Where the problem has begun to pinch hard, the Asian response to groundwater depletion has been supply-side rather than demand-side. The standard reasoning is that even after building 800,000 big and small dams around the world, the reservoirs can capture and store no more than one-fifth of the rainwater, the bulk of the remainder still running off to the seas. In India, which has built more than its share of the world's dams, 1150 km3 of the rainwater precipitation still runs off to the seas annually in the form of 'rejected recharge' (INCID, 1999). If a fraction of this could be stored underground by reducing the velocity of the runoff and providing time for recharge, groundwater supplies could be enhanced significantly. But this presumes active aquifer management where planned drawing down of the water table in the premonsoon dry months is an important element of the strategy for enhancing the recharge from monsoon rainwater as well as from irrigation return flows. Such proactive aquifer management is an established practice in many industrialized countries; for instance, the share of artificial groundwater recharge to total groundwater use is 30% in western Germany, 25% in Switzerland, 22% in the USA, 22% in Holland, 15% in Sweden and 12% in England (Y. Li, 2001).
Mega projects for interbasin transfer of water from surplus to deficit basins are increasingly talked about in groundwater irrigation areas of Asia. China is already executing a mega project for trans-basin diversions of approximately 25 km3/year of water from the Yangtzi river in the water-surplus South to the water-scarce Yellow River basin in the North (Keller et al., 2000). India has for a long time talked about a garland canal to link Himalayan rivers with Cauvery and other South Indian rivers; these have so far remained at the ideas level but with the passing of every drought, these seemingly impractical ideas acquire new appeal and credibility. In 2002, the Supreme Court of India enjoined the central government to undertake such linking of rivers on a war footing partly to alleviate the pressure on groundwater in western and peninsular India. Gujarat, the western Indian state chronically dependent on groundwater overdraft for its agriculture, has already started using interbasin transfer of water from the controversial Narmada project to counter groundwater depletion in parts of Saurashtra and North Gujarat.
The economics of interbasin transfer are deeply influenced by the groundwater economy. In Gujarat, for example, it has been argued that the overall economics of the Narmada project become far more favourable when we include into the cost-benefit calculus the beneficial impact of Narmada waters in significantly countering groundwater depletion in North Gujarat where farmers are using subsidized electricity to pump groundwater from 250 to 300 m. The saving of electricity subsidy required to sustain groundwater-irrigated agriculture and rural livelihood systems in such regions can tilt the cost-benefit ratios in favour of surface irrigation projects.
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