This GRACE-based paper was just published in Nature: 'Groundwater Depletion Embedded in International Food Trade' by Carole Dalin, Yoshihide Wada, Thomas Kastner, and Michael J. Puma, Nature 543, 700–704 doi:10.1038/nature21403.
Click on the graphics to enlarge them.
Recent hydrological modelling and Earth observations have located and quantified alarming rates of groundwater depletion worldwide. This depletion is primarily due to water withdrawals for irrigation, but its connection with the main driver of irrigation, global food consumption, has not yet been explored. Here we show that approximately eleven per cent of non-renewable groundwater use for irrigation is embedded in international food trade, of which two-thirds are exported by Pakistan, the USA and India alone. Our quantification of groundwater depletion embedded in the world’s food trade is based on a combination of global, crop-specific estimates of non-renewable groundwater abstraction and international food trade data. A vast majority of the world’s population lives in countries sourcing nearly all their staple crop imports from partners who deplete groundwater to produce these crops, highlighting risks for global food and water security. Some countries, such as the USA, Mexico, Iran and China, are particularly exposed to these risks because they both produce and import food irrigated from rapidly depleting aquifers. Our results could help to improve the sustainability of global food production and groundwater resource management by identifying priority regions and agricultural products at risk as well as the end consumers of these products.
From an article in Phys.Org
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 percent 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 percent of the global non-renewable groundwater drawn up for irrigation goes to produce crops that are then traded on the international market. Additionally, two-thirds of the exported crops that depend on non-renewable groundwater are produced in Pakistan (29 percent), the United States (27 percent), and India (12 percent).
"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."
This is quite a study, but are the results that surprising? No. We've known for several years about global groundwater depletion. Most of that water is used to irrigate crops. A lot of those crops are sold internationally. So a fair amount of that unsustainable groundwater goes internationally as well - as virtual water. But now we have a handle on the numbers, and that's important.
Only one quote will do today - Lord Kelvin's classic one on numbers....
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind..." - William Thomson (Lord Kelvin)