'Over 200 km cube of groundwater lost in Ganga basin between 2002-2016'

Ganga basin has lost about 225 km cube of groundwater during 2002-2016, which is about 20 times the storage of the largest reservoir in India, a new research has found.

Of this groundwater lost, non-renewable groundwater abstraction is responsible for 80 per cent of the total water lost, a study Swarup Dangar and Vimal Mishra from Indian Institute of Technology, Gandhinagar (IIT-G) said.

The study, titled, 'Natural and anthropogenic drivers of the lost groundwater from the Ganga river basin' was published online on Tuesday in IOPScience, an online service for journal by IOP Publishing.

"Groundwater pumping for irrigation from confined aquifers has been a concern for groundwater sustainability in many parts of the country. The assessment in the study based on the H08 model showed the influence of non-renewable groundwater pumping on the loss of groundwater storage in the Ganga river basin," corresponding author of the study and Associate Professor, Department of Earth Sciences at the IIT-G, Mishra said.

The H08 model is one that considers human influence and provides assessment on water availability and water demand.

If cropland is equipped with groundwater irrigation facilities, all irrigation water requirements are met from groundwater pumping.

Water is first abstracted from renewable groundwater storage to meet the irrigation water requirements and it is abstracted from the non-renewable groundwater storage if the renewable groundwater is depleted.

"Since non-renewable groundwater does not get recharged, pumping from these reservoirs contributes to considerable groundwater storage depletion," the study said.

"...non-renewable groundwater abstraction for irrigation is the primary driver of more than 200 km cube loss of groundwater from the Ganga basin during 2002-2016. While the human footprint dominates the massive loss of groundwater in the basin, the long-term (1951-2016) changes in the climate have also not been supportive," it noted.

"For instance, a significant decline in the summer monsoon season precipitation, frequent droughts, and warming has contributed to the rapid groundwater depletion in the basin. The occurrence of severe droughts has intensified the groundwater abstraction in the Ganga basin during recent decades," the study said.

The authors flagged two limitations by way of availability of observed dataset given the fact that Ganga is a trans-boundary river and its stream flow observations are classified and the other being, static nature of inputs, such as land use or land cover, being used for a single year.

"The H08 model does not consider any capillary rise. Therefore, water from renewable groundwater reservoir does not move into the above lying soil column. Non-renewable groundwater storage is a hypothetical reservoir of infinite volume, which does not assume any recharge from the renewable storage or capillary rise," they pointed out.

In addition, droughts pose double-whammy impacts with increased pumping and reduced recharge in the basin.

"For example, groundwater abstraction was increased by 14 per cent, while recharge was reduced by 13 per cent during the drought of 2015. The non-renewable groundwater abstraction from confined aquifers is a vital resource that would hamper water availability during droughts once depleted," the study said.

Warning that the overdependence on groundwater in certain regions has to be reduced, given the negative impacts of over-withdrawal, the study said, "Intensive groundwater irrigation with changing precipitation (recharge) patterns and increasing climate extremes (such as drought and heat waves) can worsen groundwater availability in the future. Better groundwater management practices will determine the future of groundwater sustainability in the Ganga basin."