A Study on Heavy Rainfall Environments and Radar Echoes in Macau

Macau, owing to its unique geographical location, experiences complex and highly variable weather conditions and is frequently affected by heavy rainfall during the flood season. To comprehensively investigate the environmental conditions and characteristics of heavy rainfall events in Macau, this study identifies heavy rainfall events occurring from 2014 to 2023 using multi-source observational and reanalysis data and classifies them according to weather patterns, for subsequent environment and radar-echo analysis. The annual, monthly and categorical distributions indicate that heavy rainfall events predominantly occur between May and October. Among the classified types, tropical-cyclone (TC) and warm-sector (WS) events are the most frequent overall. WS, frontal (FT), and low-vortex shear (LS) events occur more frequently during the pre-flood season (May ~ July), whereas TC and southeast wind (SW) events dominate in the post-flood season (August ~ October). Analyses of key environmental parameters reveal that LS and WS events are characterized by stronger thermodynamic instability, whereas SW and TC events generally exhibit more favorable moisture conditions throughout the atmospheric column and in the lower troposphere. Despite similar moisture-rich environments, SW and TC events differ in terms of moisture replenishment capability and near-surface moisture conditions. Radar echoes of each associated with different heavy rainfall types exhibit distinct characteristics in terms of mobility, initiation, centroid height and echo intensity. Statistical results indicate that WS and LS events tend to have lower centroid heights and relatively stronger echo intensities, whereas FT and SW echoes generally exhibit higher centroid heights, with SW echoes being weaker in intensity. In contrast, TC echoes are associated with relatively lower centroid heights, with echo intensity spanning a wide range from strong to weak. Furthermore, dual-polarization parameter analysis further reveals that WS and LS events frequently exhibit a  column on the upstream side and a  column on the downstream side, indicating relatively larger raindrop sizes and higher particle concentrations over Macau. In contrast, TC and SW echoes over Macau are generally characterized by lower  values but higher  values, implying smaller raindrop sizes accompanied by higher particle concentrations.