Sensitivity of Reservoir Performance to Hydroclimatic Forcing Pathways: A Coupled SWAT+–MSPA-2024 Framework

Accurate reservoir performance assessment increasingly relies on hydrological model-derived inflow series; however, the effects of hydroclimatic forcing pathways on reservoir design outcomes remain insufficiently understood. This study evaluates the sensitivity of reservoir performance to alternative forcing pathways by comparing observed inflows with SWAT+-simulated streamflow driven by ERA5-Land reanalysis data in the Cidadelhe catchment, Portugal. An integrated hydrology–reservoir modeling framework couples SWAT+ simulations with three analytical approaches: Behavior Analysis, the Modified Sequent Peak Algorithm (MSPA), and the Resilience-Regulated MSPA-2024. Results show that, despite strong hydrological model performance (NSE up to 0.83), SWAT+-simulated inflows exhibit systematic attenuation of variability, approximately 20–25%, leading to substantially lower storage capacity (up to 60–65%) and evaporation estimates relative to those derived from observed data. While volumetric reliability remains largely insensitive to forcing pathways, resilience, sustainability, and drought risk indices display pronounced method-dependent behavior. MSPA-2024 demonstrates strong robustness by maintaining near-invariant performance metrics across forcing conditions through embedded resilience constraints. These findings show that inflow statistical structure, rather than mean flow alone, controls reservoir design outcomes and that forcing-pathway consistency is critical for reliable performance assessment. The proposed SWAT+–MSPA-2024 framework supports more reliable model-based reservoir planning, particularly in data-scarce basins and climate-scenario applications.