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. Plain Language Abstract

Climate change is severely impacting the hydrologic cycle at global scale, enhancing long‐term fluctuations of flow regimes. This phenomenon is likely to threaten ecologic and human uses of regulated streamflows, especially in view of the current increase of anthropogenic pressure on freshwater resources. Here, climatic controls on regulated river regimes are investigated by analyzing interannual changes in the probability associated with different flow ranges upstream and downstream of 19 dams in the Central‐Eastern United States. In spite of the ability of dams to manage water fluxes, we found that river regulation is unlikely to mitigate the impact of fluctuating climate drivers on river flow regimes. In the majority of cases, dams leave unaltered, if not reduce, streamflow stability over the entire spectrum of discharges. Water supply structures instead smooth climate‐induced streamflow fluctuations, though systematically filtering out a wide range of discharge releases due to water withdrawals. Accordingly, in Central‐Eastern United States, as they are currently operated, dams are unable to mitigate the sensitivity of regulated flow regimes to climate change, balancing human and environmental requirements.