According to a new study led by University College London researchers, collective groundwater pumping by millions of farmers in Bangladesh during the dry season each year has created vast underground natural reservoirs that, over a 30-year period, rival the largest dams in the world. These sustain irrigation, which has turned this formerly famine-prone country into a food-secure nation.
The study, which was published in Science, looks at the effects of 16 million smallholder farmers in Bangladesh’s Bengal Basin pumping shallow groundwater during the dry season to water rice paddies between 1988 and 2018.
According to the study, groundwater replenishment during the subsequent monsoon was sped up by lowering groundwater levels through dry season pumping. Surface water was collected, which not only helped groundwater levels rise, but also made flooding less of a problem.
Over a 30-year period, this process, which the authors call “The Bengal Water Machine,” “captured” more than 75 cubic kilometers of freshwater. This is the same amount of water that can be stored in the reservoirs of the US’s Hoover Dam and China’s Three Gorges Dam.
They promote this intervention as a long-term replacement for traditional ways of storing seasonal river flow for irrigation, like dams and reservoirs, which are hard to build in densely populated alluvial plains like the Bengal Basin, which have large flat landforms made of sand, silt, and clay that were left behind by annual floodwaters.
According to co-lead author Dr. Mohammad Shamsudduha of the University College London Institute for Risk and Disaster Reduction, “this scalable, decentralized form of freshwater capture has sustained irrigated food production since the 1990s, despite significant variations in annual rainfall and an overall decline in basin rainfall.”
By increasing the capture and storage of seasonal freshwater surpluses and reducing the risk of monsoon floods without using dams, “this novel intervention helps to address seasonal imbalances in rainfall.”
The Mekong Delta and the Huang He (Yellow River) Delta are two Asian mega-deltas that are similarly susceptible to the effects of climate change, and the study’s authors contend that this straightforward intervention has the potential to be replicated across more alluvial plains. With the help of this Bengal water machine, food security and climate resiliency could both be improved globally.
“Our analysis has profound implications for the expansion and optimization of this crucial, underappreciated engineering marvel that sustains irrigated food production within the alluvial plains of the seasonally humid tropics,” said co-lead author Professor Richard Taylor (UCL Geography).
“Global food security is a strategic issue in a world that is getting warmer because this method of using both surface water and groundwater has shown that it can withstand the hydrological extremes of the dry and monsoon seasons, which are made worse by climate change.”
For their calculations, the researchers used a million weekly groundwater level measurements from 465 wells in Bangladesh taken between 1988 and 2018 at 1,250 monitoring stations.
Professor Taylor said that this is the first study to measure the volume of groundwater based on observations, which shows its great potential. Previous estimates of the amount of freshwater captured were based on guesses and models.
The authors state that, in light of our changing climate, their findings emphasize the value of long-term hydrological monitoring to evaluate the status and trends of a nation’s groundwater resources.
The research does, however, also point out Bengal Water Machine operational limitations in regions of the nation where water leakage during the monsoon season is insufficient to fully replenish groundwater withdrawn during the dry season. Homes that get their drinking water from shallow wells can’t use groundwater resources in these areas because they’ve been pumped dry.
The authors recommend more research into this natural method of storing seasonal freshwater surpluses.
According to co-author Professor Kazi Matin Ahmed of Dhaka University, it is important to figure out where the Bengal Water Machine can work best so that farmers can get the most out of it and the risk of groundwater depletion is kept to a minimum.
Before the operation can be made bigger to deal with operational uncertainties caused by the changing monsoons due to climate change, it must be tested in the right places first.
