Assessing Climate Change Impacts on Streamflow, Sediment and Nutrient Loadings of the Minija River (Lithuania): A Hillslope Watershed Discretization Application with High-Resolution Spatial Inputs
Round 1
Reviewer 1 Report
This manuscript investigated the impact of climate change on streamflow, sediment and nutrient loadings in the Minija River basin (Lithuania) using SWAT model of high-resolution input data. Overall, the manuscript is well written and the results are useful. However, it should be revised before published in the journal. My comments are as below:
1. The authors may have to re-consider the title. Climate change impact is a huge topic and I think you should give specific information here like”assessing climate change impacts on streamflow, sediment and nutrient loadings”. Also, ‘high-resolution modeling’ is vague, maybe ‘high-resolution spatial inputs’ could be used.
2. Line 59 ‘leeching’? I think it should be ‘leaching’. But I think ‘transport’ or ‘export’ is more appropriate to be used here since ‘leaching’ refers to the dissolved phase of nutrient.
3. Line 225 It is not clear here. Based on Figure 6, monthly average sediment concentration was used for sediment calibration? How was monthly sediment concentration calculated? Monthly TN and TP loadings were used for nutrient calibration. How were nutrient loadings calculated? If loading estimation is possible, why sediment loading was not used for sediment calibration？
4. Line 230 why only one GCM model was used for predicting the climate change impacts. There are uncertainties for the future projects based on different GCM models. Therefore, multiple GCM models are usually used to account for the uncertainties.
5. Line 229 how other climate data in the future such as solar radiation, wind speed and relative humidity were determined?
6. Line 226 I suggest using another model performance measure percent bias (PBIAS) to assess model performances because it reflects the systematic errors of the model.
7. Line 278-279 I suggest citing this recent papers (https://www.sciencedirect.com/science/article/pii/S1364815218302299), which discussed the reason for underestimating peak values in SWAT model.
8. Line 206-207 how this sediment routing method was chosen?
Author Response
Dear Reviewer,
Thank you for your time and effort to review our article and providing valuable comments. We carefully considered all your comments and made some changes in the manuscript. For detailed answers to your comments, please refer to the attached document.
We think that the article has improved much since its initial draft and we hope that the readers will find it instructive and enlightening.
All the best,
The Authors
Author Response File: 
Author Response.docx
Reviewer 2 Report
This study focuses on the effects of climate change on Minija River Basin by making some modifications in SWAT. Overall the work is interesting. I have some comments/concerns, please see below:
Authors mentioned a study on the effect of input data resolution on SWAT performance. This study concluded that watersheds with mean annual precipitation of <800 ml/yr authorize low resolution DEM (Chaplot, 2014). Having this into account, why DEM was resampled to 35*35 m?
Did authors consider a warm-up period for SWAT? And if yes, how many years?
Have the authors tested the performance of SWAT model using default approaches in comparison with hillslope delineation and data simplification?
Can author explain how they estimated such a long auto-calibration process? SWAT-CUP is a straight forward and quick software to use for SWAT calibration.
I could not find Supplementary Material B to see the full list of parameters used in the calibrations and their values.
Authors mentioned few times in the text the uncertainties exist in the water quality data and having one sample for some months throughout the year. This raises the concern of trusting the model to be used further to assess the climate change effects.
Line 304, typo “these kind of …”
Typo on Figure 4 “Debit Staton”
Figure 3 shows monthly scale data, but the figure title says annual precipitation.
Author Response
Dear Reviewer,
Thank you for your time
and effort to review our article and providing valuable comments. We
carefully considered all your comments and made some changes in the
manuscript. For detailed answers to your comments, please refer to the
attached document.
We think that the article has improved much since its initial draft and we hope that the readers will find it instructive and enlightening.
All the best,
The Authors
Author Response File: Author Response.docx
Reviewer 3 Report
Please find attached file.
Comments for author File: 
Comments.pdf
Author Response
Dear Reviewer,
Thank you for your time
and effort to review our article and providing valuable comments. We
carefully considered all your comments and made some changes in the
manuscript. For detailed answers to your comments, please refer to the
attached document.
We think that the article has improved much since its initial draft and we hope that the readers will find it instructive and enlightening.
All the best,
The Authors
Author Response File: Author Response.docx
Reviewer 4 Report
In this paper, the authors attempted to extend the study conducted in the Baltic Sea region into one sub-basin in this region - Minija sub-basin. SWAT was selected to model flow and loading of sediments, TN, and TP, and to assess the climate change impact on flow and water quality. Most model parameters were also transferred from previous study. Thus this paper is viewed as an “extension” of previous studies. In addition, the model developed here for investigating the climate change impact was not considered as feasible to fulfill the objective of this paper – assessing climate change impact, due to several critical issues addressed among the comments below. Therefore, the paper is not acceptable.
Major comments:
1. Section of Introduction: The introduction section reviewed the studies conducted in the study region (the Baltic Sea area) and their results. However, this section should review the study topic in general, not just limited to the studies conducted in the region.
2. In the sections of Introduction and Materials and Methods, this paper argued the importance of incorporating changes in the land use and land management into the model (Lines 79-80). The primary objective of this paper is to investigate the climate change impact (changes in temperature and precipitation) on flow and water quality. Knowing the importance of the changes in land use, was the effect of the change in land use removed for studying climate change impacts?
3. This paper also argued that the river basin is under stress from different sources of pollution, including agriculture and aquaculture, recreational activities, domestic and industrial wastewater and others (Lines 103-104). The authors also pointed out that the pint source contribution has changed dramatically in the past 5 years (Lines 369-371). So similar to the previous comment, were these potential effects on water quality removed when developing the model for projecting water quality in the future?
4. Lines 128-130: This paper stated that the purposes of modeling study include identifying the most dominant forcing factors, and quantifying the anthropogenic influence. However, they were not considered in this paper.
5. In section 2.2: It seems that the model discretization scheme adopted in this paper is different from the one commonly used. This paper also stated that this approach allows to model land management and support practice applications comprehensively on a medium to large watersheds. This argument should be supported using the results from this study. In addition, this paper did not intend to study the impact of land use/ land management.
6. Fig. 3, which seems to be the result from this study, should not be included into section 2.1.
7. Regarding to the model calibration, the manual calibration approach was adopted knowing that the automatic calibration may provide better solution, due to the limitation of computational resources. This is not strong justification for the use of manual calibration approach.
8. Lines 183-187: The simplified/coarse model was applied to assess the climate change impact. Thus the phrase in the title “high-resolution modeling” is not appropriate. In addition, the authors mentioned the high-resolution model, which was not adopted in the paper, and thus the high-resolution model should not be included here.
9. Table 2 and Lines 241-243: There are large differences in projected seasonal temperature between 2b and 3b. This should be discussed.
10. Table 3: More details description on the SWAT may help readers better understanding the parameters to be calibrated in the model. Looking through the parameter list, it seems that no parameters are associated with snowmelt modeling.
11. Lines 323-324: I do not agree with this statement. Better model performance is not always dependent on the increase of observations. It mainly relies on if the model represents the physical processes well.
12. Lines 329-332: The statement argues that the model performs well when modeling the lower part of the watershed. If the model cannot model the upper part of the watershed well, this would affect the modeling results in the lower part of the watershed. Thus this statement here is not feasible.
13. This paper argued the importance of groundwater contribution in the reduction of flow and phosphorus loading (Lines 377-380). Line 266 stated that “one starts with flow calibration (baseflow and surface runoff)”. Was the model calibrated for based flow and surface runoff? If yes, the results (for base flow and surface runoff) should be reported in this paper? What approach was adopted to separate baseflow and surface runoff from the observed flow?
14. This paper stated “uncertainty” in several places (e.g., Lines 224, 279, 312, etc.). It is apparent that uncertainty is a critical issue in the modeling study.
Author Response
Dear Reviewer,
Thank you for your time
and effort to review our article and providing valuable comments. We
carefully considered all your comments and made some changes in the
manuscript. For detailed answers to your comments, please refer to the
attached document.
We think that the article has improved much since its initial draft and we hope that the readers will find it instructive and enlightening.
All the best,
The Authors
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Thanks for the authors’ efforts to address my comments. My comments were responded well except comment 3 and the manuscript was improved after revision. As to comment 3, first, I still think you should use sediment loads to show the model calibration results, which is consist with the nutrient calibration. In addition, I think it’s not right to use arithmetic mean to calculate the average concentration during a month because this assumes the flow is the same for different sampling dates. Also, there are high uncertainties using ‘average concentration’ and ‘average flow’ to calculate month loads. For load estimation, you could use the widely used USGS LOADEST software or refer to many literatures about load estimation.
Author Response
Dear Reviewer,
Thank you for your time and effort to review our article and providing valuable suggestions and guidance. We now revised the method used in our study for sediment load estimation and made some improvements. A detailed reply to your suggestion is in the attached document.
All the best,
The Authors
Author Response File: Author Response.docx
Reviewer 4 Report
Thank you for responding my comments. Several concerns/questions are cleared up, however I still do not agree with the authors’ responses to several key comments.
1. The objective of this paper is to investigate the climate change impact. As stated in this paper, the study area has been subject to several other changes including changes in land use and pollutant loading from nonpoint and point sources during the study period. The average inputs for the last 5 years were used for developing the model for future projection. I do not think that the approach adopted here is feasible to investigate the climate change impact on flow and water quality if the above mentioned factors (except climate) result in significant changes in flow and water quality. In this case, the effects of these factors should be removed for studying climate change impact. Without removing the effects of these factors, the developed model cannot capture the effect of climate on flow and water quality well. Then it is questionable to apply it to project the impact of climate change.
2. This paper cannot argue the importance of the groundwater contribution of flow and phosphorus loading if groundwater is not modeled separately.
3. Regarding to the authors’ response to Comment 4: I do not agree with the authors that the developed model in this paper can be further used to quantify the anthropogenic influence and detect what will be the main driving forces, since the model did not taken the effect of the anthropogenic influence into the modeling. As stated in the response, the average inputs were used. The effects of the anthropogenic influence was not really taken into consideration. Thus new model should be developed for investigating the anthropogenic influence.
Author Response
Dear Reviewer,
Thank you for your time and effort to review our article and providing feedback. We provide comments to clarify the issues and made several changes in the manuscript. A detailed reply to your suggestion is in the attached document.
All the best,
The Authors
Author Response File: Author Response.docx
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.
Round 1
Reviewer 1 Report
The paper by Čerkasova et al. entitled 'Impact of climate change on the Minija River basin (Lithuania) through high resolution modeling' deals with an interesting issue of climate change impact on hydrology and water quality in a coastal catchment using a hydrologic modelling. The topic is well suited to the scope of the journal, and particularly to the water management. However, I think that the paper needs substantial improvement to better highlight the main implications of the investigated case study. The consideration of the following general comments should hopefully help the authors to submit an improved version.
- the structure of the article is misleading. I would expect that Introduction section should be focused on the research background and higlighting the reasearch gaps which this study is trying to fill. Now the Introduction is focused on the study site description. The objectives are not clear and after reading the Introduction I was not sure what this article was investigating.
- The title is suggesting the impact of climaete change on water quantity and quality but the moast part of the M&M section describes the model setup and techniqes of units discretization. Authors state clearly that it is crucial stage of the model design and that it shuold improve the results. However, not a single comment is given on that in results and discussion. If it doesn't require a special focus why to overload the manuscript with the discretization stage. If in authors' opinion it is crucial, than an extanded comment is required. Presently, the M&M section describes the labor and time consuming work which is not presented in results and discussion. Moreover, the main topic (climate change signal) is not desribed at all in the M&M section which in my opinion should be added and commented.
- The discussion in my opinion does not discuss anything here. I would expect some comments on the use of detailed disretization if such an extended summary on this topic was given in the M&M section. I believe that there are many studies in neighbouring countries investigatin climate change impact on water quality and quantity usin hydrological models. Their results should be compared and novelties of this research should be hihligted. Now it stands more like a technical report with no scientific sound.
- Figures presented in the study are rather poor quality and should be improved.
Other specific comments are given in the attached file.
Comments for author File: Comments.pdf
Reviewer 2 Report
The manuscript reads like a report rather than a research article. I do not find a research question that this study tried to answer. The methodology is not explained and justified enough to convince readers including me. I could not find a strong statement highlighting a contribution made by this study to the existing literature. My specific comments are left on the attached document.
Comments for author File: Comments.pdf
