This is a worthwhile study, although it is far from the first to evaluate model simulations of SWE, SCE and albedo in comparison with satellite-based datasets. It may be that this paper is the first with this precise combination of snow properties, reanalyses and observations, but it is mostly restricted to documenting differences without adding understanding. How much of the exaggerated SCE trend in ERA5 is due to the discontinuity in IMS assimilation? How closely are SCE and albedo anomalies related, and to what extent are they masked by forest cover? Difference plots for the means in Figure 1 would be useful. What can be said about the relative contributions of assimilation and resolution to differences between ERA5 and ERA5-Land?

The abstract states that “The analysis shows that both ERA5 and ERA5-Land overestimate SWE”.  The three datasets used as the reference for SWE in mountainous regions are themselves model products, two of them driven by the ERA-Interim predecessor of ERA5. All that is conclusively shown here is that ERA5 and ERA5-Land have larger SWE in mountainous regions than these other model products. Does the overestimate of SCE in ERA5, even after 2004, just show that IMS overestimates SCE? How much of the differences in SWE be attributed to differences in precipitation and temperature driving data between ERA5 and ERA-Interim?

Because discussion of hemispheric timeseries trends is followed by the same for continents, Figures 2 and 3 and much of the discussion in 3.1 could be cut.

Minor points:

The albedo paragraph starting at line 34 interrupts the discussion of snow cover; I think it would sit better at a later point in the introduction.

88

“relatively sparse” – relative to what?

110

Important to note here that IMS does not provide information on SWE, and it is not assimilated in ERA5 at elevations above 1500 m. Describe how assimilation of SCE is used to update SWE.

136

This sentence is a repeat from line 98.

141

Note that Equation (1) is from the HTESSEL documentation (and needs to be limited to a maximum of one).

168

Not all of the datasets in 2.2 are satellite based.

184

Mortimer et al. (2022) referenced here did not evaluate the bias-correct SnowCCI and states that v2 is an improvement relative to v1.

208-214

Availability of albedo estimates from ERA5 and ERA5-Land, and differences between them, have already been discussed in 2.1.

261-265, Figure 1

Differences in SCE dominates differences in albedo, so should be discussed and shown first.

Figure 2

Axis labels for the second row should show that this is change in SWE, not SWE.

393

“whether the positive trend”

400

“deforestation”

498-499

Is this intended to say that ERA5 and ERA5-Land are well correlated with observations of annual variability? That is not very obvious in Figures 10 and 11, but could be quantified.

519

“the SWE values themselves”

520

“a considerable difference”

525

“uncertainties related to”

 

The writing is generally good. I noted a number of incorrect commas, but the Finns have a word for reviewers who pay excessive attention to commas.

In this manuscript, the authors presented an evaluation of ERA5 and ERA5-Land SWE, albedo, and SCE products with different satellite-based datasets in the NH during the spring from 1982-2018. While the study is not that innovative, the manuscript is comprehensive, well-written and of interest to the snow community and final users. However, I think that some restructuring of the Introduction is needed, and some issues need to be better discussed throughout the manuscript.

Abstract

I would appreciate seeing some quantitative results about the agreement among datasets rather than inserting all the information about trends, that is for sure useful but a little bit difficult to follow. Also, when you mention “other datasets” (L20), it is not completely clear if you refer to the satellite-based datasets used as “reference” or if you are also accounting for differences between ERA5 and ERA5-Land.

L18 IMS first entire name than acronym

Introduction

To make it easier to follow, I would always keep the same order as in the abstract, i.e., SWE, albedo and SCE (or maybe a different order that better suits for discussion). I think the introduction needs restructuring. First, you introduce the snow importance, hence L48-56 should be moved at the beginning. Secondly, you introduce SWE, albedo and SCE. Then you should introduce the reanalysis data and their importance also linked to climate change. However, L58-67 might be shortened. Finally, the aim of the work.

It should also be clearly stated why you focus on the NH. Is that because of the lack of studies? Is a global evaluation of the snow properties already available for such a period? I suggest highlighting the importance of snow in the NH in general, despite mentioning the Arctic region throughout the text (as L86) that still belongs to the NH but it is just a part of that.

Minor comments

L51 “limits water availability” is expressed in a negative way. I would use something like “stores water”

Provide short information about IMS and what kind of data is assimilated.

Section 2

L138 keep same order SWE, albedo, SCE

Eq. 1 is not completely clear to me. From the first term you get the snow height, that is then multiplied by 1/0.1 to derive the snow cover fraction. Does this derive from a depletion curve? Please, add a reference.

L159 very close: please quantify!

Table 1. I would add the period of availability of the different data sources.

L190 I am wondering if it might be problematic to use products that assimilate another reanalysis product (ERA-Interim) as “reference”. Might be that the differences that you obtain are due to the assimilation of the ERA-Interim product? I think this point needs further discussion.

L212 How can you explain that the differences are negligible?

L237 What is the reason why you choose the nearest neighbor interpolation instead of a cubic for example?

I am wondering also why you haven’t used the snow CCI SCF product as additional reference dataset.

Section 3 Results

I would appreciate to see some more metrics (RMSE, correlation).

L308 Please, explain better what you mean with “explained with the uncertainties”.

Discussion

L488 quantify “typically” or add a reference