Date: September 18, 2022
The global rise in irrigation over the last half century has unquestionably improved the volume and
resilience of food production to climate variability and change. However, groundwater depletion in
the world’s most productive food-growing regions now threatens global food security.
Under Asia’s Green Revolution, use of shallow groundwater for irrigated rice production during the
dry season by smallholder farmers rose dramatically and continues to occur from large alluvial
aquifers within seasonally humid river basins. Today, Asian farmers account for 90% of the world’s
rice production. Conventional approaches to the storage of seasonal river flow employ dams but
the low-lying relief of densely populated alluvial plains challenges the implementation of such
infrastructure.
A new study published today in Science highlights an alternative solution to freshwater storage in
the Bengal Basin of Bangladesh whereby incremental increases in dry-season groundwater
pumping for irrigation lower groundwater levels and enhance leakage under gravity of surface
water from rivers, ponds and canals during the subsequent monsoon. The authors describe this
broad set of recharge pathways induced by dry-season groundwater pumping as ‘The Bengal
Water Machine’.
As the study’s Lead Author, Dr. Mohammad Shamsudduha of UCL IRDR, argues, “this intervention
seeks to increase the capture and storage of seasonal freshwater surpluses while mitigating the
monsoonal flood risk.”
“We quantify for the first time this nature-based solution to seasonal freshwater storage capture,
showing that the collective operation of ~16 million smallholder farmers in Bangladesh from 1988
to 2018 has induced cumulative freshwater capture of between 75 and 90 cubic kilometres, a
volume that is equivalent to the combined reservoir capacities of the Three Gorges and Hoover
Dams.”
The authors’ research also highlights limitations to the operation of the Bengal Water Machine in
areas of Bangladesh where induced monsoonal recharge is insufficient to fully replenish
groundwater abstracted during the dry season, depleting groundwater storage and rendering
groundwater inaccessible to households reliant on shallow wells. Professor Kazi Matin Ahmed of
Dhaka University, a co-author of the study, cautions “It is vital to assess the suitability of locations
for the operation of The Bengal Water Machine in order to maximise benefits to farmers and
minimise the risks of groundwater depletion.”
The authors’ calculations are rooted in analysis of 465 multi-decadal records of groundwater levels
across Bangladesh. As co-author Dr Anward Zahid of the Bangladesh Water Development Board
notes, “our findings highlight the importance of long-term hydrological monitoring to assess the
status and trends of country's groundwater resources.”
The study’s other Lead Author, Professor Richard Taylor of UCL Geography, points out, “this
scalable, decentralised form of freshwater capture has sustained irrigated food production despite
substantial variations in annual rainfall and an overall decline in basin rainfall since the 1990s. As
such, our analysis has profound implications for the expansion and optimisation of this vital, under-
recognized engineering marvel that sustains irrigated food production within alluvial plains of the
seasonally humid tropics. In a warming world, the demonstrated resilience of this conjunctive use
of surface water and groundwater to hydrological extremes amplified by climate change, is of
strategic importance to global food security.”
Co-author Dr. Sara Nowreen of the Bangladesh University of Engineering and Technology argues
for “the piloting of the operation of The Bengal Water Machine in suitable areas before upscaling
more widely to address uncertainties in its operation to monsoonal variability under climate
change.”