Irrigated Area Stays Stable

by Ling Li

In 2003, the latest year with data, the world’s irrigated area stagnated at about 277 million hectares—150,000 hectares less than in 2002.1 (See Figure 1.) The annual expansion rate of world irrigated land has fallen from an average of over 2 percent from 1961 to 1992 to around 1 percent from 1993 to 2003.2 Irrigated area per person in 2003 stood at 0.044 hectares, 7 percent below the 1978 peak.3 (See Figure 2.)

Irrigation is distributed unevenly around the world: 42 percent of arable land in Asia was irrigated in 2000, while in sub-Saharan Africa the figure was only 4 percent.4 Irrigated areas in China, India, Pakistan, and the United States account for half of the world total, but China and India each have almost 20 percent.5 (See Figure 3.) In 1992, India passed China as the country with the most irrigated land.6

Irrigated area accounted for only 20 percent of total arable land in 1997–99, yet farmers worldwide harvested 40 percent of all crops and nearly 60 percent of cereals from these lands.7 In China, the 45 percent of agricultural land that is irrigated produced 75 percent of the nation’s food in 2002.8 By 2030, 70 percent of world cereal grains will come from irrigated land.9

The worldwide slowdown in irrigation expansion has several sources. For one, it is becoming more expensive for farmers and governments to put in new irrigation because of rising costs of investment in irrigation systems and difficulties developing new sites.10 But the two major constraints on expansion are soil salinization—a particularly acute problem in semiarid areas when salts build up in the soil as irrigation water evaporates—and shortages of irrigation water, which are driven by both aquifer depletion and competition for water.11 An estimated 20–30 million hectares of world irrigated land have been degraded by the accumulation of salts.12

The overpumping of groundwater for irrigation is now a widespread problem.13 The number of tubewells supplying underground water to irrigated land has grown rapidly in the last 40 years in India, China, Pakistan, Mexico, and many other countries.14 Groundwater levels in large areas in India and China are estimated to drop 1–3 meters each year, allowing saltwater to intrude into aquifers, raising pumping costs, and causing land subsidence.15

Agriculture accounted for nearly 70 percent of the world’s use of fresh water in 2000, although in Asia and the Pacific region the figure was as high as 90 percent.16 Nevertheless, more irrigation water continues to be transferred to nonfarm uses because of the rapidly growing demands of industries and cities.17 Yet in China, irrigation’s share of total water use dropped from 85 percent in 1980 to 64 percent in 2005.18 More municipal and industrial wastewater is reused for irrigation, although this raises significant environmental and health concerns when the wastewater receives little or no treatment.19

Climate change also threatens irrigation by shifting world rainfall patterns, changing river flows, raising sea levels, and intensifying hurricanes and monsoons.20 Irrigated areas that rely on water from mountain snowmelt are at particular risk.21 In South Asia, accelerated glacial melt and reduced rainfall pose problems for the major local crops, such as paddy rice and wheat.22

More than half of the irrigation water removed from rivers and aquifers disappears before bene- fiting a crop, either wasted through evaporation and inefficient irrigation practices or recharged to groundwater.23 In Asia, the widespread use of pump irrigation is believed to create natural incentives for farmers to be more careful in water management, as they have to pay for energy even though the water is free.24

Low-cost treadle pumps and small mechanical pumps have been introduced in South Asia and Africa to help poor farmers get access to irrigation.25 Drip irrigation is a more efficient technology than flooding and sprinklers, reducing water use by 30–70 percent and increasing crop yields by 20–90 percent.26 In Kenya, a type of bucket drip irrigation kit costing some $15 has been used for irrigation of small plots of vegetables and fruit trees, generating monthly revenue of about $20.27 Planting more water efficient grains can also help reduce water use.28

Includes the following charts and graphs
World Irrigated Area, 1961-2003
World Irrigated Area Per Thousand People, 1961-2003
Irrigated Area in Selected Countries, 1961-2003

Notes
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