Observation of Daily Flood Hazard During the SWOT Cal/Val Orbit

Abstract Flood peaks can develop and recede within a day, making them difficult to capture with satellites with multi‐day revisit intervals. Here, we exploit daily observations during the Calibration and Validation phase of the SWOT mission to examine a short‐lived flood in May 2023 along the Du Gouffre River in Canada. Despite channel widths below 100 m, SWOT tracked day‐to‐day changes in water surface elevation, capturing a rapid rise of approximately 5 m consistent in timing and magnitude with in situ measurements. We derived flood extent based on classification and confidence information. The results show partial spatial overlap with an independent post‐event flood hazard map, with differences primarily associated with reduced classification confidence in vegetated floodplains and narrow reaches. Some areas not identified as water may reflect erosion, sediment deposition, or post‐peak conditions. These results highlight the value of high‐frequency wide‐swath radar altimetry for monitoring transient floods.