SWOT‐Fitted River Bathymetry for Global Hydrodynamic Models

Abstract We present a robust, global method to reconcile absolute water surface elevations (WSE) from the Surface Water and Ocean Topography (SWOT) mission with a large‐scale hydrodynamic model by iteratively correcting river bathymetry. After removing sensor and representativeness bias, we update riverbed elevations under DEM and min‐depth feasibility constraints and interpolate corrections along reaches. Applied worldwide at 0.05° resolution over 2023–2025, the approach reduces the global median absolute WSE bias (3.10 m → 0.18 m), preserving the same global median correlation (0.38). A modest ∼4% increase in the standard deviation ratio (1.07 → 1.11) indicates slight variance inflation. Independent evaluation over 2015–2025 at 16,746 Hydroweb sites and 2123 GRDC gauges, restricted to reaches with updated beds, confirms substantially reduced bias, negligible change in both correlation and variance, and no significant change in global median discharge skill. When combined with models, this bias‐aware bathymetry will enable a refined numerical representation of floods globally.