The 1000-Year Context of Extreme Precipitation in the Central United States from a Novel Blend of Observations and Climate Model Simulations

Abstract Global warming is increasing the frequency of extreme precipitation events, including those referred to as having a return period of 1000 years. Yet frequency estimates of these high-end extremes are plagued by large uncertainties that result from the short record of weather station observations used to assess their historical context. To more robustly assess modern extreme precipitation events, we develop a novel approach that lengthens the data record by blending historical observations from NOAA’s Applied Climate Information System with Community Earth System Model simulations run from 850 to 2100 CE. We apply this method as a proof of concept to the record-breaking rainfall event in the central United States in July 2022. We find that the return period for this storm’s 24-h rainfall is ∼530 years (90% confidence interval: 370–700 years) for the greater St. Louis region and ∼280 years (90% confidence interval: 115–340 years) for eastern Kentucky. Moreover, the rainfall amount from this event is ∼2–4 times more likely to occur in the future relative to the preindustrial era. Compared to previous best practices, this study’s approach more precisely evaluates extreme precipitation magnitude and frequency, demonstrating potentially large reductions in the uncertainty associated with classifying a 1-in-1000-yr rainfall event. This blended data approach can be used to update previous methods used for assessing modern extreme precipitation events and to better prepare society and critical infrastructure for the present and future risks posed by precipitation extremes. Significance Statement We present a new method aimed at improving estimates of the magnitude and frequency of extreme precipitation. Our method lengthens the time coverage of precipitation data by combining weather station observations with climate model simulations spanning 850–2100 CE. We apply this methodology to a record-breaking rainfall event that occurred in July 2022 in the central United States. Our approach provides a more precise estimate of this event’s frequency and demonstrates that the rainfall amount from this event is ∼2–4 times more likely to occur in the future relative to the preceding millennium. Our findings can be used to better prepare society and infrastructure for the present and future risks posed by extreme precipitation.