General summary

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Water resources
Withdrawals
Irrigation potential
Water managed areas
Irrigated crops
Rate of use of equipped areas
Environment and health

The 53 African countries have been grouped into seven regions on a basis of geographic and climatic homogeneity, which has a direct influence on irrigation. These regions, presented in Figure 1, are referred to as the Northern, the Sudano-Sahelian, the Gulf of Guinea, Central, Eastern, Indian Ocean islands, and Southern. This section briefly presents the particularities which can be observed at national and regional level, as well as trends which emerge from the information which was collected.

Water resources

The survey concentrated mostly on renewable resources. Distinction is made between the water resources generated from precipitation falling on the territory of the country or internal renewable resources, and global renewable resources which includes transfers from neighbouring countries (mostly through rivers). In both cases, the figure represents the maximum potential water resource irrespective of development potential, such as regulation of stream flow, or extractable groundwater.

Table 1 presents, for each region, data relative to internal resources and compares these results with precipitation figures. The ratio between these two figures can be assimilated to some kind of "runoff coefficient" which would take into account recharge of that portion of the aquifers which are not connected to the river network. At regional level, this coefficient varies from 6% in arid areas to 32% in the humid zones of the Gulf of Guinea and 34% in Madagascar. Data collected in the countries show that the coefficient varies from 2% in arid countries like Libya, Niger or Botswana, up to extreme values higher than 80% in the most humid areas of Sierra Leone and Liberia. Although they cover the largest part of the continent, the Northern and Sudano-Sahelian regions contribute only respectively 1.2% and 4.3% of the total water resources of Africa. The Southern region also shows a very low runoff coefficient (9%).

Withdrawals

Table 2 shows the distribution of water withdrawals by region between the three major sectors of water use: agriculture, communities and industries. Water requirements for navigation, fisheries, mining, environment and recreation, although they can represent a significant part of the water resources, have a very low net consumption rate and are computed in very different manners by the countries, which complicates the regional analyses. For these reasons, they are not included in the computation of regional withdrawals but they appear, when available, in the country profiles.

For the continent as a whole, about 85% of water withdrawals are directed towards agriculture but this figure varies considerably from one region to another. Arid regions, where irrigation plays an important role in agriculture, have the highest level of water withdrawal for agriculture. The Northern region alone represents more than half of the agricultural withdrawal of the continent. In contrast, the humid regions show the lowest agricultural withdrawals: 62% for the Gulf of Guinea and 43% for the Central region, where it is the same as domestic use.

The percentage of water withdrawal over internal renewable water resources is an indicator of the importance of transfers for some countries. Libya, Tunisia, Morocco and Algeria have almost no transfer from other countries. The rate of utilization of water resources is high. This situation requires a very strict management of the resources and leads to a competition between the sectors of water use. In Libya, annual water withdrawal is higher than the volume of renewable resources, the difference coming from non-renewable resources (fossil water). Egypt and Mauritania also withdraw more water than is produced on their territory, but benefit from transfer from other countries through the Nile and Senegal rivers respectively. Niger, Somalia, Eritrea and Chad, in the Northern hemisphere, and Namibia and Botswana in the South, have few internal renewable resources but benefit from important transfers. In these countries, withdrawal is still less than their internal resources, but some of it is already taken from incoming water.

TABLE 1
Regional distribution of water resources

Sudan, South Africa and Swaziland have high rates of use of their internal resources, but benefit from important resources and significant amounts of incoming water.

Wastewater treatment and reuse (Tunisia, Egypt and Morocco) and desalinated water (Cape Verde, Egypt, Libya, Mauritania and South Africa) are also indicators of scarce water resources.

Irrigation potential

Due to its close relationship with water resources, irrigation potential is also unevenly distributed between the regions. It is significant to observe that this value is much less known and studied in countries benefitting from important water resources than in more arid countries. It should also be noted that the important transfers of water resources from humid to arid regions allow these latter to benefit from an irrigation potential much larger than their internal water resources would permit. This is the case of the regions traversed by the rivers Senegal, Chari and Niger in West Africa; Nile, Juba and Shebele in Eastern Africa; and Limpopo, Orange and Zambezi in Southern Africa, to name some of the most important.

TABLE 2
Regional distribution of water withdrawal

The existence of inter-regional rivers and the transfers of water they implu hampers the computation of irrigation potential on a regional basis. In the same way, the computation of irrigation potential as it is presented in Table 5 may lead to a double counting of part of the shared resources, which could be avoided only through a river-basin approach. It should be noted also that the methods used in estimating irrigation potential vary from country to country, and that the choice of method can significantly affect the result, especially in humid countries. Estimates for Zaïre, for instance, vary from 1 to 40 million hectares, and irrigation potential of Congo, estimated at around 40 000 hectares in the literature, is probably only a small portion of the physical potential of the country.

Bearing in mind these uncertainties, one can notice that seven countries concentrate about 60% of the irrigation potential of Africa (Angola, Sudan, Egypt, Zaire, Ethiopia, Mozambique and Nigeria), while at the other end of the list, 18 countries share only 5% of this potential.

Water managed areas

The diversity of water management situations encountered in Africa requests the choice of a classification which would best represent the situation of irrigation in each country. The land on which water is used for the purpose of agricultural production has been called in the text wafer managed areas. The term irrigated areas has been limited to that part of the water managed areas equipped with hydraulic structures: full or partial control irrigation, equipped wetland or valley bottoms and areas equipped for spate irrigation (see Table 3). The difference between the two categories comprises cultivated wetland and valley bottoms without irrigation equipment and recession cropping areas.

Water managed areas comprise 14.3 million ha in Africa. There is a very heterogenous geographical distribution of water managed areas: the North represents more than 40% of the total. The part of water managed areas in national agriculture varies from less than 1% of cultivated land (Zaïre, Uganda, Ghana, Togo and Comoros) to 100% in the most arid countries (Egypt and Djibouti, where agriculture is impossible without irrigation). This distribution of water managed areas shows clearly the relation between climate and the role of irrigation in agriculture. In Equatorial Africa, where precipitation is greatest, rainfed agriculture is dominant. Irrigation is used for winter cropping, rice cultivation, to secure high value crops, or in wetlands and inland valleys. In Madagascar, rice cultivation on the plateaus is very developed, which explains the high percentage of irrigation in that country even though rainfall is relatively favourable.

At national level, the distribution of water managed areas is very uneven. Five countries (Egypt, Sudan, South Africa, Morocco and Madagascar), which cover 19% of Africa, hold more than 60% of the water managed areas. By adding Nigeria, Algeria, Libya, Angola and Tunisia, more than 80% of the water managed area is controlled by 10 countries. In contrast, 28 countries, covering more than 30% of Africa, share a mere 5% of water managed lands.

Among the five classes of water management presented in Table 3, one can notice that full or partial control irrigation is the most widespread (81% of the area). Among the other classes of water management, cultivated wetlands and valley bottoms and recession cropping are a majority (15% of the total). Apart from full and partial control irrigation, present in almost all countries, the other categories are usually concentrated in a few countries. Recession cropping is used essentially on the rims of the rivers Niger and Senegal and of their tributaries, or along the Logone, Chari, Zaïre, Molopo and Okavango. The fadamas of Northwestern Nigeria, classified here as recession cropping due to lack of detailed information on their degree of development, represent 70% of that category. Spate irrigation is concentrated in the Maghreb and the Horn of Africa.

When analysing irrigation techniques used in the full and partial control schemes, Table 9 shows that surface irrigation is by far the most widely used technique (more than 80% of the total). However, more than one million hectares of irrigation by aspersion have been reported, most of it being concentrated in the North (Libya, Egypt, Morocco, Tunisia), in Zimbabwe, in South Africa and, to a lesser degree, in Kenya and Zambia. In relative terms, aspersion represents the most widely used technique in Botswana, Zimbabwe and South Africa, which benefit from a relatively long tradition in this field. Finally, the most important areas under micro-irrigation are concentrated in Egypt and South Africa.

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