River flow response to changing electricity demand and centralized hydropower operations in the Paranapanema River basin, Brazil

Abstract

Study region: The Paranapanema River Basin, located in southeastern Brazil, is characterized by a cascade of large hydropower plants regulated by a nationally coordinated dispatch system. This basin is a representative case of reservoir-regulated rivers in the country, where multiple dams interact to supply electricity while reshaping natural flow regimes. Study focus: This study examines hydropower-induced variability in river discharge and reservoir volumes using multiresolution wavelet decomposition and signal reconstruction. By analyzing continuous records under operational conditions, the method isolates fluctuations from sub-daily to multi-annual scales. This approach moves beyond average-based analyses, providing a scale-specific view of hydropower modulation. It shows how discharge dynamics arise not only from cascade configuration but also from dispatch coordination, plant design, and hydrological conditions. New hydrological insights for the region: Results show that flow variability patterns align with electricity demand profiles, drought episodes, and institutional milestones in the Brazilian power sector. Hydropower operations display distinct signatures at different time scales, highlighting the responsiveness and complexity of reservoir management. Reconstructing signals in original units improves interpretability and supports regulatory evaluation and energy planning. The proposed framework provides a standardized and reproducible way to assess variability in reservoir-regulated systems, enhancing comparability of hydropower assessments and identifying operational dynamics that shape river flow regimes. It also supports more adaptive and ecologically grounded approaches to hydropower governance in the Paranapanema Basin and beyond