Response of extreme precipitation to urban expansion over the Guangdong-Hong Kong-Macao Greater Bay Area

Investigating the response of extreme precipitation to urban expansion across megaregions plays a pivotal role in flood and related risk management. This study focuses on the Guangdong-Hong Kong-Macau Greater Bay Area (GBA) and comprehensively analyzes various factors of urban expansion, such as area, shape, aggregation, and density, and their impacts on the magnitude, intensity, frequency, and duration of extreme rainfall events. The study utilizes data from 29 daily rainfall observation gauges in the GBA and high-resolution impervious surface change datasets spanning from 1986 to 2018. The structural equation model (SEM) is employed for the first time to explore the influence of urban expansion on precipitation. The results reveal an increasing trend in the magnitude, intensity, and frequency of extreme precipitation in the GBA, with significantly increased gauges predominantly clustering in urbanized areas. While the continuity of extreme precipitation exhibits an opposite trend. The SEM models demonstrates good performance across all 10 urbanized gauges, and identifies the fractal dimensions of urban expansion as having the most significant impact on extreme precipitation, with fractal-related metrics such as PARFAR and LSI appearing most frequently in the SEM model. The results indicate that compact urban footprints may lead to higher rainfall anomalies.