In earlier posts I have referred to data about water availability and utilisation without looking at it in any great detail. The estimates, made by government bodies in turn form the basis of many papers, essays and analysis by administrators, researchers and others (see 1 and 2). In a recent report the Planning Commission too uses the same numbers.
While I had also pointed out several conceptual deficiencies in the estimates I had not examined the data. It is time to do so.
It is instructive here to quote from A Vaidyanathan at some length. In his latest book, India’s Water Resources, while discussing surface flows as estimated by the CWC, he writes:
“………….These estimates have gaps and limitations. The flow observations sites are known to be relatively few, located along the main rivers of each basin and, until recently measurement devices were relatively crude. Locations for which long time series are available are even fewer. Releases from all major and medium reservoirs are supposed to be measured and recorded regularly. However, this information is not available for all reservoirs and in such cases utilisation is estimated on the basis of reported irrigated area.
More importantly, extensive changes have taken place in land use patterns: forest area has declined and the quality of the forest cover has deteriorated; extension of cultivation to marginal lands and soil erosion has led to degradation of land; and natural drainage channels (have) been disrupted by the expansion of road and rail networks and urbanization. These changes are likely to make a significant difference to the quantum, duration, and seasonal profile of surface flows. But their impact on the above has not been adequately and systematically studied. ………….”(pg. 34)
While noting that CWC estimates of utilizable surface flows relate mostly to large storages, he remarks about small structures:
“……….Their extent has been increasing and there is reason to believe that official statistics understate the area irrigated and volume of water harnessed. ……”(pg. 34)
And about Central Ground Water Board estimates of natural recharge from rainfall and recharge from irrigated areas of groundwater, he says:
“..… The Commission (NCIWRD) draws attention to the limitations of these estimates and the need for further research and observation to improve them. While it does not modify the estimate of overall recharge, their projections assume, rather arbitrarily and without citing any reason, that only two-thirds of the total recharge is utilizable in all the basins. ……………”(pg. 34-35)
It would thus seem that the estimate of aggregate water availability and utilisation as well as its categorisation as surface flows and groundwater is based on faulty or inadequate measurements and untenable assumptions.
For several purposes, water flows (irrespective of source and sink) can be treated as one system as the distinction between groundwater and surface flows may not be relevant. Remember water continually flows between the two – surface and ground – and this is not merely natural but human induced as well.
While the overall quantum of water that falls in the form of rain and snow (the starting point of water estimates) is known with a great degree of certainty, evaporation rates and return-flows, to name two important variables need to be measured adequately to estimate aggregate availability and utilisation. However, in several instances it is not only flow quantities but also withdrawals from stocks that matter as for instance if groundwater levels are falling over large tracts of land area.
In other words not only we don’t quite know how much of the total water is flowing on the surface and how much of it is seeping into the ground but that the estimates of both aggregate availability and utilisation too are fraught with severe problems of data that it seems little more than guess work.
Precise estimates as are put out by official agencies should be taken with more than a pinch of salt.
