The benefits of irrigation and its environmental problems

Overview

Main agricultural benefits of irrigation in a dryland region, how irrigation supports food security and mechanism by which irrigation causes salinisation.

What you need to know

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Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What are the main agricultural benefits of irrigation in a dryland region?

   Model answer

   Yields per hectare rise sharply because the crop no longer suffers moisture stress at critical growth stages. Land that was too dry to cultivate at all can be brought into production, extending the cultivated area. Because water is available in the dry season, farmers can grow two or even three crops a year on the same field instead of one, a practice called multiple cropping. And output becomes far more reliable from year to year, since a late or failed wet season no longer means a failed harvest.

2. 2

   How does irrigation change what farmers are able to grow, and why does that matter economically?

   Model answer

   A reliable water supply allows a shift away from low-value drought-tolerant subsistence grains such as millet and sorghum towards higher-value crops: wheat and rice for the domestic market, and cash crops such as cotton, sugar cane, fruit and vegetables for sale and export. That matters because it converts farming from subsistence into a source of cash income, which can pay for inputs, schooling and health care, and because export crops earn foreign exchange for the national economy.

3. 3

   Explain how irrigation supports food security.

   Model answer

   It raises total production and, more importantly, stabilises it. In a rain-fed dryland system the harvest fluctuates enormously with the rains, so a bad year means hunger, distress sale of livestock and dependence on food aid. Irrigation decouples production from the timing and reliability of the ITCZ, so a national or regional food supply becomes predictable, the country can reduce expensive food imports, and grain surpluses in good years can be stored against future shortage.

4. 4

   What socio-economic benefits does irrigation bring beyond the farm gate?

   Model answer

   Employment expands, both directly, because irrigated farming is more labour-intensive and needs workers for a longer season, and indirectly in canal maintenance, pump repair, transport, storage, food processing and marketing. Rising farm incomes create local demand that supports shops and services, encouraging the growth of market towns. Large schemes usually bring associated infrastructure such as roads, electricity, clinics and schools into a remote region. Reliable livelihoods reduce the pressure on young people to migrate away to the cities, helping to keep rural communities intact.

5. 5

   Are there environmental benefits to irrigation as well as costs?

   Model answer

   There can be, and a balanced answer should say so. Raising yields on irrigated land can take pressure off marginal land, so that fragile grazing and scrub that would otherwise be ploughed or overgrazed is left alone, reducing wind erosion and desertification. A permanent vegetation cover on irrigated fields protects the soil surface and can slightly increase local humidity and reduce dust. Reservoirs create wetland habitat for birds and fish where none existed, and tree planting and shelter belts around irrigated plots add habitat and organic matter. These gains are real but conditional, and they only hold where the scheme is well managed.

6. 6

   How can a large dam-and-canal scheme benefit a region in ways that have nothing to do with crops?

   Model answer

   The dam that stores the irrigation water usually generates hydroelectric power, supplying industry and households and reducing dependence on imported fuel. The reservoir regulates river flow, reducing downstream flood peaks in the wet season and maintaining flow in the dry season. It can supply treated drinking water to towns, support a reservoir fishery that adds protein to local diets, and provide a route for navigation and a site for tourism and recreation. These multi-purpose benefits are often what justifies the cost of the scheme in the first place.

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