Official Records Reveal Megacity‐Scale Precursory Precipitation Thresholds for Urban Inundation: Shanghai, China

Investigating characteristics of urban flood‐related precipitation is vital to mitigate socio‐economic impacts under global warming. This study analyzes the spatiotemporal characteristics of Shanghai's urban inundation using 10‐year official inundation records and, for the first time, quantifies the precursory precipitation indicators at the megacity scale. Results show distinct spatiotemporal variability of inundation in Shanghai, with high occurrences in the old‐built regions and recent years. Categorization of inundation‐related precipitation events based on synoptic conditions reveals consistent precursory indicators in precipitation, with most events generating pronounced hourly precipitation within 2–3 hr prior to the inundation onset. Accordingly, threshold values for accumulated rainfall over 1, 2, and 3 hr are found to be 16.1, 28.2, and 31.8 mm, respectively. Based on these thresholds, climatological analysis suggests that the megacity Shanghai has witnessed an increasing trend in the frequency of inundation‐associated heavy precipitation during the rainy seasons of 1972–2022.