Why worry? Because the ideal sites where streams freely carry water from snow clad mountains now may be exploited, the expansion of irrigation is slowing. Even fields already irrigated are being abandoned as levels in wells sink, soils become salty, and competition for water sharpens. The transfer of water from irrigation to other uses in Colorado and Arizona exemplifies competition's impact on irrigation (Council for Agricultural Science and Technology, 1992[fAST92], 31). The conventional view finds irrigation in trouble.
Figure 9.2.1. The cropland irrigated in the world as reported by ministries of agriculture to the FAO. Solid blocks and lines mark the rise of the absolute area. The percentage rise can be judged from the logarithms shown by circles. A dashed line provides a reference of an annual 2% rise (Food and Agriculture Organization of the United Nations, various years; Higgins et al., 1987). [FotUN][HDA87]
The expansion of irrigated area is a central issue (Figure 9.2.1.). Although estimates of the area vary, the FAO annually tallies the agricultural area purposely provided with water, according to national ministries of agriculture. From about 40 million ha in 1900, this area expanded to 237 million in 1990. Although the absolute area continues to expand, Postel (1992[Pos92], 51) points out that the irrigated area/1,000 people has fallen back to its level of 45 during the 1960s from a maximum of 47 in 1980. Jensen (1993[Jen93]) focused on a decline of the percentage rise in area since about 1975; the slowing relative rise can be seen as the logarithms in the figure rise more slowly than the dashed, reference line for 2%/yr.
Postel and others have cautioned about rising costs and less lending by the World Bank, irrigation's proper role and effect on the environment, and water logging and salinity. She understates her conclusion: ``...The spread of irrigation will not quicken much in the next decade" (Postel, 1992[Pos92], 52).
Crosson and Anderson (1992[CA92]) add to the already long list of reasons that expanding irrigation will be hard: They recur to the sharp competition of urban demands with irrigation.
Less obviously, the potential for reducing management inefficiencies may be less than hoped. For example, farmers pumping from their own wells in India and Pakistan already are efficient. Further, water from an irrigation supply that percolates to an aquifer or reaches a stream and is then recaptured by a pump or a farmer downstream is not lost to a region. So lining canals, for example, to raise efficiency upstream could decrease supply downstream, making the gain in efficiency illusory for the region as a whole.