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).
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.
Country |
Irrigation potential |
Area under irrigation |
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 |
C�te 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.
FIGURE 2
Distribution of basement aquifers in Africa