An Assessment of the Recent Evolution of the Streamflow in a Near-Natural System: A Case Study in the Headwaters of the Mero Basin (Galicia, Spain)
Round 1
Reviewer 1 Report
The authors describe the trend of recent stream discharge in a headwater catchment in NW Spain few influenced by human activities. Their results appear to be interesting, showing no significant decrease in annual stream discharge, but significantly lower summer and autumn stream discharge and flow increase or decrease trends in different seasons, not in accordance with the rainfall pattern. The observed trend in stream discharge may be explained in terms of other parameters, such as air temperature and evapotranspiration rates. Good and concise paper, well-written and addressed to an international audience.
Author Response
We would like to acknowledge the reviewer for the very positive comments of the manuscript.
Reviewer 2 Report
The introduction includes references to every possible impact to hydrology and is way, way too broad for the content of this paper. Introduction needs to be re-written for the scope of what sub-topic this paper actually covers. This paper is not about quantifying every control to discharge. This paper has a narrow scope -- namely, discharge trend in a headwater catchment of NW Spain. Stick with that subtopic.
Lines 47-51: Authors' general statement is simply not true. "Much less effort has been devoted to studying stream discharge and extreme flow (low and high flows) trends in natural or near-natural-regimes [5], i.e., rivers that are almost or totally unchanged by human modification of flow regime, such as reservoirs, dams, channeling and water extraction." -- there have been many, many studies on streamflow in natural headwater systems.
Lines 51-54: "Near-natural systems are commonly located in headwater catchments, which are strategic areas in hydrological systems because they contribute a substantial part of the flow in a river network. They are particularly sensitive to many changes occurring in the environment" --> Catchment size determines whether or not headwater systems contribute a substantial part of the flow in the river network. Small headwater catchments themselves do not necessarily contribute substantial parts of the flow. Again, this general statement is misleading and simply not always true. Further, part of why they are sensitive to changes in the environment is because they are small.
Line 99: Specify what do you mean that the reservoir has been "extended" - do you mean the dam was enlarged?
Line 122: Change the word "registered" to "occurs".
Line 170: instead of using the word value, I suggest stating what you mean by "value" -- discharge value?
Line 178-180: Authors conducted no physical analysis of soils, water storage, or modeling of either. They cannot claim that -- by doing a summary assessment of discharge values alone -- that : "This points to streamflow in this area being largely dependent on water storage in the soils, which together with evapotranspiration and, obviously, the distribution of rainfall are key variables controlling the hydrological response of the catchment. Authors would need to utilize physical modeling and a sensitivity analysis in order to make this sort of claim. The authors did an analysis of streamflow trends --- that is all. Making these sorts of claims without justification is simply not publishable.
Author Response
Authors: The introduction of the paper was completely rewritten following your indications and those of the reviewer 4.
Line 99: Specify what do you mean that the reservoir has been "extended" - do you mean the dam was enlarged?
Authors: the sentence was deleted.
Line 122: Change the word "registered" to "occurs".
Authors: This have been changed in the revised manuscript. L. 142.
Line 170: instead of using the word value, I suggest stating what you mean by "value" -- discharge value?
Authors: The term value has been avoided in the revised manuscript.
Line 178-180: Authors conducted no physical analysis of soils, water storage, or modeling of either. They cannot claim that -- by doing a summary assessment of discharge values alone -- that : "This points to streamflow in this area being largely dependent on water storage in the soils, which together with evapotranspiration and, obviously, the distribution of rainfall are key variables controlling the hydrological response of the catchment. Authors would need to utilize physical modeling and a sensitivity analysis in order to make this sort of claim. The authors did an analysis of streamflow trends --- that is all.
Authors: In this part we wanted to refer to previous field and modeling works carried out in the catchment, which have allowed us to highlight the importance of the previous soil moisture conditions in the response of the basin. Perhaps it was not correctly reflected in the first version of the manuscript, therefore it has been revised.
Reviewer 3 Report
The subject of this paper is the stream discharge trend in a headwater catchment in NW Spain, which has been observed during period 2004-2019. The trend analysis was performed with the well-known non-parametric Mann Kendall test and the Sen method, which means that a methodological contribution does not exist. The contribution to local hydrology is explained in discussion and summary. However, it should emphasize that the conclusion is based on the data collected during the period of only 15 years, which is too short for a reliable trend analysis. Concerning presentational issues, everything seems o.k. The importance of study is highlighted, purpose of the work is presented, key publications are cited, methods and results are presented clearly, findings are discussed in the context of previous results obtained in study area. Format of text in lines 188-196 is incorrect.
Author Response
Authors: We are aware that the recording period is relatively short, as in order investigations in areas were monitoring is recent with fewer data available. However, we believe that this study can provide an idea of what is happening in an area, where the local perception is that water is an abundant resource that shows no signs of reduction. The study can provide perspective on catchment dynamics and can be valuable for modelers, watershed managers and disasters. On the other hand, we think that the findings from this study will provide important baseline information and bring out issues that need to be considered in future studies when more data are available.
The introduction was completely rewritten and the discussion and summary corrected.
Reviewer 4 Report
This paper investigates on stremflow monitoring and analysis in near-natural river basins where human development has been not significant. 15 years of flow records are gathered on a selected river basin in Spain. Trends, averages, seasonal fluctuations are analyzed looking at the hydrological data series of available flow records and land and climatic variables - land use, temperature and rainfall - are also used to assess the causes and effects of river flow variability in time. Statistical analyses is, then, developed and presented in the paper to evaluate the high and low flows with the seasonality and trending regimes of the observations.
The paper is worth consideration for a publication in hydrology. The topic is absolutely relevant and actual and authors demonstrated to have solid scientific and analytical skills. Nevertheless, there are some issues I found while performing a carefull reading and commenting of the manuscript, especially in the introduction and in the discussion. I am happy of the presented analysis. Data records were partial (only 15 years) and authors did their best to address the aim of providing an analysis of the statistical variability and trends of the hydrology (flow) in the selected river basin. On the other side, the introduction is missing to properly consider relevant references on hydrologic uncertainty especially referring to small ungauged basins, to free flowing rivers versus human-impacted river systems. The novelty and scientific value of this work is not clearly presented. In the discussion authors try to claim about motivations for the flow record fluctuations that are sometimes not supported by the presented results. The discussion make reference to other studies that are not developed in the same river basins.
As a result, I do suggest authors to attentively consider the major remarks I am inserting here below, and to consider all the specific comments I inserted in the attached pdf using the commenting tool. I do believe, after this first round of major edits, the manuscript can be surely worth consideration for a publication on hydrology.
General remarks
- Introduction. A sharp definition by authors of near-natural rivers is needed. Authors should also check, cite and compare with other relevant definitions referring to similar concepts with specific regard to free flowing rivers, flow/floodplain disconnectivity. I inserted in the specific comments in the attached pdf some sample studies authors can look. This point is very important also for contextualize this work and make it more discoverable by researchers working on the hydrology of small ungauged river basins, on human impacts on rivers and floodplains
- The novelty and scientific value of this work. I found an hard time in the introduction in finding where authors explain which is the novelty of this work and the added scientific value. I do suggest to refer to hydrologic uncertaintly as linked to climate variability. I also provided some sample studies that recently investigates on the importance of the hydrologic uncertainty in the rainfall-runoff modelling chain. There are several steps and components that characterize the processes governing river flow fluctuations from climate variability (rainfall and temperature) to land use changes (impacting infiltration and roughness conditions). River flow routing (hydraulic modelling) is too often looking to calibrate roughness to validate river models while it is demonstrated that runoff fluctuations have other sources of uncertainty. This is crucial and authors are presenting good material for these topics. I’d suggest to make it more clear
- Discussion. You are referring to literature works instead of working on your output. I do think you should move some of the paragraphs to the introduction and make the discussion more coincise and to the point. You have done a very good job in the statistics, just discuss that results without wondering around climate considerations. Please consider you have inly 15 years of records. This is not enough for making any long term comment
Specific comments
See attached commented PDF
Comments for author File: 
Comments.pdf
Author Response
Authors: We would like to acknowledge the reviewer for the careful review of our manuscript and their very positive assessment.
Authors: The introduction of the paper was completely rewritten following the indications of the reviewer, i.e. including the definition of near-natural catchment, the uncertaintly of rainfall-runoff modelling, …The discussion was also corrected following the comments of the reviewer
Reviewer 5 Report
In the paper, the purpose of the study was to characterize the recent stream discharge trend in a headwater catchment in NW Spain. The structure of the paper is not okay. Generally, this paper is rather simplistic in approach, has some significant omissions and contains no particular novelty.
The abstract is needed to revise. After the reading of this abstract, I am not sure what do the authors want to do, it is very confusing. The Introduction talks about the background and talks a little bit about the content of this paper.
Figure 1 missing coordinates.
The section "Data processing and Analysis" are clear.
Figure 5 missing coordinates.
Section " Summary and Final Remarks " is not clearly written. The Conclusions of a research paper have to summarize the contents and purpose of the study and is missing in this paper.
Author Response
Authors: Following the reviewer indications, the coordinates were added in Figure 1 and Figure 5. The introduction was completely rewritten, and the conclusions revised.
Author Response File: 
Author Response.docx
Round 2
Reviewer 2 Report
The manuscript has been improved per previous comments.
Author Response
-
Reviewer 4 Report
I am glad authors carefully addressed all my main and minor comments and remarks. To my view and knowledge the manuscript can be accepted as it is
Author Response
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