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

Abstract Beijing and its surrounding areas (BSA) experienced a record-breaking rainstorm from July 23 to 29, 2025, with the area-averaged accumulated precipitation reaching 210.4 mm. Combining high-resolution simulations and Lagrangian trajectory analysis, we demonstrate that sequential tropical cyclones established a relay-like moisture conduit from the Pacific to BSA and maintained the long-lasting event. Moisture budget for rainfall-related particles revealed that terrestrial evaporation over eastern China contributed the most to this event, while the western North Pacific and the Bohai-Yellow Seas acted as key secondary moisture sources. Meanwhile, a concurrent marine heatwave in the Bohai-Yellow Seas (BYS) amplified the event by supplying additional moisture via enhanced evaporation. Sensitivity experiments show that the moisture from the BYS would be suppressed by about 25% without the heatwave, and the area-averaged accumulated rainfall would also be reduced by 22 mm (16.2%). Overall, this study highlights compound tropical cyclone-marine heatwave events as unignorable amplifiers of rainfall extremes.