ABSTRACT
This chapter examines the unique hydroclimatic factors that created the circumstances responsible for the excessive flooding-including the rainfall that fell in the months prior to the flood. A critical requirement for producing heavy summer rainfall over a large area such as the Upper Mississippi River basin is large rain areas. Normal summer rainfall across the Upper Mississippi River basin varies from roughly 8 inches in the extreme northwestern part of the basin to 13 inches in the southwestern part of the basin. A hydroclimatic analysis of the rainfall characteristics reveals that five key rain conditions combined to create record rain totals and a flood that was unprecedented for its summer season occurrence, for its areal size, and for its long duration. These five factors are high frequency of heavy multi-day events, high number of extreme flash-flood-producing rainstorms, high number of large-sized rain areas, persistent high soil moisture, and low evapotranspiration greatly influenced the severity and nature of the floods.
