Flood Rainfall–Streamflow Relationships in Two Contrasting U.S. River Basins

Floods are caused by complex interactions of topography, rainfall, surface runoff, and streamflow. The relationship between rainfall and river discharge is particularly important for governing flood characteristics. Previous studies have examined these relationships, but they have lacked high-resolution precipitation data that are necessary to correlate to individual flood events. This study addresses this limitation by examining rainfall-streamflow relationships in two climatically and topographically different river basins–the Wabash and Willamette River basins––using high-resolution precipitation and discharge data from a flood-producing storm climatology. Both the Wabash and Willamette basins exhibit different rainfall-streamflow relationships both within and between basins. While strong positive rainfall-streamflow correlations exist over most of the central Wabash basin, coinciding with higher terrain and urbanization, less uniformity is observed in the Willamette basin. In addition to different flood-producing storms in the Willamette basin and more complex terrain, the less spatially uniform rainfall-streamflow correlations are likely due to water management strategies. Results suggest that other factors in addition to rainfall need to be considered when examining rainfall-streamflow relationships, including human influences and topography. However, when rainfall is examined in relation to streamflow within floods, it is critical that the sub-basin variability is properly represented using high-resolution storm rainfall data. Such information is critical for understanding detailed flood processes in the current climate, in order to gain an accurate representation of how rainfall-streamflow relationships will change in a future climate.