Crop trade depletes global groundwater

A team of researchers led by Carole Dalin of University College London quantified the level of groundwater depletion linked to international exports and imports of 26 crop classes in the years 2000 and 2010.

“In particular for the Middle East and North Africa, the imports per capita are high,” says Dalin, of her research published in Nature¹. “Up to nearly 150m³ per capita per year [of non-renewable groundwater] are involved in Qatar’s food imports. This comes in addition to the direct water consumption in Qatar, which has been found to be one of the highest in the world."

According to the researcher, that 150m³ is only non-renewable groundwater; to produce Qatar’s food imports, the country consumes water from other sources, such as renewable groundwater, surface water and rainfall.

The study placed Qatar, Bahrain, Oman, Kuwait and the United Arab Emirates in the top ten largest importers of groundwater depletion per capita in 2010. Groundwater depletion is the unsustainable use of groundwater for crop production and is defined as the volume of groundwater that is extracted for irrigation use in excess of the natural recharge rate and irrigation return flow.

Iran, Saudi Arabia, Libya and Turkey together account for nearly a quarter of the world’s non-renewable groundwater used for irrigation, says Dalin. 

The study found that Kuwait showed extreme groundwater depletion intensity for wheat: 21,900 litres of groundwater per kilogram, compared to an average of 812 l/kg in other countries with groundwater depletion. 

Saudi Arabia showed extremes in groundwater depletion for maize: 790 l/kg compared to an average of 72 l/kg in other countries with groundwater depletion.

Saudi Arabia is among the top five countries — the others being the US, China, India and Mexico — for groundwater depletion that are also among the top importers of groundwater depletion via food trade. 

“These key countries import or export crops irrigated from the world’s most stressed aquifer systems. The food production relying on these aquifers is particularly unsustainable as the extraction rates are 20 to 50 times higher than required for sustainable groundwater use,” write the researchers. 

Exhausting threatened aquifers in these countries will impact food supply both domestically and in their water-stressed trade partners, the researchers emphasize. 

“Regardless of where food is sourced, it is critical that a greater understanding and quantification of the inputs and outputs of our agricultural systems is determined. Only then can informed strategies towards food and water security be developed,” says hydrologist Matthew McCabe of King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, who was not involved in the study. 

Since the 1990s, there has been rapid agricultural expansion throughout the Middle East, explains McCabe. “Unfortunately, this growth in agricultural production over the last few decades has come at the cost of considerable groundwater depletion, since renewable water resources are scarce.”

It is not a sustainable solution for food production, according to the researcher. 

“Growing populations combined with increasing incomes throughout the region have seen an increase in demand not just for cereal crops, but also meat: one of the major users of water per kilogram of product … In dryland systems such as the Middle East and North Africa region, establishing a balance between food and water security will be a major challenge,” he says.

McCabe’s group at KAUST is developing techniques to better estimate water consumption using high-resolution satellite data. Their aim is to provide a more accurate and timely accounting of water use, in addition to more detailed information on crop types, health and production. 

“Our approach is to shift from precision agriculture into decision agriculture, helping farmers, farm managers and governments to optimize inputs of water and nutrients to maximize crop yield,” explains McCabe.

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