Exploitation of satellite earth observation datasets for hydrologic analysis of large reservoirs in Thailand

• Validates satellite water level and surface water extent in reservoirs against in-situ measurements. • Integrates satellite observations with hydrological models to estimate reservoir release. • Analyzes the effects of reservoir operation on downstream river flow. Today, many rivers worldwide are regulated by reservoirs, significantly altering natural flow regimes and affecting downstream hydrology. Understanding these impacts is essential for effective water resources management, yet obtaining in-situ release data or actual reservoir operation rules remains challenging, especially in remote areas or transboundary basins, where release data is often classified. This study employs Sentinel-3 satellite altimetry data and Sentinel-1 and 2 imagery to estimate reservoir volumes and validate satellite-derived water level, surface area, and storage changes against in-situ data. A hydrological model is then applied to simulate reservoir water balance and releases and validated against observed release in Thailand. Focusing on Lam Pao reservoir as a representative case, results demonstrate that satellite-derived water levels closely align with ground measurements (average RMSE = 0.53 m; r = 0.94), and imagery-based surface extent effectively tracks measured trends (average NRMSE = 0.78). The NAM rainfall-runoff model provides moderately accurate inflow estimates (average NRMSE = 0.628; r = 0.817), and simulated releases show reasonable agreement with observed data (average r = 0.65). These findings highlight the potential of satellite-based earth observation as a valuable tool for reservoir monitoring and water resource management, especially in data-scarce regions.