‘Bengal Water Machine’ Data Offers Potential For Increasing Food Security

The People’s Republic of Bangladesh is one of the most densely populated countries on Earth, with a population of 168 million people in an area a bit smaller than the state of Iowa. To feed everyone, farmers in Bangladesh work year round. In addition to growing crops during the rainy monsoon season, they grow a second or even third crop during the dry season. To do so, they irrigate with groundwater—which helps store water and improves food security. 

Although using groundwater for irrigation isn’t always an effective agricultural technique, research published in the journal Science last month proved that under the right conditions, pumping groundwater can actually help replenish aquifers. By irrigating crops in the dry season, Bangladeshi farmers create space in the water table, helping them capture more of the rainy monsoon season. The researchers call this irrigation technique the ‘Bengal Water Machine.’

“The Bengal Water Machine is an invisible but giant machine that operates underground in many parts of Bangladesh by millions of farmers,” said Dr. Mohammad Shamsudduha, lead author on the Science paper and a geoscientist and associate professor in the Institute for Risk and Disaster Reduction of University College London. Through the Bengal Water Machine, “more [water is captured] than twice the size of the Three Gorges Dam in China,” said Shamsudduha. That’s about 26 trillion gallons of water.

The success of the Bengal Water Machine stems from the unique hydrogeology of the region. Bangladesh gets a lot of rain during the monsoon season, and because its landscape is very permeable—there’s not a lot of concrete, for example—there are many opportunities for the water table to refill.

“This is one of those few cases in the natural sciences where it’s almost like a win-win solution,” said Dr. Aditi Mukherji, a principal researcher in the International Water Management Institute in New Delhi.

In some parts of the world, there are places where pumping groundwater “results in a long term decline in groundwater tables, simply because the rainfall isn’t sufficient to recharge all that was extracted,” said Mukherji. However, “Bangladesh got quite lucky in terms of these natural systems.”

The hypothesis that water storage during the monsoon season in the Ganges River Basin in India, Nepal, Tibet, and Bangladesh contributes to farming success in the dry season has existed for almost 50 years. But Shamsudduha and his colleagues were finally able to prove that the method works through Bangladesh’s robust water monitoring data. 

There are over one thousand government data stations around the country that monitor weekly groundwater levels, according to Shamsudduha. Using about a million data points at 465 monitoring stations, the researchers saw an incremental increase in water levels during the dry season at “about a third of the borehole records we looked at,” Shamsuddha explains, showing how critical the method is to the region. 

Researchers believe that in places with similar environmental conditions, this method might already be contributing to water storage, or could be intentionally added to help store water. “You need a certain kind of aquifer that is closely connected to the surface water body, and you also need high amounts of rainfall—1,000 to 1,200 plus millimeter [40-48 inches] rainfall,” Mukherji said. “When these two things come together, this water machine is likely to deliver.” 

But without sufficient data from other countries, proving it is a challenge.

“This kind of empirical study is only possible with very high-density data for a long period of time,” said Mukherji. She explains that because India shares a border with Bangladesh, it’s reasonable to predict that a similar process is already working in some parts of India. But without similarly robust data monitoring, it’s only a prediction. 

The technique won’t work everywhere, Mukherji and Shamsudduha caution. “Arid places like West India, the North China Plains, and California have seen intensive use of groundwater—and therefore a long-term decline in groundwater overall,” said Mukherji. But in places like Bangladesh, eastern India, and parts of Nepal, “groundwater can be a very powerful tool for poverty alleviation,” she said. 

Climate change may also affect the water machine’s continued function. In the future, monsoon rains are projected to both intensify and occur less frequently, according to Mukherji. More research is required to understand how those trends might affect groundwater recharge.

Also, more than 90% of groundwater pumps in Bangladesh are powered with diesel fuel. Over time, carbon emissions from the extraction process add up.  “One of the ways we have to pay attention is [figuring out] how we provide clean sources of irrigation,” said Mukherji. 

Researching effective ways to implement this strategy in appropriate places could be a key to food security in regions with an unstable climate regime. 

“The discovery of the Bengal Water Machine will definitely inform climate adaptation policies for groundwater pumping strategies in Bangladesh and beyond. This finding will guide us in developing better strategies for groundwater resource management to ensure food security in the future,” said Shamsudduha.

The findings shake up the general apprehension around groundwater extraction as a major form of irrigation, Mukherji said. The study validates Bangladesh’s agricultural strategy, and may also pave the way for more farmers to work together to identify, maintain, or even build their own regional water machines going forward.

“I think my takeaways are that groundwater extraction is not necessarily bad,” Mukherji said. “We just have to be careful, like we are with any other natural resource.”

This article is based on a Science Friday on-air interview with Dr. Mohammad Shamsudduha and Dr. Aditi Mukherji from September 2022. Their quotes have been edited for length and clarity.