This study analyzes the uncertainty in flood predictions due to river bathymetry estimation using a Monte Carlo framework. Three important parameters are considered, and the influence of the uncertainties in these parameters on the bathymetry estimation are analyzed. Although this is an important question in flood predictions, I find some important issues not described clearly in the paper. My major concerns are as followed.

1. The relation between flood predictions and river bathymetry estimation is not clear for me. When talking about flood prediction, I would expect the simulation or prediction of streamflow, the peak flow volume and peak time. However, reading the paper, I only find results of bathymetry and flood extents. The authors didn’t provide many details about the calculation of flood extents, but it seems that the flood extents can be determined by the river bathymetry directly. Consequently, in my understanding, it seems that “flood prediction” and “bathymetry estimation” in this study is one thing to some extent.
2. Related to the first comment, I am also confused about the flood prediction model used in this study. The authors provide little descriptions on the LISFLOOD-FP model, missing some important issues. For example: what is the input and output of the model? What’s the relationship between this model and the two formulas for river bathymetry estimation? Is the estimated river bathymetry used in this model?
3. The uncertainties in flood predictions come from several sources, including the accuracy of three parameters (S, Q and w), the accuracy of two formulas for bathymetry estimation, and the influence of bathymetry uncertainties on flood prediction. Unfortunately, the analysis conducted in this study is more likely a sensitivity analysis, without addressing these uncertainty sources clearly. The authors analyzed the uncertainty brought by a standard deviation of 10%, but the question should be what is the actual uncertainty in S, Q and w estimation themselves. Besides, the study didn’t use any measurement data to validate the estimated bathymetry, so the analysis actually only shows the range of estimated bathymetry caused by a 10% variation in S/Q/w, which, in my opinion, is a rather direct procedure from the viewpoint of mathematic, since the formulas for bathymetry (Eq.2) is a very simple equation.
4. Some questions about UF and CMR formulas. 1) According to section 2.2 the only difference in these two formulas is the different value of α and β, am I right? 2) Table 1: In my understanding, Manning’s n should be a parameter reflecting the characteristics of riverbed. Why is it different in different formulas?

In the end, as I am not an expert in river bathymetry estimation, my concerns are primarily raised from the perspective of hydrological modeling. I’m not sure whether I may have misunderstood or overlooked some critical aspects of this study. Therefore, I recommend a major revision and encourage the authors to address the issues mentioned above and to highlight any inaccuracies in my understanding.

The manuscript presents a sensitivity analysis of floods due to the uncertainty in river bathymetry. In the context of flood prediction, understanding the sources of errors is crucial. Although this is an important question, the current manuscript lacks a thorough analysis and description of the procedures. 

Please find my major comments as follows:

1. Generally, the authors need to significantly improve the methods section to convey the methods used in this study. In particular, they did not provide enough explanation regarding the LISFLOOD modeling and the input data utilized. It is important to summarize the processes implemented by the model to understand the relationships presented in the results section. For example, processes such as, backwater effect, sediment processes, human regulations, etc.
2. I do not believe the authors adequately assess the uncertainty of floods, as they primarily evaluate the uncertainty of DEMs, bathymetry estimations, and roughness coefficients. In addition, the authors did not indicate whether their sources of uncertainty are valid by referring to the ranges of DEM values, any reported roughness, etc.
3. In addition, they refer to a previous publication, Nguyen et al. (2024b), to get the key details for the methods used. For a smooth reading experience, the authors should summarize that key information in this manuscript as well.
4. Moreover, the authors did not explain the context of this uncertainty analysis of the flood prediction. Also, they need to include the details about the flood event they used in this study to demonstrate what they want to establish from this study.
5. The authors need to enhance their experimental methods to strengthen the robustness of their findings, such as applying these analyses to various case studies across a wide range of rivers.