The 2008 Spring Midwest Floods: A Signal of Changing Climatic Conditions?

Abstract

Intense precipitation fell across the American Midwest almost continuously for a three-week period between the last week in May and the middle of June 2008 on already-saturated soils. These circumstances contributed to widespread flooding across five states and two river basins. Most extreme rains fell and flooding occurred across Iowa, southern Wisconsin, and southern Indiana, encompassing various tributaries of the Upper Mississippi and Wabash River Basins. We examine historical records of river discharge rates and stage levels at 16 gauging stations in these areas to assess the severity and impact of flooding on local river systems and place the event in historical perspective. Discharge rates were higher than expected in May, peaking in June when magnitudes often reached record levels; estimated return periods for June often exceeded between 100 and 200 years on rivers across Iowa, southern Wisconsin, and southern Indiana. Daily flood stage levels were exceeded, often for extended periods of time, during May and June, with stage levels peaking during the first two weeks in June. River conditions began to recover in late June and continued to recede through July and August. We also placed the observations in the context of simultaneous weather and synoptic conditions, changing precipitation regimes across the region, and anticipated future climate change due to anthropogenic forcing.