Assessing SWOT capabilities for monitoring floodplain water dynamics in the Paraná Basin

The Surface Water and Ocean Topography (SWOT) mission provides unprecedented spatial coverage and temporal resolution of inland water surface elevation (WSE) and extent. This study examines SWOT high-rate raster product during a drought-to-flood transition in the Paraná River floodplain. SWOT observations are evaluated using in situ and satellite datasets, including multispectral imagery and nadir radar altimetry. These multi-sensor comparisons are used to characterize the spatial and temporal consistency of SWOT observations in floodplains under contrasting hydrological conditions, from disconnected low-water stages to widespread inundation. Results show that SWOT captures water level variability in channels with Pearson correlation coefficients exceeding 0.87 and mean absolute errors between 0.09 m and 0.21 m. Comparisons with Sentinel-6 A and Sentinel-3B reveal coherent WSE profiles (correlations up to 0.78) for transects covering channels and vegetated wetlands. Floodplain inundation extents derived from SWOT show high Precision (> 0.96) relative to multispectral products but moderate Recall (0.38-0.50 for GLAD), indicating inundated areas not detected by multispectral sensors. The inundated fraction detected only by SWOT increases with the flood pulse, reaching 53% of total water extent at peak flood in vegetated wetlands. These findings demonstrate SWOT's capability to monitor river-floodplain hydrodynamics and to improve large-scale water storage and budget assessments.