Primary Atmospheric Drivers of Pluvial Years in the Great Plain of the United States
Climate change impacts on a regional scale are variable across the globe. Within the Great Plains (GP) of the United States, precipitation variability has been increasing in recent decades. Owing to this, changes in the occurrence of hydrological extremes have been ongoing across the region. To understand this increased variability, knowledge into the causes of deficits and surpluses in precipitation is critical. While, GP droughts have been a topic of study in the recent decades, precipitation surpluses (or pluvials) have been limited focusing manily on key pluvial events or on shorter, interannual timescales. However a comprehensive examination of the primary drivers of pluvial years has not been completed. This study was designed to fill this gap with the overall goal of understanding GP precipitation variability and the ongoing change this particular feature of the GP is incurring.
To complete the study, the ERA 20th Century (ERA-20C) dataset was used to investigate primary atmospheric variables that lead to precipitation occurrences over the GP. Special focus was placed on features that were noted to be the primary factors in causing specific pluvial events or seasons from previous studies. Results show an anomalous location of the 250 mb wave guide (North Pacific Jet (NPJ)) and corresponding wave activity are the primary factors leading to enhanced precipitation over the GP on an annual and seasonal time scales. However, the analysis revealed key differences between Southern Great Plains (SGP) and Northern Great Plains (NGP) pluvial periods giving two different regimes that lead to these pluvial periods. Finally, a case study of two different pluvial years was investigated to determine the utility of the results found in the composite analysis. Overall, results show that defining the drivers of GP pluvial periods is a complex and difficult issue, yet one that is necessary to understand the changes in the overall GP hydroclimate owing to shifts in the global climate.