|Social and Environmental Aspects of Desertification (UNU, 1980, 38 pages)|
Desertification of the environment is generally related to man's attempts to earn a living in the drylands. In the southwestern United States, desertification is commonly associated with irrigated farming and grazing, activities which formed the basis of original settlement but which are not perhaps well adapted to the present environment, and are indeed now of relatively little importance in terms of gross production from the area. This topic was discussed by a panel of Tucson scientists, with particular but not exclusive reference to the local region.
Economics of Irrigation Agriculture
Dr. William E. Martin of the Department of Agricultural Economics, University of Arizona, described the low return from water used for agricultural crops compared with other uses, and the cost-limitation in moving water uphill or over long distances as an agricultural input. He stressed the need for greater use of cost-benefit analysis in the assessment of development projects, in addition to the usual environmental impact statements, referring to economics as "the conscience of arid lands research." Case-studies from a variety of arid areas were reviewed as illustrations of economic irrationality in water development.
In Arizona, the first US Bureau of Reclamation project, namely the Salt-River Project, was probably justified. But current construction of the Central Arizona Project is not rational. With the high energy costs involved in a water lift of 600 m, estimated returns could justify an investment of not more than US$100 million, and certainly not US$2000 million.
Similarly, Dr. Martin criticized the proposed Northwest Project in the Sonoran Desert of Mexico, based on interbasin transfer. An analysis of the project had indicated that it was not economically justified on the basis of net benefits to either traditional or commercial agriculture.
Problems in the Cuyo region of Argentina are similar, in that agriculture is demanding large amounts of cheap water. The need is to save water for subsequent investment in less waterintensive activities. The existing policies, whereby individual self-interest encourages public investment in irrigation facilities, actually result in slower economic growth.
Martin also cited findings in Australia which question the economics of further extension of irrigation agriculture. He stressed the need for agriculture to adapt to aridity rather than attempt to eliminate it, and affirmed that the problems of water shortage in relation to irrigation agriculture are largely manmade.
Dr. Martin M. Fogel of the Department of Watershed Management, University of Arizona, was even stronger in his warning concerning the drawbacks of irrigation development. Drawing on experiences in Saudi Arabia and Egypt, he concluded that projects for water resources development must consider social accounting and environmental protection equally with economic considerations. Selection of a particular development plan, therefore, will usually involve a procedure for evaluating a trade-off between economic returns and environmental degradation.
Irrigation and Desertification
Dr. Jerry Matlock, Professor of Soils, Water and Engineering at the University of Arizona, and Director of International Programs, discussed reasons for the failure of so many schemes in the long history of irrigation, often in association with extensive and intensive desertification.
Some of the factors have been soil problems, including salinization, decline in fertility and loss of soil through accelerated wind and water erosion; others have been problems of water supply, such as failure of the supply system, depletion of resources through over-use, or deterioration in water quality; others are related to the people themselves, including excessive population growth in relation to water availability, out-migration, and the impact of natural disasters.
Matlock compared the rates of appearance of problems in modern and ancient irrigation schemes as follows:
|Salt accumulation||centuries||5 - 15 years|
|Groundwater depletion||centuries||35 - 50 years|
For time-scales of recovery programmes in modern schemes he cited periods of 17 years for soil reclamation, and possibly 40 years for the stabilization of groundwater reserves.
Irrigation in Arizona, and in the south-western United States in general, began about 100 years ago and has a "modern" perspective, but it nevertheless now faces difficult technological choices, as between irrigation and drainage, de. salinization and water management, and pumping and importing water.
Modern irrigation practice can contribute to desertification in many ways
In the sphere of water engineering, failure to appreciate supply limitations can result in the depletion of reserves and eventual failure of a scheme. Matlock cited the example of Arizona, and particularly the impact of the deep-well turbine pump in accelerating depletion rates and leading to a lowering of watertables by as much as 60 m since the Second World War. The situation now is that Arizona's annual water supply is 2500 x 106 m³, whilst its use rate is 7400 x 106m³, whence the argument for the Central Arizona Project, although this will provide only 1250 x 106 m³ towards the deficit. Abandonment of irrigated land must be the result, although this involves difficult social decisions and can lead to salt accumulation and accelerated wind erosion.
Land preparation also creates problems. Initially only the naturally occurring, almost flat land was used for flood irrigation, but this was recognized as inefficient in terms of water use and production. Modern land preparation involves clearing, smoothing and levelling, even using laser beams for precision. This leads to efficiency in water application but at the same time increases the risk of wind erosion, both during land preparation and in pre-seeding farming operations.
A third group of risks stems from poor water management, particularly over-irrigation, which leads to groundwater rise and salt accumulation, erosion at the lower ends of bays, problems of drainage, and accelerated depletion of water resources. This was exemplified in the early history of the Wellton-Mohawk Scheme, based on pumping from a small groundwater basin and recycling irrigation water. Salt levels rose to 14,000 ppm in the absence of additional recharge, and water had eventually to be brought in from the Colorado River.
Dr. Matlock then discussed ways in which modern irrigation practices can reverse or check the processes of land degradation, particularly through improved systems design. For instance, improved collection and analysis of hydrologic data give a better understanding of limitations to supply. New methods of application, including surface, sprinkler, trickle and subsurface irrigation, have led to more economical use of water and have reduced the need for leaching applications. Systems which now aim at less than maximum yield in the interests of better management of limited water supplies can also reduce the threat of land abandonment.
Crop science is another important tool in combating failure in irrigation schemes, or in providing more stable supportive or alternative systems of agricultural production. Its applications include the introduction of water-efficient varieties, improved dryland farming, and the use of indigenous xerophytic plants for commercial production.
Engineering technology can be applied in the reclamation of abandoned lands through surface treatments and reseeding.
Other techniques now available include economic measures such as controls over costs and prices, and legal controls over land and water use.
Considering future prospects in the light of past experience, Dr. Matlock considered that whereas we have the necessary understanding of the technical aspects of design, operation and maintenance, we show less ability to solve the social and political problems that threaten the permanence of irrigation schemes. Despite improvements, we are still striving for the attainment of balanced, permanent irrigation systems. Arizona, Egypt and the Sahel still pose problems and, with increasing populations, our irrigation resources are constantly being stretched to the maximum.
The key lies in resource management, but individuals are poor stewards of resources and individual actions may conflict with community interests. Rational economic decisions in the short term may have adverse environmental consequences in the long term. There is a need for geographers and engineers to co-operate if disaster is to be averted.
New Crops for Arid Lands
Dr. William H. Brooks of the Office of Arid Lands Studies, University of Arizona, spoke on some new xerophytic crops as possible alternatives to irrigation agriculture. So far these investigations still remain at the research stage, with a need to evaluate the physical and social environments that are appropriate for their introduction before large commercial plantations can be advocated as agricultural alternatives for developing arid-zone countries. He mentioned specifically:
Jojoba (Simmondsia chinensis), of which the mature seed yields a high-value oil. At present it requires hand-harvesting, and commercial production has begun on the Apache Indian Reservation at San Carlos in central Arizona. It provides revenue and a source of seasonal employment and might be an appropriate introduction for the semi-arid zone of the Sahel.
Buffalo Gourd (Cucurbita foetidissim), produces edible oil and protein byproducts from seeds at the rate of 1000 kg/ha protein and oil at the same level. It is rapidgrowing and productive-for example large taproots may grow to 72 kg in 100 to 120 days-and it could be a source of industrial starch. It remains to be seen how it will respond to cultivation and plant-breeding programmes.
Guayule (Parthenium argentatum) is a source of rubber and root fibre that was grown commercially in California during wartime shortage. It belongs to the 1220 to 2130 m altitudinal zone, with 250 to 400 mm rainfall. The necessary technology is relatively sophisticated, and it is upon this and the economics of processing that present research is being concentrated.
Gopher Weed (Euphorbia lathyris) is also being investigated as a source of oil and energy. It is a crop that is relatively easy to maintain and which can tolerate rainfall as low as 250 to 400 mm, but it will be necessary to raise present estimated yields of 15 barrels/ha to 30 barrels/ha of crude oil for worthwhile economic production.
Viewpoints from the Developing Countries
Mr. S.P. Malhotra of the Central Arid Zone Research Institute, Jodhpur, India, noted that a dismal picture had been presented of the prospects for irrigation agriculture, but claimed that the situation was different in the Indian arid zone, where only 4 per cent of the area was presently irrigated and where It was necessary to extend the irrigated area. Their experience in general was good, or at least not as unfavourable as depicted for the southwestern United States. In dry farming areas supplemental irrigation and microcatchment techniques had proved particularly successful, although irrigation from dug wells had been less so. Given the existing structure of agriculture, however, greater emphasis was being placed on improvements in dry farming, particularly the introduction of better crop varieties and the increased use of fertilizers. Other priority developments were the increased use of biogas and the development of appropriate technology.
Dr. M.M. Khogali of the University of Khartoum stressed the need for an integrative analysis of all arid lands development. There is nevertheless an overriding need for development within traditional frameworks in the sense of adaptation to change. One of the chief faults, in his view, was the failure to take into account the human aspect of the situation.