[A-HW24] Human- and Climate-induced variability in water cycle and (sub)surface water resources

[AHW24-P09] Estimating River Discharge Using SWOT: Application of Different Formulas to the Mekong River

*JIARUI XU¹, Tsuyoshi Kinouchi¹ (1.Institute of science tokyo )

Keywords:Remote sensing, SWOT, River cross-section, River discharge, Mekong River

The Surface Water and Ocean Topography (SWOT) mission provides improved vertical accuracy and spatial coverage compared to previous satellites and can simultaneously measure the extent of surface water extent, effectively addressing the issue of inconsistent orbits and cycles between altimetry satellites and optical satellites. In this study, we estimated the discharge of selected sections of the Mekong River using a discharge empirical formula (Method 1) based on the global river database and the Manning equation (Method 2). It contributes to improving river discharge estimation in regions with limited hydrological stations or restricted data access, thereby supporting integrated water resource management and planning. For Method 1, the simulation of the river cross-section relies on the relationship between river surface width and elevation for the portion above the minimum water level observed by the satellite. For the portion below the minimum water level, cross-sectional area is estimated based on the ratio of upstream catchment areas between field observation stations and discharge estimation stations. Method 2 involves fitting the river cross-section with a parabolic function based on the relationship between river surface width and elevation and the Manning roughness coefficient for different water levels is estimated using the bankfull flow velocity and bankfull roughness. Method 1 requires reference discharge data from observation stations, while Method 2 can rely entirely on remote sensing data for estimation which also leads to a decrease in discharge estimation accuracy. For Method 1, the discharge estimation at all three stations achieved an R² value above 0.98 and an NSE above 0.93. However, the results from Method 2 showed a slight decrease in accuracy, with a significant drop in NSE at the Pakse station, reaching 0.86. Based on the methods and results presented above, we conclude that SWOT, as a provider of hydraulic variables for discharge calculation, has sufficient accuracy for estimating the discharge of the Mekong River. This will play an important role in the future management of the Mekong River Basin and related water resource planning.