I have been asked to serve as reviewer for the manuscript entitled "Is higher resolution always better? Open-access DEM comparison for Slope Units delineation and regional landslide prediction".

The manuscript presents results of a study aimed to analyze and compare different public-domain Digital Elevation Models (DEMs) to identify the most suitable for landslide susceptibility mapping. The presented approach was tested for the Marche region (Central Italy) allowing 1) to reach the optimal discretization of the terrain into Slope Units (SUs) thus, 2) to map the landslide susceptibility of the study area.

I really appreciated the representativeness and the quality of the presented research. The manuscript generally appears well structured and both approach and results are well presented and commented. Thus I consider it as ready for possible publication on Natural Hazards and Earth System Sciences after some minor changes. Specific comments and suggestions are detailed as follows:

Lines 16-19: consider to revise the sentence because too long and a bit confused due to repeating words (e.g. DEM);

Line 28: the acronym DEM was already introduced in the Abstract. Check for similar issues ahead in the manuscript:

Line 38: check the sentence for a possible colon that should be used;

Line 46: the acronym ALOS was introduced first buti t was indicated later at Line 56. Check for similar issues ahead in the manuscript;

Line 76: the acronym SUs was already indicated in the Abstract section;

Line 82: the acronym DTM was already indicated at Line 46;

Line 100: consider to replace “…have been characterized by…” with “”is characterized” or “is constituted”; furthermore consider “calcareous-marly and arenaceous units“.

Line 113: check to solve a possible issue;

Lines 113-115: consider to use “inventoried landslides”; furthermore, I strongly suggest to indicate the worldwide classification adopted to indicate the type of landslides (e.g. Cruden & Varnes 1996 or Hungr et al., 2014);

Line 128: “…in the first phase…”;

Line 162: the acronym DTM was already indicated at Line 46;

Lines 225-226: consider to revise the sentence because it is not clear its meaning;

Line 240: check for a possible missing of a comma “Ranging from 0, signifying no similarity, to 1 that…”

Line 282: the acronym SUs was already indicated in the Abstract section;

Lines 439-440: consider to improve the definition of a landslide reported in this sentence according to more recent landslide classifications (e.g. Cruden & Varnes 1996 or Hungr et al., 2014);

Line 527: “…than in the S-worst case. This…”;

Line 572: check the reference section for possible issues in terms of formatting indicated by Journal’s guidelines;

Figure 1: this figure could be improved 1) preferring a geological map in background to the satellite one, with the DEM overlapped with a trasparency, for the AOIa and b; 2) reporting the landslide inventory classified for different types (if possible); 3) using lecters for frames (e.g.: A, B, C) also indicating them in the caption; 4) defining a single legend for all frames.

Figures 3-4-5: this figure could be improved graphically 1) improving readability of axes; 2) adding primary grids of axes 3) removing the external boudary of frames also reorganizing them;

Figure 8: this figure could be improved 1) changing size and colour of the scale text because ureadable actually; 2) it should be interesting to show results also through a zoomed frames coinciding with the AOIb.

Figure 9: consider to remove the external boudary of frames;

Figure 10: consider 1) to reduce the extension of the area showed in the frames, thus allowing “readability” of differences; 2) to change the scale unit in km thus uniforming it with the other maps; 3) to relocate/indicate the north and the scale in each frame;

Figures 11 and 13: the LIPs are not clear. Consider 1) to change the type of representation (e.g. colour); 2) to overlap the SU layer on the landslide inventory one; 3) to indicate landslides inventoried for types; 4) eventually to use a unique simplified legend for all frames;

Figure 14: this figure could be improved graphically adding primary grids of axes.

The manuscript presents a comparison of the available Digital Elevation Models (DEMs) and their application in Slope Unit (SU) delineation, emphasizing the importance of selecting the most suitable DEM for landslide susceptibility mapping. The study is clear, well-structured, and offers valuable insights for readers of NHESS. My recommendation is for minor revisions focusing on the following aspects:

1)  I recommend explicitly stating in the abstract that the overarching objective of this research is to contribute to landslide susceptibility studies.

2) Consider including a simplified geological map to accompany the description of the geology of the case study. This will enhance the clarity and context for readers.

3) Ensure all DEM acronyms are fully defined when introduced for the first time.

4) I suggest providing the download links for the DEMs used in this study, either at the point where they are first cited or in the concluding section of the manuscript.

5)  It might be helpful to include additional comments on the resampling of TINITALY to 30 m resolution, specifically discussing how this impacts the results of the study.

6) (Lines 362–367): Presenting this data in a table or a plot could significantly improve its clarity and reader comprehension.

7) Figure 9: Adjust the legend so that it does not obscure the plot.

8) Please ensure thorough English proofreading. Below are a few examples of typos or language suggestions identified:

Line 38: Replace ; with :.

Line 58: Consider whether "popularized" is the best choice of term.

Lines 60–61: Rephrase "Considerations to be considered" to avoid redundancy.

Line 113: Remove "click [...] text."