|Thanks very much to the authors for their thorough revisions to the manuscript. In particular, I appreciate the effort to add data from Canada, which means there is now better spatial coverage of the surface snow observations. I have a small number of final comments for the authors to consider:|
1. The methodology now explicitly describes the identification of stations that were assimilated into ERA5, and how these were treated within the analysis (Line 165: “These stations were kept for the stability analysis, since their addition to ERA5 may explain some of the discontinuities observed, but were removed from the accuracy analysis to guarantee the independence of the validation set.”).
In line 264 it states that 387 stations were used for validation; how many of these stations are part of the 235 stations assimilated into ERA5? Is it possible to use different symbol shapes in Figure 3a to indicate which stations are assimilated?
2. Justification for the use of the 2.5 cm snow depth threshold for determining snow cover (and subsequently snow cover duration) is now more clearly described. As noted in my original review, I appreciate the effort taken to quantify the spatial representativeness of the point measurements.
3. As noted in my review of the original manuscript, the effort to address the fall trends in the NOAA CDR is important. In Section 5, the key findings are clearly stated (lines 517-522). The original presentation of these findings in Section 3.2.2 is, however, written less clearly. I think this is because the spurious nature of the NOAA CDR fall trends is illustrated by a positive trend in the bias (as opposed to Figure 11 which shows the false trend in actual snow extent), and the wording is sometimes ambiguous as to whether the trend in extent is positive or the trend in bias is positive. I suggest revising Section 3.2.2 for clarity, so that it more clearly links to the conclusions in Section 5.
4. In general, the manuscript is clearly written, but a final editorial review for grammar would be helpful.
Abstract, line 14: suggest changing “…with the increasing number of satellite data used.” to “…with changes to the available satellite data.”
Abstract line 21: suggest changing to “…while in drier regions such as Russia earlier snow melt occurs despite increased maximum seasonal snow depth.”
Line 69: Since the first version of this manuscript was submitted, a new manuscript has come out which shows the SMMR to SSM/I transition creates a temporal inhomogeneity in the Snow CCI dataset. I leave it up to the authors to decide whether there is value to add a citation.
Mortimer, C., L. Mudryk, C. Derksen, M. Brady, K. Luojus, P. Venäläinen, M. Moisander, J. Lemmetyinen, M. Takala, C. Tanis, and J. Pulliainen. 2022. Benchmarking algorithm changes to the Snow CCI+ snow water equivalent product. Remote Sensing of Environment. DOI: 10.1016/j.rse.2022.112988.
Line 306: consider changing the wording here to “The positive trend in fall has been previously reported as problematic in several studies.”
Figure 6: One too many C’s in the ECCC label.