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There is growing concern about food security in Africa and especially in sub-Saharan Africa. While the aggregate global food supply/demand picture is relatively good, there will be a worsening in food security in sub-Saharan Africa and cereal imports are projected to triple between 1990 and 2020; imports for which the region will not be able to pay. Although the food situation is less severe in north Africa, projections here too indicate increasing cereal imports to 2020 [24].
Africa, with the exception of the Congo/Zaire river basin, is the driest continent (apart from Australia) and suffers from the most unstable rainfall regime. Droughts are frequent in most African countries and each year more people are at risk from the effects of inevitable droughts of greater or lesser severity. Furthermore, Africa's water resources are relatively less developed than those in other regions.
Agricultural productivity per caput in sub-Saharan Africa has not kept pace with population increase, and the region is now in a worse position nutritionally than it was 30 years ago: food production has achieved a growth of about 2.5% per year, while population has risen at a rate of over 3% per year. In the past, additional food in Africa came from increase in the area cultivated, but as good land becomes less available, the region will be forced to increase yields. Both rainfed and irrigated agriculture will need to be intensified, but irrigated agriculture has a higher potential for intensification.
Global estimates indicate that irrigated agriculture produces nearly 40 % of food and agriculture commodities on 17% of agricultural land. At present in Africa, about 12.2 million hectares benefit from irrigation1, which is equal to only about 8.5% of the cultivated land [21a]. In sub-Saharan Africa, only about 10% of the agricultural production comes from irrigated land. Trends in irrigated land expansion over the last 30 years show that, on average, irrigation in Africa increased at a rate of 1.2% per year. However, this rate began to fall in the mid-1980s and is now below 1% per year, but varies widely from country to country [8].
1This includes irrigation schemes with full or partial control (11.5 million ha), spate irrigation (0.5 million ha) and wetland and inland valley bottoms, that are equipped for water control (0.2 million ha). Another 2 million hectares benefit from other minor kinds of water management, mainly flood recession cropping (1 million ha) and wetland cropping (1 million ha). In addition, water harvesting methods are becoming more widespread.
While it is true that there still exists considerable potential for the future expansion of irrigation, it is also true that water is growing scarcer in those regions where the need for irrigation is greatest. Over half of the total water withdrawal takes place in the northern, drier part of Africa. Moreover, in this part the withdrawal for domestic and industrial uses will grow fastest, though it will also grow in sub-Saharan Africa in the coming years, as a result of the rapid urbanization.
To enable careful planning of the development of the water resources, especially for agriculture, which is by far the largest water user, a good knowledge of the irrigation potential for the African continent is necessary. This is the subject of the present study.
In the past, several studies have already attempted to assess the irrigation potential for Africa.
In 1987 FAO conducted a study to assess the land and water resources potential for irrigation for Africa on the basis of river basins and countries [20]. It was one of the first GIS-based studies of its kind at continental level. It proposed a natural resources based approach to assessing irrigation potential. Its main limitation was in the sensitivity of the criteria for defining land suitability for irrigation and in the water allocation scenarios needed for the computation of the potential.
In 1995 another study was conducted by FAO as part of the AQUASTAT programme, which is a programme of collection of secondary information on water resources and irrigation by country. A survey was carried out for all African countries, in which information on irrigation potential was systematically collected from master plans and sectoral studies [21a]. Such an approach integrates many more considerations than a simple physical approach to assessing irrigation potential. However, it cannot account for the possible double counting of water resources shared by several countries.
The present study has taken the above limitations into consideration. It concentrates mainly on a quantitative assessment based on physical criteria (land and water), but relies heavily on information collected from the countries. A river basin approach has been used to ensure consistency at river basin level. Where country information was unavailable or incomplete, potential was assessed on the basis of available information on land and water resources at regional and continental level. The FAO Geographic Information System (GIS) facilities were extensively used for this purpose.
A physical approach to irrigation potential must be understood as setting the global limit for irrigation development. Future developments will be dictated by a whole set of factors, including political choices, investment capacity, technological improvement . and environmental requirements.
Chapter 2 of this report describes the methodology and data used for the assessment of the irrigation potential. Chapters 3 to 7 refer to a series of detailed studies conducted in the framework of this study. Chapter 3 summarizes the assessment of the soil and terrain suitability for irrigation. Chapter 4 gives a brief review of the African water resources [21]. The computation of irrigation water requirements is summarized in Chapter 5. The main component of the present study, the review of existing information on irrigation potential by basin and country and its cross-checking with the results of the studies of Chapters 3, 4 and 5, is summarized in Chapter 6. Chapter 7 summarizes some environmental considerations in the development of irrigation, though without presuming to be exhaustive on these complex issues. The general results and conclusions are presented in Chapter 8. Finally, a list of the main sources of information is presented by country.