|Irrigation-Induced Salinity - A Growing Problem for Development and the Environment (World Bank, 1993)|
Irrigation has been and continues to be an important force in agricultural development. Irrigation enabled the expansion of cultivable land and the intensification of production, which spawned sizable production increases in both developed and developing countries. For some developing countries, its contribution to the attainment of development objectives of food security, poverty alleviation, and the improvement of the quality of life of the rural population has been significant.
The sustainability of irrigated agriculture, however, is now threatened. The expanded dependence on irrigation has not been without cost: salinity and waterlogging, soil erosion and sedimentation, the spread of disease-carrying organisms, and water pollution are a few of the serious problems that have gone hand-inhand with irrigation. UNEP (1987) estimated that the rate of loss of agricultural land is approximately 5-7 million ha per year and overall, salinization is the second major cause of such losses. In irrigated areas, it is the primary cause. As the Hydraulics Research Ltd. (1990, p. 1) reports, "...FAO earlier predicted that...[the area] under irrigation in the world will expand to 320 million ha by the year 2000. For many years, the rate of growth has been 5 million ha per year, but recently it has fallen to 2 million ha per year. However, this growth is counteracted by 2-3 million ha going out of production each year due to salinity problems-this means that cultivated land is being lost at a similar rate to new land being brought into production..
This report describes the process by which irrigation-induced salinity develops and the extent of the problem in various countries. It examines the physical, economic, social, and political factors that spur the onset of salinity, drawing on the experiences in World Bank projects. It explores the role that: farmers, the government and donor agencies can play in dealing with the problem of irrigation-induced salinity.
Irrigation-induced salinity can arise as a result of the use of any irrigation water, irrigation of saline soils, and rising levels of saline ground water. When surface or ground water containing mineral salts is used for irrigating crops, salts are carried into the root zone. Most of the water returns to the atmosphere through transpiration by plants and through evaporation from the soil surface. In the process, the salt is left behind in the soil, since the amount taken up by plants and removed at harvest is quite negligible. The more arid the region, the larger is the quantity of irrigation water and, consequently, the salts applied, and the smaller is the quantity of rainfall that is available to leach away the accumulating salts. The amount of salt which accumulates is further influenced by the water table depth, the capillary characteristics of the soil, and the management decisions regarding the amount of water applied in excess of plant evapo-transpiration to leach the salt away (Young and Homer 1986).
Although plants can tolerate and even require certain levels of salinity for growth, excess salinity within the root zone reduces plant growth. Moreover, different crops exhibit varying degrees of tolerance to salinity. For example, clover and rice are more sensitive to salts than barley and wheat. For rice, a salinity level of 7.2 dS/m will result in a 50 percent yield loss, while it will have no effect at all on barley. The impact of irrigation-related salinity is not restricted to the production areas alone. For example, the disposal of saline drainage water back into rivers have adverse effects on downstream riparians. In some regions, the effects are felt across international borders.
Very limited research has been done to empirically quantify the economic impact of irrigation induced salinity. Quantitativs measurements have generally been limited to the amount of land affected or abandoned. Of more critical importance is its impact at the micro-level on farm productivity and farm incomes and at the macro-level on the performance of the rural sector. The Secretaria de Agricultura y Recursos Hidraulicos (SARH, Secretariat of Agriculture and Water Resources, cited in World Bank 1991c) of Mexico found that agricultural productivity in the Northwest districts and Lerma Balsas region decreased between 30 to 50 percent in the last ten years due to salinity. In the Menemem irrigation and drainage project in Izmir, Turkey, the average net returns per ha for cotton and paddy production were TL307 and TL415 respectively in the salinity affected areas, which is equivalent 42 and 35 percent of the income in the unaffected areas (Republic of Turkey 1990).
The FAO report, An International Action Programme on Water and Sustainable Agricultural Development. A Strategy for the Implementation of the Mar del Plate Action Plan of the 1990s (1990, p. 15) estimates that "...about 20 to 30 million hectares are severely affected by salinity and an additional 60 to 80 million hectares are affected to some extent.. Estimates of the area affected have ranged from 10 to 48 percent of total irrigated area. Clearly, the countries in the arid and semi-arid regions that ranked high in irrigation investments have extensive salinity problems: salinity-affected areas as a percentage total irrigated area amount to 11 percent in India, 21 percent in Pakistan, 10 percent in Mexico, 23 percent in China, and 28 percent in the United States. In the case of India, for example, 11 percent translates to 4.7 million ha, and given the generally small farm sizes, this translates to thousands of farm households: 100,000 households assuming an average farm size of 5 ha. The newly-formed Central Asian Republics in the Aral BasinKazakhstan (17%), Turkmenistan (48%), and Uzbekistan (24%)-also exhibit serious salinity problems. In other regions, the effects are felt across international borders. The increasing use of the Euphrates system by Syria and Turkey not only reduces the flow of the river to Iraq, but is also contributing to degradation of water quality (higher salinity) for the downstream riparian (Keenan 1992b). Similar problems are being encountered in Israel and Jordan with respect to the Jordan River and the United States and Mexico with respect to the Colorado River (Keenan 1992b; Schilfgaarde 1992).
The Operations Evaluation Division (QED) of the World Bank reviewed 21 projects that were approved between 1961 and 1978 and completed in 1970-86. These comprised medium- and large-scale public irrigation systems which were typical of the Bank's lending policy for irrigation projects in the 1960s and 1970s. The OED evaluation found that more than half the 21 projects were very successful but had some degree of adverse impact on the environment (World Bank l991b). Increasing waterlogging problems were found in 11 projects and soil salinity problems were found in four (Pyongtaek-Kumgang Irrigation Project in Korea, the Seyhan Irrigation Project in Turkey, the San Lorenzo Project Irrigation and Land Settlement project in Peru and the Rio Sinaloa Project in Mexico), caused mainly by poor drainage. The drainage network was insufficient or incomplete in half of the 21 projects.
Although irrigation-induced salinity is a technical problem, the factors contributing to its existence are a complex web of technical, economic, political, and social elements. At the technical level, irrigation induced salinity has developed in some areas due to: (i) poor on-farm water use efficiency; (ii) poor construction, operation and maintenance of irrigation canals leading to excessive seepage; (iii) the inadequacy or lack of drainage infrastructure; and (iv) even when drainage structures are provided, their poor quality of construction, operation and maintenance. These technical problems, however, maybe the product of several other factors. Distortive government policies lead to inefficient use of water resources. In the case of irrigation water, it is frequently priced below its true economic value, thus leading to overapplication. Water use efficiency is further aggravated by a lack of awareness of farmers of more efficient and water application methods and poor water management by irrigation authorities. Off-farm, excessive irrigation and drainage canal seepage can be traced to ineffective project planning, poor quality of construction, and inadequate monitoring and maintenance, which lead to rapid infrastructural deterioration. In some cases, no provision for drainage is made at all. These weaknesses in the planning and implementation of irrigation and drainage projects can stem from the shortsighted perspectives assumed by many policy makers. Often, there is a lack of or weak understanding of the consequences of inaction or at the extreme, weak or lack of commitment to environmental protection. In the presence of competing demands for financial resources, priority is directed to other areas other than salinity abatement. At the same time, donor agencies have inadvertently contributed to the problem. Weaknesses in donor project planning and supervision and, not until recently, the inadequate priority to environmental consequences of projects, have similarly contributed to the problem.
In summary, poor project planning and implementation, scarce financial resources of governments in many countries to undertake corrective measures, the short-term outlook and inadequate priority assigned to agricultural sustainability and environmental protection by policymakers, and the inability of donor agencies to ensure adherence to project plans all contribute to the advent of salinity. The technologies exist to ameliorate or eliminate the problem and delays in taking action will only escalate the economic, social, and environmental damage and the cost of repairing such damage. In light of the externalities associated with corrective measures, governments will have to play a major role in correcting or alleviating salinity problems. Donor agencies will also have an important role in enhancing the capacities of governments to do so.
The battle against salinity will have to be launched in three fronts. Governments have to commit to a policy of sound water management and to the fostering of an economic environment promoting efficient resource use. At the same time, agricultural strategies should promote the adoption of improved production methods, particularly efficient water-use practices among farmers. Lastly, greater effort has to be directed at examining the environmental impact of projects that involve water resource use and development to ensure that only economically and environmentally sound projects are undertaken.
As the World Commission on Environment and Development (WCED) wisely describes it, ..."development which destroys the natural resources on which it is based is not development. (cited in FAO, 1990, p. 6). It is widely recognized that irrigation has been a powerful force in fostering development in many countries. But when it is pursued injudiciously, it can become the progenitor of agricultural devastation, embodied in form of irrigation-induced salinity. Irrigation-induced salinity has began to cause drastic reductions in agricultural productivity in many parts of the world and the time has come for farmers, governments and donors to take it seriously.