The Disturbing Recent Heavy Precipitation Trend across Parts of the Upper Mississippi River Valley

Flash flooding continues to be a leading cause of weather-related deaths. River flooding can devastate entire communities and cause major financial loss. This work examines the recent and decadal trends in precipitation, rainfall, river streamflow, and flooding over the Upper Midwest. The motivation for this research was to quantitatively evaluate and understand these trends as a foundation to better support both the NWS warning program and stakeholder decision making.

The calendar year of 2018 was the wettest year on record across the contiguous United States. Across parts of the Upper Mississippi River Valley into the western Great Lakes, 2018 was also the wettest on record (for the 1895-2018 period). Much of the region received between 150% and 200% of the 30-year normal precipitation. Further, regional precipitation totals ranked in the upper 20% of the record for the 2015 through 2018 period. This trend continued into the first-half of 2019.

Decadal trends continue to reflect a wet period across the Upper Midwest. Over the past 21 years, the annual mean precipitation is over 5 inches greater than the previous 21 year period (1977-1997). Extreme rainfall events are on the increase too with nearly double the amount of days recording over 1” in some parts of the region. This rainfall has translated into anomalously high river streamflows and crests over the past 20 years when compared to the historical record.