A new study by researchers at the University College London and NASA’s Goddard Institute of Space Studies in New York City shows that 11 per cent of the global non-renewable groundwater drawn up for irrigation goes to produce crops that are then traded on the international market. Two-thirds of the exported crops that depend on non-renewable groundwater are produced in Pakistan (29 per cent), the United States (27 per cent), and India (12 per cent).
The analysis is the first to determine which specific crops come from groundwater reservoirs that can’t quickly be replenished and where they are consumed.
Some underground aquifers replenish so slowly that they are essentially a non-renewable resource.
Countries that export and import these crops may be at risk of losing the crops (and economic benefits) produced with non-renewable groundwater. Importers may need to find alternative sources, possibly at a higher cost.
The results were published in Nature on March 30 (see HERE).
“When people consume certain imported foods, they should be aware that they can have an impact on the environment elsewhere,” said lead author Carole Dalin, of the University College London.
Dalin and her colleagues used trade data on countries’ agricultural commodities from the United Nations Food and Agriculture Organisation. They then combined it with a global hydrologic model — validated with ground information and NASA satellite data — to trace the sources of water used to produce 26 specific crop classes from their country of origin to their final destination.
Co-author Michael Puma, of NASA’s Goddard Institute for Space Studies and Columbia University, explained conjectured on how the data might be used.
“Say I’m in Japan, and I’m importing corn from the United States. It’s important from Japan’s perspective to know whether that corn is being produced with a sustainable source of water, because you can imagine in the long term if groundwater declines too much, the United States will have difficulty producing that crop.”
Globally, 18 per cent of all crops are traded internationally. The remaining 82 per cent stays in country for the domestic market. But the amounts of various exported crops produced using unsustainable groundwater rose significantly between 2000 and 2010.
In India, for example, exports of groundwater-depleting crops doubled in that period while Pakistan’s increased by 70 per cent and the United States’ rose by 57 percent.
Major importers of crops raised with non-renewable groundwater include the United States, Iran, Mexico, Japan, Saudi Arabia, Canada, Bangladesh, the United Kingdom, Iraq, and China, which went from a net exporter in 2000 to a net importer in 2010. Countries on both lists often export different commodities than they import.
Wheat, rice, sugar, cotton and maize are among the essential internationally traded crops in the global economy. To produce them many countries rely on irrigated agriculture that accounts for about 70 per cent of global freshwater withdrawals, according to the United Nations Water programme.
Aquifers form when water accumulates in the ground over time, sometimes over hundreds or thousands of years. Non-renewable aquifers are those that do not accumulate rainfall fast enough to replace what is drawn out to the surface, either naturally to lakes and rivers or in this case by people via pumping.
Dalin explained that once the groundwater is depleted, it will effectively be gone for good on the scale of a human life-time, and will no longer be available for relief during crises such as droughts.
Drawdowns in aquifers worldwide have been observed over the last 15 years by NASA’s Gravity Recovery and Climate Experiment, a pair of satellites that detect changes in Earth’s gravity field to see the movement of masses such as ice sheets and, in this case, underground water.
“What’s innovative about this study is it connects groundwater depletion estimates with country level data,” said NASA hydrologist Matt Rodell at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in the study.
More research was needed to consider population growth, changing diets, climate change, the implementation of irrigation technology and policy changes to understand when these aquifers may begin to run dry, he said.
Dalin said the absolute amount of water in many of these aquifers is difficult to quantify, though experts in many regions are already looking at better methods to determine how much water remains and how long it may last. Now and in the future, decision-makers and local farmers will need to decide on a strategy for using this non-renewable water that balances the needs of short-term production versus long-term sustainability, she said.