US researchers have calculated that accessing untapped freshwater around the world would allow farmers to feed 620 to 840 million more people without depleting water resources or expanding agriculture into natural ecosystems.
Agriculture uses 90% of the world’s water and is thus by far the biggest driver of water scarcity, a serious problem as the planet faces increasing droughts as a result of climate change.
This water scarcity doesn’t just have physical constraints but also economic limitations to harnessing available water for agriculture, with most severe impacts on vulnerable and disadvantaged populations.
Lorenzo Rosa, from the University of California, US, and colleagues call this “agricultural economic water scarcity”, defined as “lack of irrigation due to limited institutional and economic capacity instead of hydrologic constraints”.
To explore this, they used a hydrological model to simulate monthly global crop water demand and estimate the amount of freshwater that is sustainably available for local agriculture, publishing their findings in the journal Science Advances.
They found that half of irrigated land is unsustainable, depleting groundwater and environmental flows – stream flows needed to conserve aquatic habitats – but is a major food source.
“Alarmingly, unsustainable irrigation produces food for 1.3 billion people globally,” says Rosa. “However, we also find that 140 million hectares of croplands are suitable for sustainable irrigation expansion and with potential to feed 800 million more people.”
Two thirds of regions with economic water scarcity are in Sub-Saharan Africa, Eastern Europe and Central Asia. Overall, results showed that expanding sustainable irrigation in 19 low-income countries would increase calorie production by at least a third.
Importantly, by using sustainable irrigation practices, they show that agricultural output can be intensified without deforestation and cropland expansion into pristine habitats.
This would involve building small reservoirs to store water locally during months when there is excess run-off, which can then be used during seasons with water shortfalls.
Other approaches include minimising water evaporation, using indigenous farming methods to increase soil moisture and reduce runoff, mulching, no-till farming and providing shade – a win-win here would be using solar panels to block sun while generating energy.
It would also be prudent to plant less water-intensive crops.
Beyond improving agricultural productivity, they note that other ways to feed humanity sustainably include cutting food waste, reducing red meat consumption and employing sensible strategies to reduce population growth.
Natalie Parletta is a freelance science writer based in Adelaide and an adjunct senior research fellow with the University of South Australia.
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