United States floods within the context of atmospheric moisture sources and pathways

ABSTRACT Floods are devastating and costly, making accurate flood frequency and magnitude estimates essential for engineering and planning. This study examines flood characterization within a hydroclimate context. At-site analysis links flood events to atmospheric moisture pathways and source origins to understand the floods regionality and develop new modalities for flood frequency estimation in a changing climate. A novel principal curves approach is developed and applied to 623 stream gauges across the conterminous United States (US) over the 1956–2015 period, analyzing 37,380 annual floods, with Atmospheric Rivers (ARs) contributing ∼73%. The Northwest, West, Northeast, and Southeast experienced 70–100% AR-driven floods, while the East North Central, Central, South, and Southwest saw <70%, and the West North Central had <15%. Attributing floods to their moisture source significantly improves flood frequency curves, enhancing upper-tail fit and reducing uncertainties. Pacific Ocean ARs increase the 100-year flood magnitude by up to 345% in the West, Atlantic Ocean ARs amplify it by 400% in the East North Central, Caribbean Sea and Gulf of Mexico ARs raise it by 350% in the South, and Local Moisture increases it by 600% in the Southeast. These findings enhance flood risk management and climate adaptation strategies.