Climate variability and flood frequency estimation for the Upper Mississippi and Lower Missouri Rivers

This paper considers the distribution of flood flows in the Upper Mississip pi, Lower Missouri, and Illinois Rivers and their relationship to climatic indices. Global climate patterns including El Nino/Southern Oscillation, th e Pacific Decadal Oscillation, and the North Atlantic Oscillation explained very little of the variations in flow peaks. However, large and statistica lly significant upward trends were found in many gauge records along the Up per Mississippi and Missouri Rivers: at Hermann on the Missouri River above the confluence with the Mississippi (p = 2 percent), at Hannibal on the Mi ssissippi River (p < 0.1 percent), at Meredosia on the Illinois River (p = 0.7 percent), and at St. Louis on the Mississippi below the confluence of a ll three rivers (p = 1 percent). This challenges the traditional assumption that flood series are independent and identically distributed random varia bles and suggests that flood risk changes over time.