Water Vapor Transport Mechanisms During the Henan ‘7.20’ Extreme Rainfall Event Inferred From GNSS, ERA5, and GDAS1 Data

The processes linking remote moisture supply to extreme inland rainfall remain insufficiently quantified. This study integrates high‐frequency Global Navigation Satellite System‐derived Precipitable water vapor (PWV) (GNSS‐derived PWV), radiosonde observations, ERA5 reanalysis, a four‐boundary moisture budget, HYSPLIT trajectories, and moist potential vorticity diagnostics for the July 2021 Henan extreme rainfall event. GNSS and ERA5 capture similar regional moisture evolution, while GNSS resolves sharper station‐scale variations. Absolute PWV has its strongest regional correlation with subsequent rainfall at a 7‐hr lead, whereas the 3‐hr PWV change identifies a 2–6 hr precursor window, with maximum correlation at 4 hr. Eastern transport contributes 85% of gross inflow during preconditioning, and gross inflow peaks at 303 mm day −1 during development. During peak rainfall, southern transport contributes 61% of the 280 mm day −1 gross inflow. Trajectories identify complementary western North Pacific‐eastern China and South China Sea‐Beibu Gulf‐southern China pathways. The Beibu Gulf is a key transitional sector within the southern corridor, although trajectories do not directly quantify moisture‐source contributions. Horizontal moisture transport is concentrated at 850‐700 hPa, while vertically aligned moisture‐flux convergence and ascent extend to 500 hPa during peak rainfall. This circulation coincides with high lower‐tropospheric equivalent potential temperature, locally reduced MPV1, and vertically extensive negative MPV2. Maximum gross moisture import precedes peak rainfall, indicating that extreme precipitation followed substantial moisture preconditioning and developed when sustained replenishment overlapped with deep convergence, ascent, and moist‐baroclinic instability. These results quantitatively link sub‐daily GNSS moisture precursors, phase‐dependent boundary transport, parcel evolution, and dynamical moisture conversion.