Spatial and Temporal Patterns in Baseflow Recession in the Continental United States

Baseflow is often treated according to a unique storage-discharge relationship. However, recent innovations in baseflow recession analysis have allowed novel findings regarding the variability of both the stability of baseflow and its nonlinearity (i.e., the concavity of the hydrograph), as well as the regional clustering of these characteristics. We investigate spatial and temporal patterns in the character of baseflow recession for over 1,000 watersheds in the continental United States. We discover seasonal patterns in both the stability and nonlinearity of baseflow which vary systematically across large regions. Further, we relate these baseflow characteristics to their potential physical drivers, including estimates of evapotranspiration, watershed storage, the distribution of watershed storage, and precipitation. While coincident watershed storage is the best predictor of baseflow stability in many regions (particularly the Appalachian Mountains), evapotranspiration from 2 to 3 months previous is the best predictor of baseflow stability in other regions (particularly the Pacific Northwest). We also discuss the novel finding that baseflow nonlinearity has increased significantly in most watersheds across the United States since 1980