The Role of Aerosol-Cloud Interaction in Improving Summer Precipitation Forecast Over North China

Human activities emit massive aerosol that profoundly influence cloud and precipitation processes, yet their effects on precipitation forecast remain poorly understood in numerical weather prediction (NWP). Using the chemistry-weather model CMA-CW v1.0, this study investigates the role of aerosol-cloud interaction (ACI) in summer precipitation forecast over North China during 2023-2025. Results show that incorporating ACI improves 24-hour accumulated precipitation forecast in an intensity‑dependent manner, with the largest gains for heavy rainstorm (>100 mm, +29.2% in overall score), followed by light rain (0.1-10 mm, +6%), while other precipitation intensities show slight changes. Mechanistically, aerosol mainly enhances cold-rain production for heavy rainstorm via increased cloud droplets and ice-phase hydrometeors, and promotes warm-rain processes for light rain by accelerating cloud droplets growth to expand rainfall areas, effectively addressing previously missed events. Offsetting effects from large case-to-case variability account for the rest. These findings highlight the importance of chemistry-weather NWP for improving precipitation forecast.