An objective drought index that measures the dry and hot conditions adversely affecting crop yields is used in a regression analysis to test whether corn and soybeans have become more drought tolerant. Results indicate that corn yield losses from a drought of a given severity, whether measured in quantity terms or as a percentage of mean yield, have decreased over time. The null hypothesis that the absolute level of soybean yield losses due to drought has not changed cannot be rejected. But soybean yield losses in percentage terms have decreased over time. Because drought is the primary cause of yield loss in the U.S. crop insurance program and because U.S. crop insurance rates assume that percentage yield losses are constant over time, these results indicate that U.S. crop insurance rates in the Corn Belt are too high.
This working paper was published as Yu, Tian and Bruce A. Babcock, "Are U.S. Corn and Soybeans Becoming More Drought Tolerant?," American Journal of Agricultural Economics 92 (2010): 1310–1323, doi:10.1093/ajae/aaq074.
Yu, Tian and Babcock, Bruce A., "Are U.S. Corn and Soybeans Becoming More Drought Tolerant?" (2009). CARD Working Papers. 523.