Daily Continuous River Discharge Estimation for Ungauged Basins Using a Hydrologic Model Calibrated by Satellite Altimetry: Implications for the SWOT Mission

The emergence of state‐of‐the‐art satellite altimetry has provided new prospects for integrating water surface elevation (water level) measurements with a hydrologic model for river discharge estimation, which is particularly suited for poorly gauged or ungauged basins. In this context, we explored the possibility of model calibration using Jason‐2‐derived water levels, followed by SWOT (the Surface Water and Ocean Topography mission)‐like data (the combination of Landsat 5/8‐derived at‐a‐section river widths and concurrent gauged water levels). Two types of empirical formulas designed specifically for altimetry‐derived water levels and the joint use of water levels and river widths, respectively, were used to derive discharge, which was integrated with a hydrologic model (CREST‐RS). Here we present results of estimating daily continuous river discharge in narrow rivers for the upper Brahmaputra River (UBR) and Lhasa River (LR) using the developed approach independent of in situ discharge measurements. Five scenarios were performed: (1) model calibration using the Jason‐2‐derived water levels and SWOT‐like data in the UBR (scenarios I–III) and (2) model calibration using the SWOT‐like data for the LR (scenarios IV–V). Results showed that model calibration using the Jason‐2‐derived water levels could provide reasonably well‐constrained parameters for discharge estimation, with the Nash‐Sutcliffe Efficiency coefficient (NSE) reaching 0.85 during 2003–2014. For the SWOT‐like data, the NSE reached 0.85 for the UBR and 0.75 for the LR. This study highlights the potential of performing model calibration using satellite altimetry and SWOT‐like observations, which paves the way to estimate river discharge for ungauged basins globally. Key Points Jason‐2‐derived water levels and SWOT‐like observations could be used as references for model calibration The calibrated hydrologic model produced daily continuous discharge in ungauged basin Important implications for discharge estimation using SWOT were provided