Examining Extreme Precipitation Events within the Mississippi River Basin with an Eye Toward Climate Change

The precipitation variability and connectivity across the greater Mississippi River Basin (MRB) is evident and climate change is projected to disrupt the amount, frequency, extent, and timing of precipitation events across the MRB. These changes have direct and indirect impacts on aquatic and riverine ecosystems, especially if the precipitation events break long-standing records on either the dry or wet sides of the historical range. An all-basin approach to examine the impacts of climate change in the MRB is necessary, yet most studies to date have focused on sub-basins.

Extreme precipitation events are one of the indicators of climate change. The study established the climatology of 14-day extreme precipitation episodes across the basin from 1990 to 2019 based on the criteria defined by Dickinson et al. (2021). The algorithm imposes thresholds for both the total precipitation and the duration of the precipitation, allowing to identify events with sufficient length to accentuate the synoptic and longer time scale contribution to the precipitation event. The climatology comprises the regions of extreme events that were classified into geographical clusters that fell within the boundaries of the whole basin. On average, from 1990 to 2019, 6-7 episodes occurred somewhere in the MRB each year. Only 2012 (a year of extreme to exceptional drought) did not have an extreme precipitation episode. Four years had a maximum of 11 episodes. In some cases, these episodes were occurring simultaneously in different parts of the MRB. Analyses revealed that there is a positive trend in the total yearly counts of recorded extreme events, indicating an average of 0.43 more annual episodes each decade. However, there is a cyclical pattern demonstrated by the data. Thus, climate variability remains a stronger forcing mechanism throughout these three decades than climate change. The area-average precipitation, maximum total precipitation, and maximum 1-day precipitation of extreme precipitation events all indicate an upward trend from 1990 to 2019. There are nine geographical clusters within the MRB where 14-day extreme precipitation episodes have in-cluster commonalities. The seasonal distribution of 14-day extreme precipitation events varied from cluster to cluster.

We conducted a preliminary review of all historic floods across the MRB and of precipitation events that broke long-standing, historical precipitation records to find cases when there was significant disturbance to ecosystems. We arrived at two case studies: 1993 and 2019. For each, we detailed the evolution of extreme precipitation events and the evolution of flooding, identified synoptic-scale atmospheric, oceanic, and global teleconnection patterns that were conducive and precursors to these events, and identified the responses of specific aquatic species, wildlife, and terrestrial plants.

The research has provided a foundation to identifying risks and impacts of extreme precipitation events on specific aquatic species, wildlife, and agroecosystems supported by the rivers and streams of the MRB. This research is an initial step to understand the impacts of climate change on the region, as it helps to identify what atmospheric, oceanic, and teleconnection patterns to examine in the future for changes in amount, frequency, extent, and timing as a result of climate change. We consider our research as an early step to understand the impacts of climate change on the greater MRB.