routes, but nonetheless continued to serve as a hub for regional salt, rice, fish and livestock commerce. In the 19th century, before colonisation, the Niger River’s inland delta was the base of one last realm, the Peul Empire of Massina (1818-1862). This empire instigated a remarkable form of territorial organisation – and its handed-down traditions still have a strong bearing on livestock farming today. Its traditions indeed laid down the rules for land, water and natural-resource management that people here still refer to today (Gallais, 1967).

Table 1 – Correspondance table questions/main answers

Table 1 – Correspondance table questions/main answers

The Niger River

8The Niger River stretches some 4,200 km from its source in Guinea to its mouth in Nigeria. Its upper and middle reaches cover 1,700 km and cross Mali, heading northeast, east, and then south across the border into Niger. In Mali, its tributary basin spans about 300,000 km2 (which is 20% of the total basin surface).

9The Niger is a tropical river and sees very sharp seasonal and year-to-year flow variations. In Mopti, for example, common flow readings can swing one-hundred-fold from less than 30 m3/s to more than 3,000 m3/s. Beyond Mopti – excluding the Yamé, a tributary from the Bandiagara plateau – only a handful of tributaries feed into the Niger until it flows through Niamey. These minor tributaries (the Gorouol, Dargol and Sirba) only have a marginal impact on the Niger’s flow (so it is fair to say that the Niger crosses the desert in this area). Not unlike the Nile’s stretch across the Eastern Sahara, the Niger loses half its water in this stretch.

10The seasonal rain feeding the Niger’s upper and middle reaches falls at very regular intervals, but the amount of water it brings can vary considerably from one year to the next. This swell crests in September in Bamako, in October or early November in Mopti, in December in Kabara (Timbuktu) and in late January in Gao. The flooding recedes until December, January or February going downstream. The sharp low-water stage then continues until May, June or July. Downstream regions (Gao in Mali or Niamey in Niger) have seen water levels drop to very low levels. In Niamey, for instance, levels slumped to 20 m3/s in 1943, 1944, 1945, 1947, 1948 and 1950, and the flow practically dried up in 1975/76 and 1984/85.

Figure 1. Annual water level cycles at Ké-Massina (Middle Niger, Mali)
The Niger River, it is also important to point out, is Mali’s main source of water: its flow can reach 46 billion m3 a year in Koulikoro, compared to the Senegal River’s 10 billion m3 a year in Kayes.

The Niger River’s inland delta

11The Niger River’s inland delta – still also referred to as the “central delta” or “cuvette lacustre” (lake basin) – is one of Mali’s most remarkable hydrographic features. This vast 40,000 km2 flooding area stands nestled in the semi-arid Sahel, stretching more than 350 km from Ké-Massina (southwest) and Timbuktu (northeast). It is situated between parallels 13 and 17 north and meridians 2°30 and 6°30 west. It hosts a very dense and hierarchical network of distributaries fed by the Niger River and the Bani, a tributary that flows into it near Mopti. Between Ké-Massina and Lake Debo, this inland delta comprises a series of potholes and plains that flood every year (provided the swell is substantial enough). This is one of Africa’s wettest areas. After Lake Debo, naturally-occurring dunes haphazardly feed water through a vast web of thoroughfares and into a number of lakes.

Figure 2. Mali (inset), the Niger River and the inland delta (oval)

The weather

12Two large subtropical anticyclones govern the seasons: the northeast-southwest Sahara anticyclone produces the hot and dry Harmattan winds, and the Saint Helen anticyclone produces the southwest/northeast warm and very damp monsoon. The hot and dry northerly Harmattan and the damp southerly monsoon meet in the Inter-Tropical Convergence Zone (ITCZ). Its trace on the earth’s surface is called the Inter-Tropical Front (ITF), and rain is associated with its passage. The ITF follows a roughly south-north-south pattern through the year. July, August and September find it in the north, December, January and February in the south. The ITF moves north slowly and erratically over a six-month period, but only takes four months to travel back towards the equator.

13These atmospheric cycles dictate Mali’s climatic year. The dry season lasts nine months in the north and five or six months in the south; the rainy season starts in April and finishes in October in the south of Mali, but only begins in July and ends in September in the north. Rain at the beginning and end of the rainy season is mostly easterly, and linked to particularly important squall lines in the Sahel latitudes. During the dry season, north-easterly winds dry the air and magnify the heat that blankets Mali in April and May.

14Total monthly and annual rainfall (over 1,400 mm a year south of Sikasso and under 100 mm a year in Tessalit) decline gradually as latitudes rise. Evapotranspiration (over 1,700 mm a year south of Sikasso and more than 2,500 mm a year in Tessalit) runs in the opposite direction. In all cases, however, rainfall peaks in August.

15We usually cut this area into four zones to characterise this climatic gradient, as follows:

  • the Sudano-Guinean zone (south of the line between Bougouni and Sikasso and spanning the Upper Niger and High Bani), where over 1,100 mm of rain fall over seven or eight months a year;
  • the Saudi zone (on and around a line between Bamako, Segu and San), where it rains between 1,100 and 600 mm for less than six months a year;
  • the Sahel zone (north of Mopti and across the Niger’s inland delta and oxbow), where it rains between 600 and 100 mm during only three months a year (from mid-June to mid-September);
  • the Sahara or desert zone (north of the line between Timbuktu and Bourem), where it rains less than 100 mm a year. The scant tropical rain falls between June and September. Cold-season rain sometimes falls in January or February.

Table des illustrations

Titre Table 1 – Correspondance table questions/main answers
URL http://books.openedition.org/irdeditions/docannexe/image/5194/img-1.jpg
Fichier image/jpeg, 276k
Légende Figure 1. Annual water level cycles at Ké-Massina (Middle Niger, Mali)The Niger River, it is also important to point out, is Mali’s main source of water: its flow can reach 46 billion m3 a year in Koulikoro, compared to the Senegal River’s 10 billion m3 a year in Kayes.
URL http://books.openedition.org/irdeditions/docannexe/image/5194/img-2.jpg
Fichier image/jpeg, 49k
Légende Figure 2. Mali (inset), the Niger River and the inland delta (oval)
URL http://books.openedition.org/irdeditions/docannexe/image/5194/img-3.jpg
Fichier image/jpeg, 167k

© IRD Éditions, 2007

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