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Chapter 1

Food security and irrigation

The outlook for the food security of many developing nations is a cause for serious concern. Widespread denudation and accelerated erosion diminish the productivity of both cultivated and grazed rain-fed lands. Especially vulnerable are semi-arid regions to climatic instability and frequent droughts. At the same time, depletion and pollution of limited freshwater resources and competing demands for water - among neighbouring states as well as between different sectors within each state - constrain the further expansion of irrigation.

The problem of food security is exacerbated by the rapid growth of population and hence of the demand for food. In fact, the prices of foodstuffs in the world market have recently begun to rise. Beyond that looms the spectre of a fundamental change in climate (a consequence of the enhanced greenhouse effect), that may increase the severity and variability of weather and thus disrupt established systems of production. Such a change could require expensive invest-ments in modifying existing systems and establishing new ones.
All these problems are particularly acute in the continent of Africa, parts of which are already in the throes of a severe population-environment crisis. The population of sub-Saharan Africa, now nearing 600 million, is projected to double by the year 2020. Therefore, a much greater effort must be made by the international community to assist the African nations in the difficult task of improving their prospects for food security (Figure 1).

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FIGURE 1
Water availability in Africa

Source: Irrigation and water resources potential for Africa, FAO (1987).

Clearly, irrigation can and should play an important role in raising and stabilizing food production, especially in the less-developed parts of Africa south of the Sahara. There are, however, many obstacles to the rapid development of irrigation there. Large parts of the region have only limited freshwater resources. In other areas, potential resources are insufficiently known to permit reliable planning. Even where water resources are definitely known to be substantial, other conditions may not be conducive to irrigation development. Such conditions may include unfavourable topography and soils, distant markets and inadequate infrastructure, as well as lack of credit, labour, information and other services to farmers.
These problems, while real, do not entirely explain the historical failure to develop the full irrigation potential of sub-Saharan Africa. The data available (Table 1) on that potential suggest that it is considerable. By some estimates it may be as great as 30 million hectares, whereas other estimates project less than 10 million hectares. A reasonable figure may be in the order of 15 to 20 million hectares which, if fully developed and properly managed, could contribute significantly to the food security of the African continent. The fact that some earlier efforts at irrigation development produced disappointing results may be more the consequence of flaws in approach and implementation than of truly insurmountable obstacles. The time is ripe for a new approach.
Irrigation is the supply of water to agricultural crops by artificial means, designed to permit farming in arid regions and to offset drought in semi-arid regions. Even in areas where total seasonal rainfall is adequate on average, it may be poorly distributed during the year and variable from year to year. Where traditional rain-fed farming is a high-risk enterprise, irrigation can help to ensure stable production.

TABLE 1

Sub-Saharan Africa: estimates of irrigated areas in relation to potential, 1991

Country

Irrigation potential
(ha)

Area under irrigation
(ha)

Total in % of potential

Angola

3 700 000

75 000

2.0

Benin

300 000

10 236

3.4

Botswana

14 640

1 381

9.4

Burkina Faso

164 460

24 330

14.8

Burundi

185 000

14 400

7.8

Cameroon

290 000

20 970

7.2

Cape Verde

2 990

2 779

92.9

Central African Republic

1 900 000

135

0.0

Chad

835 000

14 020

1.7

Comoros

300

130

43.3

Congo

340 000

217

0.0

Côte d'Ivoire

475 000

72 750

15.3

Djibouti

1 000

674

67.4

Equatorial Guinea

30 000

-

-

Eritrea

187 500

28 124

15.0

Ethiopia

3 637 300

189 556

5.2

Gabon

440 000

4 450

1.0

Gambia

80 000

1 670

2.1

Ghana

1 900 000

6 374

0.3

Guinea

340 000

15 541

4.6

Guinea-Bissau

281 290

17 115

6.1

Kenya

353 060

66 610

18.9

Lesotho

12 500

2 722

21.8

Liberia

600 000

2 100

0.4

Madagascar

1 500 000

1 087 000

72.5

Malawi

161 900

28 000

17.3

Mali

566 000

78 620

13.9

Mauritania

165 000

49 200

29.8

Mauritius

20 000

17 500

87.5

Mozambique

3 072 000

106 710

3.5

Namibia

47 300

6 142

13.0

Niger

270 000

66 480

24.6

Nigeria

2 330 510

232 821

10.0

Rwanda

159 000

4 000

2.5

Sao Tome and Principe

10 700

9 700

90.7

Senegal

340 000

71 400

21.0

Seychelles

1 000

-

0.0

Sierra Leone

807 000

29 360

3.6

Somalia

240 000

200 000

83.3

South Africa

1 445 000

1 270 000

87.9

Sudan

2 784 000

1 946 200

69.9

Swaziland

93 220

67 400

72.3

Tanzania, United Rep.

990 420

150 000

15.1

Togo

180 000

7 008

3.9

Uganda

202 000

9 120

4.5

Zaire

7 000 000

10 500

0.2

Zambia

523 000

46 400

8.9

Zimbabwe

388 400

116 577

30.0

Sub-Saharan Africa

39 366 490

6 181 422

15.7

Source: Irrigation in Africa - a basin approach, FAO (in press).

Irrigation has long played a key role in feeding expanding populations and is undoubtedly destined to play a still greater role in the future. It not only raises the yields of specific crops, but also prolongs the effective crop-growing period in areas with dry seasons, thus permitting multiple cropping (two or three, and sometimes four, crops per year) where only a single crop could be grown otherwise. With the security provided by irrigation, additional inputs needed to intensify production further (pest control, fertilizers, improved varieties and better tillage) become economically feasible. Irrigation reduces the risk of these expensive inputs being wasted by crop failure resulting from lack of water.
The practice of irrigation consists of applying water to the part of the soil profile that serves as the root zone, for the immediate and subsequent use of the crop. Well-managed irrigation systems are those which control the spatial and temporal supply of water so as to promote growth and yield, and to enhance the economic efficiency of crop production. Such systems apply water in amounts and at frequencies calibrated to answer the time-variable crop needs. The aim is not merely to optimize growing conditions in a specific plot or season, but also to protect the field environment as a whole against degradation in the long term. Only thus can water and land resources be utilized efficiently and sustainably. On the other hand, poorly managed irrigation systems are those which waste water and energy, deplete or pollute water resources, fail to produce good crops and/or pose the danger of soil degradation.
The vital task of increasing and stabilizing food production in drought-prone regions must therefore include a concerted effort to improve on-farm water management. Some traditional irrigation schemes need to be modernized so as to achieve higher yields as well as better resource utilization. New schemes being planned should likewise be based on sound principles and techniques for efficient water use and for optimizing irrigation in relation to all other essential agricultural inputs and operations.
In recent decades, revolutionary developments have taken place in the science and art of irrigation. A more comprehensive understanding has evolved regarding the soil-crop-water regime as affected by climatic, physiological and soil factors. These conceptual developments have led to technical innovations in water control that have made possible the maintenance of near-optimal moisture and nutrient conditions throughout the growing season.
Foremost among these innovations are techniques for high-frequency, low-volume, partial-area applications of water and of nutrients at rates calibrated to satisfy crop needs. Such methods are now applied on a large scale in industrialized countries, where they tend to be highly mechanized and to rely on energy-intensive labour-saving technologies. However, they need not necessarily depend on expensive manufactured equipment and intensive energy inputs. Instead, they can be simplified to fit the special low-capital circumstances of the less-developed countries. Moreover, they are flexible enough to permit downscaling in order to fit the requirements of small-scale farmers.
Properly applied, the new irrigation methods can raise yields while minimizing waste (by runoff, evaporation and excessive seepage), reducing drainage requirements and promoting the integration of irrigation with essential concurrent operations (fertilization, tillage and pest control). The use of brackish water has become more feasible, as has application to sandy, stony or steep lands previously considered unirrigable. Other potential benefits include increased crop diversification and cropping intensity.
Despite all the new advances and promising possibilities, wasteful practices still persist in many irrigated areas. In some places, inefficiency is perpetuated by fixed, institutionally imposed standards that foster unmeasured and typically excessive applications of water. Such inflexible regimes offer farmers no incentive to improve water management and even discourage them from taking independent initiatives to do so. However, institutional inertia and rigid patterns are only part of the problem. Some of the new irrigation systems developed in the industrialized countries are in fact too complex, energy-intensive, dependent on expensive imported equipment and large in scale to be directly applicable to the low-capital, low-technology circumstances of the less-industrialized countries, where farming is often practised on a small scale and the relative costs of labour and capital are very different.
Hence, ready-made modern technology often fails when introduced arbitrarily into developing countries. Elaborate and expensive systems (such as large centre-pivot booms and even drip-irrigation assemblies complete with automated pumps, filters, pressure regulators, metering valves and fertilizer injectors), imported and installed in the grand hope of achieving instant modernization, typically fail for lack of expert maintenance and spare parts. Such installations can quickly become white elephants - idle monuments to hasty "progress" relying on ill-adapted technology.
Instead of introducing prepackaged hardware systems, developers should apply the best principles of efficient irrigation, in so far as possible using indigenous skills and materials. Rather than simply transfer Western technology as such, the aim should be to adapt or redesign technology flexibly so as to suit the prevailing conditions and requirements.

 

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FIGURE 2
Distribution of basement aquifers in Africa

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