Spectral Signatures of Flow Regime Alteration by Dams Across the United States

River scientists strive to understand how streamflow regimes vary across space and time because it is fundamental predicting the impacts of climate change human activities on riverine ecosystems. Here we tested whether flow periodicity differs between rivers that are regulated or unregulated by large dams, dominant periodicities over in response dam regulation. These questions were addressed calculating wavelet power at different timescales, ranging from 6 hr 10 years, 175 pairs dam-regulated USGS gages with long-term discharge data, spanning conterminous United States. We then focused eight focal reservoirs high-quality high-frequency data examine spectral signatures dam-induced alteration their time-varying nature. found regulation dams induces changes not only magnitude variability, but also a river's regime. Our analysis revealed generally alter multi-annual annual higher extent than seasonal daily periodicity. Based reservoirs, illustrate varying, operations (e.g., peaking vs. baseload operation), capacity, environmental policies shifting relative importance time. demonstrates pervasiveness now characterizing U.S. rivers' regimes, may inform restoration downstream via controlled releases—a critical need light new damming retrofitting for hydropower globally.