Analysis on Multi-Factor Synergistic Hazards Mechanism of Wet Micro-downburst: Multi-Source Data Fusion Analysis based on Passenger Ship Capsizing Accident in Qianxi Region, Guizhou on May 4^th, 2025

Abstract. To reveal the multi-factor synergistic hazards mechanism of downbursts, this study takes the passenger ship capsizing accident at Dongfeng Reservoir in Qianxi, Guizhou Province around 08:32 (UTC) on May 4, 2025 ("May 4" accident) as the research object, and utilizes the data of integrates radar, ground observation, lightning monitoring, video and on-site disaster trace data to systematically analyze the hazard process of wet microburst. A strong persistence intense radar echoes (≥60 dBZ) was observed over the incident area. At 08:29 (UTC), the core intense echoes broke through the zero-degree layer and rapidly descended from 6–8 km to 2–4 km, which synchronized with the strongest downdraft, accompanied by localized high differential reflectance at 2–4 km showed a local high value R > 2 dB) . After the intense echoes touched the ground, an explosive near-surface divergent flow field was triggered: wind speed surged from 0.8 m/s to 34.7 m/s within 6 minutes, temperature dropped by 14.9 °C in 10 minutes, and air pressure jumped by 5.4 hPa in 5 minutes, and cumulative rainfall reached 40.6 mm. Lightning activity was dominated by cloud flashes (85.1 %), with high-density areas coincided with convective paths. The phase transition of ice particles (indicated by ZDR) intensified downdrafts through "mass loading – cooling enhancement effect" feedback, which triggered wind direction reversal and the occurrence of hailfall. The distribution of disaster traces (directional lodging, quadrant-switching damage) spatial-temporal matched with the wind field evolution, which verifying the coupling disaster-causing mechanism of dynamic attenuation and microphysical transport.