The manuscript explores the impact of DEM source and resolution on the NOAA Office of Water Predictions (OWP) Flood Inundation Mapping (FIM) framework. The framework is based on the topographic Height Above Nearest Drainage (HAND) approach and is thus very sensitive to DEM quality. The OWP HAND-FIM is an operational framework at the US Weather Service and its simplicity (relative to hydraulic solvers) is a tradeoff between numerical/physics complexity and computation costs. Exploring sources of uncertainty and pathways for improving its accuracy is thus of great importance and interest. The manuscript is very well written, the methodology is sound and the interpretation of the results is, overall,  fair and meaningful. Below I highlight issues that could be quite easily addressed with limited additional analyses and edits.

Major Issues:

Consider extending the analysis for 30 and 90 m resolutions - these are the most common DEM resolution for many national and global DEMs

Figure 4. A very busy map that makes it hard to read - consider aggregating the key classes into 4-5 major LULC classes.

Section 3.1 and Figure 6: I found it hard to understand what is the actual/overall improvement in HAND-FIM predictions using 3DEP. The authors should provide summary statistics in a table and/or additional plots (e.g. PDF, Box Violine).

Section 3.2 and Figure 7: this was the most unclear section of the manuscript. The results did not make much sense to me and the figure was hard to read/understand. The authors should re-think how to present and analyze the results. They may want to consider removing this section altogether.  

Section 3.3 and Figure 8: I don't recall that the authors explained how these distributions were calculated. Similar to section 3.1, summary (overall) statistics of the FIM accuracy metrics should be reported.

Figure 9 and relevant text: report the computer hardware that was used.  

Minor Issues:

Line 35: '...scales [often] requires'

Line 109: 'omb' ?

Line 168: 'due to the (...'

Line 183: '?'

Line 256: '(of DEMs ,...'; '(, WBM)...'

Line 257: '(, MRLC)'

Line 373: 'we used investigate...'

Line 400: 'two-way interactions' - do you mean cross-correlation? 

The paper analyzes the improvement expected from the availability of high quality and high resolution digital elevation models (3DEP) with respect to performances of a HAND (Height Above Nearest Drainage) based procedure to recognize flood inundation maps trugh topographic information.

To this purpose a set of analyses is performed involving the use of different metrics for performance evaluation and different factors\covariates used to diagnose the different metrics performances with respect to the increase in spatial resolution of dem.

The paper is well written and organized and also the topic is quite relevant and up-to-date with respect to institutional and scientifical purposes that could be achieved in this framework.

One of the most important outcomes stems from the analysis of Figure 6 where the comparison in terms of metric enhancements is shown with respect to the benchmark provided by the use of dems sourced from the NHDPlusHR program.

Less intriguing are results produced in the analysis of the role of different spatial resolution on FIM detection and on the capability of explanatory factors and covariates on explaining the variance of obtained results.

While the methodology is clearly depicted and can be considered of general purpose, results generality is limited by the presence of only one study area characterized by “low terrain slope and minimal anthropogenic influence”.

The most important perplexity in my reading of the paper regards the choice of the basic source of information for both evaluation and validation of the method, which is a 1D HEC-RAS flood inundation extents, involving hydrologic and 1-dimensional hydraulic of Saint Venant equations. From the reading it seems that the BLE (Base Level Engineering) cross sections provided by InFRM were used both for comparison of flood inundation maps (validation) and for the evaluation of the HAND metric. If this is true, I believe the authors should better specify the reason of such a choice. I may imagine that such a choice can make sense in the aim of a larger comparison at the continental scale, on the other hand I think that it is hard to look for improvements based on higher quality and higher resolution DEM, whenever the benchmark has not the same quality. I would suggest, maybe for future works, a comparison with flood inundation maps obtained with a shallow-water complete 2D hydraulic modeling supported by high resolution dems. Another feasible analysis could be carried out over real inundation maps.

Minor comments

The sentence in lines 320-321 seems not consistent with equation (1).

Lines 343 (and around it) it is not clear the difference between covariates and factors. The different role they play in the regression analysis and also how their combination are made.

It is not clear if and/or how the spatial resolution of dem affects results in figures 11 and 12.