Farmers pumping groundwater for irrigation might help reduce floods: Study

Millions of small scale farmers in Bangladesh pumping huge amounts of groundwater for irrigation might possibly end up helping mitigate floods during monsoon season, says a study.

Researchers involved in the study are - Mohammad Shamsudduha, associate professor, Institute for Risk and Disaster Reduction, University College London, London, UK; Richard Taylor, professor, Department of Geography, University College London, London, UK; Md Izazul Haq, doctoral researcher, Department of Geography, University College London, London, UK and Lecturer, Department of Disaster Science and Climate Resilience, University of Dhaka; Sara Nowreen, associate professor, Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka; Anwar Zahid, director, Ground Water Hydrology Circle, Bangladesh Water Development Board, Dhaka; and Kazi Matin Uddin Ahmed, professor, Department of Geology, University of Dhaka, Dhaka.

Using millions of groundwater measurements from 465 sites across Bangladesh, Kazi Matin Ahmed and his colleagues at Dhaka University estimated how much groundwater was pumped by more than 16 million farmers between 1988 and 2018.

Intensive irrigation and other agricultural developments since the 1980s have enabled Bangladesh to produce enough food each year to be nearly self-sufficient.

Bangladesh has a lot of groundwater but there are concerns it could be depleted, says Kazi Matin Ahmed.

Together, the farmers operate more than 1 million diesel and electric pumps to flood paddy fields during the dry season, which has enabled more food to be produced on more land, reads the NewScientist.

At roughly 25% of the sites, the records showed depleting groundwater levels. At around 40% levels during the dry season and monsoon remained steady. In the remaining 35%, levels declined during the dry season due to irrigation but aquifers were completely refilled during the monsoon.

"In our part of the world there is a lot of rainfall, there is a lot of river flow," says Kazi Matin. "Not all of that can find its way to the aquifers, because they first become full. When [farmers] extract more groundwater, the water level falls and it creates room for additional recharge."

This additional recharge amounted to between 75 and 90 cubic kilometres of freshwater captured between 1988 and 2018, which is more than twice as much as is held back by the Hoover Dam in the US.

In addition to boosting yields, this "Bengal Water Machine", as the researchers refer to it, may have helped lessen flooding during monsoon seasons.

"If there is no recharge, all the water would be on the surface. Then you have a bigger flood," says Kazi Matin.