PNNL

The Science
Water scarcity poses a significant threat to global food supplies. To determine how the agriculture sector might respond to this threat, researchers from the U.S. Department of Energy’s Pacific Northwest National Laboratory embedded groundwater availability and cost estimates by region into a global model that simulates behaviors of water users. In the model, crop growers in any region can respond to increasing water costs by replacing crop types or by expanding or contracting land allocated to irrigated and rainfed crops.

This study showed that the agriculture sector may be able to adapt through slight increases in irrigated and rainfed crop production across regions where water remains plentiful. Regions with unsustainable groundwater use could experience major agricultural and economic declines.

The Impact
An estimated 90 percent of the world’s population lives in countries that import more than four-fifths of their staple food crops from regions that irrigate crops by drawing down groundwater. When groundwater starts running out in these regions, global food producers must adapt—or the supply will decline. The study identifies ways in which the agricultural sector could adapt to meet global food demands by the year 2100.

Summary
Many of the world’s major freshwater aquifers are being unsustainably tapped. Some of these aquifers are projected to approach environmentally unsafe drawdown limits within the 21st century. Because aquifer depletion tends to occur in important crop-producing regions, the prospect of running dry poses a significant threat to global food security. Researchers explored the response of land use and agriculture sectors to severe constraints on global water resources using the Global Change Assessment Model (GCAM). The model simulated a scenario in which water withdrawal from numerous important groundwater aquifers became unviable, either because of excessive extraction costs or reaching environmental limits. Researchers compared those findings against a scenario without constraints on water withdrawals. The team found that groundwater depletion and associated increases in water price led to an expansion of rainfed crops, primarily within regions that already had rainfed agriculture. Researchers also saw a shift in irrigated crop production toward regions with cheaper water resources, such as the Orinoco and La Plata basins of South America. The most pronounced losses in crop production occurred in water-stressed regions experiencing unsustainable groundwater depletion to meet irrigation demands—namely northwest India, Pakistan, the Middle East, the western United States, Mexico, and central Asia. While these results highlighted substantial risks for the affected regional agricultural economies, the study showed that, in a world with frictionless trade, modest changes in irrigation and crop growth location could help fulfill global food demands despite severe water constraints.

PI Contact
Mohamad Hejazi 
mohamad.hejazi@pnnl.gov  

Funding
This research was supported by the Office of Science of the U.S. Department of Energy through the MultiSector Dynamics, Earth and Environmental System Modeling program.