the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Apr 2026
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.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2026-2046', Anonymous Referee #1, 11 May 2026
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AC1: 'Reply on RC1', Caiming Wu, 02 Jun 2026
We are profoundly grateful for the anonymous Referee 1’s insightful comments and constructive suggestions, which have substantially enhanced the quality and rigor of the manuscript. In response to the issues and limitations identified, we have carefully revised the manuscript accordingly. For a detailed account of our revisions, including point-by-point responses to Referee 1’s concerns, please refer to the PDF document titled “Reply on RC1”.
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AC1: 'Reply on RC1', Caiming Wu, 02 Jun 2026
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RC2: 'Comment on egusphere-2026-2046', Anonymous Referee #2, 20 May 2026
The authors presented a study that examines the spatiotemporal characteristics of Tropical Cyclones (Typhoons) in their study area and how they compare to existing IDF and spatial rainfall distribution methods used for design purposes. The study tackles an important issue that has a potential positive impact on the ability to identify areas at risk, for example, by improving the rainfall inputs used in applications like hydrodynamic modeling. The manuscript is well-written, and the portion of the results that is presented is well-presented.
That said, I highly recommend including additional details about the results and analysis at all the monitoring stations used and intermediary steps etc. in the supplementary materials since the amount of results presented within the manuscript itself is limited. Additionally, while there was enough explanation of the methods used to create the IDF analysis, much less detailes were presented about the spatial analysis side of the study. Below are some detailed comments:
Abstract: The abstract is well-written but quite long and can benefit from shortening.
L32: Helene was not a typhoon; it was an Atlantic hurricane. If the authors intend to refer collectively to Helene and Kalmaegi, a more appropriate umbrella term would be ‘tropical cyclones.’ But since the study is focused on Typhoons, I’d recommend eliminating Helene or separating it as a Hurricane.
L54: NOAA acronym mentioned for the first time and not explained, same with MLIT, NILIM and BURGER in Lines 57 through 58. Please check for others like that as well.
L94: I recommend checking the literature in this field, for example (Amorim, R., Villarini, G., Kim, H., Jane, R. A., & Wahl, T. (2025). A Practitioner’s Approach to Process-Driven Modeling of Compound Rainfall and Storm Surge Extremes for Coastal Texas. Journal of Hydrologic Engineering, 30(5), 04025025.) and the literature cited in it by Thomas Wahl and his team. This approach allows the use of spatial rainfall observations of historical Tropical Cyclones.
L121 This line mentions TC which I am assuming refers to Tropical Cyclones. It is not explained.
L124 The figure is small and the station names are only visible at 200%+ Zoom level, also the text color makes it difficult to read.
L130 Please explain how 0.0625 degrees translate to km or meters in your study area.
L135 Please check if 1.12 meters MAE is globally or for built areas.
L 146 Please explain what is this curve fitting for, IDF curves? “For sample selection in curve fitting, each station was processed independently.”
L150- 162 I think an example or a diagram (in addition to figure 2) of this in the supplementary materials would greatly help visualize and understand the process.
L215: A reference to K-means and explanation of the method is needed.
L226: Please explain “For spatial patterns, the classification indices were defined as follows. First, the location of the main rainfall area was considered.”
L227-234: Can you please explain why you chose these constrains/conditions.
L237-244: Can you please mention if the existing IDF curves produced in 2015 took tropical vs. non-tropical events into consideration and how that might affect the comparison with your work.
L 245-250: I think you should present the different attempts for different distributions etc. and how they performed either within the body of the manuscript or in the supplementary materials so the readers can compare the performance.
L250: It was previously mentioned that the RMSE threshold is 0.05 mm/min (L 199).
L255: So far only one station is shown, I believe the other stations should be presented too in the supplementary materials.
L256-257: Please explain why you chose different definitions for how events start and end for tropical versus non-tropical and why you chose 24 hours of no rain as an indication for both non-typhoon and ‘complete rainfall data’ (which I assume includes typhoons). Would that impact short duration storms and exclude some of them?
Fig 4 and Figure 5: Please show the confidence intervals of the fitted curves.
Fig 5: similar to what I mentioned in L237-244 I think the fitted curve is TC only and it is compared to ‘complete record’ IDF. I think this should be mentioned in the figure caption similar to Figure 4. Also, station name should be mentioned in the caption.
Figure 6: The text is very hard to read. Also, I think using lines is easier to interpret (or something else). It is currently difficult to extract patterns or information directly from the figure.
L347: Please explain what is the marked rainfall phase “while the mean proportions of rainfall during the marked rainfall phase were 60.69%, 56.09%, and 62.69%.” maybe use something like ‘The peak rainfall (rainfall accumulations) were 0.79 (60.69%), 0.24 (56.09%), 0.51 (62.69%) respectively. That’s if I understood the sentence correctly and if proportion means accumulated rainfall.
L376- 377 Please explain how you reached this conclusion by explaining what is observed in the figure “All three metrics consistently showed that the gridded data reliably captured the spatial rainfall distributions reflected by the station observations.”
Figure 9: While the methods section explains the overall process of how this was produced. Additional explanation of how the analysis was executed (similar to the temporal portion) including equations and R-packages (if applicable) which were used so the readers can replicate the analysis if needed.
L409-424 References are needed to explain and back up the processes that the authors suggest explaining the results. Moreover, showing the TC tracks with the clusters will help (maybe additional figures with the TC tracks mapped on top of the clusters in the supplementary materials can help).
Citation: https://doi.org/10.5194/egusphere-2026-2046-RC2 -
AC2: 'Reply on RC2', Caiming Wu, 02 Jun 2026
We are truly grateful to Anonymous Referee 2 for the critical assessment and valuable recommendations, all of which have contributed to a substantial improvement in the clarity and scientific rigor of the work. In response to the issues raised, we have thoroughly revised the manuscript accordingly. Please refer to “Reply on RC2 & Supplementary materials.zip” for the supporting documents and detailed responses.
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AC2: 'Reply on RC2', Caiming Wu, 02 Jun 2026
Data sets
FABDEM data The company Fathom (UK) and the University of Bristol (UK) https://doi.org/10.5523/bris.25wfy0f9ukoge2gs7a5mqpq2j7
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This paper presents an analysis of urban-scale typhoon precipitation characteristics and spatiotemporal patterns, using Ningbo, China as a case study. The findings are of great significance for enhancing the understanding of typhoon-induced rainfall and for flood mitigation and disaster reduction. The study is based on a meticulous analysis and makes a valuable contribution to advancing the knowledge of coastal typhoon precipitation.
The following specific revision suggestions are provided for your reference.
Why was 500 km selected as the threshold for typhoon rainfall? Please provide the specific basis for this choice. Additionally, could you please conduct a corresponding sensitivity analysis?
For Figure 3, it is recommended to add a legend for the different rainfall durations. Although the authors have included labels in the figure, the one-to-one correspondence between the labels and the data remains unclear.
To enhance accessibility for an international audience, please refrain from mentioning specific place names. The manuscript should minimize the use of overly detailed or localized geographical terms.
While the paper presents extensive analyses of rainfall characteristics, it lacks mechanistic explanations. The authors should strengthen the mechanistic analysis and discuss the potential implications. Specifically, the mechanisms driving differences in rainfall patterns—such as how they relate to typhoon intensity, duration, and landfall processes—warrant further investigation.