Dear authors,

Your manuscript has received two referee comments. Due to the late submission of your replies
a discussion did not follow. Both reviewers struggle with the structure/setup/content. One reviewer questions the validity of your results. Given their comments and findings major revisions of the manuscript are necessary. The basic structure of your paper is fine (introduction-data&methods-results&discussion and conclusions). However, a clear description of the hypothesis tested, the experiments conducted, the methods used, and a thorough analysis&discussion are clearly needed to allow a second evaluation of the manuscript and eventually publication in HESS.

Please pay careful attention to the comments of both reviewers, also address the concerns of reviewer 2 regarding the setup of the experiments and the doubts about the obtained results, a structured/proper description of the experiments in data& methods section and presentation and discussion in results& discussion section is necessary here.

I will analyse the revised manuscript and will make a decision if it is good enough for another round of reviews (given the comments of both reviewers).

Sincerely,

Albrecht Weerts

Dear Authors,

The two reviewers have judged your manuscript again. You made considerable improvements. according to both reviewers.

Please find their findings in the reports. I agree with reviewer 2 that you must
make sure the reader understands that the references that you use is not 'measured'
but is also derived and have bias/errors. If you can do more to demonstrate this even better.

After adjustments/explanation I will send it out for review to reviewer 2 only.

Regards

Albrecht Weerts

PS I have to choose major revisions otherwise I cannot send it out for review again.

Dear Authors

Although you did a good job there are some minor revisions needed according to the reviewer.
Please provide a new version with changes and detailed explanation what you changed and what not (and if so why).

Regards,

Albrecht Weerts

Comments by the reviewer

Many thanks authors’ efforts on improving the manuscript by adding more explanation. I believed what the authors want to emphasize and demonstrate are very important for the remote sensing soil moisture community. Nevertheless, some more clarifications and explanations are still needed to deliver clearly the message that the authors would like to deliver. I hope the authors would not be discouraged to do so, with my comments as following. I have organized my comments following the structure of the manuscript:


Section 1:
1. Line 24-26, Page 11, It really depends on how you define the hydraulic properties. Nevertheless, in soil physics, no one say hydraulic properties -> saturated and residual soil water content. You can say, saturated and residual soil water content are part of soil hydraulic properties (only loosely).


Section 2.2:
2. The incidence angles for TB_HT and TB_OR are at 40deg and 42.5deg, respectively. Could the authors explain the possible inconsistency caused by this different configuration? This is suggested to do so to convince readers that such difference in incidence angels will not affect the results and the conclusions.
3. For “simulation 2”, the “Soil Discretization” is merely the average of ORCHIDEE’s soil temperature simulation into 3 soil layers. This is actually not physical “soil discretization”, which used to configure ORCHIDEE runs. This means the “soil discretization” as the current manuscript proposed didn’t change any simulated soil states by ORCHIDEE, while just using the same ORCHIDEE simulation with averaging the finer layering into coarser layering. As such, this “simulation 2” doesn’t seem provide add-value information, unless the authors use different soil discretization configuration to run the ORCHIDEE one more time.


Section 2.3
4. I appreciated authors’ efforts in explaining this with more details. It is quite understandable to use E-OBS or other precipitation data, LandSAF’s LST or other LST products, as independent data to verify ERA-Interim data. Nevertheless, it is still needed to describe a bit more details on those reference datasets. For example, for E-OBS data over IP, you can further demonstrate how many rain gauge stations were included, while for LandSAF’s LST, you can provide further information on how it was validated by others, with what in-situ data/other means, over IP.
5. It seems the conclusion in the manuscript will not change too much if you used different reference data? If it is the case, please indicate it in the manuscript. Or if different reference data will change the conclusion here, could the author help to illustrate/discuss such difference in terms of how and what?


Section 3.1.2.
6. For Table 3, I see the TB_HT is filtered based on orography, while there is no similar filtering rules for TB_OR, why is that?


Section 3.2.1
7. It is not very clear how the spatial correlation analysis was performed. Please give more details. For example, how was the “5-day window” applied? Could you give a concreate example to demonstrate?
Section 4.1
8. For Table 4, why not temporal correlation calculated for the three simulations (VC, SD, FW)?


Section 4.2.1
9. I believe that the Table 5 here is not correct and messed up somehow. Please clarify and correct.
10. It is not clear what is the difference between EC and the spation correlation in 4.1.2. Please elaborate.
11. Line 18-24, page 25, it seems to me from Figure 2 I can understand easier for this paragraph.?
12. Line 21, “… evidences that …” , from what results it is evident?
13. Line 22-24, “… confirm …”, why need to confirm here and how it was confirmed? Is it not already demonstrated in Figure 1? And, the hypothesis you mentioned is not clearly explicitly explained in earlier sections, or please use a reference to point out where you put forward this hypothesis.
14. In general, I didn’t see clear link between the statements in this paragraph (Line 18-24) and results you were referring to (Figure 3 & 4)
15. Line 27, page 25, What does it mean by the ECMWF’S mean first guess departure? Could the authors present an equation to demonstrate how it was calculated? For the time being, this is confusing for readers. For example, the first guess departure is expressed as “obs-model”, why not using “model-obs” to keep it consistent with Figure 3, 4 etc.
16. Line 5-7page 26, what is the add-value of this statement, in the context of this study?
17. Line 8, page 26, “two TB errors” refer to TB_HT and TB_OR?


Section 4.2.2
18. Line 17, page 26, “two TB errors” refer to TB_HT and TB_OR?
19. Line 29-30, page 26. I assumed this is mainly due to the difference in simulated LST by ORCHIDEE and by HTESSEL? However, here you claimed this is most likely explained by forcing induced bias? This statement as in line 29-30 onwards to me is wrong.
20. Line 4-10, page 27, this paragraph to me is too abrupt without any supports or proofs. Or you can refer to Figure 10. Anyhow, all statements should be backed up by results (data, table or figures).
21. Line 16 page 27 “higher frequency” , is this corresponding to first or second model? How to see it from Figure 7 not clear to me.
22. Line 20-23 page 27, “… The EOF analysis …” I don’t agree with this statement. You actually present in earlier section that precipitation can explain the error source for spatial patterns? Other than this, the claim on the “.., errors in their surface temperature …” is not correct as what I mentioned in comment nr. 18.
23. Line 7-10, page 28, not surprised, no big differences as stated, because it is not physical “soil discretization’ as I mentioned in comment nr. 2.


Section 4.3
24. Line 19, page 28, “The slow varying component” means P1 mode?
25. Line 21, page 28, “ … (Fig.5)” , Fig.2 can be put in this bracket as well?
26. Line 1, page 29. Please add a sentence here to say something like “the annual cycle variation of TBs do correspond well as shown in Figure 1?”
27. Line 12, page 29, How it was different not clear. It looks similar in Fig.10.
28. Line 22-25. “This might explain why …” onwards. In my view, emissivity is not the sole factor affecting the TB calculation, effective temperature is another one.
29. Line 1-3, page 30, this sentence is too long and not clear what do you mean.
30. Line 4-6. Page 30, Again, the TB is affected by both emissivity and effective temperature. I would suggest authors to compare effective temperatures as calculated from both HTESSEL and ORCHIDEE. Perhaps the difference in TBs are induced by different Teff calculation from the two models.
31. Line 6-8, page 30, “on the other hand, … tose of TBs.” these two sentences seem conflicting with each other.


Section 5
32. Line 13-15 Page 31, English is awkward here.
33. For the explanations to the discrepancies, I suggested two more points, worthy of discussion:
a) Is it possible due to different Plant Functional Types (PFT) as defined in ORCHIDEE and HTESSEL?
b) The role of Teff in calculating TB can be another important factor, please see following references：
Lv, S., Wen, J., Zeng, Y., Tian, H., & Su, Z. (2014). An improved two-layer algorithm for estimating effective soil temperature in microwave radiometry using in situ temperature and soil moisture measurements. Remote Sensing of Environment, 152, 356-363

Lv, S., Zeng, Y., Wen, J., & Su, Z. (2016). A reappraisal of global soil effective temperature schemes. Remote Sensing of Environment, 183, 144-153

Dear Authors

I think you addressed all comments adequately and accept this version for publication in HESS, congratulations!

Sincerely,

Albrecht