Dr. Avnish Jolly, Chandigarh, 21 June:According to a study optimistic projections made by the Planning Commission of India in 2007 regarding availability of water in the country are incorrect.
Professor TN Narasimhan, University of California stressed in his study says the Indian government has “seriously overestimated” available and utilisable water resources and these estimates were based on data provided by the Water Resources Ministry of India in 1999.
The study describes it significantly underestimated Evapo – Transpiration (ET)—a term used to describe the amount of water lost due to evaporation of surface water and transpiration by plants and trees and the use of more realistic value for ET would reduce the amount of water available for human use by at least 37 per cent. This is the second time in 12 months that scientists have raised an alarm over water availability in India.
Last year also N.K. Garg , Indian Institute of Technology-Delhi (IIT-Delhi) called for urgent action before water scarcity becomes unmanageable and he said the government has overestimated utilisable water by as much as 68 per cent and that India is unlikely to meet the annual demand of 897 billion cubic metres (BCM) projected for 2050, even after full development of utilisable water resources.
The source of water for all uses in India is the 3,838 BCM of rainfall it receives annually. Part of it enters rivers and streams, another part recharges the groundwater, and the third part is lost due to ET. According to the Planning Commission’s calculations, the surface flow and recharge components add up to 60 per cent—or 2,301 BCM—of the total rainfall and this is available for human use. This implies that the remaining 40 per cent is lost due to ET. For instance, the ET is 90 per cent for Australia, 82.1 per cent for the Amazon basin, 82.8 per cent for France and between 60.5 and 66.4 per cent for the world’s total land area.
Narasimhan, however, argues that this figure of 40 per cent is significantly lower than published estimates of ET for a number of regions in the world and using a higher ET of 69 per cent—has estimated the available water in India to be 1,460 BCM or almost 37 per cent less than the government projection.
Narasimhan shared that due to engineering and environmental constraints, only about half of the available water—or 712 BCM—is actually utilizable and if we compare this 712 BCM of utilisable water with the current use of 634 BCM, it is clear that India is already at the threshold of over-development of water resources.
The study carried out by IIT-Delhi’s Garg concluded that India has to be seriously concerned about shortage of water right now rather than a few decades from now and his analysis published last year, almost all the basins in India would become water-deficit, thereby raising a big question about the availability of water for inter-basin transfer.
Muthaia Perumal, Hydrologist, IIT-Roorkee said that the study by Narasimhan should serve as a warning and that a credible estimate of ET for India is urgently needed to revise the estimates of utilisable water and impounding more and more water for power production means that ET will further increase, thereby accelerating water scarcity.
Fore more information visit on line issue of June of the Journal of Earth Systems Science published by the Indian Academy of Sciences.