It doesn’t take a PhD in agriculture to understand how important water is to crop production. But for years, experts like Jonathan Proctor, who has a PhD in Agriculture and Resource Economics from the University of California, Berkeley, have been trying to explain why crop yield statistics don’t take water’s importance into account enough.
Even though we know from plant physiology that temperature and water supply are both very important for crops, studies examining how crop yields respond to temperature and rainfall typically find that temperature matters much more than water, said Proctor, a postdoctoral fellow in Prof. Peter Huybers’ group at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). This puzzle must be solved to quantify how crop yields will be impacted by climate change.
The research team considered the possibility that the models were detecting the incorrect type of water. The Harvard team used satellites to measure soil moisture around the root zone for maize, soybeans, millet, and sorghum growing all over the world, as opposed to measuring precipitation, as previous studies had done.
The team discovered that soil moisture models explain 30% to 120% more of the variation in yield across crops from year to year than models that rely on rainfall.
According to Proctor, evaporation, infiltration, and runoff can cause a significant difference between rainfall and soil moisture. We discover that what is in the soil for the crops to drink is what actually matters for their yield and that what falls from the sky is not always what is in the soil for the crops to drink.
The team was able to better separate and comprehend the individual influences of temperature and water supply on yield, which are frequently confused because heat and dryness are strongly correlated. They did this by using measurements of soil moisture from satellites and a statistical method.
In particular, the team discovered that extreme heat had less of an impact on crop yields than predicted by earlier models, which reduced the projected harm from global warming. The team did, however, discover increased sensitivity to drought and flooding.
“We need to take into account how temperature and water availability will evolve together when it comes to predicting agricultural productivity in a changing climate,” said Huybers, professor of environmental science and engineering at SEAS and Earth and Planetary Sciences.
Changes in the amount of water will be more regional and seasonal than changes in temperature, so planning and management strategies at the regional level will be more important for dealing with climate change.
The team wants to investigate how climate change might impact other aspects of human wellbeing, such as migration choices or the stability of food supplies, using this improved understanding of how soil moisture and temperature influence global agricultural productivity.
