OUTGROWING THE EARTH
THE FOOD SECURITY CHALLENGE IN AN AGE OF FALLING WATER TABLES AND RISING TEMPERATURES
Chapter 6: Stabilizing Water Tables
Although public attention has recently focused on the depletion of oil resources, the depletion of underground water resources poses a far greater threat to our future. While there are substitutes for oil, there are none for water. Indeed, we lived for millions of years without oil, but we would live for only a matter of days without water.
Not only are there no substitutes for water, but we need vast amounts of it to produce food. At the personal level, we drink roughly four liters of water a day (nearly four quarts), either directly or indirectly in various beverages. But it takes 2,000 liters of water – 500 times as much – to produce the food we consume each day.
Since food is such an extraordinarily water-intensive product, it comes as no surprise that 70% of world water use is for irrigation. Although it is now widely accepted that the world is facing water shortages, most people have not yet connected the dots to see that a future of water shortages will also be a future of food shortages.
Falling water tables
Over much of the earth, the demand for water exceeds the sustainable yield of aquifers and rivers. The gap between the continuously growing use of water and the sustainable supply is widening each year, making it more and more difficult to support rapid growth in food production.
With river water in key farming regions rather fully exploited, the world has turned to underground water sources in recent decades to keep expanding the irrigated area. As a result, the climbing demand for water has now exceeded the natural recharge of many aquifers.
- The effects of aquifer depletion vary, depending on whether it is a replenishable or fossil aquifer.
- Fossil aquifers include the Ogallala under the US Great Plains, the aquifer the Saudis use to irrigate wheat, and the deeper of the two aquifers under the North China Plain.
- In Saudi Arabia, the wheat harvest peaked in 1992 at 4.1 million tons, and then dropped to 1.6 million tons in 2004 – a drop of 61%.
- The wheat harvest in China peaked at 123 million tons in 1997, and dropped to 90 million tons in 2004 – a decline of 27%.
- In India’s North Gujarat, wells powered by heavily subsidized electricity, are dropping water tables at an accelerating rate – 6 meters or 20 feet per year.
- In Tamil Nadu, a state of 62 million people in southern India, falling water tables have dried up 95% of the wells owned by small farmers, reducing the irrigated area in the state by half over the last decade.
- In the United States, the loss of irrigation water is making it more difficult for farmers to respond to the future import needs of other countries. In the southern Great Plains the irrigated area has shrunk by 24% since 1980.
In a rational world, falling water tables would trigger alarm, setting in motion a series of government actions to reduce demand and reestablish a stable balance with the sustainable supply. Unfortunately, not a single government appears to have done this. Official responses to falling water tables have been consistently belated and grossly inadequate.
Rivers running dry
While falling tables are largely invisible, rivers that are drained dry before they reach the sea are highly visible. Two rivers where this phenomenon can be seen are the Colorado, the major river in the southwestern United States, and the Yellow, the largest river in northern China. Other large rivers that either run dry or are reduced to a mere trickle during the dry season are the Nile, the lifeline of Egypt; the Indus, which supplies most of Pakistan’s irrigation water; and the Ganges in India’s densely populated Gangetic basin. (See Table 6-2.)
- Egypt now gets the lion’s share of the Nile’s water partly because it developed much sooner than Ethiopia. But as Ethiopia begins to develop, it is planning to build dams on the upper (Blue) Nile that will reduce the flow in the lower reaches of the Nile river basin.
- With virtually all the water in the basin now spoken for and with the combined population of the Egypt, Ethiopia and Sudan projected to grow from 179 million to 358 million by 2050, the potential for the basin’s population to outgrow its water resources – setting the stage for conflict – is clear.
- China’s construction of several huge hydroelectric dams on the upper reaches of the river system, is reducing the Mekong’s flow, directly affecting fisheries, navigation, and irrigation prospects downstream in Cambodia, Laos, and Vietnam.
Cities versus farms
At the international level, water conflicts among countries dominate the headlines. But within countries it is the competition for water between cities and farms that preoccupies political leaders. Neither economics nor politics favors farms. They almost always lose out to cities.
- In many countries farmers are now faced with not only a shrinking water supply but also a shrinking share of that shrinking supply.
- In the competition between cities and farms, cities have the advantage simply because they can pay much more for water.
- In China, a thousand tons of water can be used to produce 1 ton of wheat, worth at most $200, or it can be used to expand industrial output by $14,000 – 70 times as much
- Agriculture is becoming the residual claimant on the world’s increasingly scarce supply of water.
Scarcity crossing national boundaries
Raising water productivity
To avoid a water crunch that leads to a food crunch requires a worldwide effort to raise water productivity.
- After World War II, as governments assessed the food prospect for the remainder of the century, they saw enormous projected growth in world population and little new land to bring under the plow.
- In response, they joined with international development institutions in a worldwide effort to raise land productivity.
- The result was a rise in world grainland productivity from 1.1 tons per hectare in 1950 to 2.9 tons in 2004.
Today the world needs to launch a similar effort to raise water productivity. Land productivity is measured in tons of grain per hectare or bushels per acre, but there are no universally used indicators used to measure and discuss water productivity. The indicator likely to emerge for irrigation water is kilograms of grain produced per ton of water. Worldwide that average is now roughly 1 kilogram of grain per ton of water used.
The first challenge is to raise the efficiency of irrigation water, since this accounts for 70% of world water used. Some data have been compiled on water irrigation efficiency at the international level for surface water projects – that is, dams that deliver water to farmers through a network of canals. Water policy analysts Sandra Postel and Amy Vickers write about a 2000 review that found that “surface water irrigation efficiency ranges between 25% and 40% in India, Mexico, Pakistan, the Philippines, and Thailand; between 40% and 45% in Malaysia and Morocco; and between 50% and 60% in Israel, Japan, and Taiwan. Irrigation water efficiency is affected not only by the mode and condition of irrigation systems but also by soil type, temperature, and humidity. In arid regions with high temperatures, the evaporation of irrigation water is far higher than in humid regions with lower temperatures.
- China’s Minister of Water Resources outlined plans to raise China’s irrigation efficiency from 43% in 2000 to 51% in 2010 and then to 55% in 2030.
- The steps he described included raising the price of water, providing incentives for adopting more irrigation-efficient technologies, and developing the local institutions to manage this process.
- When attempting to raise the water efficiency of irrigation, the trend is to shift from the less efficient flood-or-furrow system to overhead sprinkler irrigation or to drip irrigation, the gold standard of irrigation water efficiency.
- Low pressure sprinkler systems reduce water use by an estimated 30% over flood or furrow irrigation, while switching from flood or furrow to drip irrigation typically cuts water use in half.
- Since drip systems are both labor-intensive and water-efficient , they are well suited to countries with underemployment and water shortages.
- Among the big three agricultural producers – China, India, and the United States – the share of irrigated land using these more-efficient technologies ranges from less than 1% in India and China to 4% in the United States.
In many cities in water-short parts of the world, it may be time to rethink the typical urban water use model, one where water flows into the city, is used once, and then leaves the city – usually becoming polluted in the process. This flush-and-forget model that so dominates urban water systems will not be viable over the longer term in water-scarce regions. One alternative sewage system is the use of so-called dry toilets, which do not use water and which convert human waste into a rich humus, a highly valued fertilizer.
Another variation on the existing urban water use models is one that comprehensively recycles urban water supplies. Water can be used indefinitely in cities and by industry if it is recycled. Some cities are beginning to do this. Singapore, for example, which buys its water from Malaysia, is starting to recycle its water in order to reduce this vulnerable dependence.
- Some countries can realize large water savings by restructuring the energy sector, shifting from fossil-fuel-powered thermal plants, which require large amounts of water for cooling, to renewable energy sources, such as wind and solar.
- What is needed now is a new mindset, a new way of thinking about water use. In addition to more-efficient irrigation technologies, for example, shifting to more water-efficient crops wherever possible also boosts water productivity.
- Anything that raises the productivity of irrigated land typically raises the productivity of irrigation water.
- Anything that increases the efficiency with which grain is converted into animal protein increases water productivity.
- For people consuming excessive amounts of livestock products, moving down the food chain means not only a healthier diet and reduced health care costs, but also a reduction in water use.
- Reducing water use to a level that can be sustained by aquifers and rivers worldwide involves a wide range of measures not only in agriculture but also throughout the economy.
- Among some of the more obvious steps are shifting to more water-efficient irrigation practices and technologies, planting more water-efficient crops, adopting more water–efficient industrial processes, and using more water-efficient household appliances.
- One of the less conventional steps is to shift from outdated coal-fired power plants, which require vast amounts of water for thermal cooling, to wind power.
- Recycling urban water supplies is another obvious step to consider in countries facing acute water shortages.
The need to stabilize water tables is urgent, thanks to the sheer geographic scale of overpumping, the simultaneity of falling water tables among countries, and the accelerating drop in water level. Although falling water tables are historically a recent phenomenon, they now threaten the security of water supplies and, hence, of food supplies in countries containing 3.2 billion people. Beyond this, the shortfall – the gap between the use of water and the sustainable yield of aquifers – grows larger each year, which means the water level drop is greater than the year before. Underlying the urgency of dealing with the fast-tightening water situation is the sobering realization that not a single country has succeeded in stopping the fall in its water tables and stabilizing water levels. The fast-unfolding water crunch has not yet translated into food shortages, but if unaddressed, it may soon do so.
Data for figures and additional information can be found at www.earth-policy.org/Books/Out/index.htm