Topographically informed satellite monitoring of reservoir storage: A multi-regional evaluation across contrasting hydroclimatic settings

Study region The study evaluates four reservoirs located in Europe (Spain), South America (Chile), Australia, and North America (USA), representing contrasting hydroclimatic and morphometric conditions. Study focus Reliable monitoring of reservoir storage is essential for water allocation and drought preparedness. However, many regions lack consistent in-situ observations or high-resolution bathymetry. This study develops a topographically informed optimisation framework that departs from conventional sequential workflows by jointly coupling spectral water delineation and elevation-derived inundation within a single objective function. Water-index thresholds and inundation levels are simultaneously optimised by minimising discrepancies between satellite-derived water masks and elevation-constrained flooded surfaces. The framework was tested across reservoirs with contrasting morphometry (from steep canyon systems to shallow floodplain lakes), storage dynamics, and climatic conditions, and compared against fixed and histogram-based thresholding approaches. New hydrological insight for the region The proposed framework consistently improves storage estimation across diverse hydroclimatic settings by enforcing hydraulic consistency between spectral delineation and topographic constraints. Results show that elevation representation dominates estimation uncertainty, accounting for more than 89% of variability, while spectral threshold selection plays a secondary role. The method remains robust under moderate elevation data degradation, supporting its application in data-scarce regions where reservoir morphology is reasonably represented. These findings highlight the importance of integrating topographic information into satellite-based reservoir monitoring and provide a transferable approach for improving water storage assessment across contrasting regional environments.