Improving Reservoir Outflow Estimation for Ungauged Basins Using Satellite Observations and a Hydrological Model

Nowadays, most of rivers globally are regulated by dams and reservoirs, which have substantially altered natural streamflow regimes. Understanding the impacts of these dams and reservoirs on streamflow is essential for water resources management. In situ reservoir release data or actual reservoir operating rules are difficult to obtain, particularly for transboundary rivers, resulting in the tremendous difficulty of simulating exact reservoir behaviors. This study aims to use easy-to-obtain satellite observations combined with a distributed hydrological model to estimate reservoir releases at the daily time scale. The developed Satellite-Based Reservoir routing Scheme (SBRS) was applied to two individual reservoirs in the United States and Thailand and cascade reservoirs on the Lancang River in China. The normalized root-mean-square error (NRMSE), correlation coefficient (CC), and hydrographs of daily regulated streamflow simulations were used to assess the performance of the reservoir release simulations. The SBRS was compared with four other global reservoir operation schemes and showed better overall performance with higherCCand lowerNRMSE. In addition, the SBRS performed better for the individual reservoirs (CC > 0.6,NRMSE < 0.2) than the cascade reservoirs, which is attributed to the uncertainty in the simulation of inflow and reservoir storage changes and to the lack of remote sensing data for all the cascade reservoirs. This study explores the potential of satellite observations combined with hydrological modeling in elucidating reservoir behaviors in ungauged and/or transboundary river basins. A better understanding of reservoir behaviors serves as a basis for water resources management and provides a more cooperative environment for all stakeholders of a basin.