28 March 2013

Warming could degrade U.S. Midwest farmlands while boosting African, Chinese harvests

Posted by kramsayer

A new study examines the effects of global warming on water availability for farmers worldwide (Credit: NRCS)

Rising global temperatures will concentrate arable land in southern Africa, northern China and the west coast of South America – but leave the United States’ Midwest desiccated, according to new research.

Two scientists used computer models to forecast the future water budget for farming worldwide. For several future climate scenarios, they calculated the combined effect of precipitation and farmland water consumption. Their findings show that the time period 2070 to 2099 will experience a slight increase in the global water budget available for farming. However, much of the lushest land in the future will be located in regions that could face difficulties sustaining the growing demand for food, said Ximing Cai, a professor of water resources engineering at the University of Illinois, Urbana-Champaign.

Many researchers who study climate change and agriculture “have predicted that Africa will have a greater opportunity for agricultural development, and that the water deficits in the Midwest will continue to worsen,” said Cai, author of the new study recently published in Geophysical Research Letters, a journal of the American Geophysical Union. “Our study not only confirms these predictions, but also shows the impacts of climate change on farming in every region of the world.”

Cai’s previous research tested and evaluated climate change models. He and PhD candidate Xiao Zhang have now applied the results from this past work to global crop data to create a comprehensive analysis of the future effects of climate change on agriculture.

“For ten years, my team has worked to extract meaning from climate-change models and evaluate their accuracy based on how close their predictions align with reality and the likelihood they can predict the future,” Cai said. “This way we minimize model uncertainty and get better climate-change predictions.”

After evaluating 20 different climate-change models, Cai and his team aggregated the results from the six best models under two emission scenarios to estimate future rainfall and temperatures in four possible future climates. They then determined the resulting balance between crop water consumption and precipitation for 26 crops—such as corn fields in Iowa and sugar cane in the Caribbean—under each potential climate and under both rain-fed and irrigated conditions.

Agricultural water availability will change in the future due to global warming, according to a new study. Regions in red are projected to have a drop in available water for farming, while those in blue are projected to see an increase. (Credit: Cai, GRL)

All four climate-change scenarios agree that Africa, China and South America will have an average increase in the amount of water available for farming, but the results for the United States and Europe are less clear-cut. Within the United States, the simulations predict an increasingly disparate distribution of water—with more in the Northwest and a sharp decline in states bordering the Mississippi River.

Overall, the global water budget for farming is expected to increase slightly. This slight increase is counter-intuitive, Cai said, but as the Earth continues to warm, the gap between the highest and lowest daily temperatures has decreased in past decades. And scientists expect it to continue to decrease in the future.

“Studies have shown that when there is less temperature variation throughout the day, there is more cloud cover and higher humidity, which reduces the rate of evaporation,” Cai said.

Despite the ominous forecasts of a drier Midwest, Cai said farmers will undoubtedly adapt to changing conditions by planting crops that don’t need as much water, or by changing the times they plant and harvest. It also shows that global warming will not have a universally desiccating effect, but affect every region of the world uniquely, Cai said.

“Global warming will give some regions a great opportunity for agricultural development,” Cai said. “But a concern is whether these regions, such as Africa, will have the infrastructure to support it. The world may need to pay attention to the new infrastructure development requirements to optimize opportunities in some regions, as well as face the challenges in other regions.”

- Sarah Charley is AGU’s science writing intern