The Impact of Shift in Growing Season Timing on US Corn Yield

Abstract To adapt crop production to climate change, particularly the rising global temperature, farmers adjust sowing dates and cultivars. These two adjustments combined shift growing season timing and consequently alter crop’s exposure to growing degree days (GDD) and killing degree days (KDD). This study investigates how the resulting changes in GDD and KDD have affected corn yield across the US Corn Belt since 1983. Firstly, for each year from 1982 to 2021, we calculate cumulative GDD and KDD over each of the four critical growing stages (silking, doughing, dented, mature) at county-level. Then we develop a multiple linear regression model for each state, relating county-level annual corn yield to GDDs and KDDs of the four growing stages (1982–2021). Secondly, we calculate counterfactual GDDs and KDDs for each year (1983–2021) with fixed corn development data of 1982. Then we calculate the differences of the true GDDs and KDDs from the counterfactual ones for each county-year (1983–2021). Lastly, we obtain the yield change for each county-year by applying respective yield sensitivity model with the differences in GDDs and KDDs. We find that the changes in GDD and KDD reduced corn yield in most years of the 39-year period (1983–2021) in all states except Missouri and Nebraska. This finding highlights the challenge of corn production in face of climate change. Whereas the results on the direction and magnitude of GDD/KDD impact on corn yield over the growing stages can serve as tangible metrics in adaptation of corn production to climate change.