Predicting Tropical Monsoon Hydrology Using CFSR and CMADS Data over the Cau River Basin in Vietnam

Round 1

Reviewer 1 Report

Ms. Ref. No.: water-1189855

Title: Predicting tropical monsoon hydrology using gridded meteorological products over the Cau River basin in Vietnam

Journal: Water

General Comments

The authors have done a good amount of work to justify the evaluation of different gridded meteorological products in the tropical monsoon climatology of Cau River Basin, Vietnam using SWAT model. However, there are some points described below that have to be considered before publication. For instance, though authors have mentioned the literature survey part, it fails to provide clear view on the previous attempts for understanding the different hydrological models and satellite products results. The introduction section need some rework and restructuring to make a precise outline of study.

Currently, many of the statements are not supported by published works. Authors may like to find studies in line with their statements to add scientific weight to their observations. I believe that after duly addressing the comments authors can improve the quality of the manuscript substantially to make it more insightful.

My second concern is about interpolation of these datasets as all of them have different spatial resolutions. How you interpolated the cases such as "if a grid is showing hit event and another adjacent grid is showing false event"/ "if a grid is showing miss event and another adjacent grid is showing false event"/ "if a grid is showing miss event and another adjacent grid is showing hit event"? Please explain.

There are no line numbers in the manuscript, which makes hard for the reviewers to point out the exact location of the corrections; hence I would suggest authors to keep the line numbers in the manuscript in future.

** Title**

The title of the manuscript is too general, and it should be more specific to better demonstrate the uniqueness of the work.

**Abstract**

Expand SWAT at right place

Rearrange the CMADS position before SWAT

**Introduction**

Please elaborate the dynamic climatic conditions in the first paragraph.

In the second paragraph, it is seen that authors have not adequately focused on the literature review for different hydrological models. As it can be seen, there are very few studies mention only. However, authors have talked about SWAT semi-distributed approach model; however there are other wide variety of conceptual models and semi-distributed models such as VIC, SHM, IHACRES etc. VIC model is a globally applied hydrological model that accounts for sub-grid variability and is an important hydrological tool, which has been successfully at grid scale in tropical monsoon climatology (Srivastava et al., 2017). I would strongly recommend the authors to add some recent studies that have applied the VIC model in various river basins. Further, authors are suggested to mention about conceptual hydrological models too. There have been various studies which have studied the land use land cover change, irrigation scheduling, climate feedback mechanisms and water balance estimations (Srivastava et al., 2017; Paul et al., 2018; Srivastava et al., 2020). Just one or two reference gives the impression that the extensive literature review is not being conducted and it is needed to address the problem. The findings or conclusions in terms of their modelling approaches are not mentioned. Elaborate more on how this paper differs or affirms the findings and conclusion of those studies. These points need to be clearly addressed in the introduction section. Hence, I would strongly recommend adding these recent and important references to add more scientific weight in their Introduction in the lines mentioned above.

Srivastava, A., Sahoo, B., Raghuwanshi, N. S., & Singh, R. (2017). Evaluation of variable-infiltration capacity model and MODIS-terra satellite-derived grid-scale evapotranspiration estimates in a River Basin with Tropical Monsoon-Type climatology. Journal of Irrigation and Drainage Engineering, 143(8), 04017028. https://doi.org/10.1061/(ASCE)IR.1943-4774.0001199

Srivastava, A., Deb, P. & Kumari, N. (2020a). Multi-Model Approach to Assess the Dynamics of Hydrologic Components in a Tropical Ecosystem. Water Resour Manage 34, 327–341. https://doi.org/10.1007/s11269-019-02452-z

Paul, P. K., Kumari, N., Panigrahi, N., Mishra, A., & Singh, R. (2018). Implementation of cell-to-cell routing scheme in a large scale conceptual hydrological model. Environmental Modelling & Software, 101, 23-33. https://doi.org/10.1016/j.envsoft.2017.12.003

Apart from this authors are talking about satellite products, however they have not mention what types of satellite products use for input into hydrological models such as (CMORPH), (PERSIANN), (TRMM), (APHRODITE) and (NOAA) Climate Prediction Center.

The authors should elaborate more on the selection of the models selected in the study. The selection of all models over other existing models should be expounded. There needs to be a detailed comparison of various simulation models. The similarities, differences, shortfalls of other simulation models. While discussing these points authors can take into account some of the studies mention below:

1. Srivastava, A., Deb, P., & Kumari, N. (2020). Multi-Model Approach to Assess the Dynamics of Hydrologic Components in a Tropical Ecosystem. Water Resources Management, 34(1), 327-341. https://doi.org/10.1007/s11269-019-02452-z
2. Darbandsari, P., & Coulibaly, P. (2020). Inter-comparison of lumped hydrological models in data-scarce watersheds using different precipitation forcing data sets: Case study of Northern Ontario, Canada. Journal of Hydrology: Regional Studies, 31, 100730. https://doi.org/10.1016/j.ejrh.2020.100730

Authors are required to mention the limitations or assumptions considered in this study at the end of Introduction.

**Data and Methods**

Authors are requested to add equation used in the SWAT model for generating the streamflow and other water balance components.

I would suggest authors to provide a result showing the segregation of overall rainfall time series into low, medium and high rainfall time series (RF is rainfall, µ is mean of rainfall, and σ is standard deviation of rainfall).

**Results and Discussion**

Authors have use less training datasets, which may lead to underestimation and overestimation of streamflow also other kinds of uncertainty in flow simulation. I would suggest author to rerun the model and distribute the 60% datasets for training and 40% for the testing period. Also, add precipitation on secondary axis of the Figure 6. Authors have generalized and shown the hydrograph, which hides the several important aspects, therefore I would recommend authors to add the flow duration curves to make the results section more comprehensible. The authors can compare findings of the results from the studies mention below. They can add the description from various studies. In addition, author can use the exceedance probability distribution to highlight the frequency distribution.

I suggest authors to add water balance components as there are several studies showing these components using SWAT and compare their results with the previous studies top showcase how other hydrological processes responds to this input variations.

**Conclusions**

Please revise the conclusions based on the revised Introduction.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

This study considers two gridded meteorological datasets, CFSR and CMADS, comparing them to data from meteorological stations over the Cau River basin and investigating their suitability when used in a hydraulic model. Various metrics are used compare temperature and rainfall estimates, and flow simulations when driving the SWAT model. The analysis is thorough, considering temporal and spatial variations, and various extremes (e.g. high and low temperatures and rainfall). The structure is similar to a previous paper (reference 2), but for a basin with different climatological conditions and, crucially, outside of China.

I have no broad comments, rather many specific comments that must be addressed.

Abstract

• The statement “approximately 99%” is ambiguous, perhaps change to “percentage bias approximately 99%”.
• CFSR-SWAT produced “unsatisfactory” results, as stated on page 16. This should be emphasised more in the abstract which currently only has the (rather weak) statement that “CMADS-SWAT performs better than CFSR-SWAT on the monthly scale”

Section 2.2.1: the CFSR data does not have a resolution of ~38 km² as stated, rather (~38km)², or ~1444 km²

Section 2.2.2: remove the “.” used in the numbers 40,000 and 2,421. Comma or nothing.

Section 2.2.3: specify the data is necessary for this study, since the dates are not generic.

Table 1:

• correct “1979-7/2014” to “1979 – 2014” and correct “2103” to “2013”
• I would prefer footnote numbers/symbols next to the source acronyms, so that the reader knows that these are explained in the footnote

Section 2.3: add a citation to the sentence “The 2012 ArcSWAT version, an interface in ArcGIS 10.2, was used to build hydrological studies in the CRB.” Unless it was built specifically for this study, in which case clarify this with “Here” or “In this study” and maybe remove the pluralisation “studies”.

Section 3.1 “Table 2” correct to “Table 3”

Section 3.2.1

• Re-structure the first sentence, as it make it look as though 0.45 and 15.5 are both CC values, and 0.31 and 16.63 are both RMSE values, which is not true.
• Correct “CFSR underestimated the actual precipitation” to “CFSR overestimated the actual precipitation”

Figure 3

• I prefer equal spacing for colour bar intervals as it is easy to misinterpret plots otherwise, I realise this would result in many unnecessary intervals in Figure 3 e-h so perhaps a continuous colour bar would work better? If not, the variable intervals should at least be noted in the caption.
• In Figure 3a,b the colour scale should be reversed so that a higher correlation is green and a lower correlation is red.
• In Figure 3g,h I would recommend a colour bar that has a “good” colour, like green, around 0, and other colours either end – probably blue for positive bias and red for negative bias. The current colour bar implies that a large negative bias is a good thing.

Section 3.2.2

• I am confused by the sentence starting “Overall, the MAE values of the CMADS precipitation data..”. It refers to “observed data” where I think it means CFSR data. Please clarify.
• Final paragraph, the statement “so the statistics were more balanced with these data than those of the CFSR data”, I assumed “these data” are CMADS? If so, please replace with “the CMADS data”

Section 3.4:

• Please clarify what the polymerization station is.
• It is claimed that the cold temperatures explain the high pbias values for the CMADS data in the dry season, but the CMADS data matches the number of cold days recorded by GMS reasonably well, so I’m not sure the logic holds. If the CMADS data was significantly underestimating the number of cold days then it would make more sense.
• When mentioning the box plots, refer to Figure 2.
• “CFSR data are superior to the CMADS and GMS data” implies better performance, but I think the authors mean that CFSR has a greater number of hot days - please reword this.

Figure 5: there is too much to untangle in this figure, perhaps have two figures with the Tmx37-39 and the Tmx39 separately, or simply another table.

Figure 6: is difficult to interpret, perhaps just show one or two representative years (especially since the whole time period is shown at a monthly scale in figure 7)?

Figure 7: the colours for each dataset should be kept constant between figures 6 and 7, also the order.

Table 7: the sign of the pbias seems to be reversed – CFSR seems to overestimate flow in figure 7 but the pbias is negative?

Conclusion:

• Specify “Therefore, the CMADS and CFSR data can be reliably used” as “Therefore, the CMADS and CFSR temperature data can be reliably used”
• “the CMADS data obtain more suitable results than the other studied datasets” should be changed to “the CMADS data obtain more suitable results than the CFSR data”

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

Review of article entitled "Predicting tropical monsoon hydrology using gridded meteorological products over the Cau River Basin in Vietnam" By Lu et al.

General comments: The paper is generally sound in science though some writings need improvements (there are a lot and I have pointed out some of them in specific comments). The topic is within the scope of the journal. Recommend publication with minor revision.

Specific comments:

1. Abstract needs improvement: please concisely provide new findings/results only. Thus remove Lines 18-21: "Gridded .. to be conducted. To improve knowledge of this matter"
2. Line 24: over 5 years, from 2008 to 2013. Is it 6 years from 2008 to 2013? double check the temporal coverage.
3. Line 57: please expand NCEP when it first appears.
4. Line 64: what is MPEG?
5. Line 67: PED and HBV appear first, they need expansion for clear meaning.
6. Line 82: "superior" is not a proper word here. Maybe "better" is better.
7. Line 101: What is QUAL2K? Please spell it out.
8. Line 161: what is LAPS/STMAS?

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have addressed all previous concerns expressed by the reviewers and in the process have improved the work, confirmed the validity of their findings and gained confidence in their introduction, methods, results and conclusions. I would like to congratulate the authors for an interesting and well executed work and I recommend this manuscript for publication in Water (MDPI) in its current form.