Explainer: Decoding India’s groundwater data | The Financial Express

Explainer: Decoding India’s groundwater data

The World Bank, some years ago, had predicted 21 Indian cities, including Delhi, Bengaluru, and Chennai,  to run out of groundwater.

Explainer: Decoding India’s groundwater data
Groundwater resources that can be replenished annually are called dynamic groundwater resources. (Photo source: Bloomberg)

The 2022 Dynamic Groundwater Resources of India report, which says that the country’s annual groundwater recharge and extractable groundwater levels have improved since 2020, has drawn criticism from experts. They believe the assessment isn’t accurate. Sarthak Ray explains how the data on groundwater is reported.

What are dynamic and static groundwater resources?

Groundwater resources that can be replenished annually are called dynamic groundwater resources. They are more important from a development planning perspective since annual replenishment of the other source of groundwater—static or in-storage resources—is often not possible. Indeed, any change to such resources indicates long-term impact of groundwater mining. Extraction from in-storage resources, the Central Ground Water Board says, may only be allowed during exigencies, with planning for “augmentation in succeeding excess rainfall years”. The World Bank, some years ago, had predicted 21 Indian cities, including Delhi, Bengaluru, and Chennai, to run out of groundwater.

What has the 2022 report found, and why is it being criticised?

The total annual groundwater recharge is estimated at 437.60 billion cubic metres, higher than 2020’s 436.15 bcm by 1.45 bcm. Crucially, the annual extraction is reported to have dropped from 244.92 bcm to 239.16 bcm. Of the 7,089 assessment units, 1,006 are classified as over-exploited (annual extraction exceeds recharge), while 260 are ‘critical’ (extraction at 90-100%). Both categories report improvement from 2020 (1,114 and 270).The findings have been criticised by water experts. Himanshu Thakkar of South Asia Network on Dams, Rivers and People says, “The findings on recharge and extraction both seem counter-intuitive. What is happening on the ground doesn’t seem to reflect what has been reported.” He also said that given aquifers—except the alluvial formations—are very localised, the assessment units are too large to reflect the condition accurately. Also, whether the additional recharge is happening in water-logged areas or saline areas—accrual in the latter would mean the recharge can’t be used—needs to be seen.

“Communities need to be made aware and empowered to collectively conserve groundwater,” Thakkar says. 
How do dynamic groundwater sources get replenished? Rainfall is the main source of recharge. It accounts for over three-fifths of the total annual groundwater recharge. However, there is high spatial and temporal variation. Large swathes of India receive rainfall primarily during the Southwest Monsoon season (June to September). Tamil Nadu, on the other hand, depends on the Northeast Monsoon (October to December). J&K, Himachal Pradesh and Uttarakhand receive significant rainfall throughout the year. Rock types have a significant effect on recharge. Porous ones, such as alluvial formation in the Ganga-Brahmaputra basin, are good repositories. Groundwater in two-thirds of the country, on the other hand, is limited to weathered, jointed, and fractured portions of the rock.

How is groundwater data calculated?

Assessment of dynamic groundwater in India focuses on annual extractable groundwater, extraction, and percentage of use with respect to resources. The assessment units are talukas/blocks/mandals/firkas. Assessment has been done in 1980, 1995, 2004, 2009, 2011, 2013, 2017, 2020, and 2022. Earlier, the Groundwater Estimation Committee 1997 (GEC 97) norms were used. Since 2017, GEC 2015 is used. Under GEC 2015, if aquifer geometry has not been established for the unconfined aquifer (whose upper water surface rises and falls) in an assessment unit, the static resources have to be assessed in the alluvial areas down to the depth of bedrock or 300 m, whichever is less. For hard rock aquifers, the depth would be limited to 100 m. For confined aquifers, if groundwater extraction is being done, the dynamic, as well as static, resources are to be estimated. 

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First published on: 24-11-2022 at 01:26:18 pm
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