Globally Traded Crops Guzzle 11% of Groundwater

Wheat, rice, sugar, cotton and maize are among the essential internationally traded crops in the global economy.

To produce these crops, many countries rely on irrigated agriculture that accounts for about 70% of global freshwater withdrawals, according to the United Nations Water program. One freshwater source is underground aquifers, some of which replenish so slowly that they are essentially a non-renewable resource.

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% of the global non-renewable groundwater drawn up for irrigation goes to produce crops that are traded on the international market, Phys.org reported.

Additionally, two-thirds of the exported crops that depend on non-renewable groundwater are produced in Pakistan (29%), the United States (27%) and India (12%).

"It's not just individual countries that experience groundwater depletion, but also their trade partners," said lead author Carole Dalin of the University College London. "When people consume certain imported foods, they should be aware that they can have an impact on the environment elsewhere."

The results were published on March 30 in Nature.

Dalin and her colleagues used trade data on countries' agricultural commodities from the United Nations Food and Agriculture Organization. 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.

Their analysis is the first to determine which specific crops come from groundwater reservoirs that won't renew on human time-scales and where they are consumed.

"It's important from [the importer's] perspective to know whether the crop they're importing is being produced with a sustainable source of water, because you can imagine in the long term if groundwater declines too much, [the exporter] will have difficulty producing that crop," said co-author Michael Puma of NASA's Goddard Institute.

Globally, 18% of all crops grown are traded internationally. The remaining 82% stay in country for the domestic market. However, the amounts of various exported crops produced using unsustainable groundwater rose significantly between 2000 and 2010.

India, for example, saw its exports of groundwater-depleting crops double in that period, while Pakistan's rose by 70% and the United States' rose by 57%.

  Trouble for Exporter, Importers

Countries that export and import these crops may be at risk in the future of losing the crops and their profits, produced with non-renewable groundwater. Importers may need to find alternative sources, possibly at a higher cost.

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.

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.

Once that 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.

Puma said more research needs to be done which considers population growth, changing diets, climate change, the implementation of irrigation technology and policy changes to understand when these aquifers may begin to run dry.

"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," Dalin said.