Groundwater in TN: Extraction spikes, recharge areas dip

CHENNAI: With Tamil Nadu becoming increasingly reliant on groundwater, especially for irrigation purposes, and the recharge-worthy area remaining the same where rainwater can be harvested, over-exploitation of the available recharge-worthy areas has increased to 30.66% in 2024 from 28.64% in 2023.

According to ‘Dynamic Ground Water Resources of India, 2024’, released by Central Ground Water Board (CGWB), total annual groundwater recharge of the state has been assessed as 21.51 BCM (billion cubic metres) and annual extractable groundwater resources as 19.46 BCM.

In 2023, the annual groundwater recharge and extractable groundwater resources were higher when compared to 2024. But in 2024, the annual groundwater extraction was increased to 14.45 BCM from 14.42 BCM, suggesting that the extraction is going up despite declining resources.

Of the total 14.45 BCM of groundwater, 13.51 BCM is drawn for irrigation purposes. On the other hand, 0.14 BCM and 0.80 BCM are only extracted for industrial and domestic purposes.

Among the districts, Chennai extracts 124.89% of its extractable groundwater and a majority of the groundwater is being used for domestic purposes. Other districts that extract more than 100% of extractable groundwater are Dindigul, Namakkal, Perambalur, Salem, Thanjavur, Tirupattur and Vellore.

Interestingly, except Chennai, all the other districts, which draw more than 100% of groundwater, use a majority of groundwater for irrigation purposes.

During the study, 313 taluks in the State were assessed of which 127 taluks are categorised as safe. On the other hand, 106 taluks are over-exploited and 20 are under critical category. As many as 55 taluks are under the semi-critical category. Groundwater in 5 assessed taluks have salinity. Of the 16 taluks assessed in Chennai, 81% (13 taluks) have been identified as over-exploited.

Similarly, out of 1,08,613.35 sq km recharge worthy area of the State, 33,301.69 sq km (30.66 %) area are under ‘Over-Exploited’, 8,540.25 sq km (7.86 %) under ‘Critical’, 19,244.96 sq km (17.72 %) under ‘Semi-critical’, 45,614.89 sq km (42 %) under ‘Safe’ and 19,11.56 sq km (1.76 %) area under ‘Saline’ categories of assessment units.

Out of total 19,461.53 mcm annual extractable groundwater resources of the State, 5,094.25 mcm (26.18 %) are under ‘Over-exploited’, 1,619.24 mcm (8.32 %) under ‘Critical’, 3,550.20 mcm (18.24 %) under ‘Semi-critical’ and 9,197.84 mcm (47.26 %) are under ‘Safe’ categories of assessment units.

A majority of the over-exploited, critical and semi-critical taluks are in west and south Tamil Nadu districts while a significant number of taluks are under over-exploited category in central coastal districts. “In peninsular India, over-exploited units are wide spread in the states of Karnataka, Tamil Nadu and parts of Andhra Pradesh and Telangana, which could be attributed mainly to the low storage and transmission capacities of aquifers of the hard rock terrains, which results in reduced availability of the resource,” the report pointed out.