Supplemental nature of groundwater irrigation in South Asia

In order to better understand the nature of groundwater irrigation in South Asia, IWMI, in collaboration with several partners, undertook a large-scale survey of 2600 well owners from 300 villages selected to represent all regions of India, Pakistan, Bangladesh and 20 districts of Nepal Terai (see DebRoy and Shah, 2003, and Shah et a/., 2006, for details of the survey design and results). One of the aims was to find out if intensive groundwater irrigation occurs in regions with large-scale canal irrigation. Figure 2.9, which summarizes the results, shows that almost everywhere in the subcontinent, groundwater contribution to irrigated areas exceeds that of surface water; that outside of Pakistan Punjab and Sind, conjunctive use of surface and groundwaters at the farmer level is small; that in North-western India, despite massive investments in canal irrigation, the bulk of the irrigation is delivered by wells and tube wells. Figure 2.10, again based on the IWMI survey, suggests that thanks to the groundwater revolution, rain-fed regions, districts or even villages are rare in South Asia; there are just rain-fed and irrigated plots. Just around 5% of the 278 villages covered reported completely rain-fed agriculture; nearly half of the villages had groundwater-dominated irrigated agriculture; pure canal irrigation (i.e. with no wells or tube wells) accounted for just 10% of the villages and 20% of the irrigated area in the sample.

Another key feature of groundwater irrigation in South Asia is its predominantly supplemental nature. The IWMI survey of 2002 collected information from 2629 sample farmers about the depth of pumping water level, hours pumped for different crops and the capacity of pumps. Using these data, rough estimates were made of the actual average application of irrigation water for key crops. When these are compared with cropwat recommendations, we find that farmers provide around one-third of the crop-water requirements through groundwater.

Other studies show that such supplemental groundwater irrigation is also significantly more productive compared with surface irrigation, because it offers individual farmer irrigation 'on demand' which few surface systems can offer; and because its use entails significant incremental cost of lift, farmers tend to economize on its use and maximize application efficiency. Evidence in India suggests that crop yield per cubic metre of water applied on groundwater-irrigated farms tends to be 1.2-3 times higher than that applied on surface water-irrigated farms (Dhawan, 1989, p. 167).5 In terms of return on investment, groundwater irrigation in South Asia has done very well. In Pakistan Punjab, capital investment in private tube wells is estimated to be of the order of Pak Rs. 25 billion6 ($0.4 billion at 2001 prices), whereas, according to one

j% rainfed ■% under pure canal irrigation

C% under pure groundwater irrigation i % under conjunctive use of surface and groundwater

Fig. 2.9. Sources of irrigation in different hydro-economic zones of South Asia. (From IWMI-Tata Survey.)

j% rainfed ■% under pure canal irrigation

C% under pure groundwater irrigation i % under conjunctive use of surface and groundwater

Fig. 2.9. Sources of irrigation in different hydro-economic zones of South Asia. (From IWMI-Tata Survey.)

3 20

3 20

Only rainfed

Canal-dominated villages

Groundwater-dominated villages

Conjunctive use villages

Villages dominated by other sources

Canal-dominated villages

Groundwater-dominated villages

c No. of sample villages

Net cultivated land

-iTotal geographical area

Net irrigated area

l: Total population

Fig. 2.10. Relative importance of wells, canals and other sources of irrigation in sample villages. (From IWMI-Tata Survey.)

Table 2.4. Comparison of farms with and without tube well water supply, Pakistan. (From Ministry of Agriculture, 1988.)

Item Unit Type Sugarcane Rice Cotton Wheat

Cropped area Percent With TW

Yield per acre

Gross value per acre farm area Tonnes

Pak Rs.a

Without TW

With TW Without TW With TW Without TW

13 3

60 50

8,624 56,808

5,060 33,300

a$1 = Pak Rs. 65 in September 2001. TW = Tube wells.

estimate, the annual benefits in the form of agricultural production of the order of Pak Rs.150 billion ($2.3 billion) accrue to over 2.5 million farmers, who either own tube wells or hire the services of tube wells from their neighbours. The best farm level productivity performance of course is obtained by those who can use a judicious combination of surface and groundwater. Table 2.4 reports physical and value productivity on 521 canal-irrigated farms in the Indus system in Pakistan Punjab and shows that farmers with wells obtain 50-100% higher yield per acre and 80% higher value of output per acre compared with canal irrigators without wells. Groundwater users in South Asia often use only a small fraction of scientifically recommended water requirements; rather than aiming at fully irrigated yields, they use sparse, life-saving irrigation to obtain substantial increases over rain-fed yields (see Fig. 2.11). This is because of the high marginal cost of groundwater use; some of the poorest irrigators in arid parts of South Asia - who purchase pump irrigation from well owners - commonly pay 10-14 cents/m3 of water compared to a fraction of a cent paid by canal

J 150

g 100

P 50

J 150

g 100

P 50

Wheat, Agra

Wheat, Rewa

Sorghum, Tobacco, Anand

Bellary Crop, region

Fig. 2.11. Yield impact of life-saving 5 cm irrigation on rainfed crops in India. (From Dhawan, 1989, after Singh and Vijaylakshmi, 1987.)

Wheat, Agra

Wheat, Rewa

Sorghum, Tobacco, Anand

Bellary Crop, region

Fig. 2.11. Yield impact of life-saving 5 cm irrigation on rainfed crops in India. (From Dhawan, 1989, after Singh and Vijaylakshmi, 1987.)

irrigators. Finally, compared to large surface systems whose design is driven by topography and hydraulics, groundwater development is often much more amenable to poverty targeting. No wonder, then, that in developing regions of South Asia, groundwater development has become the central element of livelihood creation programmes for the poor (Kahnert and Levine, 1993, for the GBM basin; Shah, 1993, for India; Calow et al., 1997, for Africa).

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