Replacing rice crop could help recover groundwater lost since 2000: Study

Replacing about 40 per cent of the area sown with rice with other crops could help recover 60-100 cubic kilometres of groundwater lost since 2000 in north India, a study has found.

Current cropping patterns -- dominated by rice, which relies heavily on groundwater for irrigation -- could result in a loss of about 13-43 cubic kilometres of groundwater if warming of the planet continues, a team of researchers, including those from the Indian Institute of Technology Gandhinagar, Gujarat, said.

The researchers proposed shifting from existing cropping habits by cutting down on cultivating rice as a potential solution for sustaining the fast-depleting resource in a warmer world that threatens food and water security.

"Replacing 37 per cent area of rice with other crops can recover 61 to 108 cubic kilometres groundwater compared to 13 to 43 cubic kilometres with current cropping pattern under the 1.5-3 degrees Celsius global warming levels," the authors wrote in the study accepted for publication in the journal Proceedings of the National Academy of Sciences (PNAS) Nexus.

Compared to current cropping trends, the benefits of switching crops in saving groundwater are more during the prolonged dry periods predicted under global warming, the researchers said

According to the 2018 Intergovernmental Panel on Climate Change's (IPCC's) Special Report: Global Warming of 1.5 degrees Celsius, if current trends continue, global warming is likely to reach 1.5 degrees Celsius between 2030 and 2050 and could reach 3 degrees Celsius by 2100.

Changing crop patterns can be substantially beneficial -- particularly for the states of Punjab, Haryana, and Uttar Pradesh -- for ensuring groundwater sustainability and farmers' profitability, the authors said.

They also found that switching of crops did not substantially impact groundwater levels where recovery rates were low such as in the states of Himachal Pradesh, Uttarakhand, and Jharkhand.

The findings have policy implications for identifying optimal cropping patterns for sustaining groundwater in the irrigated regions of north India, along with ensuring farmers' profitability and income, they said.

Previous estimates have suggested that about 300 cubic kilometres of groundwater have been lost between 2002 and 2022 as a result of the cropping trends in north India, where 80 per cent of the cultivated area is sown with rice.

Parts of Punjab and the Ganga basin experienced the fastest rates of groundwater depletion in the world, the researchers said, and added that northern and northwestern regions of India are among the global groundwater hotspots.

Studies have shown crop switching to be beneficial for environmental sustainability and farmers' income in China, the US and India.

In this study, the researchers looked at current cropping patterns in regions that have seen considerable groundwater depletion. The team then used groundwater, well and satellite observations and models to estimate groundwater lost between 2002 and 2022.

For estimating the effects of switching crops on groundwater, the team evaluated two scenarios -- in one, the rice-grown area is cut down by five per cent, while in the other, an additional 37 per cent of rice-area is replaced with cereals, pulses and oilseeds, resulting in a total of 42 per cent reduction of rice-grown area.

The authors found 45 cubic kilometres of groundwater could have been saved in the first scenario and 91 cubic kilometres of groundwater could have been saved in northern India during 2002-2022 in the second scenario, compared to the current cropping patterns.

They also found that in Punjab and Uttar Pradesh, the groundwater saved over the last two decades could have been around one to four times the maximum holding capacity of the largest dam in India, the Indira Sagar, under the two scenarios.

Further, under scenario one, the researchers estimated a 13.5 per cent boost in farmers' profits, whilst maintaining the same rice production.

However, under the second scenario, the authors estimated about 86 per cent increase in farmers' profits, but at the cost of a notable 45 per cent reduction in rice production.

Suggesting alternatives to cultivating rice, the researchers proposed cereals for Uttar Pradesh and oilseeds for West Bengal.