FY-4B Satellite-Derived Cloud-Parameter Responses to Localized Short-Duration Heavy Rainfall over Complex Terrain in Sichuan

This study investigated short-duration heavy-rainfall events in Sichuan during 2023–2025. A 35 km × 35 km cloud window centered on heavy-rainfall stations was constructed. Multiple cloud parameters in the window were statistically analyzed to examine their responses to heavy rainfall under different rainfall-intensity classes. Representative cases were also examined. The results showed that: (1) Eight major cloud parameters, including minimum cloud-top brightness temperature and deep convection index, showed clear responses to heavy rainfall in both rainfall-intensity classes. (2) Heavy-rainfall locations were mainly found in large-gradient zones near the edges of low cloud-top brightness temperature regions (<220 K) and high cloud-top height regions (>12 km). Cloud-parameter extrema generally appeared before the end of peak rainfall. Samples with rainfall intensity > 50 mm·h−1 were mainly associated with ice-phase cold cloud-tops. These cloud-tops had brightness temperatures below 200 K, heights above 15 km, and pressures below 100 hPa, indicating stronger convective activity. In contrast, the 20–50 mm·h−1 samples showed relatively weaker convective activity. (3) When cloud-top brightness temperature < 220 K, deep convection index ≥ 40, cloud-top height ≥ 15 km, DTB13 ≤ −1 K, and cloud-top pressure ≤ 130 hPa occurred simultaneously or successively, the cloud window indicated potential for short-duration heavy rainfall.