GROUNDWATER IS the life-line of India’s food and drinking water security. With about 250 cubic km of extraction in a year, of which 85 per cent is used for agriculture, India is the largest extractor of groundwater in the world. Almost the entire rural water supply and over half of urban water demand is catered by aquifers. It is essential to assess this invaluable, invisible resource for its proper management.
Southwestern monsoon is the major source of groundwater recharge. In India, we divide ground- water resource into dynamic or replenishable and static or in-situ. The dynamic component is the annual recharge of aquifers, while the static resource is the groundwater volume available at depth of rock formations, stored over hundreds or thousands of years. India is one of the few countries engaged in a detailed assessment of the dynamic component at regular intervals since 2005. Post 2009, the estima tion is made every two years, the latest being in 2013. The resource is assessed for each block/taluka/firka for all states and union territories in a joint endea vour by states and the Centre under the supervision of the Central Ground Water Board (CGWB). The assessment calculates the recharge to aquifer and the extraction to work out the Stage of Groundwater Development (extraction/resourcex100), or SOD. The lower the SOD, the better the aquifer or area is. The dynamic resource and SOD are extensively used in policy and governance, for instance, to prioritise government funding for schemes or issuing no objection certificates by the Central Ground Water Authority to extract groundwater by industries.
The latest assessment in 2013 pegs India’s dynamic resources at 447 cu km, an increase of 14 cu km from 2011. The extraction (an estimate of how much is taken out from aquifer for different societal uses) has also increased by 8 cu km. SOD has remained the same, at 62 per cent. However, recharge of the deeper aquifers and extraction from the deeper aquifer is not a part of this assessment. This is creating some confusion because a few researchers, when using satellite data for assessing groundwater extraction, report the volume extracted as more than the assessment made by CGWB (groundwater can be extracted from shallow and deep aquifers. CGWB estimates extraction from shallow aquifers, but researchers who use satellite data incorporate total draft, both from shallow and deeper aquifers. Hence their draft estimates are more than those of CGWB). This is particularly true of the Indo-Ganga-Brahmaputra plains that have multi-tiered aquifers. There are places where the near-surface shallow aquifers have ample unutilised resources, while the deeper ones are exploited and show desaturation. This is evident in urban areas in the plains, which almost entirely depend on aquifers. The issue will be solved once the National Aquifer Mapping and Management Programme undertaken by the Union water ministry is completed.
There is no firm and detailed policy on the static resource conservation, rejuvenation and use, only an understanding that we must restrict extraction within the dynamic resource available in that area. The static component should be used in case of emergency like drought. In fact, in overexploited areas there is an incremental eating up of the static resource, resulting in permanent damage to aquifers. A preliminary assessment shows substantial static resource in alluvial areas and not so much in hard rock aquifers because of inherent aquifer properties. Effort should be made to assess the static resource countrywide. We look forward for a firm policy on the extent of spatial and time-domain use of static resource and its rejuvenation in various aquifer typology and agroclimatic zones.
(The writer is former member of the Central Ground Water Board)