I have read the manuscript entitled " Validation of precipitation reanalysis products for rainfall-runoff modeling in Slovenia", which is a comparative analysis of two reanalysis precipitation datasets, ERA5-Land and COSMO-ERA6, to runoff simulation over different regions of Slovenia

the manuscript is relatively interesting and well written. I consider that it is suitable for publication in the EGUsphere journal, although, I would like to give some comments to the authors for the general improvement of the manuscript.

1- Please use more recent papers that are relevant to your topic. Below you can find some new studies:

https://link.springer.com/article/10.1007/s11269-022-03081-9

https://www.tandfonline.com/doi/full/10.1080/02626667.2019.1691217

2- Improve the quality of all figures.  For example, in Fig1, 2, texts and numbers are blurred and need to improve.

3- What are your criteria for mesoscale, large-scale, and microscale categories?

4- Some of the studied catchments have an Area value lower than 100 km2, While ERA5-Land cells are higher than 100 km2. How did you deal with this issue? I think using this dataset for small catchments is not suitable. However, Still I don't understand your criteria for mesoscale. these catchments fall in the microscale category.

5- The values of numbers in Table 3 are not clear and I can't check the dataset combinations.

6- The authors used the GR4H model for runoff simulation. Based on the model structure (Fig 4), this model doesn't consider the snow component through the modeling. How do you explain this issue for snowy catchments of Slovenia?

7- For precipitation comparison, which approach is used in this study? Point-scale or Grid-scale approach? However, Based on fig1 and fig3 the density of your ground-gauge observations is not so good.

8- It is recommended to plot stream flow time series for a better understanding of model performance for simulating peak and low flows.

9- For the estimation of ET, which formulas and datasets are used for running the GR4H model? Please clarify this issue in the revised paper.

10- Why didn't the authors consider the uncertainty analysis for using the GR4H model? 

Best

The authors present a study evaluating two reanalysis products against a gridded precipitation dataset that was constructed based on ground observational data from errors in input sources and errors propagated into hydrologic simulation across 16 catchments in Slovenia. The paper is within the scope of EGUsphere, however, major revisions must be made before considering publication. Below lists my major concerns regarding the scope of this study, methodology, and results presentation.



Major comments:



1. The scope or motivation of this study is not well articulated. Apparently, reanalysis datasets are not used to solve precipitation, but rather other meteorological variables. Precipitation variable is a by-product. Most of the reanalysis datasets do not directly assimilate precipitation into model chain (Although ERA5 and MERRA2 did assimilate precipitation). For hydrologic utilities - like floods the authors mentioned, a reanalysis dataset is not qualified and should not be a supplement for real observations unless no observations available. In summary, the authors should provide a strong argument prior to their analysis - why use reanalysis for hydrologic modelling since observational datasets exist.

2. In the introduction, I am not convinced by the facts why the authors chose to evaluate reanalysis data. In line 61-63, the authors stated that " mostly data gathered by means of remote sensing technology. ". First, I would like the authors to state why they are not considering other satellite derived products which have been proven to perform better than reanalysis. I am concerned the scope of this study. See my first comment.

3. The authors site a range of literature on evaluation of reanalysis in Lines 52- 93. However, I don’t see a summary of what the reviewed studies did not do, that is compensated by the current study and why reanalysis for Slovenian catchments.  The authors should make this clear in the introduction.

4. Why is the ARSO-d data considered as the benchmark? There are other observational precipitation datasets available such as IMERG, MSWEP and GSMaP. The authors should provide more information to claim that ARSO-d data is more accurate than reanalysis products. More details of the on this data should be provided, such as data quality, and the data source, validation etc.

5. How is calibration applied to different forcing?

6. Include the location of the catchments in Table 1 (Lat and Lon), catchment characteristics relevant in the formation and dominant hydrological processes

In line 250 – 254, the authors state “The simulation period is split-sampled into…..”but do not justify the use of Split Sample method in model calibration. Refer to Arsenault et. al., 2018. The hazards of split-sample validation in hydrological model calibration.

7.  Line 268 – 273 Please check the font and line spacing