Spatiotemporal Variability and Attribution of Hourly Extreme Rainfall in Hong Kong: A Multi-Regional Analysis Using Structural Equation Modelling

Under global warming, the intensification of extreme precipitation poses a critical threat to dense coastal metropolises like Hong Kong, where complex terrain and high population density amplify flood risks. While daily rainfall trends are well-documented, existing studies largely focus on coarse regional simulations or daily-scale metrics, leaving a gap in understanding the granular evolution of sub-daily extremes and their specific drivers within complex intra-urban environments. This study investigates the spatiotemporal characteristics of hourly extreme rainfall in Hong Kong from 1991 to 2024, utilizing continuous hourly records from approximately 80 Geotechnical Engineering Office (GEO) stations. We spatially categorize the territory into four distinct subregions—Hong Kong Island, Kowloon, New Territories, and Lantau—to examine regional heterogeneity. The analysis employs indices including hourly precipitation percentiles (95th, 97.5th, 99th, and 99.9th) and Maximum Rolling Rainfall (MRR) across 1, 3, 6, and 12-hour durations to capture both short-term intensity and cumulative event magnitude. Furthermore, a Structural Equation Modelling (SEM) framework is developed to disentangle the contributions of key drivers, specifically quantifying the impact of urbanization (e.g., built-up area, patch density) alongside large-scale climate variability (e.g., ENSO, monsoons) and socioeconomic factors. We hypothesize that short-duration rainfall intensity (1-hour MRR) exhibits a more significant upward trend than longer durations, particularly in highly urbanized sectors like Kowloon. The SEM analysis is expected to reveal that urbanization acts as a primary localized driver exacerbating extreme rainfall frequency and intensity, distinct from background climatic warming. These findings will provide essential insights for refining urban drainage standards and disaster mitigation strategies in high-density mountainous cities.