Variability and Transitions in Precipitation Extremes in the Midwest United States

Monthly to seasonal precipitation extremes, both flood and drought, are important components of regional climates worldwide, and are the subjects of numerous investigations. However, variability in and transition between precipitation extremes, and associated impacts are the subject of far fewer studies. Recent such events in the Midwest region of the United States, such as the 2011-12 flood to drought transition in the upper Mississippi River basin and the flood to drought transition experienced in parts of Kentucky, Ohio, Indiana, and Illinois in 2019, have sparked concerns of increased variability and rapid transitions between precipitation extremes and compounded economic and environmental impacts. In response to these concerns, this study focuses on characterizing variability and change in Midwest precipitation extremes and transitions between extremes over the last 70 years. Overall we find that the Midwest as a region has gotten wetter over the last seven decades, and that in general the annual maximum and median wetness, defined using the standardized precipitation index (SPI), have increased at a larger magnitude than the annual minimum. We find large areas of the southern Midwest have experienced a significant increase in the annual SPI range and associated magnitude of transition between annual maximum and minimum SPI. We additionally find wet to dry transitions between extremes have largely increased in speed (i.e., less time between extremes), while long-term changes in transition frequency are more regional within the Midwest. SIGNIFICANCE STATEMENTThe U.S. Midwest has experienced several rapid transitions in precipitation extremes over the past decade. These events, such as the 2012-13 drought to flood transition, have sparked concerns of more frequent, rapid swings in precipitation extremes. We use a 69-yr daily precipitation record to document transitions in precipitation extremes across the Midwest. We find that since the 1950s the Midwest has gotten wetter, but annual wet extremes have increased at a much larger rate than annual dry extremes. Furthermore, we find the area from eastern Missouri to western Ohio has experienced more frequent, more rapid flood to drought transitions in recent decades. This provides evidence of increased precipitation variability in this region, and associated rapid transitions between extremes.

Automated summary

This study focuses on characterizing variability and change in Midwest precipitation extremes and transitions between extremes over the last 70 years. The research findings show that the Midwest region has become wetter overall, with annual maximum and median wetness increasing more significantly than the annual minimum. The transitions between wet and dry extremes have accelerated in speed, while long-term changes in transition frequency vary regionally within the Midwest.