Hapi: a U-Net Swin Transformer for continental-scale 24–72h hydrological forecasts
Hapi is a multivariable U-Net Swin Transformer that forecasts discharge, surface runoff, snow water equivalent, and soil wetness across the contiguous United States at 0.05° resolution for 24–72 hour lead times. On 2024 test data using reconstructed ERA5‑Land inputs it outperformed an operational physics-based model and a state-of-the-art AI model in flood detection, was validated against 3,881 USGS gauges and a Hurricane Helene case study, and runs a four-variable 72-hour forecast in an average 0.11 s on a single A100 GPU.