A new research study by Harvard faculty sheds light on the significant influence of water supply on global crop yields and its link to climate change.
The team – led by Peter Huybers, professor of earth and planetary sciences at Harvard – included Jonathan Proctor, postdoctoral fellow at the Harvard Center for the Environment, Duo Chan, postdoctoral fellow at the Woods Hole Oceanographic Institute, and Angela Rigden, professor at UC Irvine.
Proctor said that although rainfall is often used in crop yield studies, 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 assess the role of moisture on crop yields on a ‘global’ scale.
“One of the key findings from the analysis is that soil moisture matters as much, and sometimes more, to global agricultural productivity than temperature,” Proctor said. “This is really important because it means that to understand future climate influences on agriculture, we need to understand how surface metrology will change.”
Huybers compared the process by which satellites detect soil moisture thousands of miles above Earth to the operation of a kitchen microwave.
“The reason 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 the interactions between molecules and radiation is such that if they absorb at a good frequency, they also emit at that frequency.”
“When you look out into space and you look 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 water content near the surface,” Huybers added.
Proctor said the study has positive and negative implications regarding climate change and its relationship to temperature and water.
“Aspects of the paper are good news in terms of less severe potential temperature damage from climate change,” Proctor said. “But there’s also instant bad news that water is probably going to play a very big role in the future, and there’s a lot of uncertainty about how the soil moisture conditions in surface will change.”
He said the group is currently studying how climate change could disrupt global food supplies and spur human environmental migration in response to unsustainable agricultural conditions.
Huybers said the importance of water to the food supply also has policy implications.
“Temperature changes pretty much evenly everywhere, but water variability is heterogeneous, so climate change is going to impact local water policy in very complicated ways,” Huybers said.