Harvard Study Identifies Key Role of Soil Moisture on Crop Yields

A new research study by Harvard faculty is shedding light on the significant influence of water supply on global crop yields and its connection to climate change.

The team — led by Harvard Earth and Planetary Sciences professor Peter Huybers — included Harvard Center for the Environment postdoctoral fellow Jonathan Proctor, Woods Hole Oceanographic Institute postdoctoral fellow Duo Chan, and UC Irvine professor Angela Rigden.

Proctor said while precipitation is often used in studies of crop yield, soil moisture seemed like a “natural” measurement to consider. The group used soil moisture measurements from satellite data collected by the European Space Agency, which allowed them to evaluate the role of moisture on crop yields on a “global” scale.

“One of the primary findings of the analysis is that soil moisture really matters to global agricultural productivity as much, and sometimes more than, temperature,” Proctor said. “That is really important because it means that to understand future climatic influences on agriculture, we need to understand how surface metrology will change.”

Huybers likened the process by which satellites detect soil moisture from several thousand miles above Earth to the way a kitchen microwave operates.

“The reason why we can see soil moisture from space is the same reason that, when you microwave something, the water molecules get hot,” he said. “The nature of interactions between molecules and radiation is such that if they absorb at a good frequency, they also emit at that frequency.”

“When you're looking at space and you’re looking at the microwave emissions from the surface, those are dominated by the amount of water that's on the surface. So there are calibrations that are used to go from microwave intensity to the water content near the surface,” Huybers added.

Proctor said there are positive and negative implications from the study regarding climate change and its relationship with temperature and water.

“There are some aspects of the paper that are good news in terms of potentially temperature damages from climate change being less severe,” Proctor said. “But there is also instantly some bad news in that water is probably going to play a really big role in the future, and there is a lot of uncertainty about how surface soil moisture conditions will change.”

He said the group is now looking into how changes in climate might disrupt global food supply and spur human environmental migration in response to untenable agricultural conditions.

Huybers said the importance of water on food supply has political implications as well.

“Temperature changes pretty much uniformly everywhere, but water variability is heterogeneous. So climate change is going to map in a really complicated way on to local water politics,” Huybers said.

—Staff writer Jeremiah C. Curran can be reached at jeremiah.curran@thecrimson.com. Follow him on Twitter @jerryccurran.