"Nearly all of the moisture that falls as precipitation over these "breadbasket" regions ultimately originates from and returns to the ocean," Justin Bagley of the University of Illinois Urbana-Champaign, US, told environmentalresearchweb. "However, on the moisture's trip it may rain over land and be re-evaporated into the atmosphere several times before it reaches its destination. During these events, the vegetation and the land surface properties determine the amount of moisture that returns to the atmosphere."

Bagley, who was previously at the University of Wisconsin-Madison, says his study indicates the potential for land-cover change to directly impact crop growth through the hydrological cycle. But it's possible that future changes in atmospheric circulation and crop management decisions may reduce these impacts.

The team, from the University of Wisconsin-Madison, Center for Ocean-Land-Atmosphere Studies, and University of Minnesota, used the "relatively simple approach" of a new land-surface model and global long-term estimates of moisture sources for precipitation determined using model-data fusion techniques. According to Bagley, "this approach reduced computational requirements and minimized pitfalls associated with simulating the full atmospheric hydrological cycle".

The investigation focused on three key rain-fed crops – maize, spring wheat and soybeans – that together make up about 40% of global cropland. Rice was omitted because it's generally grown under irrigation. The team selected five breadbasket areas – maize in the Midwest US, soybeans in Southeast South America, maize in West Africa, the Central Asian wheat belt, and wheat in East Asia.

"This represents a first attempt at quantifying where moisture for major crop-growing regions of the world comes from, how changes in land cover may alter these moisture sources, and how altered moisture may impact crop yield," said Bagley.

Global population is expected to reach around 9 billion by 2050, up from 7 billion today. In combination with changing diets, that's likely to mean an 80–120% increase in global food production. Since managed croplands and pastures currently take up 30–40% of Earth's ice-free land surface, this will no doubt require both technological improvements and conversion of natural ecosystems.

"With changing global population, diet, and climate, the breadbasket regions are likely to become even more vital in the coming century," said Bagley. " In these regions this study indicates that changes in land cover have the potential to significantly impact moisture available to crops, and hence yield. As such, future changes in land cover should be assessed to determine their hydrological impacts."

The team found that the breadbasket areas were susceptible to moisture availability reductions of 7–17% due to land-cover change. South American soybeans and Central Asian wheat saw the largest potential decrease, probably because their moisture tends to come from heavily forested areas, where land-cover change can have a big influence on growing-season evapotranspiration.

These moisture reductions could decrease crop yield by 1–17%, with the East and Central Asian wheat and North American maize regions likely to be most affected, and West African maize least disturbed. Areas predicted to have greater reductions in moisture availability tended to show larger drops in potential crop yield; yields in regions that had moister soil during the growing season were generally less affected.

"While this study benefited from a simplified approach, it would be interesting to make a more detailed study of the individual regions," said Bagley. "I am currently pursuing this by using a more detailed fully coupled land-atmosphere model in key regions to test the role that changes in atmospheric circulation and stability have for the impacts of realistic land-cover change."

The scientists reported their work in Environmental Research Letters.