Water Balance Standardization Approach for Reconstructing Runoff Using GPS at the Basin Upstream

Round 1

Reviewer 1 Report

This paper uses TRMM, MODIS, GRACE and GPS data to calculate runoff in Mekong river basin. Here is the list of technical comments:

1. The authors use too much acronyms. It makes it difficult to read.
2. According to equation 1 (page 5) GRACE data has been used to convert GPS VCD to GPS S. Also Figure 4. shows clearly, different GRACE data, result to different GPS S. These two points should be very clear in the abstract. I find the following lines (lines21-24) in the abstract misleading: ‘The resulting R based on GPS-inferred water storage is comparable to that inferred from satellite gravimetry, attaining the lowest normalized rootmean-square error (NRMSE) of 0.08, and the highest Pearson correlation coefficient of 0.97 and Nash-Sutcliffe efficiency of 0.93, regardless of in-situ stations within MRD being used for the R reconstruction.’ Of course GPS S is correlated to the GRACE S, because GRACE S has been used to calculate GPS S. Also in page 3, lines 100-102 are misleading:
‘Other remotely-sensed water balance variables from TRMM, MODIS, and GRACE are used for direct comparison to show the applicability of the GPS VCD.’ GRACE data has not just been used for comparison; GRACE data has
been used to convert GPS VCD to GPS S for reconstruction of run-off.
3. page 4, line 146: The CSR mascon solution is different from GFZ spherical harmonics coefficients. This paragraph is confusing. The authors are using both CSR mascon data and spherical harmonics coefficients, which they refer in the figures and tables as GRACE mascon and GRACE G350. Please make clear explanation about these two GRACE data and why these two set of data are chosen for this study.
4. page 6, line 203: please write down the formulation for ‘correlation coefficient’ here.
5. page 7, figure 4: there are two GRACE solutions in this figure, and they are slightly different; authors do not comment about the difference of these two solutions.
6. page 9, figure 5: here there is just GRACE mascon solution. Authors should say why they picked the mascon solution but not the GRACE-S G350 solution.
7. page 10, figure 6: Here again there are two GRACE solutions: GRACE mascon and GRACE-S G350. There is not consistency in figures 4,5 and
6. Either for all, show two GRACE solutions or just keep one solution, and comment about why there is one GRACE solution in the figure.
8. page 7, lines 244-247, definition of estimated runoff and reconstructed runoff should be more clear. According to equation 6 for reconstructed runoff , TRIMM-P and MODIS-ET can not result to the reconstructed runoff by themselves; therefore I do not understand the RSHMVs reconstructed runoff values in Table 1 and Table 2 and Figure 5.

Comments for author File: Comments.pdf

Author Response

Dear reviewer, please find our response in the attached PDF in "Author's Notes File". Thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

I liked this paper and thought the topic was interesting and valuable.

I thought the methodology and analysis was fairly well done.  I have some questions/comments:

1. Line 193: Why was D chosen to be 3 degrees?  I couldn't find a justification.

2. Line 205: Would publishing the average alpha and beta be useful for others or are these numbers very specific to your study site?

3. Line 232: How was 2 months chosen?  Was 2 months chosen based on a correlation analysis that found the highest correlation at a 2-month lag?

4. In the Discussion section, can you put the WBS 4% improvement in context?  Are there situations where that would be important?  Best case improvement (estimating from Figure 6) is 4% of 100 mm/month = 4 mm/month.  It seems like that would fall within the variation of the peak yearly Runoff?  If it's not important, would you recommend still using this method?

5. Did you use WBR and WBS interchangeably in the text or am I misunderstanding something? 

6. Referring back to your first paragraph, how many gauges would this technique replace?

Author Response

Please find our response in the attached PDF.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript has been improved.

Author Response

Thank you.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.