High‐resolution flood precipitation and streamflow relationships in two US river basins

Relationships between rainfall and river discharge are important for governing flood characteristics and predicting flood impacts. Previous studies have examined these relationships, but they lacked the high‐resolution precipitation data necessary to analyse rainfall–streamflow correlations for individual flood episodes. The present study addresses this limitation by examining rainfall–streamflow relationships in two topographically and climatically different river basins: the Wabash River basin in Indiana and the Willamette River basin in Oregon, using high‐resolution, sub‐basin precipitation and discharge data. Results show that flood rainfall–streamflow relationships are highly spatially variable on a sub‐basin scale. In the Wabash basin, strong positive correlations exist between rainfall and streamflow near urban areas and slight terrain gradients during flash floods, while weaker correlations between rainfall and streamflow are observed in other areas of the basin and for slow‐rise floods. In the Willamette basin, strong positive slow‐rise flood rainfall–streamflow relationships occur in referenced gauges in the eastern, mountainous part of the basin, while strong negative correlations occur in non‐referenced gauges near reservoirs along the main rivers. Results suggest that in addition to high‐resolution rainfall variability, the influence of urbanization, topography and water management on flood rainfall–streamflow relationships needs to be considered in order to forecast local flood impacts better. Flood rainfall and streamflow generally display a weak relationship, but this is often using coarse precipitation data. In the present study, the relationships between high‐resolution, hourly precipitation data and instantaneous streamflow data are examined for flood‐producing storms on a sub‐basin scale in two US river basins. Results indicate that these relationships can be strong in some locations, but they are highly variable on a sub‐basin scale, which is important for better predicting flood risk.