In the north-central U.S. one of the most pronounced climate changes since the mid-20th century has been an increase in extreme precipitation events.  We show observations for 1951-2010 of both the annual and seasonal frequency of these events (defined here as rainfall at least 4 inches or 101.6 mm per day).  As well as the annual increase found by other investigators we found that there has been a pronounced shift in seasonality of extreme precipitation.  The frequency of extreme precipitation has increased by about 81% in spring and decreased by about 25% in fall.  Since soil moisture usually is closer to saturation in spring this means earlier occurrence of extreme precipitation could increase flooding and interfere with field operations.  We also used numerical model simulations to explore possible future changes in heavy precipitation. Results show that the observed increase in frequency of heavy precipitation is predicted to continue and intensify. This is a robust finding as it is produced regardless of the model configuration that is used.

This research was sponsored by USDA NIFA.