This paper presents the flood model can reproduce the historical flood maps due to a compound flooding in a specific area during a typical typhoon event.  The flood model proves its ability to examine the compound effects of precipitation and levee breach on the inundation. The paper is well structured and well written. My big concern is what the innovation of this paper is. The modelling approach seems reasonable but it is hardly seen innovative stuff in this paper. It was mentioned that the critical time to minimize damage (should further take actions) is the first a few hours after levee breach; however, readers would perhaps anticipate this conclusion before reading this article.  In addition, I’m not fully convinced by one of conclusion, which concludes that the model is strongly sensitive to roughness value (but the difference of max. average water depth is very small (~5cm) when the roughness value differs 10 times).  Maybe it should further explain that why the flood extent not consistently increases with the increasing of the roughness value after levee breach (compares to the flood extent before levee breach). Moreover, the vertical uncertainty of the topographical data could lead to large impact thus as a sensitive value on the flood extent and water depth in the flooding model.

Minor comments:

1. I feel parts of the introduction is concatenated with literatures (e.g. line 68 to 86), it would be nice to summarize the findings rather than simply list the findings one after another.
2. Line 25-26: ‘In low-elevation areas, temporary drainage measures and flood defenses are equally important’. This has neither studied and nor proved in the paper.
3. Line 66: what is the economic damage in this area?
4. How does the model control the levee height during the breaching process in section 2.3?
5. Line 184: what does ‘remaining’ mean? Does it mean the height of floodwall was decreased to 4.9-5m?
6. Line 269: the assumed evapotranspiration value is based on what?
7. it would be better to combine figure 2 and 5, which can clearly show the inundation process due to rainfall and sustained high water level in the river.
8. Line 321: maybe it’s better to show the breach location or highlight waterfront area in Figure 4.
9. Line 348: decreased from 0.6 to 0.55?
10. In Figure 3, it seems that these six points are building locations, how about the roadway and farmland? This is not consistent to the text line 367-369.

This is a valuable study that creatively modeled a flood event induced by a levee breach in Shanghai. Apparently, the authors have made great efforts to quantitatively identify the evolutionary process and pattern of the flood event. However, several specific and key points were not sufficiently clarified in the current paper, see below my specific comments. Thus I suggest a major revision from the authors for further considering it for publish.

1. In abstract, there shall be a statement on the effectiveness of the 2D Floodmap model. To what extent do the modeling results match with the real flood patterns? What are the advantages of the model? This is a key message that must be clearly stated in the abstract.
2. Page 3, line 54-56, the “Himalaya glacier outburst flood in northern India” needs a reference.
3. Figure 1, the sources of the image and picture shall be clarified.
4. Figure 2, there needs more explanations of the three peaks of the water level curve. Especially why is there a “third peak”, what caused it?
5. As I understand, Compound flooding is an extreme impact event resulting from the interaction of multiple drivers (Zscheischler et al. 2018), mostly rainfall and tides (Bavacqua, et al 2020). But in this study, the flood was obviously mainly caused by heavy rainfall from Fitow, and there seems no tides or storm surges at the study site. Thus I suppose the authors shall not call it as a compound flood.
6. The discussion and conclusion section is weak. The discussion shall be improved and extended with more on the possible strategies and measures to reduce such levee breach and associated risks. E.g. according to the flood pattern and process, which areas and which measures could be most effective in reducing the flood impacts? From engineering perspective, how could the levee be strengthened, to which level? In addition, it would be also valuable to compare the present study findings with otherSome flood adaptation studies and household responses measures may be referred and compared, for instance:

• Assessment of Flood Losses with Household Responses: Agent-Based Simulation in an Urban Catchment Area. Environmental Modeling & Assessment 23, 369-388. https://doi.org/10.1007/s10666-018-9597-3
• Levee Failures and Social Vulnerability in the Sacramento-San Joaquin Delta Area, California. Natural Hazards Review. Vol. 9, Issue 3 (August 2008). https://doi.org/10.1061/(ASCE)1527-6988(2008)9:3(136)
• Climate-related flood risks and urban responses in the Pearl River Delta, China. Regional Environmental Change 15 (2), 379-391. https://doi.org/10.1007/s10113-014-0651-7
• Urban flood risks and emerging challenges in a Chinese delta: The case of the Pearl River Delta. Environmental Science & Policy 122, 101-115. https://doi.org/10.1016/j.envsci.2021.04.009
• Enhancing the resilience to flooding induced by levee breaches in lowland areas: a methodology based on numerical modelling. Nat. Hazards Earth Syst. Sci., 20, 59–72, 2020. https://doi.org/10.5194/nhess-20-59-2020

7. Meanwhile, there is no conclusion in the current section 4. I would suggest to add a paragraph to summarize the key findings in this study, with simple and clear sentences. This helps readers to quickly get the key points of the study.
8. The English language is in general not sufficiently good for a scientific publication, which must be further modified.