World agriculture towards 2030/2050: the 2012 revision - Fao

PROOF COPY
The developed countries account for over a fifth of the world’s irrigated area, 68 out of
302 million ha (Table 4.10). Annual growth of their irrigated area reached a peak of 3.0
percent in the 1970s, dropping to 1.1 percent in the 1980s and to only 0.1 percent over the last
decade for which data are available (1997-2007). For the developed countries as a group only
a very marginal expansion of the irrigated area (supplemented with improvements on existing
areas) is foreseen over the projection period so that the world irrigation scene will remain
dominated by events in the developing countries. In terms of annual growth, the projected net
increase in land equipped for irrigation would represent a sharp slowdown as compared with
the historical growth. The projected slowdown which applies to most countries and regions,
reflects the projected lower growth rate of crop production combined with the increasing
scarcity of suitable areas for irrigation and of water resources in some countries, as well as the
rising costs of irrigation investment.
Most of the expansion of irrigated land is achieved by converting land in use in rainfed
agriculture into irrigated land. Part of irrigation, however, takes place on arid and hyper-arid
(desert) land which is not suitable for rainfed agriculture. It is estimated that of the 235
million ha irrigated at present in developing countries, some 39 million ha are on arid and
hyper-arid land which could slightly increase over the period to 2050. In some regions and
countries, irrigated arid and hyper-arid land forms an important part of the total irrigated land
presently in use: 17 out of 31 million ha in the Near East/North Africa, and 16 out of 90
million ha in South Asia.
For the purpose of this study a distinction was made between the area equipped for
irrigation and the irrigated area actually in use. Areas equipped might be temporarily or even
permanently out of use for various reasons, including for maintenance, or because of
degradation of irrigation infrastructure or since the area does not need to be irrigated in a
particular year (the latter occurs often in developed countries with temperate climates where
sprinkler irrigation is practiced only in dry summers). The percentage of the area equipped
actually in use differs from country to country and could range from a low 40 to a high 100
percent, but on average over all countries is at present about 85 percent (expected to increase
very slightly to 86 percent in 2050). So out of the 235 million ha equipped for irrigation in the
developing countries in 2005/07, some 201 million ha were assumed to be in use increasing to
220 million ha in 2050 (253 million ha equipped; see also Figure 4.9).
Although the irrigated area in use in developing countries would rise by 2050 by ‘only’
10 percent (from 201 to 220 million ha from 2005/07 to 2050), the harvested irrigated area
could expand by 34 million ha (or 12 percent) due to a continuing increase in multiple
cropping on both existing and newly irrigated areas (from 137 to 141 percent in 2050) and
would account for well over a quarter of the total increase in harvested land (Table 4.9).
One should bear in mind that the projected expansion of irrigated land by 20 million ha is
the increase in net terms. It assumes that losses of existing irrigated land due to, for example,
water shortages or degradation because of salinization and water-logging, will be compensated
for through rehabilitation or substitution by new areas for those lost. The few existing historical
data on such losses are too uncertain and anecdotal to provide a reliable basis for drawing
inferences about the future. In investment terms, rehabilitation of existing irrigation schemes will
represent the bulk of future expenditure on irrigation: if it is assumed that 2.5 percent of existing
irrigation must be rehabilitated or substituted by new irrigation each year, that is, if the average
life of irrigation schemes were 40 years, then the total irrigation investment activity over the
projection period to 2050 would include some 172 million ha, of which nearly 90 percent would
be for rehabilitation or substitution and the balance for net expansion.
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