SWOT versus legacy satellite missions: assessing water surface elevation and surface water extent in complex river settings

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The Surface Water and Ocean Topography (SWOT) mission represents a significant advancement in satellite altimetry for hydrological applications, yet its performance in complex river systems remains insufficiently characterized. We assess SWOT's capability to monitor water surface elevation (WSE) and surface water extent (SWE) through comparison with earlier satellite missions in the Ganges River. Results demonstrate that SWOT WSE outperforms all previous satellite altimeters, achieving median residual errors of 26.1–28.2 cm and high temporal agreement with gauge observations (median Spearman ρ = 0.94–0.96). Similarly, SWOT-derived SWE exhibits moderate correspondence with reference SWE from Sentinel satellites (Jaccard indices 0.54–0.70) due to coarse resolution and systematic misclassification yet offers unique value through simultaneous co-located WSE and SWE measurements for integrated hydrodynamic applications. While SWOT demonstrates substantial potential, our findings underscore the need for improved quality control and processing algorithms to fully realize its operational capabilities.