How July Temperatures and Precipitation Correlate to Corn Yields

How July Temperatures and Precipitation Correlate to Corn Yields

June 29, 2012


Figure 1.  Correlation between corn yield and July temperatures, 1947-2010.  A more negative correlation (larger red dot) indicates that the higher the temperature, the lower the yield.

July temperature-corn correlation map of Nebraska

Figure 2. Correlation between corn yield and July precipitation, 1947-2010. A more positive correlation (larger green dot) indicates that the greater the precipiation, the higher the yield.

Concern is developing about how high temperatures and dry conditions may affect corn yield across the state this summer.

To get a long-term perspective of how they’ve affected production in previous seasons, dryland corn yields were correlated with monthly temperature and rainfall data for the 1947 to 2010 growing seasons. Corn yields were adjusted to remove technological influences, such as seed variety or fertilizer improvements, on yield over this 64-year period. (This was done before correlating with precipitation and temperature so that technological developments didn’t influence the statistical correlations.) Non-irrigated county average corn yield data were obtained from the USDA NASS database.

Out of 61 counties, correlations of corn yield with July temperatures (Figure 1) and July rainfall (Figure 2) were significant for 100% and 93% of the counties, respectively. August temperatures also showed significant correlation with 85% of county corn yield but not as strong as July temperatures. Corn yields increased with cooler and wetter conditions during those critical months, and decreased with hotter, drier conditions. Precipitation during other months did not show such strong correlation with corn yield. The correlation with temperature was particularly high in the southern tier of counties.

July has the highest correlations with corn yield due to the fact that it coincides with the most critical stages of corn development: silking and pollination.

To help identify potential impacts from weather on this year’s yield, you can track one-month and three-month climate outlooks at

Tapan Pathak
Extension Educator in Climate Variability