Study says north India lost 450 cubic km of groundwater in 2 decades. What does it mean?
The amount of water lost from 2002 to 2021 is 37 times the full capacity of India's largest reservoir, Indira Sagar Dam according to the study.
In two decades, northern India has lost around 450 cubic kilometres of groundwater, with the depletion rate only to be much faster due to climate change, according to a new study.
The study's lead author, Vimal Mishra, Vikram Sarabhai Chair professor of Civil Engineering and Earth Sciences at IIT Gandhinagar, said the amount of water lost from 2002 to 2021 is 37 times the full capacity of India's largest reservoir, Indira Sagar dam, reported news agency PTI.
The study has also found that rainfall in the monsoon season (June to September), across north India has reduced by 8.5 per cent from 1951 to 2021. The reduced rainfall strains the groundwater resources and pulls down its recharge further contributing to groundwater depletion.
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"The accelerating trend of depleting groundwater is expected to continue as the planet warms because even though climate change causes more rainfall, most of it is projected to occur in the form of extreme events, which does not support groundwater replenishment," Mishra told PTI.
The study done by a team comprising researchers from the National Geophysical Research Institute (NGRI) in Hyderabad also claim that winters in the region have become warmer by 0.3 degrees Celsius from 1951 to 2021. This also affects the groundwater resources badly.
The researchers observed during the unusually warm winter of 2022 that warmer winters result in relatively drier soils which requires more irrigation. The winters of 2022 was the fifth warmest for India since the India Meteorological Department started records in 1901, reported PTI.
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Moisture lost from soil has increased over the past 4 decades, which has demanded more irrigation for agriculture, the study says.
The warming across north India by 1-3 degrees Celsius will hamper groundwater replenishment considerably by 7-10 per cent, they said, reported PTI.
This cycle of less rainfall during monsoons followed warm winters combined with climate changes forecasts a "substantial decline" by about 6-12 per cent in groundwater recharge.
The author found, in 2009, groundwater storage had depleted by 10 per cent following a monsoon drier by 20 per cent and a winter warmer by one degree Celsius.
The author predicts an 6-20 per cent increase in irrigation demands with the monsoons set to be drier by 10-15 per cent and winters warmer by 1-5 degrees Celsius.
"For groundwater to get recharged, we need low-intensity rainfall spread over more days," Mishra added.
Changes in groundwater levels largely depends on the rainfall received during summer monsoons and the usage of groundwater to irrigate crops during Kharif (June to September) and Rabi seasons (December to March).
Intensified irrigation demands and reduced groundwater recharge puts strain on resource which is already depleting at a swift pace, Mishra said.
The study also challenges the optimistic perception that the rise in rainfall which is driven by climate change will put an end to water problems, Mishra said.
These findings will have “policy implications” highlighting the need for judicious utilisation of groundwater which is vital food security in India especially in warmer climate due to increased irrigation and industry demands, Mishra told PTI.
According to the author, surface water storage such as in reservoirs and dams are not enough to meet the needs of summer as observed in Delhi and Bengaluru. He said, "Not paying attention to the resource could pose water security challenges in the future."
The study's manuscript, accepted for publishing in the journal Earth's Future, was shared exclusively with PTI.