Analysis of urban-scale typhoon precipitation characteristics and spatiotemporal patterns: A case study of Ningbo, China

Abstract. Rainstorm characterization, which is the fundamental design basis for urban flood control and drainage systems, currently relies primarily on general statistical regularities of heavy rainfall. The current design rainstorm profile (e.g., Chicago hyetograph) overlooks the spatial non-uniformity and unique intensity–duration–frequency (IDF) relationships of typhoon rainfall. This deficiency constitutes a key reason for the systemic failure of urban flood defence engineering when facing extreme typhoon rainfall events. To address this problem, the current study focused on the area of Ningbo in China. Using meteorological station observations, county-level IDF curves for annual maximum typhoon rainfall at specific durations were established, and then the K-means clustering method was applied to extract typical spatiotemporal patterns of typhoon rainfall, which produced the following results. The impact of typhoons in the Ningbo area manifests primarily as extreme rainfall of long duration, with 24-h rainfall being the most notable contributor. Current published IDF curves underestimate the extremes for such prolonged typhoon-related events. Owing to the spatial non-uniformity of typhoon rainfall, marked regional variations of IDF curves are observed across county-level areas. Furthermore, typhoon impacts, as revealed by extension of the study period from 1980–2014 to 1980–2024, exhibited spatially inhomogeneous enhancement, with notable increase in the northern region, reflected primarily in the frequency of extreme events. The extracted temporal rainfall patterns for typhoon events are dominated by the central-peaked pattern (with rainfall concentrated in the middle phase) and the late-peaked pattern, differing substantially from the Chicago hyetograph. The latter exhibits limitations in characterizing the structure of long-duration typhoon-related rainfall because it tends to overestimate peak rainfall intensity. Spatially, rainfall patterns are categorized into dispersed-dominated and concentrated types. Topography is the key driver of local rainfall patterns, dictating the spatial loci and temporal windows in which heavy rainfall develops and suddenly intensifies. Typhoons and their interactions with other weather systems also enhance the local specificity of rainfall patterns. These insights could help in designing realistic typhoon rainfall scenarios for urban flood defence planning.