Response of the United States streamgage network to high- and low-flow periods

Monitoring of streamflow is critical to the assessment and management of water resources. In particular, understanding the response of watersheds in a streamgage network to low- and high-flow periods is important to assessing the uniqueness and redundancy in the network during these critical periods, and has implications for understanding the potential response of watersheds to future changes in hydrologic extremes. Streamgages that respond similarly (have correlated data) to drought conditions may not exhibit similar response to floods. To understand similarities and dissimilarities in the response of watersheds to hydrologic extremes, significant cross-correlations between high- and low-flow periods were examined for 1,630 unregulated streamgages located across the United States and its territories. The number of coincident days that a pair of streamgages was experiencing a high- or low-flow period was examined. Low-flow conditions were defined as the days in which the streamflow values observed at the streamgage were less than the streamflow value at the 90-percent exceedence probability; high-flow conditions were defined as the days in which the streamflow values observed at the streamgage were greater than streamflow value at the 10-percent exceedence probability. Preliminary analysis shows that, as expected, cross-correlations between streamflow were observed to be larger for high-flow conditions than for low-flow conditions. Furthermore, even for areas of the United States with abundant streamgages, few streamgages experience low-flows over the same period. In contrast, high-flow events are observed to occur over similar periods at many of these streamgages. These analyses could provide insight into understanding differences between the utility of regionalization techniques to estimate floods and droughts at ungauged locations.