In a new study in the journal Environmental Research Letters, Stanford Ph.D. student Christopher Seifert and professor David Lobell find that between 1988 and 2012, the area of farmland in the United States on which farmers were able to harvest two crops per year on the same plot of land grew by as much as 28 percent as a result of warmer temperatures and later fall freezes. Applying their model to two future climate change scenarios, the team projects that the amount of land suitable for double cropping in the United States – in this case, winter wheat followed by soybeans – may double or even triple by the end of the century.

Seifert and Lobell’s analysis includes 22 U.S. states east of the continental divide. They define the area suitable for double cropping as having at least 750 mm per year of rainfall and a 75 percent likelihood that both crops will survive to harvest.

The team built a first-of-its-kind model for a double cropping combination of winter wheat and soybeans, to measure the expansion of farmland that has become theoretically suitable to double cropping since 1988. Combining the model with existing U.S. government data, they find that their estimate of 28 percent growth closely mirrors the actual observed expansion of double cropping in the United States over this time period.

Seifert and Lobell then applied their model to two future climate change scenarios and found that as average temperatures rise, the area suitable for double cropping will likely grow steadily until 2060, then spike sharply between 2060 and 2080. Expansion is projected to slow between 2080-2100, as parts of the South become unsuitable due to a lack of the cold winter temperatures that winter wheat requires.

An expansion of double cropping area could be an important tool for U.S. farmers to protect against the negative effects of climate change on agriculture productivity. Yields of major staple crops like corn, soybeans and wheat are already showing increasing vulnerability to extreme heat, especially for plants that go through critical growth stages such as pollination during the hot summer months. Double cropping can help protect against these risks, and provide other benefits such as year-round ground cover that reduces soil erosion.

The new study does not incorporate data about yields, potential yields, or the changing moisture requirements of each crop as temperatures rise. Adding these factors to future analysis will improve scientists’ understanding of the value of double cropping, said lead author Seifert, a PhD student in environmental Earth system science at Stanford.

The study also suggests that the negative impacts that climate change is expected to have on crops like corn and soybeans will likely be larger than the boost that double cropping can offer.

“Double cropping can be an important tool, but it’s important not to overstate its potential to ‘save’ American agriculture from climate change,” said co-author David Lobell, a professor of environmental earth system science, deputy director of the Center on Food Security and the Environment at Stanford (FSE) and a Woods senior fellow. 

“In the United States, double cropping can potentially make agriculture more resilient to climate change by improving overall productivity and by increasing farmers’ annual incomes,” said Seifert. “But the gains from double cropping will probably not be able to make up for the overall drop in crop yields that we expect to see with future climate change.”