Over time, the area irrigated by groundwater has increased in importance around the world. Groundwater development has been growing at an exceptional rate in recent decades. More reliable water delivery and declining extraction costs due to advances in technology and, in many instances, government subsidies for power and pump installation have encourages private investment in tubewells. For example, in India and Northern China, the area irrigated by groundwater rose from about 25 percent in the 1960s to well over 50 percent in the 1990s. Source of irrigation water varies widely between countries depending on the hydro-geological and climatic conditions and historical development of irrigation. Responses to a recent ICID questionnaire of irrigation practices show that, among the major countries, India has over 50 percent of its area irrigated from groundwater, followed by the USA (43 percent), China (27 percent) and Pakistan (25 percent). That percentage can reach as much as 80 percent in developed countries with mild climate (Germany) and in arid countries (Saudi Arabia, Libya). Table 1 shows the contribution of groundwater used for irrigation for a set of countries that together represent about 150 million hectares or 56.6 percent of the total irrigated area worldwide.
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Country |
Percent of groundwater as part of water resource used |
Total irrigation water use (million m3/year) |
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Saudi Arabia |
96 |
15 310 |
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Bangladesh |
69 |
12 600 |
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Tunisia |
61 |
2 730 |
|
Jordan |
55 |
740 |
|
India |
53 |
460 000 |
|
Iran |
50 |
64 160 |
|
Pakistan |
34 |
150 600 |
|
Morocco |
31 |
10 180 |
|
Mexico |
27 |
61 200 |
|
China |
18 |
407 800 |
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South Africa |
18 |
9 580 |
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Nepal |
12 |
28 700 |
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Peru |
11 |
16 300 |
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Malaysia |
8 |
9 700 |
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Egypt |
4 |
45 400 |
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Mali |
3 |
1 320 |
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Indonesia |
1 |
69 200 |
According to a report of the World Commission for Water, aquifers are being mined at an unprecedented rate. About 10 percent of the world’s agricultural food production depends on using mined groundwater. Water tables are dropping in fossil aquifers, including in the Western Unites States.
The recent development of groundwater has led to the overexploitation of groundwater resources in some semi-arid regions where water tables have been falling at an alarming rate - often one to three metres a year. These regions include some of the world’s major grain producing areas (‘breadbaskets’) such as the Punjab and the North China plain. Groundwater development for irrigation is more recent in some countries. In Thailand, the explosive use of diesel pumps in the Chao Phraya and Mekong projects has responded to the increased demand for dry season cultivation of high-value crops and the unreliable supply from these large gravity irrigation systems employed. Figure 2 shows that the expansion of irrigated areas during the last 10 years is mostly taking place in the Asian region.
Figure 2
Evolution of irrigation in Asia[3] vs rest of the World (source: FAO)
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Box no. 2: Groundwater development in India and its contribution to food production Over the last three decades, the rapid expansion in the use of groundwater primarily for irrigation has contributed significantly to agricultural and economic development in India. Groundwater irrigation potential, the number of wells and the number of energized pump sets have grown exponentially since the early 1950s. Current projections envision that the rapid rate of development will continue until the full irrigation potential estimated to be available from groundwater is reached in about 2007. With more than 17 million wells nationwide, groundwater now supplies more than 50 percent of the irrigated area and, due to higher yields in groundwater irrigated areas, it is essential for an even higher proportion of the total irrigated output. According to some estimates, 70-80 percent of the value of irrigated production in India may depend on groundwater irrigation. That yields are higher in groundwater-irrigated areas is primarily due to the fact that groundwater offers greater control over the supply of water than do other sources of water. As a result groundwater irrigation encourages complementary investments in fertilizers, pesticides, and high yielding varieties, leading to higher yields. (World Bank 1998). |
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Box no. 3: Water disaster in India? In India, which relies on extensive irrigation, water tables are falling. According to IWMI, India currently withdraws groundwater at twice the recharge rate. Eventually, the shortfall could reduce India’s harvest by as much as 25 percent. Since India - well on the way to becoming the world’s most populous nation - already maintains an uneasy balance between production and consumption, the impact could be disastrous (Shah and Strong, 2000). |
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Box no. 4: The changes in the Phitsanulok project, Thailand The Phitsanulok gravity irrigation project in Thailand built in the 1980s is complex to manage. The performance in terms of canal distribution and plan implementation is very erratic. There are large deviations between the planned and the actual allocation of water and large variations of water levels in the main canal, an indication of poor water control. Although the Phitsanulok project is not old, many changes have affected the way the system operates. Siltation has reduced the capacity of the main canal to supply the tail end of the project. But the increased role of groundwater is the biggest change. With an average of one well for 5 hectares, virtually all farmers now have access to groundwater. The development of groundwater has given farmers a greater level of control over their crop calendar. They do not have to wait for the availability of canal water, and they can plant their crop at the time that seems best according to their own situation. The benefits that the changes have brought to farmers include increased quantity of water, increased reliability of water and freedom for the farm families to choose their own crop strategies. The same set of changes has been observed in other large-scale irrigation systems in Thailand. These have become dual-source systems, in which groundwater is of similar significance to canal water (Mainuddin et al., 2000). |
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Box no. 5: Groundwater development in Pakistan Over the past 30 years, more than 12 500 public deep tubewells were installed in Pakistan with the primary objective to combat waterlogging and associated salinity. Groundwater development through private tubewells has grown exponentially, especially in Punjab. According to the latest estimates, Pakistan has more than 300 000 tubewells. According to a 1991 survey, about 46x109 cubic meters of groundwater are used for irrigation in the Indus basin, of which 85 percent comes from private tubewells. Because of groundwater extraction, water tables have declined beyond the range over which salinization can be expected. However, salinity continues to present a threat to the sustainability of irrigated agriculture in Punjab because of recycling of large quantities of poor quality groundwater from the top of underlying aquifers. Farmers reduce the risks of crop failures and improve yields by smoothing operational fluctuations in water supplies from the main canals. According to a 1978 study, average yields of wheat from farmers using canal water only (1.7 tonnes per hectare) were 25 percent lower than those from farmers owning wells (2.2 tonnes per hectare). Rice farmers using wells with yields of 2.2 tonnes per hectare are also doing better compared to those using canal water only. |
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[3] Irrigated areas for central
Asian countries were transferred from the USSR to the Asian region in
1992 |
