Ancient lessons for modern irrigation

Posted: 6 February 2001

One of the lessons of history is that most irrigation-based civilisations fall. So at the start of the Third Millennium - when irrigation is more essential than ever - will our civilisation fare any better? That is the question posed by Sandra Postel in her latest book Pillar of Sand, from which this article is drawn.

Some 40 per cent of our planet's food comes from irrigated lands, and we are betting on that share to increase in the decades ahead. But can our modern irrigation society succeed? And what will success require?

Salinised soil, PakistanJim Holmes/Panos PicturesThe parallels between the state of irrigated agriculture today and the problems that plagued failed irrigation societies of the past are both striking and unsettling. From the build-up of salts in fertile soils to the flaring of tensions over disputed waters, today's threats echo those of the past. But new elements make today's challenges more difficult than ever.

First, signs of trouble are surfacing with unprecedented speed. Sixty per cent of our irrigation base is less than 50 years old, yet threats to the continued productivity of much of this land are already apparent.

A great deal of this newer irrigated land depends on groundwater, which farmers began tapping on a large scale only after 1950, as powerful diesel and electric pumps became accessible. Today the problem of overpumping - extracting more water from underground reservoirs than nature puts in - is pervasive in most major areas of irrigated agriculture. Collectively, farmers are racking up an annual water deficit of at least 160 billion cubic metres - enough to produce half the grain harvest of the United States. This deficit suggests that a tenth of the world's grain supply is propped up by unsustainable water use, a situation that cannot persist indefinitely.

Legacy of complacency

Second, irrigation's land and water base are rapidly being eroded by salinization of soils, siltation of reservoirs, and the siphoning off of irrigation water to supply burgeoning cities. Grave as these developments are, political leaders have scarcely taken notice of them - a situation ominously reminiscent of that in ancient Mesopotamia when the Tigris and Euphrates rivers and their irrigation canals silted up and the surrounding plains suffered from a build up of salt, contributing to the downfall of a flourishing society.

Third, the phenomenal successes of the Green Revolution have left a legacy of complacency that belies the scale of the challenge ahead. Merely holding on to the agricultural gains of the last 50 years will be no mean feat, because a good share of them were won through ecologically unsound uses of land, water, and chemicals.

But we require more than that. The most likely population scenario suggests that an additional 3 billion people will join humanity's ranks during the first half of the 21st century. This will call on farmers, scientists and engineers to do again what they did in the last 50 years when human numbers grew by 3.5 billion - but this time with a greatly depleted larder of natural resources.

Water scarcity, in particular, will make a second round of success extremely difficult. In addition to depleted groundwater, the scale of water extractions today is sapping the health of the aquatic environment. Additional pressures on rivers, lakes, and wetlands will destroy more fisheries, consign more species to extinction, and unravel more of the ecological services that support the human economy (see Figure 1).

Competiton for water Fourth, the scale of the challenge ahead is also unprecedented because of the rapidly growing inbalance between human numbers and Earth's distribution of fresh water. Over the next quarter of a century we will see more than a sixfold increase in the number of people living in water stressed countries - from 470 million today to 3 billion in 2025. In most cases the competition for limited supplies will result in a shift of water out of agriculture to other uses that create more economic value.rice paddyRice Paddy in the Mekong Delta. Pressure on water could jeopardise future food production.© Peter CharlesworthAs the number of people in water-stressed countries climbs toward 3 billion, competition for water will spread across borders through the global grain trade as more countries attempt to import enough grain to fill their food gaps. Whether the exporting nations can meet that demand is one thing; whether the poorer countries, such as those in South Asia and sub-Saharan Africa, will be able to pay for the grain they need is another. No global food models, adequately incorporate water scarcity into projections of exportable food surpluses, future food prices, or access to food by the poor.

Finally, climate change, as projected for this century, adds a whole new dimension to the food and water challenge. History shows that climate wild cards, especially droughts and floods and other events which affect rainfall and river flows can overwhelm a seemingly advanced society's ability to cope.

Any of the stresses evident today would seriously challenge irrigated agriculture's future productivity. But these stresses evolving simultaneously, magnify the constraints on future food production.

Laws and policies The best answer to these stresses is preparedness and flexibility. But virtually all of the most promising techniques for improving water productivity - from drip irrigation to the use of computerised weather and soil monitoring - remain vastly underused. Water pricing and other "rules of the game" do not encourage their adoption.

Rigid water institutions and the lack of laws and policies to confront the groundwater overpumping, depleted river flows, and other environmental damage leaves irrigated agriculture vulnerable to sudden cutbacks and robs the next generation of its productive potential. Smarter policies and better technologies thus have an important role to play in working towards the goal of food and water for all in this century. This includes providing poor farmers with access to affordable small-scale irrigation techniques and the use of new crop varieties that can better withstand salt and water stress.

Successfully meeting the challenge ahead will also require a scaling back of consumption., in order to create more room for additional people, for other living things and for the work of nature to continue. Because of the size of the human population, even small changes in individual consumption can have a large collective impact on the environment.

Shifting dietary choices is one example. The typical American diet requires twice as much water to produce as nutritious but less meat-intensive diets. It may only a matter of time before China restrains the consumption of pork, which takes roughly twice as much grain per kilo to produce as chicken or farm-raised fish.

Lessening the water demands of cities and industries is also essential. Few countries have begun to measure the water-intensity of their economies, as they routinely measure their energy-intensity.

Woman collecting water, Kathmandu, NepalĀ© H. Schwarzbach/Still Pictures

A water ethic

It is difficult to imagine how we can succeed in meeting human needs sustainably without adopting a guiding water ethic, grounded in the principles of sufficiency and sharing. Humanity now appropriates for its own use more than half the Earth's accessible renewable fresh water and 40 per cent of its net photosynthetic product. This degree of human dominance leaves a dangerously thin margin of support for the millions of other species with which we share the planet - species that perform vital work of nature on which our societies rest.

It is not enough to meet a short-term goal of feeding the global population. If we do so by consuming so much land and water that ecosystems cease to function, we will have not a claim to victory but a recipe for economic and social decline.

It is possible to envision a modern form of irrigated agriculture that is resource-renewing rather than resource-depleting and that preserves Earth's natural capital rather than liquidates it. Time, however, is of the essence. If we fail to make a timely transition, we will see - just as our predecessors in the Fertile Crescent did - that we do indeed rest on a pillar of sand.

Sandra Postel is Director of the Global Water Policy Project based at Amherst, Massachusetts and a Senior Fellow with Worldwatch Institute.

Pillar of Sand, Can the Irrigation Miracle Last? is a Worldwatch book (W.W. Norton, New York,1999).