Sensitivity of Regulated Streamflow Regimes to Interannual Climate Variability

The simultaneous growth in climate-driven alterations of the hydrologic cycle and global freshwater demand threatens the security of anthropogenic and ecologic uses of streamflows. However, the impact of damming on the response of river regimes to long-term climate variability has not been fully disclosed yet. Here, this issue is assessed by investigating temporal patterns in the occurrence probability of different flow ranges upstream and downstream of a selection of dams in the Central-Eastern United States. We found that long-term fluctuations of low flows are propagated unaltered from unregulated to regulated regimes. In the majority of cases, the same applies to the entire spectrum of streamflows, although discharge interannual variability is significantly amplified by large multipurpose structures. Water supply dams instead smooth long-term streamflow fluctuations, though at the cost of systematically filtering out medium-to-high discharges. Accordingly, in Central-Eastern United States, dams are unable to mitigate the sensitivity of flow regimes to long-term hydroclimatic fluctuations and, thus, do not support the security of anthropogenic and ecologic uses of regulated streamflows.