Marine heatwave in the Bohai-Yellow Seas enhanced the July 2025 rainstorm in Beijing and its surrounding areas

Beijing and its surrounding areas (BSA) experienced a record-breaking rainstorm from July 23 to 29, 2025, with area-averaged precipitation reaching 210.4 mm (38% of the annual mean), causing unprecedented loss of life and property. Combining high-resolution WRF simulations and Lagrangian trajectory analysis, we demonstrate that sequential tropical cyclones established a relay-like moisture conduit from the western Pacific to BSA. Particularly, we found that a concurrent marine heatwave in the Bohai-Yellow Seas (BYS) amplified the event, where SST anomalies exceeding the 90th percentile enhanced evaporation, supplying additional moisture to the event. Sensitivity experiments confirm that, without it, the moisture supplied from the BYS would be suppressed by about 25%, which would reduce the rainfall over the BSA region by 22 mm (16.2%). Overall, this study highlights compound tropical cyclone-marine heatwave events as critical amplifiers of coastal rainfall extremes.