Environmental impact of irrigation

The environmental impacts of irrigation relate to the changes in quantity and quality of soil and water as a result of irrigation and the effects on natural and social conditions in river basins and downstream of an irrigation scheme. The impacts stem from the altered hydrological conditions caused by the installation and operation of the irrigation scheme.

Direct effects

An irrigation scheme draws water from groundwater, rivers, lakes or overland flow, and distributes it over an area. Hydrological, or direct, effects of doing this[1] include reduction in downstream river flow, increased evaporation in the irrigated area, increased level in the water table as groundwater recharge in the area is increased and flow increased in the irrigated area. Likewise, irrigation has immediate effects on the provision of moisture to the atmosphere, inducing atmospheric instabilities and increasing downwind rainfall,[2] or in other cases modifies the atmospheric circulation, delivering rain to different downwind areas.[3] Increases or decreases in irrigation are a key area of concern in precipitationshed studies, that examine how significant modifications to the delivery of evaporation to the atmosphere can alter downwind rainfall.[4]

Indirect Effects

Indirect effects are those that have consequences that take longer to develop and may also be longer-lasting. The indirect effects of irrigation include the following:

The indirect effects of waterlogging and soil salination occur directly on the land being irrigated. The ecological and socioeconomic consequences take longer to happen but can be more far-reaching.

Some irrigation schemes use water wells for irrigation. As a result, the overall water level decreases. This may cause water mining, land/soil subsidence, and, along the coast, saltwater intrusion.

Irrigated land area worldwide occupies about 16% of the total agricultural area and the crop yield of irrigated land is roughly 40% of the total yield.[5] In other words, irrigated land produces 2.5 times more product than non-irrigated land. This article will discuss some of the environmental and socioeconomic impacts of irrigation.

Adverse impacts

Reduced river flow

The reduced downstream river flow may cause:

Increased groundwater recharge, waterlogging, soil salinity

Looking over the shoulder of a Peruvian farmer in the Huarmey delta at waterlogged and salinised irrigated land with a poor crop stand.
This illustrates an environmental impact of upstream irrigation developments causing an increased flow of groundwater to this lower-lying area, leading to adverse conditions.

Increased groundwater recharge stems from the unavoidable deep percolation losses occurring in the irrigation scheme. The lower the irrigation efficiency, the higher the losses. Although fairly high irrigation efficiencies of 70% or more (i.e. losses of 30% or less) can occur with sophisticated techniques like sprinkler irrigation and drip irrigation, or by well managed surface irrigation, in practice the losses are commonly in the order of 40% to 60%. This may cause the following issues:

Reduced downstream river water quality

Owing to drainage of surface and groundwater in the project area, which waters may be salinized and polluted by agricultural chemicals like biocides and fertilizers, the quality of the river water below the project area can deteriorate, which makes it less fit for industrial, municipal and household use. It may lead to reduced public health.
Polluted river water entering the sea may adversely affect the ecology along the sea shore (see Aswan dam).

The natural build up of sedimentation can reduce downstream river flows due to the installation of irrigation systems. Sedimentation is an essential part of the ecosystem that requires the natural flux of the river flow. This natural cycle of sediment dispersion replenishes the nutrients in the soil, that will in turn, determine the livelihood of the plants and animals that rely on the sediments carried downstream. The benefits of heavy deposits of sedimentation can be seen in large rivers like the Nile River. The sediment from the delta has built up to form a giant aquifer during flood season, and retains water in the wetlands. The wetlands that are created and sustained due to built up sediment at the basin of the river is a habitat for numerous species of birds [10] However, heavy sedimentation can reduce downstream river water quality and can exacerbate floods up stream. This has been known to happen in the Sanmenxia reservoir in China. The Sanmenxia reservoir is part of a larger man-made project of hydro-electric dams called the Three Gorge Project [11] In 1998, uncertain calculations and heavy sediment greatly affected the reservoir’s ability to properly fulfill its flood-control function [12] This also reduces the down stream river water quality. Shifting more towards mass irrigation installments in order to meet more socioeconomic demands is going against the natural balance of nature, and use water pragmatically- use it where it is found[13]

Affected downstream water users

Water becomes scarce for nomadic pastoralist in Baluchistan due to new irrigation developments

Downstream water users often have no legal water rights and may fall victim of the development of irrigation.

Pastoralists and nomadic tribes may find their land and water resources blocked by new irrigation developments without having a legal recourse.

Flood-recession cropping may be seriously affected by the upstream interception of river water for irrigation purposes.

Lake Manantali, 477 km², displaced 12,000 people.

Lost land use opportunities

Irrigation projects may reduce the fishing opportunities of the original population and the grazing opportunities for cattle. The livestock pressure on the remaining lands may increase considerably, because the ousted traditional pastoralist tribes will have to find their subsistence and existence elsewhere, overgrazing may increase, followed by serious soil erosion and the loss of natural resources.[16]
The Manatali reservoir formed by the Manantali dam in Mali intersects the migration routes of nomadic pastoralists and destroyed 43000 ha of savannah, probably leading to overgrazing and erosion elsewhere. Further, the reservoir destroyed 120 km² of forest. The depletion of groundwater aquifers, which is caused by the suppression of the seasonal flood cycle, is damaging the forests downstream of the dam.[17][18]

Groundwater mining with wells, land subsidence

Flooding as a consequence of land subsidence

When more groundwater is pumped from wells than replenished, storage of water in the aquifer is being mined and the use of that water is no longer sustainable. As levels fail, it becomes more difficult to extract water and pumps will struggle to maintain the design flowrate and consume more may fenergy per unit of water. Eventually it may become so difficult to extract groundwater that farmers may be forced to abandon irrigated agriculture.
Some notable examples include:

Simulation and prediction

The effects of irrigation on watertable, soil salinity and salinity of drainage and groundwater, and the effects of mitigative measures can be simulated and predicted using agro-hydro-salinity models like SaltMod and SahysMod[23]

Case studies

  1. In India 2.19 million ha have been reported to suffer from waterlogging in irrigation canal commands. Also 3.47 million ha were reported to be seriously salt affected,[24][25]
  2. In the Indus Plains in Pakistan, more than 2 million hectares of land is waterlogged.[26] The soil of 13.6 million hectares within the Gross Command Area was surveyed, which revealed that 3.1 million hectares (23%) was saline. 23% of this was in Sindh and 13% in the Punjab.[26] More than 3 million ha of water-logged lands have been provided with tube-wells and drains at the cost of billions of rupees, but the reclamation objectives were only partially achieved.[27] The Asian Development Bank (ADB) states that 38% of the irrigated area is now waterlogged and 14% of the surface is too saline for use[28]
  3. In the Nile delta of Egypt, drainage is being installed in millions of hectares to combat the water-logging resulting from the introduction of massive perennial irrigation after completion of the High Dam at Assuan[29]
  4. In Mexico, 15% of the 3 million ha of irrigable land is salinized and 10% is waterlogged[30]
  5. In Peru some 0.3 million ha of the 1.05 million ha of irrigable land suffers from degradation (see Irrigation in Peru).
  6. Estimates indicate that roughly one-third of the irrigated land in the major irrigation countries is already badly affected by salinity or is expected to become so in the near future. Present estimates for Israel are 13% of the irrigated land, Australia 20%, China 15%, Iraq 50%, Egypt 30%. Irrigation-induced salinity occurs in large and small irrigation systems alike[31]
  7. FAO has estimated that by 1990 about 52 million ha of irrigated land will need to have improved drainage systems installed, much of it subsurface drainage to control salinity[32]

Reduced downstream drainage and groundwater quality

Mitigation of adverse effects

Irrigation can have a variety negative impacts on ecology and socioeconomy, which may be mitigated in a number of ways. These include siting the irrigation project in a location which minimises negative impacts.[33] The efficiency of existing projects can be improved and existing degraded croplands can be improved rather than establishing a new irrigation project[33] Developing small-scale, individually owned irrigation systems as an alternative to large-scale, publicly owned and managed schemes.[33] The use of sprinkler irrigation and micro-irrigation systems decrease the risk of waterlogging and erosion.[33] Where practicable, using treated wastewater makes more water available to other users[33] Maintaining flood flows downstream of the dams can ensure that an adequate area is flooded each year, supporting, amongst other objectives, fishery activities.[33]

Delayed environmental impacts

It often takes time to accurately predict the impact that new irrigation schemes will have on the ecology and socioeconomy of a region. By the time these predictions are available, a considerable amount of time and resources may have already been expended in the implementation of that project. When that is the case, the project managers will often only change the project if the impact would be considerably more than they had originally expected.[34]

Potential benefits outweigh the potential disadvantages

Frequently irrigation schemes are seen as extremely necessary for socioeconomic well-being especially in developing countries. One example of this can be demonstrated from a proposal for an irrigation scheme in Malawi. Here it was shown that the potential positive effects of the irrigation project that was being proposed "outweighed the potential negative impacts". It was stated that the impacts would mostly "be localized, minimal, short term occurring during the construction and operation phases of the Project". In order to help alleviate and prevent major environmental impacts, they would use techniques that minimize the potential negative impacts. As far as the region's socioeconomic well-being, there would be no "displacement and/or resettlement envisioned during the implementation of the Project activities". The original primary purposes of the irrigation project were to reduce poverty, improve food security, create local employment, increase household income and enhance the sustainability of land use.[35]

Due to this careful planning this project was successful both in improving the socialeconomic conditions in the region and ensuring that land and water are sustainability into the future.

See also

Further reading

External links


  1. Rosenburg, David; Patrick McCully; Catherine Pringle (2000). "Global-Scale Environmental Effects of Hydrological Alterations: Introduction". BioScience. Sep 2000: 746–751. doi:10.1641/0006-3568(2000)050[0746:GSEEOH]2.0.CO;2. Retrieved 17 March 2014.
  2. M. H. Lo and J. S. Famiglietti, Irrigation in California's Central Valley strengthens the southwestern U.S. water cycle, Geophysical Research Letters, Volume 40, Issue 2, pages 301–306, 28 January 20132
  3. O. A. Tuinenburg et al., The fate of evaporated water from the Ganges basin, Journal of Geophysical Research: Atmospheres, Volume 117, Issue D1, 16 January 2012
  4. P. W. Keys et al., Analyzing precipitationsheds to understand the vulnerability of rainfall dependent regions, Biogeosciences, 9, 733–746, 2012 PDF
  5. Bruce Sundquist, 2007. Chapter 1- Irrigation overview. In: The earth's carrying capacity, Some related reviews and analysis. On line :
  6. 1 2 3 4 World Wildlife Fund, WWF Names World's Top 10 Rivers at Greatest Risk, on line: http://www.ens-newswire.com/ens/mar2007/2007-03-21-01.asp
  7. Timberlake, L. 1985. Africa in Crisis - The Causes, Cures of Environmental Bankruptcy. Earthscan Paperback, IIED, London
  8. World health organization (WHO), 1983. Environmental health impact assessment of irrigated Agriculture. Geneva, Switzerland.
  9. Himanshu Thakkar. Assessment of Irrigation in India. World Commission on Dams. On line : http://www.dams.org/docs/kbase/contrib/opt161.pdf
  10. <r/r Ellen Wohl, “The Nile: Lifeline in the Desert”, A World of Rivers p. 98f>
  11. </rEllen Wohl, “The Chang Jiang: Bridling a Dragon”, A World of Rivers p 275, p.283. By calculating the amount of sediment that will be carried downstream to the Sanmenxia reservoir is difficult to estimate.
  12. <Ellen Wohl, “The Chang Jiang: Bridling a Dragon”, A World of Rivers p284
  13. </rDonald Worster, “ Thinking like a River,” in The Wealth of Nature: Environmental History and the Ecological Imagination (New York: Oxford University Press, (1993), p133ef>
  14. 1 2 Modern interferences in traditional water resources in Baluchistan. In: Annual Report 1982, pp. 23-34. ILRI, Wageningen, The Netherlands. Reprinted in Water International 9 (1984), pp. 106- 111. Elsevier Sequoia, Amsterdam. Also reprinted in Water Research Journal (1983) 139, pp. 53-60. Download from : , under nr. 10, or directly as PDF :
  15. C.A. Drijver and M. Marchand, 1985. Taming the floods. Environmental aspects of the floodplain developments of Africa. Centre of Environmental Studies, University of Leiden, The Netherlands.
  16. Ecosystems Ltd., 1983. Tana delta ecological impact study. Nairobi, Kenya.
  17. A. deGeorges and B.K. Reilly, 2006. Dams and large scale irrigation on the Senegal river: impacts on man and the environment. UNDP Human Development Report. On line: http://hdr.undp.org/en/reports/global/hdr2006/papers/DeGeorges%20Andre.pdf
  18. Peter Bosshard. A Case Study on the Manantali Dam Project (Mali, Mauritania, Senegal), Erklärung von Bern/internationalrivers:
  19. Center for development studies (CDS), 1988. A study of water distribution and management in new design public tubewells in eastern Uttar Pradesh. Lucknow, UP, India
  20. Anthropogenic subsidence
  21. D.K. Todd, 1980. Groundwater hydrology. 2nd edition. John Wiley and sons, New York
  22. US Geological Survey, Land Subsidence in the United States. on line: http://water.usgs.gov/ogw/pubs/fs00165/
  23. SaltMod: A tool for interweaving of irrigation and drainage for salinity control. In: W.B. Snellen (ed.), Towards integration of irrigation, and drainage management. ILRI Special report, pp. 41-43. Free download from : , under nr. 8: Saltmod application, or directly as PDF :
  24. N.K. Tyagi, 1996. Salinity management: the CSSRI experience and future research agenda. In: W.B. Snellen (Ed.), Towards integration of irrigation and drainage management. ILRI, Wageningen, The Netherlands, 1997, pp. 17-27.
  25. N.T. Singh, 2005. Irrigation and soil salinity in the Indian subcontinent: past and present. Lehigh University Press. ISBN 0-934223-78-5, ISBN 978-0-934223-78-2, 404 p.
  26. 1 2 Green Living Association Pakistan, Environmental Issues.
  27. A.K. Bhatti, 1987. A review of planning strategies of salinity control and reclamation projects in Pakistan. In: J. Vos (Ed.) Proceedings, Symposium 25th International Course on Land Drainage. ILRI publ. 42. International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands
  28. Asian Development Bank (ADB), Water in the 21st Century : Imperatives for Wise Water Management, From Public Good to Priced Commodity.
  29. M.S. Abdel-Dayem, 1987. Development of land drainage in Egypt. In: J. Vos (Ed.) Proceedings, Symposium 25th International Course on Land Drainage. ILRI publ. 42. International Institute for Land Reclamation and Improvement, Wageningen, The Netherlands.
  30. L. Pulido Madrigal, 1994. (in Spanish) Anexo Tecnico: Estudio general de salinidad analizada. CNA-IMTA, Cuernavaca, Mexico. The data can be seen on line in the article: "Land drainage and soil salinity: some Mexican experiences". In: Annual Report 1995, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands, pp. 44 - 52, :
  31. Claudio O. Stockle. Environmental impact of irrigation: a review. State of Washington Water Research Center, Washington State University. On line: http://www.swwrc.wsu.edu/newsletter/fall2001/irrimpact2.pdf
  32. United Nations, 1977. Water for Agriculture. In: Water Development and Management, Proceedings of the United Nations Water Conference, Part 3. Mar del Plata, Argentina.
  33. 1 2 3 4 5 6 "Irrigation potential in Africa: A basin approach". Natural Resources Management and Environment Department. Retrieved 13 March 2014.
  34. Dougherty, T.C. "FAO Irrigation and Drainage Paper 53" (PDF). Environmental Impact Assessment of Irrigation and Drainage Projects. Food and Agriculture Organization of the United Nations. Retrieved 13 March 2014.
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