Snow Cover on the Tibetan Plateau and Topographic Controls

Round 1

Reviewer 1 Report

Journal: Remote Sensing

Manuscript title: Snow cover on the Tibetan Plateau and topographic controls

Authors: Duo Chu and Linshan Liu, Zhoufeng Wang

 Review:

The manuscript is a very interesting multifaceted description of snow cover frequency (SCF) in Tibetan Plateau in relation to topographical conditions such as elevation, slope and aspect. Analysis also include the influence of longitude and latitude on the snow cover duration and its dependence on solar radiation and water vapour sources. Authors describe the distribution of the intra-annual snow cover variation at different elevations. The work is written in a simple, understandable language. The justification for undertaking the research is sufficient and clear. MODIS daily snow products with the spatial resolution of 500 m and topographic data of very good resolution (90 m) were used for the analyses. The satellite data is well described; in addition, detection accuracy is given. The Authors thoroughly explain in detail the reasons for the described spatial distributions of SCF and its variability throughout the year (bimodal and unimodal distribution). The conclusions are contained in 5 points; that gives a clear effect of the investigations.

I recommend the manuscript to be published in the journal Remote Sensing. However, some clarifications and additions are needed:

• Abstract and subchapter 2.2.: add please information on the period for which the analysis were taken (2001-2014?)
• if possible, please insert information (chart, table, map?) about the average annual and monthly air temperature and the annual and monthly precipitation totals in TP at different elevations. This would allow a better understanding of SCF distributions;
• subchapter 2.3.2: what is the area share of each elevations range in TP? what is the area share of slopes of different ranges and flat terrain in TP? what is the area share of E, S, W, N aspects in TP?
• lines 165-166: the range of slopes 20-90° is far too wide. Is it possible to divide this range into 2-3 parts?
• Figure 5: what is the reason for the SCF inversion at the elevation of 3000 m in winter, at the elevation of about 6800 m in spring and about 7500 m in annual and autumn?
• Figure 6 and Table 2: data from Figure 6 are repeated in Table 2. I suggest leaving only the CV column in Table 2;
• subchapter 3.3: in my opinion, the SCF's very weak dependence on latitude due to the predominant importance of orography and regional climatic conditions should be highlighted;
• lines 380-381: why the SCF distribution is bimodal for four aspects when it is unimodal up to 4000 m?
• Figure 9 and Table 3: I suggest to add “flat terrain” to Figure 9 and limit Table 3 to annual and seasonal values only;
• Figure 10 and Table 4: values from Figure 10 are repeated in Table 4; I propose to leave only annual and seasonal values in Table 4;
• Chapter 4. Discussion and Chapter 5. Conclusion: what is the significance of latitude and longitude in the SCF distribution? these characteristics have been omitted here;

Minor remarks:

• Keywords: SRTM DEM – this is not understandable to everyone; please write the full name;
• line 77: „Snow” instead of „Sow”
• line 102: “the TP” instead of “The TP”,
• Line 109: “SRTM (Shuttle Radar Topography Mission) DEM data” instead of “SRTM DEM data”
• Line 158: delete “Shuttle Radar Topography Mission” (explained above);
• Line 159: what do you mean by “USGS”
• Line 180: what do you mean by “the richest snow cover”? I think “highest SCF” would be enough;
• Table 3: I suggest to change "-1" to "flat terrain"; it will be more understandable;
• Line 496: does “other aspect” mean simply “southward” in this case?
• Line 510-512: this sentence is quite long; it can be divided into two.
• Chapter 5. Conclussion: point (1) is too long; I propose to shorten it.

Author Response

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Reviewer 2 Report

Comments for author File: Comments.pdf

Moderate English editing is required.

Author Response

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Reviewer 3 Report

main note - is the accuracy of MOD10A2 enough for:

- 7 zones divisions with 1 km interval of elevation if we have 500 m accuracy (line 161 )

- and as you wrote  (lines 589-600) "there is a lack of systematic accuracy evaluation for latest MODIS 594 products (v006 and v061). Our preliminary accuracy assessment shows that MODIS prod- 595 ucts(v006) and (v061) tend to overestimate snow cover on the TP and it is visually found 596 that many water body such rivers on the TP are misidentified as snow cover pixels, which 597 are largely due to NDSI > 0 used for snow cover mapping algorithm in latest versions of 598 MODIS products". It means that you understand problem of this way of research.

And some less note:

Line 188 - Snow cover distribution on the TP is not only related to atmospheric circulation over 188 the plateau, but more importantly it depends on alpine climate and local terrain. It is not obvious especially in high mountains areas. And you later wrote about it - line 200-201, 203 - that the SCF mostly forms "due to westerly disturbance during the winter and early spring" and "to more warm moist air that comes from the southern Asia". 

And last one - Line 404-406 -All these characterize that the high terrain of the plateau affects spatial 404 distribution and temporal variation of snow cover through the changing radiation balance 405 and redistribution of hydrothermal conditions in the mountain regions. I think it is necessary to add to the list an atmospheric circulation

Minor editing of English language required

Author Response

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Round 2

Reviewer 2 Report

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Comments for author File: Comments.pdf

Quality of English is good

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