We already know that humans are depleting vital groundwater resources across the globe. But a new study shows one of the biggest causes of disappearing groundwater is the international food trade.
About 70 percent of freshwater around the globe goes toward irrigation. Researchers from the University College London and NASA’s Goddard Institute of Space Studies now say that a third of that freshwater is drawn from the world’s aquifers — nonrenewable underground pockets of groundwater — and 11 percent of that nonrenewable groundwater is used to irrigate internationally-traded crops.
That means in time, “the current type of food that’s grown will not be able to be produced,” said Carole Dalin, an environmental engineer at the University College London who led the study published in Nature. “Or we’ll not have the same productivity, so it means prices will increase.”
When water is used to grow crops, it’s no longer visible to the consumer. This study keeps track of where this ‘hidden’ water is embedded and where it ends up.
To measure how irrigation drains global aquifers, Columbia University hydrologist and study co-author Yoshihide Wada used an in-house model that essentially places a computerized grid over the Earth and then measures soil moisture, along with water exchange between the atmosphere, soil layers and the underlying groundwater reservoirs, to see where water was going and why. He validated his calculations by comparing them with satellite measurements that track water flow and underground water storage.
Meanwhile, Dalin gathered information on global trade and irrigation rates. By combining the information, they could determine how much groundwater was sapped by the agriculture required for the international food supply.
Rice used 29 percent of the groundwater intended for international food crops, topping the study’s list, followed by wheat (12 percent), cotton (11 percent), maize (4 percent) and soybeans (3 percent). Citrus and sugar crops used about 5 percent each.
Source: www.pbs.org