Poster

IAMAS

M04 - Cloud-Precipitation-Aerosol Studies

Upwind inhabitant and downwind enhancement effects of a Strong precipitation induced by urbanization over the Pearl River Delta, South China

Urbanization affects precipitation and its redistribution through thermal and dynamic modifications, while the mechanisms remain debated under different environment. This study explores a heavy rainfall event using the WRF-Chem model to investigate the impact of urbanization on precipitation in the warm and humid city agglomeration, Pearl River Delta (PRD), China. Results indicate that urbanization generally elevated temperatures and CAPE, and reduced surface water vapor. Precipitation increased in urbanized areas with a redistribution pattern: reduced precipitation in the upwind (R1: west of Pearl River) and increased in the downwind (R2: east of Pearl River). The urban heat circulation enhanced surface moisture convergence and upward motion in R2, leading to increased water vapor between 925 to 200 hPa and promoting liquid-phase particle formation in the lower layer (925-600 hPa). Above the freezing level, ice-phase particles formed through desublimation and freezing processes increased by 0.6 g kg?�� in the upper layer (400-200 hPa), which raised maximum latent heat release by 16 K h?�� at 400 hPa, corresponding to increased vertical velocity of 0.8 m s?�� and area-averaged precipitation of 7.4 mm h?��. This enhanced latent heating further strengthened the upward motion, establishing positive feedback for precipitation development. In contrast, the urban dry effect and reduced moisture convergence in R1 resulted in decreased liquid water content (0.1-0.3 g kg?��) and ice particle formation (0.4 g kg?�� near 500 hPa), suppressing precipitation development. Moreover, the moisture transport from R1 to R2 due to low-level southwesterly winds intensified the influence of urbanization on rainfall redistribution.